摘要:

Mendeleev Communications Electronic Version, Issue 1, 2001 (pp. 1.42) Wedekind.Fock.Havinga salt Me(Et)N+(All)PhI. ¡�CHCl3 as historically the first object for absolute asymmetric synthesis: spontaneous resolution, structure and absolute configuration¢Ó Remir G. Kostyanovsky,*a Vasilii R. Kostyanovsky,a Gul¡�nara K. Kadorkinaa and Konstantin A. Lyssenkob a N. N. Semenov Institute of Chemical Physics, Russian Academy of Sciences, 117977 Moscow, Russian Federation. Fax: +7 095 938 2156; e-mail: kost@center.chph.ras.ru b A.N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences, 117813 Moscow, Russian Federation. Fax: +7 095 135 5085; e-mail: kostya@xlab.ineos.ac.ru 10.1070/MC2001v011n01ABEH001420 The title salt crystallises as a conglomerate (space group P212121, Z = 4) with one solvate CHCl3 molecule forming strong shortened contact with I.[Cl¡�¡�¡�I. 3.599(2) A]. Therefore, it undergoes spontaneous resolution by simple crystallisation with a deficiency of the conglomerator CHCl3 or by an internal entrainment procedure. It exhibits the (S)-(+) absolute configuration and racemises in solution (.G# rac = 26.5 kcal mol.1).The salt was almost completely converted into one enantiomer by stirred crystallisation from solution (with full evaporation) or from a melt under conditions of enantiomerisation. The contribution of autocatalysis to this process is discussed. Chiral ammonium salt Me(Et)N+(All)PhI. ¡�CHCl3 1 has attracted the attention of several generations of chemists and remains to be of much current interest because ¡°...mental adjustments are required in order to deal intuitively with ¡®improbable¡� solid-state phenomena.¡±3 Salt 1 by right should be named for three outstanding persons who are responsible for its highly important place in the history of stereochemistry (see photos on the back cover and historical outlook¢Ô).E. Wedekind was the first to synthesise5(a),(g) salt 1 and to find that it incorporates crystallisation CHCl3.He examined spontaneous racemisation of 1 and similar salts in solutions (its ¢Ó Asymmetric Nitrogen. Part 84. Previous communication see ref. 1. Preliminary results of this work have been published.2 ¢Ô E. Wedekind, born on December 31, 1870, in Altona on Elbe, studied in Tubingen and Munich (thesis). In 1897.1899, he worked at the Polytechnical Institute in Riga (Russia); in 1904, he became a Professor at the Chemical Institute of Tubingen University.Over decades, he was elaborating the problems of asymmetric four-coordinated nitrogen4 (which was earlier considered as five-coordinated). The related results obtained in Riga, Tubingen, and Strasbourg were published in 2 monographs and 60 communications in 1899.1934 (see ref. 5).The question as to whether the four-coordinated nitrogen exists has been raised first by J. Wislicenus in 1877 [ref. 5(a), p. 1], and those as to three-coordinated nitrogen by A. Hantzsch and A. Werner in 1890.6 Described in the next year by J. A. Le Bel, the optical activation of Me(Et)N+(Prn)BuiCl. under the action of microorganisms7(a) was not confirmed later (1899).7(b),(c) Despite the unsuccessful attempts to resolve the Le Bel salt using the optically active acids such as tartaric, camphoric, and mandelic ones,7(b) Wedekind, in the same year, has launched an attack on solving the problem.One of the major arguments in support of the stereoisomerism of ammonium salts that Wedekind kept in mind5(c) was identity of the Menshutkin salts prepared by means of three possible ways from the corresponding N,N-dialkylaniline and alkyl iodide.8 Studies by Wedekind of 1899 initiated the German9 and three groups of British chemists10 to be involved in the solution of this problem.These data on the synthesis, crystallographic characterisation, and unsuccessful attempts to resolve salts Me(All)N+(CH2Ph)PhHal.A using optically active tartaric and camphoric acids in aqueous solutions have been reported5(d),(e) followed by the publication of W. J. Pope et al.10(a),(b) on the resolution of salt A via camphorsulfonates in non-aqueous solutions. In 1905, M. B. Thomas and H. O. Jones first observed10(c) apparently asymmetric transformation of diastereomeric salts such as (+)-camphorsulfonate obtained from Wedekind salt 1; when heated the latter above 50 ¡ÆC in H2O, its optical activity was changed to the sign reversal. However, the authors could not make the important fact out, and just expressed their astonishment: ¡°It is curious that the rotatory power .. . vanish at some temperature above 50 ¡ÆC and then become levorotatory...¡±. Asymmetric transformation of a covalent diastereomeric salt was precisely detected9 at the first time in 1905 by M.Scholtz who has synthesised derivatives of the alkaloid coniine for biological tests. In response to the Wedekind works, he has isolated diastereomerically pure salts B and C and carried out their intertransformations under short heating up to the melting [Scheme 1 (a)]. N Et Ph Pr H I .N Et Ph Pr H I B, mp 179 ¡ÆC [a]D = .21.2¡Æ C, mp 208 ¡ÆC [a]D = +31.2¡Æ (a) (b) N Pri CH2CO2-L-menthyl 20 ¡ÆC EtOH I N Pri CH2CO2-L-menthyl I D, mp 146.148 ¡ÆC [a]D = .12.5¡Æ mp 163.164 ¡ÆC [a]D = .40.1¡Æ Scheme 1 Asymmetric diastereomeric transformations of the chiral ammonium salts. Similar transformations were observed by Wedekind under mild conditions5( j),(k) [D, Scheme 1(b)].It is amazing that till now the discovery of such phenomena important both in principle and in terms of technology, as asymmetric diastereomeric transformation was ascribed to H. Leuhs and J. Wutke (1913), and a well-known list of conglomerates11 does not include many of hemihedral crystals found by Wedekind and A. L. Fock.5,13 A. L. Fock, born on April 28, 1856, in Bobs near Lubeck (Germany), studied (1876.1880) in Strasbourg (thesis).Since 1881, he worked with H. H. Landolt as his assistant and, since 1885, as an assistant professor at the Berlin University. Famous crystallographer, the author of the monograph ¡°Introduction in Chemical Crystallography¡±12 (translated and edited by W. J. Pope, one of the most prominent chemist of that time), Fock has performed all crystallographic studies of the Wedekind salts.5,13 Both scientists were mad about hunting for conglomerates, and triumphed over each new find of the hemihedral crystal, in particular, of A5(d) and 1.5(g) It is interesting to mention a microgoniometric study when hemihedrism was observed only for the enantiomer (.)-Me(Pri)N+(CH2Ph)PhI. (mp 132 ¡ÆC) but not for the racemate (mp 133 ¡ÆC).10(c) The priority in obtaining an optically active compound containing a stereogenic heteroatom is attributed to Pope and co-workers;4,14 however, before them Wedekind and Fock have found hemihedrism (i.e., homochirality) of the crystals of iodide A5(d) and then isomorphism of halides A.5(c) This fact was confirmed by Pope himself.He wrote [ref. 10(a), p. 1130]: ¡°...Fock actually measured crystals of the optically active iodides¡±, and emphasizing identity of the crystallographic parameters found by Fock for bromide (¡¾)-A5(c) with those for enantiomers found by himself, he con-Mendeleev Communications Electronic Version, Issue 1, 2001 (pp. 1.42) rate depends on the type of anion: I > Br > Cl) and explained the racemisation by reversible dissociation into an amine and an allyl halide.5( f ) A.L. Fock pioneered microgoniometric studies of salt 1 and found the hemihedrism of its crystals;5(a),7 i.e., he found that it crystallises as a conglomerate (a mixture of homochiral crystals of the enantiomers) and hence is capable of spontaneous resolution. E. Havinga was the first to perform spontaneous resolution of 1 and proposed the idea of spontaneous asymmetric synthesis21 (absolute asymmetric synthesis or crystallisation-induced the second order asymmetric transfoh a synthesis takes place under the following conditions: (a) the material crystallises as homochiral crystals (conglomerate); (b) the characteristic time of formation of the first nucleus is long; and (c) the rate of spontaneous or catalysed racemisation in a solution or melt is higher than the rate of crystal growth.Then, crystallisation from a supersaturated solution or a melt gives an enantiomerically pure product as a result of cloning molecules on the first nucleus formed (see, e.g., refs. 3, 32 for the nucleation mechanism) from a mixture of the constant enantiomeric composition 1:1 (because of rapid racemisation).Thus, the racemate is converted into a single d- or l-enantiomer. This idea became universally recognised.11,20,22.28 However, the total enantiomeric enrichment of the precipitate and the mother liquor in a particular experiment cannot be quantitatively evaluated from the experimental data by Havinga. It was noted by himself21 that ¡°...crystals contain CHCl3, tend to liquate and soon become sticky renders exact quantitative determinations in small-scale experiments somewhat difficult¡±. Moreover, Havinga¡�s experiments ¡°...have never been repeated¡± [ref. 25(a), p. 185], and it was noted that his results ¡°...may not be reproducible¡±. 24 cluded: ¡°It follows that the inactive salt is not a racemic compound but is .. . a mere mechanical mixture of the two component salts¡± [ref. 10(b), pp. 835.836]. The components of this mixture are enantiomorphous crystals (Figure 1)10(b) like in case of the Pasteur salt. Thus, a breakthrough in the stereochemistry of asymmetric heteroatoms took place on the verge of the centuries (1899.1901) due to efforts of Wedekind, Fock, Pope, S. J. Peachey and A. W.Harvey. Wedekind has also synthesised5(h) optically active analogues of A, i.e. salts (+)- and (.)-Me(Pr)N+(CH2Ph)PhI. E, which were later prepared15 by the reductive transformation of iodides (+)-A ¢ç (+)-E. The absolute configurations of (S)-(.)-E and (S)-(+)-As-analogue were determined16(a) using the method of quasi-racemates11 by comparison with (S)-(+)-Panalogue studied16(b) by X-ray diffraction analysis.The salts like (+)- A15(a) and other15(b),(c) were used for the transfer of chirality from N to C by the Stevens reaction15(a),(c) and Hofmann cleavage.15(b) The really opposite situation was with three-coordinated nitrogen. In all instances the resolution of compounds ranging from the Troger base (V. Prelog, P. Wieland, 1944) to the chiral dialkoxyamine with the openchained asymmetric nitrogen (R.G. Kostyanovsky et al., 1979)17(d),(e) and systems with the sterically hindered nitrogen inversion1 were carried out using chiral reagents. Only then did we find out the crystallographic identity of the enantiomers and racemate of a bis-naphtho analogue of the Troger base18 (which was found to be a conglomerate like those found by Fock and Pope!) we succeeded in spontaneous resolution, again at the verge of the centuries, and obtained the above synthetic product, each individual crystal of which was optically active, [a]D 20 = 1100.1200¡Æ (c 0.1, MeOH).It is incomprehensible why either Wedekind or Pope, who realised the point perfectly well, never measured the optical rotation for the individual crystals of the salts under study. Only half a century later it was done by Havinga.E. Havinga born on May 7, 1909, in Amersfoort (the Netherlands), studied theoretical physics at the Utrecht University (with H. A. Kramers) and organic chemistry (thesis ¡°Monolayers: Structure and Chemical Reactions¡±, 1939, under the supervision of F. Kogl), worked in the laboratory of medicinal chemistry at Utrecht, then became full professor and director of the laboratory of organic chemistry at the University of Leiden (1949. 1979). His scientific interest ranged from physical organic chemistry to bioorganic chemistry including photochemistry and the chemistry of vitamin D, conformational analysis and peptide chemistry, catalysis and enzymatic reactions. He was gifted with incredible capacity for working and also with versatile talents outside chemistry.An outstanding teacher of organic chemistry (the number of theses prepared under his supervision amounts to 166), he was also an excellent tennis player, art-lover and masterly pianist who inspired the Dutch composer W. Aerts to write ¡°Thirteen variations and coda on a theme of E. Havinga in E minor¡±. PhN(Me)Et 1 All.I CHCl3 PhN(Me)All 2 1 + EtI CHCl3 PhN+(Me)(All)2I.+ 3 PhN+(Me)Et2I. 4 PhN(Me)Et 2 EtI N Me Ph Et S-(+)-1 I Ph N Et Me I (S)-1 or (R)-1 . melt . solution 0.5 CHCl3 N Me Ph Et I Ha Hb Hc R-(.)-1 Scheme 2 All = Allyl In his last year, Havinga has described his academic career in the essay ¡°Enjoying Organic Chemistry, 1927.1987¡±.19 He was ¡°a pioneer in optical activity from chiral crystals...¡± (see ref. 20). In fact, a new epoch of exploring the chirality phenomena has begun from his studies on salt 1.21 The whole flood of theoretical and experimental researches was initiated by his precisely formulated idea of spontaneous asymmetric synthesis and conditions for its accomplishment. The Havinga effect named the stereospecific autocatalysis by M. Calvin,22 has been thoroughly investigated in theoretical aspects.23 The ideas of Havinga were successfully realised.11,24.27 Over the past decade it was shown that the efficiency of the crystallisation-induced asymmetric transformation depends critically on stirring and evaporation rates.3,28 The main test sample is the salt NaClO3 capable of crystallising in chiral cubic space group P213.Three years after translation of Fock¡�s book12(b) Pope has found10(e) optical activity of the crystal of this salt (a = 3.6¡Æ mm.1 at 546 nm) and has shown that in 3137 crystals obtained by simple crystallisation, the left.right relation is practically equal to 1:1. After 92 years, D. K. Kondepudi et al.28 and then J. M. McBride et al.3 have repeated this experiment and have demonstrated that its result was dramatically changed under conditions of stirred crystallisation (100.1000 rpm) to give either only left or only right crystals.Ideas presented in the second section of Havinga¡�s paper21 were almost not cited. The readers (not exclusive of the authors of this work) seem to be so stunned when perceiving the first part of the paper that they lose sight of the second one though it is not less interesting.Havinga assumes that in the system of molecules interoriented in a certain manner (crystal or monolayer), an enantiomeric excess may be preferable, in terms of free energy, than a racemate. It is well known for crystals (existence of conglomerates) but not for solutions, and Havinga proposes the following model. It may be that 3D achiral molecules of the type of HO(CH2)n(X)C(Y)(CH2)nOH are capable of 2D (two-dimensional, or dipty) chiral self-association to form a mono-layer at the H2O.air interface.When the molecules are oriented in such a manner that one of HO group is directed into H2O phase, its oxidation (e.g., with permanganate) can result in the formation of a 3D chiral product. This fantasy was partly realised.Remarkable absolute 2D ¢ç 3D asymmetric synthesis was described29 still in Havinga times. A large monocrystal of achiral tiglic acid (space group P1) was cut in two along the planes (2 1 0) and (2 1 0), each part was coated with an epoxide resin (not touching the edges) and treated with an oxidant (Figure 2). In result both enantiomeric products were obtained in yields 40.60% with ee > 95%.By now, numerous data on the homochiral self-association of molecules in monolayers30 and 2D chiral systems31 are obtained. In case of 2D chiral molecule of 1-nitronaphthalene, the formation of decamer clusters of the composition of 8l2d and diptychiral enantiomer 8d2l are found. Similarly to the 3D chiral enantiomers of the Pasteur salt, they are sorted out but scanning tunneling microscopy31 was used instead optical microscope and forceps.Mendeleev Communications Electronic Version, Issue 1, 2001 (pp. 1.42) Therefore we analysed, reproduced, supplemented and developed the above results. We examined two versions of the synthesis of 1 on an 0.1 mol scale (Scheme 2)¡× and found that only iodoallylation at the final stage [the advantages of this synthesis were noted previously5( a),(d)] affords pure product 1, which is nonhygroscopic [in accordance with data from ref. 10(c) and in contrast to data from refs. 5(a),(d)]. In the second version of the synthesis, disproportionation by-products3,4 are formed (cf. ref. 33), which were isolated and identified. Thus, we found that the data by Wedekind are reproducible; however, the version of synthesis is of crucial importance.It is likely that this fact is responsible for discrepant results by Fock concerning studies of ¥á,¥â,¥ã-salts obtained in different manners.5,13 Unfortunately, the procedure used for the synthesis of 1 was also not specified in refs. 19, 24. Well-formed bright transparent crystals of (+)- or (.)-1 (weighing as much as 0.1 g) were prepared by crystallisation from thoroughly purified dry chloroform at .6 ¡ÆC. These crystals were somewhat different in the specific rotation (a crystal was cut in half to perform these measurements).The chiral space group P212121 and the absolute configuration S-(+)-1 were found by X-ray diffraction analysis using a portion of the crystal with maximum [a]D 28.8¡Æ (c 0.8, CHCl3).The barrier .G# = 26.5 kcal mol.1 at 25 ¡ÆC in CHCl3 was found from the kinetics of racemisation. Thus, we supported the data by Fock on the crystallisation of compound as a conglomerate, which are based on the hemihedrism of the crystals, the data by Wedekind on the spontaneous racemisation of (+)-1 and the results by Havinga on the spontaneous resolution of 1.Considering chloroform incorporated in 1 as a conglomerator, 2 we removed CHCl3 by evacuation (1 torr) (signals of CHCl3 in the 1H NMR spectra were monitored in [2H6]acetone). The crystallisation of the sample from EtOH.Et2O with the addition of a half-molar amount of the conglomerator CHCl3 (at .6 ¡ÆC) afforded S-(+)-1 in 20.35% yield, ee 61.70%. Next, we separated 1 by the internal entrainment procedure.2(c) In essence, this technique is a version of spontaneous resolution because the single crystal used for seeding was taken from a starting racemic mixture.A well-formed crystal (1.3 mg) was taken from the sample of 1 (150 mg). This crystal was used as a seed in the crystallisation (with self-evaporation) of this sample from a supersaturated solution in CHCl3 at 20.25 ¡ÆC.The crystals of (+)-1 or (.)-1 were separated in 30.35% yields and ee 70.75% after 3.5 days. In an analogous experiment, the precipitate contained a small amount of the solvent after two weeks. After the removal of the solvent in vacuo (10 torr), the starting material was completely recovered to an optically active form (ee 21%). This experiment was repeated with crystallisation for a month at .6 ¡ÆC followed by the solvent removal in vacuo (10 torr).Surprisingly, this experiment also afforded optically active 1 (ee 16%). Hence, it follows that an autocatalytic effect of enantiomerisation of 1 occurs in the formation of a solid phase. A similar effect was observed previously17(d),(e) for the asymmetric diastereomeric transformation of 1-¥á-carboxyethyl- 3,3-bis(trifluoromethyl)diaziridine (¥áS, 1S, 2S) ¢ç (¥áS, 1R, 2R).At the inversion barrier .G# = 22.5 kcal mol.1 (at 25 ¡ÆC in acetone), crystallisation even at .80 ¡ÆC gave only the first diastereomer. Analogously, the crystallisation (.6 ¡ÆC) of N,N'- dinitroso-N,N'-dimethylethylenediamine [an equilibrium 1:1 mixture of syn.syn and syn.anti rotamers (NO with respect to MeN); the barrier of hindered rotation about the N.N bond .G# = 23.3 kcal mol.1] gave only the first rotamer (relevant ¡× 1H and 13C NMR spectra were measured at 400.13 and 100.61 MHz, respectively; optical activity was studied on a Polamat A polarimeter. 1 was obtained from PhN(Me)Et and allyl iodide (12 h at 20 ¡ÆC), yield 82%; from 2 and EtI (1 month at 6 ¡ÆC, in the dark), yield 36.6%, mp 79. 80 ¡ÆC (CHCl3); for selected monocrystal [a]D 20 = .28.8¡Æ, [a]578 = .29.4¡Æ, [a]546 = .33.8¡Æ (c 0.8, CHCl3). 1H NMR (400.13 MHz, [2H6]acetone) d: 1.1 (t, 3H, MeC, 3J 7.0 Hz), 3.85 (s, 3H, MeN), 4.41 (m, 2H, CH2Me, ABX3 spectrum, .n 66.0 Hz, 2J .13.7 Hz, 3J 7.0 Hz), 5.05 (m, 2H, CH2CH, ABX spectrum, .n 40.6 Hz, 2J .13.1 Hz, 3JAX 7.7 Hz, 3JBX 6.4 Hz), 5.49 (dd, 1H, Hb, 3Jab 10.1 Hz, 2Jac 2.0 Hz), 5.69 (m, 1H, Ha), 5.80 (dd, 1H, Hc, 3Jac 16.8 Hz, 2Jbc 2.0 Hz), 7.66 and 8.21 (m, 5H, Ph), 8.38 (s, 1H, CHCl3) {for CHCl3 1H NMR ([2H6]acetone) d: 7.95}. 13C NMR ([2H6]acetone) d: 8.17 (qt, MeCH2, 1J 129.3 Hz, 2J 2.9 Hz), 47.02 (q, MeN, 1J 143.9 Hz), 63.04 (t, CH2Me, 1J 143.9 Hz), 69.67 (t, CH2CH, 1J 146.7 Hz), 79.22 (d, CHCl3, 1J 215.1 Hz), 125.12 (d, CH=CH2, 1J 159.8 Hz), 127.83 (t, CH2=CH, 1J 159.1 Hz), 122.36, 129.9, 130.0 and 141.32 (d, d, d and s, Ph, 1J 162.8, 164.2 and 164.0 Hz).Found (%): N 3.20. Calc. for C12H20NI¡�CHCl3 (%): N, 3.32. 2 was obtained from N-methylaniline and allyl bromide in abs. MeOH (boiling for 20 h), yield 80%, bp 80 ¡ÆC (5 torr). 1H NMR (CDCl3) d: 2.94 (s, 3H, Me), 3.92 (dt, 2H, CH2, 3J 5.0 Hz, 4J 1.7 Hz), 5.14 (dq, 1H, Hb, 1Jab 10.1 Hz, 2Jbc = 4J = 1.7 Hz), 5.18 (dq, 1H, Hc, 3Jac 17.1 Hz, 2Jbc = 4J = 1.7 Hz), 5.85 (ddt, 1H, Ha, 3JHaCH2 5.0 Hz, 3Jab 10.1 Hz, 3Jac 17.1 Hz), 6.7, 6.73 and 7.24 (m, 5H, Ph). 3 was identified in the mixture with 1 and 4. 13C NMR ([2H6]acetone) d: 47.2 (q, MeN, 1J 144.0 Hz), 69.05 (t, CH2CH, 1J 147.0 Hz), 125.0 (d, CHCH2, 1J 160.0 Hz), 127.8 (t, CH2CH, 1J 159.0 Hz), 122.0, 129.7, 130.4 and 140.9 (d, d, d, and s, Ph, 1J 163.0, 164.0 and 164.1 Hz). 4, mp 102.104 ¡ÆC (MeOH.Et2O), identified with the sample obtained from PhNEt2 and MeI. 1H NMR ([2H6]acetone) d: 1.15 (t, 6H, MeC, 3J 7.0 Hz), 3.83 (s, 3H, MeN), 4.37 (m, 4H, 2CH2Me, ABX3 spectrum, .n 47.0 Hz, 2J .14.1 Hz, 3J 7.0 Hz), 7.65, 7.70 and 8.12 (m, 5H, Ph). 13C NMR ([2H6]acetone): 8.42 (qt, MeCH2, 1J 127.9 Hz, 2J 2.9 Hz), 46.95 (q, MeN, 1J 142.4 Hz), 64.38 (t, CH2Me, 1J 146.8 Hz), 122.82, 130.36, 130.64 and 141.81 (d, d, d and s, Ph, 1J 162.8, 164.2 and 164.8 Hz).Asymmetric transformation of (¡¾)-1 by stirred crystallisation from a melt. The single crystal (4.5 mg) was taken from the sample of (¡¾)-1 (200 mg). The sample and a teflon-coated magnetic stirring bar (l = 8mm, 6mm in diameter) were put in a molybdenic glass ampoule (l = 10 cm, 1 cm in diameter), and the single crystal was put in a side arm of the ampoule. The ampoule was evacuated (1 Torr) and cooled with liquid nitrogen.Then, the ampoule was heated to room temperature and filled with CHCl3 vapour, then cooled again and sealed. The sample was heated to melting point, then cooled to 75 ¡ÆC.The crystal from the arm was transferred to the ampoule, and stirred (800.1000 rpm). After 2.5 h, full sample crystallisation occurred. The ampoule was opened, the sample dissolved in CHCl3 and the optical rotation of the solution was measured. The experiment was repeated three times with the following results: [a]D 18 = +28.0, .28.2 and +28.4¡Æ (c 0.8, CHCl3), ee 97.2, 97.9 and 98.5%, respectively.o a b n m r s s r o m n r r o o s s n n b m m a Mp 166.167 ¡ÆC [a]D 17 = +64.1¡Æ (c 0.49, CHCl3) R-(+)-A Mp 166.168 ¡ÆC [a]D 17 = .65.0¡Æ (c 0.58, CHCl3) S-(.)-A (¡¾)-A+Br. mp 161.163 ¡ÆC Figure 1 The enantiomorphous crystals of salt A. Figure 2 2D ¢ç 3D Absolute asymmetric synthesis in tiglic acid bishydroxylation. H Me CO2H Me H Me CO2H Me H Me CO2H Me X.X HO2C Me H Me X.X CO2H OH H HO Me Me H OH HO2C HO Me Me X.X = OsO4, cat.Ba(ClO3)2 H2O (~0 ¡AElig;C) 2R,3S 2S,3R 40.60% ee > 95%Mendeleev Communications Electronic Version, Issue 1, 2001 (pp. 1.42) data will be published elsewhere). Nevertheless, an increase in the degree of asymmetric conversion with temperature should be expected. W. A. Bonner, commenting the work by Havinga as early as 1972, wrote:25(a) ¡°...With gradual evaporation of the solvent, all of the original racemate might in principle crystallise as the (.)-isomer, provided that the (+)-isomer has not itself undergone chance nucleation in the meantime.¡± Indeed, highly enriched (+)-1, ee 31%, can be obtained by crystallisation from boiling chloroform up to almost complete evaporation.In stirred crystallisation3,28 (500.600 rpm), ee increased up to 51% and became even higher, up to 95%, on the addition of a single crystal from the starting mixture at the step of semievaporation. Stirred crystallisation from a melt (in a sealed ampoule with CHCl3 vapour) with the addition of a single crystal to the melt cooled to 75 ¡ÆC gave a somewhat greater effect (ee 98.5%).Thus, the racemic mixture of 1 was almost fully converted into one enantiomer, and the idea proposed by Havinga was completely supported. Salt 1 was studied by X-ray diffraction analysis,¢Ò initially, with the use of a random crystal and, subsequently, with a crystal known to be optically active in order to determine the absolute configuration. The crystal structure of 1 contains the (S)-(+) quaternary ammonium cation, the iodide anion and the solvate chloroform molecule [Figure 3(a)].The most striking features of 1 were found within the crystal packing analysis. In addition to the weak Cl¡�¡�¡�H contacts [Cl¡�¡�¡�H 2.83 A, Cl¡�¡�¡�H.C 172 and 137¡Æ, for Cl(2) and Cl(3), respectively] between the CHCl3 molecule and the allyl hydrogens of the cation [even shorter intramolecular constants Cl¡�¡�¡�H (2.59 A) were observed for the Ti complexes],34 the former also takes part in the formation of shortened contacts with the I.anion. The CHCl3 molecule is assembled with the I. not only by the short H(13)¡�¡�¡�I contact [H(13)¡�¡�¡�I(1' ) (.1 . x, 1/2 + y, 1/2 . z) 2.81 A, C(13).H(13)¡�¡�¡�I(1' ) 148¡Æ] but also by ¡®long¡� and ¡®short¡� I¡�¡�¡�Cl contacts [C(13).Cl(3)¡�¡�¡�I(1) 3.599(2) A, C(13).Cl(3).I(1) 168.6(1)¡Æ; Cl(1)¡�¡�¡�I(1'' ) (.1/2 .x, 1 . y, 1/2 + z) 3.889(2) A, C(13). Cl(1)¡�¡�¡�I(1'' ) 155.1(1)¡Æ] [Figure 3(b)]. Thus, the crystal packing in 1 can be described as a 3D framework formed by the CHCl3 molecule and the I. anion assembled by short I¡�¡�¡�H and I¡�¡�¡�Cl contacts, with quaternary ammonium cations located in the framework cavities [Figure 3(c)]. It is noteworthy that according to CCDB (release 2000) the Cl(3)¡�¡�¡�I(1) contact in 1 is one of the shortest for the Cl¡�¡�¡�I.type. Taking into consideration the difference in the van der Waals radii of I and Cl atoms (0.26 A),35(a) this contact is comparable with the Cl¡�¡�¡�Cl one in the crystal of chlorine (3.294 A).35(b) The recent topological analysis of the electron density function [r(r)] within the quantum theory of ¡®Atoms in molecules¡� (QTAM)36(a) have shown that such a type of the halogen¡�¡�¡� halogen shortened contacts can be described as a donor.acceptor interaction of a lone pair with an antibonding orbital.36(b),(c) The assumption of such a character for the I(1)¡�¡�¡�Cl(3) interaction will imply the elongation of the corresponding C.Cl bond, while the observed C(13).Cl(3) bond length is practically the same [1.761(3) A] as the remaining [1.768(3) and 1.766(3) A].In order to investigate the character of short I¡�¡�¡�Cl contacts, we performed the QTAM analysis in the HCl2C.Cla¡�¡�¡�I. fragment on the basis of calculations at the MP2 level of theory (Gaussian 94) using the 6-31G* basis for Cl, C and H atoms ¢Ò Crystallographic data for 1: crystals of (C12H18N)(I)(CHCl3) are orthorhombic at 100 K, space group P212121, a = 9.8591(6) A, c = 13.7637(9) A, V = 1710.5(2) A3, Z = 4, M = 422.54, dcalc = 1.641 g cm.3, m(MoK¥á) = = 23.26 cm.1, F(000) = 832.The intensities of 17743 reflections were measured with a Smart 1000 CCD diffractometer at 100 K [l(MoKa) = = 0.71072 A, w-scans with a 0.3¡Æ step in w and 10 s per frame exposure, 2q < 60¡Æ], and 4878 independent reflections (Rint = 0.0296) were used in the further refinement.The absorption correction was carried out semiempirically from equivalents using the Sadabs program. The structure was solved by a direct method and refined by the full-matrix leastsquares technique against F2 in the anisotropic.isotropic approximation.Hydrogen atoms were located from the Fourier synthesis and refined in the isotropic approximation. The absolute (+)-configuration of the N(1) atom in 1 was confirmed by estimating the Flack absolute parameter which, in case of (S) configuration of N(1), has a value close to zero with a rather small e.s.d., 0.00(2).The refinement converged to wR2 = 0.0611 and GOF = 1.062 for all independent reflections [R1 = 0.0234 was calculated against F for 4623 observed reflections with I > 2s(I)]. The number of the refined parameters was 218 (the ratio of the refined parameters for observed reflections was more than 20). All calculations were performed using SHELXTL PLUS 5.0 on IBM PC AT.Atomic coordinates, bond lengths, bond angles and thermal parameters have been deposited at the Cambridge Crystallographic Data Centre (CCDC). For details, see ¡®Notice to Authors¡�, Mendeleev Commun., Issue 1, 2001. Any request to the CCDC for data should quote the full literature citation and the reference number 1135/78. Cl(1) Cl(2) C(13) Cl(3) I(1) C(9) C(8) C(7) C(12) C(10) C(11) N(1) C(1) C(2) C(3) C(4) C(5) C(6) (a) (b) Cl(2) Cl(3) Cl(1) C(13) H(13) I(1) H(13'') a 0b c (c) b 0a c Figure 3 (a) The view of 1 [ellipsoids plot (50%)] illustrating the contents of the unit cell.The main bond lengths (A): N(1).C(1) 1.490(3), N(1).C(7) 1.546(3), N(1).C(10) 1.541(3), N(1).C(12) 1.490(3), C(13).Cl(1) 1.768(3), C(13).Cl(2) 1.766(3), C(13).Cl(3) 1.761(3); bond angles (¡Æ) C(1).N(1).C(12) 113.6(2), C(12).N(1).C(10) 109.3(2), C(1).N(1).C(10) 109.3(2), C(12).N(1).C(7) 107.3(2), C(1).N(1).C(7) 111.0(2), C(10).N(1).C(7) 105.9(2), Cl(1).C1(3).Cl(2) 110.2(1), Cl(1).C(13).Cl(3) 110.6(2), Cl(2). C(13).Cl(3) 111.1(2). (b) H¡�¡�¡�I. and I.¡�¡�¡�Cl contacts. (c) The crystal structure of 1.Mendeleev Communications Electronic Version, Issue 1, 2001 (pp. 1–42) and 3-21G* for I atoms. This calculation leads to the geometry of the I···Cl contact (Cla···I, C–Cla···I equal to 3.476 Å and 177.87°, respectively) similar to that found for I(1)···Cl(3) in 1. In spite of the shorter I···Cl contact observed in the ab initio calculation of HCl2C–Cla···I– the C–Cla bond, instead of the expected elongation, is significantly shortened (1.752 Å) in comparison with remaining (1.784 Å).The QTAM analysis of the HCl2C–Cl···I– revealed that critical points (CP) (3,–1) (the necessary and sufficient condition of the chemical bond36(a)) are observed on C–Cl and C–H bonds as well as on the I···Cl contact. All bonds in the HCCl3 molecule are characterised by negative values of the laplacian of r(r) [Ñ2r(r)]ot;··Cl contact is characterised by positive values of both Ñ2r(r) and E(r) in CP (3,–1) thus indicating the closed-shell type of this interaction. It is noteworthy that the values of r(r) (0.085 eÅ–3) and Ñ2r(r) (0.839 eÅ–5) for CP (3,–1) of the I···Cl contact are close to those obtained earlier for the Cl···Cl contact in chlorine (0.062 eÅ–3, 0.805 eÅ–5)36(b) and ClF (0.135 eÅ–3, 1.06 eÅ–5)36(c) crystals.Taking into account that the value of r(r) correlates with the bond order,36(a) this observation means that the I···Cl interaction is characterised by the comparable strengths with the Cl···Cl (3.294 Å)35(b) one in the chlorine crystal. The same conclusion can also be made on the basis of the Cl···Cl and I···Cl contacts. An analysis of the C–Cl bond polarity by means of the difference of bonded radii [the distance from the nucleus to CP (3,–1)] have revealed that the C–Cla bond is characterised by the lowest one (0.14 Å) in comparison with remaining C–Cl bonds (0.22 Å).Thus, the observed shortening, instead of the expected elongation, of the C–Cla bond is the result of the reverse polarity, which is induced by the iodine negative charge.This work was supported by the Russian Foundation for Basic Research (grant no. 00-03-32738), INTAS (grant no. 99-0157), and DFG-RFBR (grants nos. 436 RUS 113/494/0 and 98-03- 04119, respectively). We are grateful to Professor V. Schurig for the photo and biography data of E. Wedekind, to Professors G.B. Kauffman, H.-G. Schütte, and W. Thiemann for the information about A. L. Fock, to Professor J. Cornelisse for the photo and biography data of E. Havinga. Unfortunately, we failed to find a portrait of Fock. References 1 R. G. Kostyanovsky, G. K. Kadorkina, V. R. Kostyanovsky, V. Schurig, and O. Trapp, Angew. Chem., Int. Ed. Engl., 2000, 39, 2938. 2 (a) V. R. Kostyanovsky, Diploma, Moscow State University, 1998 (in Russian); (b) R. G. Kostyanovsky, G. K. Kadorkina and V. R. Kostyanovsky, Abstracts of the Vth Scientific Conference of the N. N. Semenov Institute of Chemical Physics, RAS, Moscow, 1999, p. 60 (in Russian); (c) R. G. Kostyanovsky, V. R. Kostyanovsky, G. K. Kadorkina and V. Yu. Torbeev, Mendeleev Commun., 2000, 83. 3 J. M. McBride and R. L. Carter, Angew. Chem., Int. Ed. Engl., 1991, 30, 293. 4 P. Walden, Geschichte der organischen Chemie, Verlag von Julius Springer, Berlin, 1941, B. 2, S. 202. 5 (a) E. Wedekind, Zur Stereochemie des fünfwertigen Stickstoffes mit besonderer Berücksichtigung des asymmetrischen Stickstoffes in der aromatischen Reihe, Verlag von Veit & Co., Leipzig, 1899, SS. 44, 48, 56, 57; (b) E. Wedekind, Zur Stereochemie des fünfwertigen Stickstoffes, 2, ed. E. Fröhlich, Verlag von Veit & Co., Leipzig, 1907; (c) E. Wedekind, Ber. Dtsch. Chem. Ges., 1899, 32, 511; (d) E. Wedekind, Ber. Dtsch. Chem. Ges., 1899, 32, 517; (e) E. Wedekind, Ber. Dtsch. Chem. Ges., 1899, 32, 3561; ( f ) E. Wedekind, Z. Phys. Chem., 1903, 45, 235; (g) E. Wedekind, Ber.Dtsch. Chem. Ges., 1903, 36, 3791; (h) E. Wedekind and E. Fröhlich, Ber. Dtsch. Chem. Ges., 1905, 38, 3438; (i) E. Wedekind, O. Wedekind and F. Paschke, Ber. Dtsch. Chem. Ges., 1908, 41, 1029; ( j) E. Wedekind and F. Ney, Ber. Dtsch. Chem. Ges., 1912, 45, 1298; (k) E. Wedekind and G. L. Maiser, Ber. Dtsch. Chem. Ges., 1928, 61, 2471; (l) E. Wedekind, Ber. Dtsch. Chem. Ges., 1934, 67, 2007. 6 (a) A. Hantzsch and A. Werner, Ber. Dtsch. Chem. Ges., 1890, 23, 11; (b) G. B. Kauffman, J. Chem. Educ., 1966, 43, 155. 7 (a) J. A. Le Bel, Compt. Rend., 1891, 112, 724; (b) W. Marckwald and A. F. Droste-Hülshoff, Ber. Dtsch. Chem. Ges., 1899, 32, 560; (c) J. A. Le Bel, Compt. Rend., 1899, 129, 548. 8 N. Menschutkin, Ber. Dtsch. Chem. Ges., 1895, 28, 1398. 9 M. Scholtz, Ber.Dtsch. Chem. Ges., 1905, 38, 595. 10 (a) W. J. Pope and S. J. Peachey, J. Chem. Soc., 1899, 75, 1127; (b) W. J. Pope and A. W. Harvey, J. Chem. Soc., 1901, 79, 828; (c) M. B. Thomas and H. O. Jones, J. Chem. Soc., 1906, 89, 280; (d) R. W. Everatt, J. Chem. Soc., 1908, 93, 1225; (e) F. S. Kipping and W. J. Pope, J. Chem. Soc., 1898, 73, 606. 11 (a) J. Jacques, A. Collet and S. H. Wilen, Enantiomers, Racemates, and Resolutions, Krieger Publ.Comp., Malabar, Florida, 1994; (b) A. Collet, Enantiomer, 1999, 4, 157. 12 (a) A. L. Fock, Einleitung in die chemische Krystallographie, Engelmann, Leipzig, 1888; (b) A. Fock, An Introduction in Chemical Crystallography, ed. W. J. Pope, Clarendon Press, Oxford, 1895. 13 A. Fock, Z. Krystallogr. Mineralog., 1902, 35, 394. 14 G. B. Kauffman and I. Bernal, J. Chem. Educ., 1989, 66, 293. 15 (a) R. K. Hill and T.-H. Chan, J. Am. Chem. Soc., 1966, 88, 866; (b) A. C. Cope, W. R. Funke and F. N. Jones, J. Am. Chem. Soc., 1966, 88, 4693; (c) J. H. Brewster and R. S. Jones, J. Org. Chem., 1969, 34, 354. 16 (a) L. Horner, H. Winkler and E. Meyer, Tetrahedron Lett., 1965, 789; (b) A. F. Peerdeman and J. P. C. Holst, Tetrahedron Lett., 1965, 811. 17 (a) V. F. Rudchenko and R. G. Kostyanovsky, Izv. Akad. Nauk SSSR, Ser. Khim., 1980, 733 (in Russian); (b) R. G. Kostyanovsky, V. F. Rudchenko, V. G. Shtamburg, I. I. Chervin and Sh. S. Nasibov, Tetrahedron, 1981, 37, 4245; (c) R. G. Kostyanovsky and V. F. Rudchenko, Dokl. Akad. Nauk SSSR, 1982, 263, 897 [Dokl. Chem. (Engl. Transl.), 1982, 263, 121]; (d) R.G. Kostyanovsky, G. V. Shustov and N. L. Zaichenko, Tetrahedron, 1982, 38, 949; (e) G. V. Shustov, A. B. Zolotoi, N. L. Zaichenko, O. A. Dyachenko, L. O. Atovmyan and R. G. Kostyanovsky, Tetrahedron, 1984, 40, 2151. 18 D. A. Lenev, K. A. Lyssenko and R. G. Kostyanovsky, Izv. Akad. Nauk, Ser. Khim., 2000, 1244 (Russ. Chem. Bull., 2000, 49, 1241) . 19 E. Havinga, Enjoying Organic Chemistry, 1927–1987, in Profiles, Pathways and Dreams. Autobiographies of Eminent Chemists, ed.J. I. Seeman, ACS, Washington, DC, 1991. 20 B. S. Green, M. Lahav and D. Rabinovich, Acc. Chem. Res., 1979, 12, 191. 21 (a) E. Havinga, Chem. Weekblad, 1941, 38, 642 (Chem. Abstr., 1942, 36, 5790); (b) E. Havinga, Biochim. Biophys. Acta, 1954, 13, 171. 22 M. Calvin, Chemical Evolution, Oxford University Press, London, 1969, p. 150. 23 V. Avetisov and V. Goldanskii, Proc. Nat. Acad. Sci., 1996, 93, 11435. 24 Y. Okada, T. Takebayashi, M. Hashimoto, S. Kasuga, S. Sato and C. Tamura, J. Chem. Soc., Chem. Commun., 1983, 784. 25 (a) W. A. Bonner, in Exobiology, ed. C. Ponnamperuma, North Holland, Amsterdam, 1972, p. 170; (b) W. A. Bonner, Origin Life Evol. Biosphere, 1995, 25, 175; (c) W.A. Bonner, Origin Life Evol. Biosphere, 1996, 26, 27; (d) W. A. Bonner, Chirality, 2000, 12, 114. 26 B. L. Feringa and R. A. van Deldon, Angew. Chem., Int. Ed. Engl., 1999, 38, 3419. 27 H. Buschmann, R. Thede and D. Heller, Angew. Chem., Int. Ed. Engl., 2000, 39, 4033. 28 (a) D. K. Kondepudi, R. J. Kaufman and N. Sing, Science, 1990, 250, 975; (b) D. K. Kondepudi, J.Digits and K. Bullock, Chirality, 1995, 7, 62; (c) D. K. Kondepudi, J. Laudadio and K. Asakura, J. Am. Chem. Soc., 1999, 121, 1448. 29 P. Chinna Chenhalah, H. L. Holland and M. F. Richardson, J. Chem. Soc., Chem. Commun., 1982, 436. 30 (a) I. Kuzmenko, I.Weissbuch, E. Gurovich, L. Leiserowitz and M. Lahav, Chirality, 1998, 10, 415; (b) I. Weissbuch, I. Kuzmenko, M. Berfeld, L.Leiserowitz and M. Lahav, J. Phys. Org. Chem., 2000, 13, 426. 31 (a) M. Böhringer, K. Morgenstern, W.-D. Schneider and R. Berndt, Angew. Chem., Int. Ed. Engl., 1999, 38, 821; (b) M. Lahav and L. Leiserowitz, Angew. Chem., Int. Ed. Engl., 1999, 38, 2533. 32 R.-Y. Qian and G. D. Botsaris, Chem. Eng. Sci., 1998, 53, 1745. 33 E. Fröhlich, Ber. Dtsch. Chem. Ges., 1909, 42, 1561. 34 T. Spaniel, H. Gorls and J. Scholz, Angew. Chem., Int. Ed. Engl., 1998, 37, 1862. 35 (a) R. S. Rowland and R. Taylor, J. Phys. Chem., 1996, 100, 7384; (b) R. L. Colin, Acta Crystallogr., 1956, 51, 14. 36 (a) R. F. W. Bader, Atoms in Molecules. A Quantum Theory, Clarendon Press, Oxford, 1990; (b) V. G. Tsirelson, P. F. Zou, T.-H. Tang and R. F.W. Bader, Acta Crystallogr., 1995, 51A, 144; (c) R. Boese, A. D. Boese, D. Bläser, M. Yu. Antipin, A. Ellern and K. Seppelt, Angew. Chem., Int. Ed. Engl., 1997, 36, 3489. Received: 15th January 2001; Com. 01/1746Andreas Ludwig FOCK April 28, 1856– July 30, 1928 Found the hemihedrism of crystals of this salt, i.e., found that it forms a conglomerate (a mixture of homochiral enantiomer crystals). Almost complete crystallisation-induced asymmetric transformation of a conglomerate into one enantiomer. (±)-Me(Et)N+(All)PhI–·CHCl3 Ph N All Me Et S-(+) I– + Edgar WEDEKIND January 31, 1870– October 22, 1938 Synthesised this chiral ammonium salt, found its composition and examined its spontaneous enantiomerisation in solutions. Egbert HAVINGA May 7, 1909– November 22, 1988 Was the first to observe the optical activity of separated crystals of the salt, i.e., unambigously supported the crystallographic data by Fock and proposed general ideas on spontaneous asymmetric synthesis with clearly defined conditions. Remir KOSTYANOVSKY June 30, 1934 and co-authors (see p. 1) Proposed a general idea of the spontaneous separation of conglomerates by crystallisation with a deficiency of a conglomerator and performed the spontaneous resolution of this salt and its almost complete transformation into one enantiomer, i.e., implemented the Havinga’s idea, and found the structure and absolute configuration of the salt.

ISSN:0959-9436     

出版商:RSC    

年代:2001

数据来源: RSC

摘要:

Mendeleev Communications Electronic Version, Issue 1, 2001 (pp. 1–42) Stereoregular self-assembling of diastereomeric bicyclic bis-lactam diesters Remir G. Kostyanovsky,*a Oleg N. Krutius,a Irina A. Bronzova,a Denis A. Lenev,b Konstantin A. Lyssenkoc and Boris B. Averkievc a N. N. Semenov Institute of Chemical Physics, Russian Academy of Sciences, 117977 Moscow, Russian Federation. Fax: +7 095 938 2156; e-mail: kost@center.chph.ras.ru b Higher Chemical College, Russian Academy of Sciences, 125047 Moscow, Russian Federation.E-mail: lenev@hotmail.com c A. N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences, 117813 Moscow, Russian Federation. Fax: +7 095 135 5085; e-mail: kostya@xrlab.ineos.ac.ru 10.1070/MC2001v011n01ABEH001396 Unprecedented self-assembling of diastereomers has been found in (S)-2-methylbutyl-bis-lactam dicarboxylates 1 and 2, which were not resolved into diastereomers by crystallization but formed optically active H-bonded supramolecular structures of the diastereomeric ratio 1:1.As we have observed earlier, the basic features of H-bonded heterochiral self-assembling of the molecules of bicyclic bislactam diesters A and B in crystals remained surprisingly constant regardless of the type of R in CO2R groups,1–4 and the tight-packed infinite tapes of diagonal (for A)1,2 and linear (for B)3,4 zigzag types were formed, i.e., co-crystallization of enantiomers essentially occurred.Is it possible to carry out a self-assembling of similar molecules to form optically active supramolecular structures, which are of potential interest as liquid crystals and non-linear optics materials? In principle, the presence of functional substituents like CO2R groups makes it possible to introduce homochiral alcohol or amine residues into these molecules.However, this results in formation of diastereomer mixtures, which are well known to be resolved by crystallization.The main task of this work is to determine which way takes place in case of 1 and 2, either resolution of the diastereomers by crystallization or their co-crystallization. The recently found co-crystallization rather than resolution of various configurationally opposite bis-lactam diesters like B (R = Et and Me, R = Et and Pr)4 serves as a premise for the latter way. The synthesis† of bis-lactam diesters 1 and 2 containing homochiral groups R = (S)-Et(Me)CHCH2 was affected via esterification of bis-lactam diacids C2 and D5 by alkylation of their salts with 1,8-diazabicyclo[5.1.0]undec-7-ene (DBU) using a known method.6 (S)-(+)-2-Methylbutyl bromide was obtained from (S)-(–)-2-methylbutan-1-ol using a known method.7 The structure and diastereomeric composition (1:1) of both products (+)-1 and (+)-2 were confirmed by 1H and 13C NMR spectra† (Figure 1), the parameters of which corresponded to those of analogues A, B and related co-crystals.4 It should be noted that diastereomers a and b for both 1 and 2 differ distinctively in the 1H NMR signals of diastereotopic protons of CH2O groups nearest to a chiral skeleton of diastereomers of HN NH RO2C CO2 R O O A, R = Et,1 dodecyl2 NH NH O O RO2C CO2 R B, R = Me,4 Et,3 Pr4 4.0 3.9 3.51 0.9 (a) (b) (c) (d) 6.8 6.6 4.0 3.8 3.6 2.8 2.6 1.6 1.4 1.2 1.0 0.8 Figure 1 1H NMR spectrum (CD3CN) of bis-(S)-2-methylbutyl 3,7-diazabicyclo[ 3.3.1]nonane-2,6-dione-1,5-dicarboxylate: (a) general view of the spectrum, (b) signals of MeCH2 of the diastereomers, (c) MeCH signals of 4,8-He by which the virtual spin-coupling constants with 9-CH2 protons are observed (4Jobs 1.3 Hz) and (d) signals of OCHaHbCHx of the diastereomers a, b [spectra ABX (below) and AB{Hx} (above)].d/ppm Scheme 1 Reagents and conditions: i, the salts were obtained from diacids C, D and DBU in MeOH; after removing the solvent the salt of C was kept with an alkyl bromide in MeCN (14 h at 20 °C), and the salt of D was boiled in MeCN (6 h).Compound (+)-1 was isolated by gradient chromatography on silica (40×100, eluent: light petroleum ether–ethyl acetate, 0 ® 30%), and (+)-2, by chromatography on silica (eluent: ethyl acetate–MeCN, 1:1). HN NH CO2H HO2C O O C (2 DBU) + 2 (S)-(+) Br HN NH O O O O O O (+)-1 HN NH CO2H HO2C D (2 DBU) + 2 (S)-(+) Br HN NH O O O O (+)-2 i i O O O OMendeleev Communications Electronic Version, Issue 1, 2001 (pp. 1.42) opposite configuration [Figure 1(d)]. The concentration dependence of dHN is the evidence for molecular self-association in solution (cf. ref. 8). The optical activity of (+)-1 and (+)-2 was measured by polarimetry and CD spectroscopy¢Ó (cf. ref. 4). The structure and composition of (+)-1 were determined by X-ray diffraction analysis.¢Ô It was found that the unit cell contains two independent molecules, which are diastereomers (Figure 2).Thus crystal of (+)-1 is a 1:1 co-crystal of diastereomers, which has non-centrosymmetrical space group P1. The geometry of central bicyclic fragments of two independent molecules is practically identical to that of previously studied diethyl and didodecyl derivatives.1,2 The angle between C(1).C(7).C(10) and CO2 planes varies in the range 59.5.68.5¡Æ. In spite of the presence of chiral groups, two independent molecules are arranged pseudocentrosymmetrically (Figure 2) ¢Ó (S)-(+)-1-Bromo-2-methylbutane: bp 55 ¡ÆC (80 torr), [a]D 20 4.5¡Æ (c 5.0, CHCl3). 1H NMR ([2H6]acetone) d: 0.91 (t, 3H, MeCH2, 3J 7.4 Hz), 1.00 (d, 3H, MeCH, 3J 6.4 Hz), 1.28 and 1.50 (m, 2H, CH2Me), 3.45 (m, 2H, CH2Br, ABX spectrum, .nAB 10.5 Hz, 2JAB .9.6 Hz, 3JAX 6.0 Hz, 3JBX 5.2 Hz).For 1: yield 10%, mp 135.136 ¡ÆC (from C6H6), [a]578 20 4.1¡Æ, [a]546 20 4.8¡Æ, [a]436 20 9.3¡Æ, [a]406 20 10.8¡Æ (c 1.3, MeCN); [a]578 20 4.8¡Æ, [a]546 20 6.0¡Æ, [a]436 20 10.7¡Æ, [a]406 20 14.3¡Æ (c 0.84, C6H6). 1H NMR (CDCl3) d: 0.88 (t, 6H, 2MeCH2, 3J 7.5 Hz), 0.88 (d, 6H, 2MeCH, 3J 6.7 Hz), 1.17 and 1.40 (m, 4H, 2CH2Me), 1.75 (m, 2H, 2CH), 2.62 (br.s, 2H, 9-CH2), 3.72 (m, 4H, 4,8-CH2, ABX, diastereomer a: .n 40 Hz, 2JAB .12.5 Hz, 3JHaCNH 4.3 Hz, 3JHbCNH 0 Hz), 4.02 (m, 4H, CH2O, diastereomer a: ABX, .n 40 Hz, 2JAB .10.9 Hz, 3JAX 4.8 Hz, 3JBX 4.4 Hz; diastereomer b: ABX, .n 30 Hz, 2JAB .10.9 Hz, 3JAX 4.8 Hz, 3JBX 4.4 Hz), 7.93 (br.d, 2H, 3,7-NH, 3J 4.3 Hz, diastereomer a), 7.94 (br. d, 2H, 3,7-NH, 3J 4.3 Hz, diastereomer b). 1H NMR (CD3CN) d: 0.890 and 0.893 (t, 6H, 2MeCH2, diastereomers a and b, 3J 7.1 Hz), 0.90 (d, 6H, 2MeCH, 3J 6.7 Hz), 1.18 and 1.42 (m, 4H, 2CH2Me), 1.70 (m, 2H, 2CH), 2.66 (t, 2H, 9-CH2, 4Jobs 1.3 Hz), 3.51 (ddt, 2H, 4,8-Me, 2J .12.4 Hz, 3JHCNH 4.0 Hz, 4Jobs 1.3 Hz), 3.70 (d, 2H, 4,8-Ha, 2J .12.4 Hz), 3.97 (m, 4H, 2CH2O, diastereomer a: ABX, .n 46.8 Hz, 2JAB .10.8 Hz, 3JAX 6.4 Hz, 3JBX 6.0 Hz; diastereomer b: ABX, .n 12.0 Hz, 2JAB .10.8 Hz, 3JAX 6.4 Hz, 3JBX 6.0 Hz), 6.67 (br.d, 2H, 3,7-NH, 3J 4.0 Hz). At a five-fold increase of concentration (56.8 mg in 0.5 ml) dHN 6.92 ppm. 13C NMR (CD3CN) d: 10.75 (q, MeCH2, 1J 125.1 Hz), 15.85 (q, MeCH, 1J 125.1 Hz), 26.00 (t, CH2Me, 1J 125.1 Hz), 33.20 (t, 9-CH2, 1J 136.6 Hz), 34.37 (d, CH, 1J 126.6 Hz), 47.90 (t, 4,8-CH2, 1J 147.2 Hz), 49.60 (s, 1,5-C), 70.0 (t, CH2O, 1J 147.2 Hz), 168.4 and 169.2 (s, CO).It was shown by 1H NMR monitoring that 1 is not resolved under various conditions such as sublimation (140.160 ¡ÆC, 1 torr), crystallization from C6H6 or MeOH, gradient chromatography (see Scheme 1), and TLC on silica gel 60F254 (¡®Merck¡�, the thickness of a separating layer is 0.2 mm). In the latter method, an acetone solution of 1 (5%) was applied (exposure of 10 min, iodine vapour as a visualising agent); the only spot, Rf = 0.55, was observed.Similar results were obtained using other solvent systems. For 2: yield 39%, mp 195.197 ¡ÆC, [a]578 20 4.1¡Æ, [a]546 20 4.7¡Æ, [a]436 20 8.8¡Æ, [a]406 20 10.0¡Æ (c 0.9, MeCN).CD spectrum in MeCN (c 3¡¿10.3 M), .e (lmax/nm): .0.95 (214), +0.76 (208), .1.4 (203.2). 1H NMR (C6D6) d: 0.75 and 0.77 ( 6H, 2MeCH2, 3J 7.5 Hz, diastereomers a and b), 0.79 and 0.81 (d, 6H, MeCH, 3J 6.7 Hz, diastereomers a and b), 0.88, 1.00, and 1.27 (m, 4H, 2CH2Me), 1.55 (m, 2H, CH), 1.50 and 1.96 [m, 4H, (CH2)2, AA'BB'], 3.97 (m, 2H, CH2O, ABX, .nAB 70.0 Hz, 2JAB .10.4 Hz, 3JAX 6.8 Hz, 3JBX 5.6 Hz, diastereomer a), 3.97 (m, 2H, CH2O, AB, .n ¡í ¡í 12.0, 2JAB .10.5 Hz, 3JAX = 3JBX = 0 Hz), 6.72 (s, 2H, HN). 1H NMR (CDCl3) d: 0.90 (t, 6H, 2MeCH2, 3J 7.4 Hz), 0.94 (d, 6H, 2MeCH, 3J 6.7 Hz), 1.21 and 1.44 (m, 4H, 2CH2Me), 1.79 (m, 2H, 2CH), 2.27 and 2.46 [m, 4H, (CH2)2, AA'BB'], 4.15 (m, 2H, CH2O, ABX, .n 40.0 Hz, 2JAB .10.6 Hz, 3JAX 8.0 Hz, 3JBX 6.0 Hz, diastereomer a), 4.15 (m, 2H, CH2O, ABX, .n 20.0 Hz, 2JAB .10.5 Hz, 3JAX 6.8 Hz, 3JBX 6.0 Hz, diastereomer b), 6.96 (br.s, 2H, HN). 13C NMR (CDCl3) d: 10.60 (q, MeCH2, 1J 124.7 Hz), 16.16 (q, MeCH, 1J 126.0 Hz), 25.76 (t, CH2Me, 1J 127.5 Hz), 27.99 [t, (CH2)2, 1J 134.3 Hz], 33.91 (d, CH, 1J 129.3 Hz), 64.74 (s, 4,7-C), 71.35 (t, CH2O, 1J 141.6 Hz), 165.60 and 167.20 (s and t, O=COCH2, 3J 6.6 Hz).C(21) C(20) C(19) C(18) C(17) O(5) O(6) C(11) C(5) C(6) O(2) H(7A) N(7) C(4) C(9) N(3) H(3) C(8) C(1) C(2) O(1) C(10) O(4) O(3) C(12) C(13) C(14) C(15) C(16) O(1') H(3') C(2') N(3') N(7') H(7'A) O(2') C(4') C(6') C(8') C(1') C(5') C(9') O(4') C(10') O(3') C(12') C(13') C(14') C(15') C(16') C(11') O(5') O(6') C(17') C(18') C(19') C(20') C(21') Figure 2 General view of two independent molecules of (+)-1.Disordered ester groups are omitted for clarity. ¢Ô Crystallographic data for 1: at 110 K, crystals of C19H30N2O6 are triclinic, space group P1, a = 9.752(3), b = 10.888(3), c = 11.310(3) A, a = 103.236(5)¡Æ, b = 115.168(4)¡Æ, g = 100.874(5)¡Æ, V = 1000.7(5) A3, Z = 2, M = 382.45, dcalc = 1.269 g cm.3, m(MoK¥á) = 0.094 mm.1, F(000) = 412.Intensities of 11915 reflections were measured with a SMART 1000 CCD diffractometer at 110 K [l(MoK¥á) = 0.710712 A, w-scans with a 0.4¡Æ step and 10 s per frame exposure, 2q < 60¡Æ], and 10496 independent reflections (Rint = 0.0168) were used in the further refinement. The structure was solved by a direct method and refined by full-matrix leastsquares against F2 in the anisotropic approximation for non-hydrogen atoms using the SHELXTL-97 package.All hydrogen atoms (with the exception of ester hydrogens) were located from the electron density difference synthesis and included in the refinement in an isotropic approximation. The real parameters of the unit cell are twice higher than the parameters used for the refinement procedure.While molecules in the latter unit cell appeared to be disodered, the twinned unit cell contains four independent molecules without disordering. Unfortunately, the correlation between identical central fragments of these four molecules does not allow us to carry out a correct refinement. The positions of hydrogen atoms of disodered ester were calculated from the geometrical point of view.The refinement converged to wR2 = 0.1608 and GOF = 1.061 for all independent reflections [R1 = 0.0549 was calculated against F for 8822 observed reflections with I > 2s(I)]. All calculations were performed using the SHELXTL PLUS 5.0 program on an IBM PC AT. Atomic coordinates, bond lengths, bond angles and thermal parameters have been deposited at the Cambridge Crystallographic Data Centre (CCDC).For details, see ¡®Notice to Authors¡�, Mendeleev Commun., Issue 1, 2001. Any request to the CCDC should quote the full literature citation and the reference number 1135/77. (a) (b) Figure 3 Diagonal zigzag (a) tapes and (b) layers (2-methylbutyl groups are omitted for clarity). Parameters of the N.H¡�¡�¡�O bonds: N¡�¡�¡�O, 2.795. 2.908(3) A; H¡�¡�¡�O, 1.81.2.12 A; �¢NHO, 170.178¡Æ. Parameters of the C.H¡�¡�¡�O bonds: C¡�¡�¡�O, 3.490.3.539(3) A; H¡�¡�¡�O, 2.47.2.52 A; �¢CHO, 158.159¡Æ.Mendeleev Communications Electronic Version, Issue 1, 2001 (pp. 1–42) and assembled by NH···O bonds into H-bonded diagonal zigzag tapes [Figure 3(a)]. The above tapes are drawn out along the [1 0 1] crystallographic direction and, in turn, are combined into layers parallel to the crystallographic plane (1 0 1) by C–H···O contacts [Figure 3(b)].Thus, zigzag tapes observed in the crystals of bis-lactam derivatives are rather stable supramolecular units. They are unaffected by the introduction of chiral substituents. Therefore, the impossibility to resolve (+)-1 and (+)-2 into diastereomers by crystallization is an unprecedented phenomenon.Resolution did not also occur under conditions of sublimation or chromatography.† This work was supported by the Russian Foundation for Basic Research (grants nos. 00-03-32738 and 00-15-97359) and INTAS (grant no. 99-00157). References 1 R. G. Kostyanovsky, K. A. Lyssenko, Yu. I. El’natanov, O. N. Krutius, I. A. Bronzova, Yu. A. Strelenko and V. R. Kostyanovsky, Mendeleev Commun., 1999, 106. 2 R. G. Kostyanovsky, K. A. Lyssenko, I. A. Bronzova, O. N. Krutius, Yu. A. Strelenko and A. A. Korlyukov, Mendeleev Commun., 2000, 106. 3 R. G. Kostyanovsky, Yu. I. El’natanov, O. N. Krutius, I. I. Chervin and K. A. Lyssenko, Mendeleev Commun., 1998, 228. 4 R. G. Kostyanovsky, K. A. Lyssenko and D. A. Lenev, Mendeleev Commun., 1999, 154. 5 R. G. Kostyanovsky, Yu. I. El’natanov, O. N. Krutius, K. A. Lyssenko, I. I. Chervin and D. A. Lenev, Mendeleev Commun., 1999, 109. 6 N. Ono, T. Yamada, T. Sarro, K. Tanaka and A. Kaji, Bull. Chem. Soc. Jpn., 1978, 51, 2401. 7 V. N. Odinokov, V. R. Akhmetova, Kh. D. Khasanov, A. A. Abduvakhabov, V. R. Sultanmuratova and G. A. Tolstikov, Zh. Org. Khim., 1992, 28, 1173 (Russ. J. Org. Chem., 1992, 28, 915). 8 S. C. Zimmerman and B. F. Duerr, J. Org. Chem., 1992, 57, 2215.

ISSN:0959-9436     

出版商:RSC    

年代:2001

数据来源: RSC

摘要:

Mendeleev Communications Electronic Version, Issue 1, 2001 (pp. 1.42) The electronic structure of the new cubic carbaboride NaB5C as compared to CaB6 and ¡®B4C2¡� by the full-potential LMTO method Alexander L. Ivanovskii* and Sergey V. Okatov Institute of Solid State Chemistry, Urals Branch of the Russian Academy of Sciences, 620219 Ekaterinburg, Russian Federation. Fax: + 7 3432 74 4495; e-mail: ivanovskii@ihim.uran.ru 10.1070/MC2001v011n01ABEH001393 The full-potential LMTO (FP LMTO) method was used for the first time to examine the electronic properties and chemical bonding of the new carbaboride NaB5C in comparison with isostructural and isoelectronic hexaboride CaB6 and ¡®B4C2¡�.Metal hexaborides (MB6) exhibit interesting physical and chemical properties. They are used as materials for high-temperature applications and are intensively studied both theoretically and experimentally.1,2 Extensive investigations of the modification of properties of binary hexaborides are under way.A conventional technique is the doping of the cation sublattice of MB6 with metal atoms (M' ). For example, ternary phases such as rare-earth metal.doped CaB6 (Ca1 .xLaB6,3 Ca1 . xEuxB6,4 etc.) are well known. An alternative way of changing the properties of binary hexaborides is the doping of their boron sublattice. A new group of ternary boron-rich compounds (NaB5C and KB5C) has been synthesised recently.5 They crystallise in a cubic (space group Oh 1.Pm3m) CaB6-like structure where carbon atoms statistically replace boron atoms in B6 octahedra.As distinct from metal-like NaB6 and KB6, these new compounds (carbaborides) are semiconductors.5 In this communication, we report the first findings of the electronic state investigations of a new phase, hexagonal NaB5C, and compare them with the electronic states of isostructural and isoelectronic phases of thoroughly studied CaB6,2,6.8 as well as with the hypothetical ¡®carbaboride¡� B4C2. The latter compound represents the structure model of a CaC6-like boride, in which the cation sublattice is ¡®empty¡� and one third of boron atoms in the anion sublattice is replaced by carbon atoms.The calculation of ¡®B4C2¡� makes it possible to follow the tendencies in changing the electronic spectra of hexaborides when the C/B ratio increases and to establish the role of cationic vacancies. It is well known that these lattice defects are present in some hexaborides.1,2 Recently, Mair et al.9 reported the synthesis of dilithium hexaboride. The structure of Li2B6 is of the CaB6 type with the incomplete occupancy of cationic positions.This favours the appearance of Li+-ionic conductivity. However, the role of cationic vacancies in the formation of the electronic spectra of hexaborides has not been studied until the present time.The electronic structure of CaB6, NaB5C and ¡®B4C2¡� was calculated by the self-consistent full-potential linear muffin-tin orbital method (FP LMTO)10,11 in the local electronic density approximation.12 The computational procedure was described in detail elsewhere.13 The lattice parameter corresponded to a(CaB6) = 7.8352 a.u.1 The energy bands and densities of states (DOS) of CaB6, NaB5C and ¡®B4C2¡� are given in Figures 1 and 2, and the parameters of electronic structures are listed in Table 1.The common valence band of CaB6 (width of ~1.07 Ry) contains 10 occupied energy bands. The lower quasi-core B 2slike band is separated from the group of nine hybrid B 2p,2sbands by a forbidden gap.The DOS profile of these bands has two maxima (B and B' in Figure 2) corresponding to hybrid states, which form covalent B.B sp-bonds inside and between B6 clusters. The first unoccupied band has a large wave-vector dependence, which reflects a delocalised character of the d-states of cations forming the lower edge of the conductivity band. This feature is typical of all CaB6-like hexaborides.2,6.8 The direct energy gap (.Eg) between the valence band and the conduction band (in the X point) is ~0.05 Ry (~0.7 eV).An essentially different type of the electronic spectrum was obtained for NaB5C (see Figures 1 and 2). Whereas the struc- 0.4 0.2 0.0 .0.2 .0.4 .0.6 .0.8 .1.0 .1.2 CaB6 0.4 0.2 0.0 .0.2 .0.4 .0.6 .0.8 .1.0 .1.2 NaB5C 0.4 0.2 0.0 .0.2 .0.4 .0.6 .0.8 .1.0 .1.2 ¡®B4C2¡� ¥Ã M X R ¥Ã Energy/Ry Energy/Ry Energy/Ry Figure 1 Energy bands of CaB6, NaB5C and ¡®B4C2¡�. Table 1 Electronic structure parameters of cubic CaB6, NaB5C and ¡®B4C2¡� (Ry).Parameter/ phase Forbidden gap (transition) Band widths Hybrid sp B 2s Energy gap (sp.B 2s) CaB6 0.048 (X ¢ç X) 0.664 0.080 0.328 NaB5C 0.120 (¥Ã ¢ç X) 0.792 0.056 0.304 ¡®B4C2¡� 0.125 (¥Ã ¢ç X) 0.992 0.041 0.261Mendeleev Communications Electronic Version, Issue 1, 2001 (pp. 1.42) ture of the lower edge of the conduction band of CaB6 and NaB5C remains generally the same (the replacement of a cation leads mainly to a decrease in the energy dispersion of the lower unoccupied band), the substitution of a carbon atom for a boron atom (in B6 clusters) radically alters the structure of the valence band.Figures 1 and 2 and Table 1 show that for NaB5C, as compared to CaB6, (i) the total width of the valence band and of the hybrid sp-band increases; (ii) the forbidden gap between B 2s- and sp-bands decreases; (iii) the widths of B 2s- and B sp-bands decrease; and (iv) new C 2s- (not shown in Figures 1 and 2) and C 2p-bands appear.The latter bands lie in the range from 0.8 to 0.4 Ry below the Fermi level (EF; peak A, Figure 2). The emergence of an anisotropic system of covalent B.B and B.C sp-bonds (inside and between B5C clusters, see Figure 3) disrupts the quasiatomic character of some bands. For example, the upper near-Fermi band becomes energetically dispersed along the ¥Ã.X direction (Figure 2). As a result, the type of interband transitions in CaB6 and NaB5C radically changes: instead of the direct gap in the hexaboride, the semiconducting state for NaB5C is characterised by an indirect gap [¥Ã ¢ç X transition; .Eg ~ 0.12 Ry (~1.63 eV)].The type of the electronic spectrum of the hypothetical ¡®B4C2¡� changes as well. The increase in the C/B ratio and the appearance of direct s.p C.C bonds (Figure 3) favour further growth of the total width of the valence band, near the lower edge of which isolated C 2p-like states (a group of DOS peaks in the range from 0.95 to 0.75 Ry below EF, Figure 2) emerge.The contribution of C 2p-states to the lower unoccupied band increases. The forbidden gap of ¡®B4C2¡� [indirect transition ¥Ã ¢ç X; .Eg ~ 0.13 Ry (~1.77 eV)] has an intermediate value between .Eg for the stable rhombohedral boron carbide B4C (with icosahedral B11C clusters) and the higher carbon-rich BC3 with a layered graphite-like structure.14 To draw a conclusion on the possible stabilization of ¡®B4C2¡�, it is necessary to solve correctly the equation of state for this phase.In summary, note that the imitation of the role of cation defects in the calculations of ¡®B4C2¡� with an ¡®empty¡� metallic sublattice makes it possible to arrive at the preliminary conclusion that no new occupied ¡®vacancy¡� states appear in the spectra of cation-deficient hexaborides (unlike, for example, nonstoichiometric transition metal carbides15).This can be seen in the electronic density maps of ¡®B4C2¡� (Figure 3).Qualitatively, this fact may be related to the distribution of valence states of anions (B, C), which are localised in the vicinity of nuclei and are not ¡®trapped¡� by the cation defect sphere. Hence, we can assume that the role of variable content of cation vacancies in metal hexaborides may be reduced to changes in electron concentration in the cell (i.e., to changes in the degree of near- Fermi band occupation as a futectable rearrangement of the energy spectrum structure.References 1 G. V. Samsonov, T. I. Serebrjakova and V. A. Neronov, Boridy (Borides), Atomizdat, Moscow, 1975 (in Russian). 2 G. P. Schveikin and A. L. Ivanovskii, Usp. Khim., 1994, 63, 751 (Russ. Chem. Rev., 1994, 63, 711). 3 T. Terashima, C.Terakura, Y. Umeda, N. Kimura, H. Aoki and S. Kunii, J. Phys. Soc. Jpn., 2000, 69, 2423. 4 S. Paschen, D. Pushin, M. Schlatter, P. Voltanthen, H. R. Ott, D. P. Young and Z. Fisk, Phys. Rev., 2000, B61, 4174. 5 B. Albert and K. Schmidt, Chem. Mater., 1999, 11, 3406. 6 H. Hasegawa and A. Yanase, J. Phys. C: Solid State Phys., 1979, 12, 5431. 7 H. Ripplinger, K. Schwarz and P.Blaha, J. Solid State Chem., 1997, 133, 51. 8 S. Massidda, A. Continenza, T. M. DePascale and R. Monnier, Z. Phys. B, Condens. Matter, 1997, 102, 83. 9 G. Mair, H. G. van Schering, M. Worle and R. Nesper, Z. Anorg. Allg. Chem., 1999, 625, 1207. 10 M. Methfessel, C. Rodriquez and O. K. Andersen, Phys. Rev., 1989, B40, 2009. 11 M. Methfessel and M. Scheffler, Physica B., 1991, 172, 175. 12 M. Methfessel, Phys. Rev., 1988, B38, 1537. 13 N. I. Medvedeva, D. L. Novikov, A. L. Ivanovskii, M. V. Kuznetzov and A. J. Freeman, Phys. Rev., 1998, B58, 16042. 14 A. L. Ivanovskii, Usp. Khim., 1997, 66, 511 (Russ. Chem. Rev., 1997, 66, 459). 15 V. A. Gubanov, A. L. Ivanovskii and V. P. Zhukov, Electronic Structure of Refractory Carbides and Nitrides, University Press, Cambridge, 1994. 100 80 60 40 20 0 100 80 60 40 20 0 100 80 60 40 20 0 A B B' EF C A EF EF (a) (b) (c) DOS (states/Ry cell) DOS (states/Ry cell) DOS (states/Ry cell) .1.2 .1.0 .0.8 .0.6 .0.4 .0.2 0.0 0.2 0.4 Energy/Ry Figure 2 DOS of (a) CaB6, (b) NaB5C and (c) ¡®B4C2¡�. B C Na Vac Na Na Na Vac Vac Vac C C (a) (b) Figure 3 Valence density distribution for (a) NaB5C and (b) ¡®B4C2¡�. Received: 31st October 2000; Com. 00/

ISSN:0959-9436     

出版商:RSC    

年代:2001

数据来源: RSC

摘要:

Mendeleev Communications Electronic Version, Issue 1, 2001 (pp. 1–42) Effect of metal and carbon vacancies on the electronic structure of hexagonal WC and cubic TaC Alexander L. Ivanovskii* and Nadezhda I. Medvedeva Institute of Solid State Chemistry, Urals Branch of the Russian Academy of Sciences, 620219 Ekaterinburg, Russian Federation. Fax: +7 3432 74 4445; e-mail: ivanovskii@ihim.uran.ru 10.1070/MC2001v011n01ABEH001375 The electronic states and energy characteristics of carbon and metal vacancies in hexagonal â-WC and cubic TaC were examined by the full-potential LMTO method.Group IV–VI transition metal carbides are well-known nonstoichiometric compounds. For example, the concentration of carbon vacancies in Group IV and V transition metal cubic (B1 type) carbides can be as high as 30–55 at%.As a rule, the metal sublattice of carbides remains complete.1 The electronic properties of carbon vacancies and their effect on the physico-chemical characteristics of cubic (B1 type) 3dand 4d-metal monocarbides were studied previously.2–6 At the same time, the electronic states of vacancies in VI Group metal non-cubic carbides are still not clearly understood. Hexagonal tungsten carbide (â-WC) is one of the most interesting compounds of this kind.It possesses extreme thermomechanical properties and exhibits a catalytic activity comparable to the activity of platinum.1 â-WC exhibits a narrow range of homogeneity, in which the carbon content varies within the limits 37–48 at%. Until recently, the metal lattice of WC was considered to be fully occupied.Recently,7 the presence of both C- and W-vacancies in WC was found by the positron annihilation method. We report here the results of studies concerning the electronic states of both of the types of lattice defects — carbon (VC) and metal (VW) vacancies — in hexagonal WC. By now, only the electronic structure of an ‘ideal’ (complete) â-WC crystal was examined.6 For comparison, we also calculated the electronic states of VC and VTa vacancies in cubic TaC, a typical B1 carbide, which is characterised by a wide range of homogeneity. 1 The carbides MC (M = W and Ta) were simulated by 16-atomic M8C8 supercells in hexagonal (â-WC) and cubic (TaC) structures.The M8C7VC and M7VMC8 supercells described defect carbides of the formal compositions MC0.875 and M0.875C, respectively.The electronic structures of MC, MC0.875 and M0.875C were calculated by the self-consistent full-potential linear muffin-tin orbitals method (FP-LMTO)8,9 with the Hedin–Lundqist exchange potential in the electron density functional approximation. 10,11 Valence electrons (6s, 6p and 5d for Ta and W and 2s and 2p for C) were calculated in a scalar relativist version.Vacancies in both sublattices were modelled by empty spheres with zero charges and 1s, 2s orbitals in the basis. Muffin-tin orbitals were calculated using a 3k basic set with the kinetic energies of s-, p- and d- functions –k2 = 0.01, 0.1 and 2.3 Ry. Integration over the Brillouin zone was performed by the linear method of tetrahedra. Structural data for WC and TaC are consistent with published data.1,7 Figure 1 demonstrates the densities of states (DOS) for â-WC.The valence band (VB) of the carbide is represented by two fundamental bands (A, B) separated by a forbidden gap. Lower band A is formed by contributions from C 2s states, and mixed-type band B is formed by overlapping W 5d–C 2p states. The Fermi level (EF) is located at a local DOS minimum between the bands of bonding and antibonding W–C states.Note that this case corresponds to the highest cohesive properties because all bonding states are occupied and all antibonding states are vacant. Figures 2 and 3 show the densities of states of defect WC0.875 and W0.875C. The introduction of C-vacancies (VC) results in the appearance of a new DOS peak (D') and in a change in the DOS distribution in the region of the Fermi level (Figure 2).These changes are associated with the formation of ‘vacancy’ states (VS). Figure 2 demonstrates that VS form two relatively large peaks D and D' in the spectrum of WC0.875. They originated from the partial removal of the d-states for W atoms surrounding a vacancy (solid line) into bonding and antibonding states.As a result, a portion of W d-states ‘returned’ into the nonbonding state. ‘Vacancy’ DOS peaks D and D' reflect a decrease and an increase in the energy of bonding (peak D) or antibonding (peak D') W d-states, respectively, as compared to those in complete WC (Figure 1). The effect of W-vacancies (VW) on the spectrum of WC depends on a change in the electronic states of carbon atoms nearest to the vacancy.The transition of a portion of C 2p-states into the region of nonbonding states is clearly defined in the DOS of carbon atoms nearest to a vacancy (solid line in Figure 3). As a result, the emptying of a part of bonding states takes place in the presence of both C- and W-vacancies, the Fermi level is shifted to the lower energy range and the DOS on the Fermi level [N(EF)] increases (Table 1).The shift of the Fermi level is more pronounced for W0.875C and the larger part of bonding states is empty. This results in lower cohesive properties as compared with WC0.875. The calculations for B1-TaC TaC0.875 and Ta0.875C showed that the general mechanism of changes in the electronic spectrum of the cubic carbide is similar to that described above (see also ref. 6). Differences in the VS energy between TaC and WC depend on differences between the coordination polyhedra in the structures of these carbides (regular octahedra in TaC and trigonal prisms in WC). We evaluated the effects of lattice vacancies on the energy characteristics of carbides in terms of the FP-LMTO method. For this purpose, we calculated11 the cohesive energies (Ecoh) as a total energy difference between carbide and free atoms and then estimated the energy of vacancy formation (Ev) as a difference between the cohesive energies of stoichiometry and 80 40 0 10 1 2 C W WC DOS/Ry–1 E/Ry A B EF 3 0 0 40 Figure 1 Total (top) and local densities of states for â-WC.Mendeleev Communications Electronic Version, Issue 1, 2001 (pp. 1–42) defect carbides. The results indicate that in both of the carbides the presence of both carbon and metal vacancies impairs the cohesive properties of carbides and Ev(M) > Ev(C). This fact is in agreement with our conclusion on worse cohesive properties of the carbide with metal vacancies, which was obtained from the DOS comparison. The above inequality is consistent with experimental data,1 according to which vacancies in the carbon sublattice are primarily formed in carbides, whereas the formation of M-vacancies requires special conditions (for example, annealing after electron irradiation7).In turn, the energy of formation of C-vacancies in B1-TaC is considerably lower than that in hexagonal WC. This result can explain differences between the equilibrium defect contents of these carbides.As was found experimentally, TaC exhibits a much wider range of homogeneity (as compared with â-WC). In summary, note that the electronic structures of nonstoichiometric WCx and WyC carbides were almost not examined experimentally. Preliminary data on charge-density distributions in â-WC were obtained by positron annihilation.7 The life time of positron trapped by a C-vacancy (tC ~ 136 ps) was found7 to be much shorter than that for a W-vacancy (tW ~ 175 ps).The longer value of tW was explained7 by a lower electron density near metal vacancies surrounded by carbon atoms, whereas tungsten atoms with a higher electron density form the environments of C-vacancies to result in tC < tW. We calculated the electron-density distribution in the spheres of W- and C-vacancies.We found that Q(VW) = 0.51e < Q(VC) = = 0.67e, which is consistent with the relation tC < tW. Taking into account that in â-WC positrons primarily annihilate with electrons remote from positively charged nuclei,11 we also compared so-called ‘intrasphere’ electron densities (Qis). The corresponding values were Qis(WC0.875) = 2.98e > Qis(W0.875C) = 2.77e, which are also consistent with the differences between tC and tW in â-WC.Of course, to estimate the values of t quantitatively, a special problem should be solved with the introduction of positron wave functions into the basis. References 1 L. E. Toth, Transition Metal Carbides and Nitrides, Academic Press, New York, 1971. 2 W.E. Pickett, B. M. Klein and R. Zeller, Phys. Rev., 1986, B34, 2517. 3 P. Marksteiner, P.Weinberger, A. Neckel, R. Zeller and P. H. Dederichs, Phys. Rev., 1986, B33, 812. 4 A. L. Ivanovskii, V. I. Anisimov, D. L. Novikov, A. I. Lichtenstein and V. A. Gubanov, J. Phys. Chem. Solids, 1988, 49, 465. 5 D. L. Novikov, A. L. Ivanovskii and V. A. Gubanov, Phys. Status Solidi B, 1987, 139, 257. 6 V. A. Gubanov, A. L. Ivanovskii and V. P. Zhukov, Electronic Structure of Refractory Carbides and Nitrides, University Press, Cambridge, 1994. 7 A. A. Rempel, R. Wurschum and H.-E. Schaefer, Phys. Rev., 2000, B61, 5945. 8 M. Methfessel, C. Rodriquez and O. K. Andersen, Phys. Rev., 1989, B40, 2009. 9 M. Methfessel and M. Scheffler, Physica B, 1991, 172, 175. 10 M. Methfessel, Phys.Rev., 1988, B38, 1537. 11 N. I. Medvedeva, D. L. Novikov, A. L. Ivanovskii, M. V. Kuznetzov and A. J. Freeman, Phys. Rev., 1998, B58, 16042. 12 A. A. Rempel, Usp. Fiz. Nauk, 1996, 166, 33 (Phys. Usp., 1996, 39, 31). 40 0 10 20 5 15 0 0 40 20 10 5 0 0.0 0.5 1.0 1.5 2.0 2.5 3.0 E/Ry DOS/Ry–1 WC0.875 VC W C A B EF D D' Figure 2 Total (top) and local densities of states (LDOS) for WC0.875.The LDOS of W atoms nearest to the VC-vacancy are shown by a solid line; the mean values of all nonequivalent C atoms in the W8VCC7 supercell are shown for carbon. 40 0 10 20 5 15 0 0 40 20 10 5 0 0.0 0.5 1.0 1.5 2.0 2.5 3.0 E/Ry DOS/Ry–1 W0.875C VW W C A B EF D D' Figure 3 Total (top) and local densities of states for W0.875C. The LDOS of C atoms nearest to the VW-vacancy are shown by a solid line; the mean values of all nonequvalent W atoms in the W7VWC8 supercell are shown for tungsten. Table 1 Cohesive energies Ecoh, vacancy formation energies Ev, Fermi energies EF and densities of states at the Fermi level N(EF) for complete WC and TaC and carbides containing structure vacancies. Carbide Ecoh/Ry Ev/Ry EF/Ry N(EF)/Ry–1 WC 1.76 — 1.86 3.16 WC0.875 1.63 0.13 1.84 8.26 W0.875C 1.56 0.20 1.62 9.37 TaC 1.64 — 1.80 8.90 TaC0.875 1.58 0.09 1.75 9.27 Ta0.875C 1.52 0.15 1.53 6.88 Received: 14th September 2000; Com. 00/1702

ISSN:0959-9436     

出版商:RSC    

年代:2001

数据来源: RSC

摘要:

Mendeleev Communications Electronic Version, Issue 1, 2001 (pp. 1.42) Ion pairs in the crystal structure of potassium ethyl viologen hexacyanometallates(II) Sof¡�ya A. Kostina,a Andrei B. Ilyukhin,a Boris V. Lokshinb and Vitalii Yu. Kotov*a a N. S. Kurnakov Institute of General and Inorganic Chemistry, Russian Academy of Sciences, 117907 Moscow, Russian Federation. Fax: +7 095 954 1279; e-mail: tsir@elch.chem.msu.ru b A.N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences, 117813 Moscow, Russian Federation. E-mail: bloksh@ineos.ac.ru 10.1070/MC2001v011n01ABEH001391 The isostructural potassium ethyl viologen hexacyanometallates EV1.5K[M(CN)6]¡�12.5H2O (EV2+ is N,N'-diethyl-4,4'-bipyridinium, M = Fe or Ru) were prepared and characterised.The reactions between N,N'-dialkyl-4,4'-bipyridinium cations (alkyl viologens) and the hexacyanoferrate(II) ion in aqueous solutions result in the formation of ion pairs and are accompanied by the appearance of an absorption band at 18000. 20000 cm.1 in the electronic absorption spectra.1.3 Meyer and co-authors2 calculated the rate of the redox reaction between ions using the spectral characteristics of the absorption band and the electron-transfer distance estimated from the ionic radii.However, published data1.3 on the spectroscopic and geometric characteristics of ion pairs are inconsistent. The stability constants of ion pairs and structural data are commonly used for evaluating the electron-transfer distance in ion pairs. Contact distances between ions in the test systems are difficult to calculate from the stability constants and erroneous results can be obtained because the ions are non-spherical.The compound MV2[Fe(CN)6]¡�7H2O (MV2+ is methyl viologen) was isolated;1 however, its structure was not examined. In this work, we studied the structure and spectroscopic properties of nearest analogues of this compound. Compounds EV1.5K[Fe(CN)6]¡�12.5H2O 1 and EV1.5K- [Ru(CN)6]¡�12.5H2O 2 are intensely coloured compounds.¢Ó Their diffusion-reflectance spectra (Figure 1) exhibit chargetransfer bands at 18300 (1) and 22900 cm.1 (2).In the spectra of aqueous solutions containing viologen diiodide (0.01 mol dm.3) and potassium hexacyanometallates (0.1 mol dm.3), analogous band maxima are at 19200 (1) and 23500 cm.1 (2).This fact allowed us to conclude that the structures of ion pairs in solution and in crystals are similar. In the crystal structures of 1¢Ô and 2,¡× ethyl viologen cations form the walls of channels in which hydrogen-bonded water molecules and K(H2O)3[M(CN)6] units are arranged alternately (Figure 2). The shortest distances between d-metal atoms are 8.81 and 8.89 A for 1 and 2, respectively.The [M(CN)6]4. ion is surrounded with six ethyl viologen cations. The distances between d-metal atoms and nitrogen atoms of the pyridine rings of viologen are 5.05 (A) and 5.40 A (B) for 1 or 5.07 (Figure 3, A) and 5.45 A (Figure 3, B) for 2. The distances from metal atoms to the centres of pyridine rings are 5.96 (Figure 3, A) and 5.62 A (Figure 3, B) for 1 or 5.99 (Figure 3, A) and 5.67 A (Figure 3, B) for 2.The above crystallographic distances are much shorter than the distances between ions in the ion pair MV2+,[Fe(CN)6]4. estimated at 6.3.8.12 or 10.4 A,3 on the basis of the hexacyanoferrate ion radius 4.4.4.6 A with respect to the fourfold axis of an octahedral complex.2,3 Previously,4,5 it was found that the effective radius of hexacyanoferrate ions with respect to the twofold axis of an octahedral complex, which is aligned with the direction of t2g orbitals participating in electron ¢Ó The compounds EV1.5K[M(CN)6]¡�12.5H2O (M = Fe or Ru for 1 or 2, respectively) were isolated by the isothermal (T = 277 K) evaporation of solutions of ethyl viologen diiodide (Aldrich) and potassium hexacyanoferrate (analytical grade) or potassium hexacyanoruthenate (Alfa) in the 1:1 molar ratio. 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0.0 15000 20000 25000 30000 35000 n/cm.1 A Figure 1 Diffuse-reflectance spectra of compounds 1 and 2. 1 2 ¢Ô Crystallographic data for 1: C27H52FeKN9O12.5, M = 797.73, trigonal, space group P3c1 (no. 165), a = 15.0433(14), c = 20.853(5) A, V = = 4086.8(11) A3, Z = 4, dcalc = 1.297 g cm.3, F(000) = 1688.Crystal size 0.20¡¿0.20¡¿0.10 mm. Experiments were performed on an Enraf Nonius CAD-4 diffractometer using MoK¥á radiation (l = 0.71073 A) and 294 K. The intensities of 3965 reflections were measured within the range 1.56 < q < 25.96¡Æ (w/2q scan); 2683 independent reflections were used in the calculations (Rint = 0.0356). The crystal was not decomposed in the course of experiments (the intensities of reference reflections decreased by 2.1%); absorption was not taken into account (minimum and maximum transmission was 0.90 and 0.95, respectively).The structure was solved by a direct method and refined by the least-squares technique in an anisotropic.isotropic approximation (H atoms). The maximum electron density peak in the zero Fourier synthesis was 0.481 e A.3 (near a disordered water molecule). The final refinement parameters: wR2 = = 0.1830, R1 = 0.1587 (all reflections), wR2 = 0.1418, R1 = 0.0529 [1270 reflections with I > 2s(I)], GOF = 1.013 (193 refinement parameters).All calculations were performed using the SHELXS.97 and SHELXL.97 programs.7,8 ¡× Crystallographic data for 2: C27H52RuKN9O12.5, M = 842.95, trigonal, space group P3c1 (no. 165), a = 15.1572(17), c = 20.956(5) A, V = = 4169.4(12) A3, Z = 4, dcalc = 1.343 g cm.3, F(000) = 1760. Crystal size 0.15¡¿0.15¡¿0.09 mm. Experiments were performed on an Enraf Nonius CAD-4 diffractometer using MoK¥á radiation (l = 0.71073 A) and 294 K. The intensities of 8227 reflections were measured within the range 1.55 < q < 28.01¡Æ (w/2q scan); 3356 independent reflections were used in the calculations (Rint = 0.0911).The crystal was not decomposed in the course of experiments (the intensities of reference reflections decreased by 3.1%); y-correction of the reflection array was performed (minimum and maximum transmission was 0.79 and 0.95, respectively). As a starting approximation in the refinement, the model of 1 was taken (without oxygen atoms of crystal water molecules).The refinement was performed by the least-squares technique in an anisotropic.isotropic approximation (H atoms). The maximum electron density peak in the zero Fourier synthesis was 1.004 e A.3 (near a disordered water molecule). The final refinement parameters: wR2 = 0.1645, R1 = 0.0990 (all reflections), wR2 = 0.1438, R1 = 0.0519 [2035 reflections with I > 2s(I)], GOF = 1.058 (185 refinement parameters).All calculations were performed using the SHELXL.97 program.8 Atomic coordinates, bond lengths, bond angles and thermal parameters for compounds 1 and 2 have been deposited at the Cambridge Crystallographic Data Centre (CCDC). For details, see ¡®Notice to Authors¡�, Mendeleev Commun., Issue 1, 2001. Any request to the CCDC for data should quote the full literature citation and the reference number 1135/76.Mendeleev Communications Electronic Version, Issue 1, 2001 (pp. 1–42) transfer, is 3.4–3.7 Å. The effective radius of hexacyanoferrate ions with respect to the threefold axis of an octahedral complex can be estimated at 2.7 Å from the shortest distance between ions in the K(H2O)3[Fe(CN)6] unit taking the potassium ion radius to be equal to 1.38 Å (Figure 4).The above distances between EV2+ and [M(CN)6]4– ions lie between minimally and maximally possible values and are consistent with the fact that ethyl viologen ions are located in general positions. The structure of a K(H2O)3[Fe(CN)6] unit, in which potassium ions are coordinated to three cyanide ligands (Figure 4; N(1)– K(1), 3.218(4) Å; C(1)–K(1), 3.302(4) Å), is similar to the structure of the contact ion pair K+,[Fe(CN)6]4–.This is supported by the similarity of the she 4.07 Å between ions with a value of 4.3±0.1 Å derived from the thermodynamic stability constant of an ion pair.6 The structure of a doubled K(H2O)3[Fe(CN)6] unit makes it possible to estimate the distance between K+ and [Fe(CN)6]4– ions in a solvent-separated ion pair at 6.35 Å. In this case, hexacyanoferrate ions are hydrogen-bonded to water molecules of a hydrated potassium cation [Figure 4; O(1C)…N(2), 2.895(6) Å].Taking into account that the above value is close to 6.6±0.2 Å found6 from the thermodynamic stability constant of the ion pair K+,[Fe(CN)6]3–, we may believe that ions in this ion pair are separated by water molecules.In the structures of 1 and 2, [M(CN)6]4– ions exhibit C3 symmetry. The geometry parameters of two crystallographically independent cyanide ligands differ from one another [C(1)– N(1) 1.149(5) and 1.144(5) Å, M(1)–C(1) 1.928(5) and 2.039(4) Å, M(1)–C(1)–N(1) 174.6(4)° and 175.6(3)°; C(2)– N(2) 1.171(5) and 1.152(5) Å, M(1)–C(2) 1.910(5) and 2.030(4) Å, M(1)–C(2)–N(2) 177.5(4)° and 177.9(3)° for 1 and 2, respectively]. The low symmetry of [M(CN)6]4– ions in crystals results in an increase in the number of active nCN vibrations in the IR spectra (Figure 5).¶ The free [M(CN)6]4– ion having Oh symmetry should exhibit only a single nCN band due to threefold degenerate F1u vibrations.The correlation diagram that describes a change in the vibrational spectra in the nCN frequency region on going from an isolated ion to an ion in a crystal cell with C3 site symmetry of anions for the D3d group suggests that the spectra of a crystal should exhibit six (2A2u + 4Eu) bands, and these bands were observed in the measured spectra. References 1 A. Nakahara and J.H. Wang, J. Phys. Chem., 1963, 67, 496. 2 J. C. Curtis, B. P. Sullivan and T. J. Meyer, Inorg. Chem., 1980, 19, 3833. 3 H. E. Toma, Can. J. Chem., 1979, 57, 2079. 4 V. Yu. Kotov and G. A. Tsirlina, Mendeleev Commun., 1999, 181. 5 S. I.Gorel’skii, T. G. Kim, T. P. Klimova, V. Yu. Kotov, B. V. Lokshin, Yu. D. Perfil’ev, T. I. Sherbak and G. A. Tsirlina, Mendeleev Commun., 2000, 86. 6 W. A. Eaton, P. George and G. I. H. Hanania, J. Phys. Chem., 1967, 71, 2016. 7 G.M.Sheldrick, SHELXS-97. Program for the Solution of Crystal Structures, University of Göttingen, Germany. 8 G.M.Sheldrick, SHELXL-97. Program for the Refinement of Crystal Structures, University of Göttingen, Germany. Figure 2 Projection of the structure of 1 along the z-axis. Figure 3 Structure fragment of 1. A A A B B B Figure 4 Chains of the K(H2O)3[Fe(CN)6] ion pairs in the structure of 1. Fe(1A) O(1A) O(1B) K(1) O(1) O(1AA) O(1BA) K(1A) O(1C) N(2B) C(2B) C(2) N(2) N(2A) C(2A) Fe(1) N(1A) C(1A) C(1B) N(1B) C(1) N(1) ¶ The IR spectra of samples as Vaseline oil mulls were measured on a Nicolet Magna-750 Fourier spectrometer with a resolution of 2 cm–1. The computer deconvolution of a spectrum on a mixed-contour (Gaussian + Lorentzian) basis revealed six components with frequencies of 2094, 2064, 2045, 2031, 2015 and 2005 cm–1 for 1 and 2113, 2076, 2055, 2040, 2027 and 2018 cm–1 for 2. 1.2 1.0 0.8 0.6 0.4 0.2 0.0 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0.0 Absorbance 2100 2050 2000 n/cm–1 Figure 5 IR spectra of 1 and 2 in the region of nCN stretching vibrations. 1 2 Received: 30th October 2000; Com. 00/1717

ISSN:0959-9436     

出版商:RSC    

年代:2001

数据来源: RSC

摘要:

Mendeleev Communications Electronic Version, Issue 1, 2001 (pp. 1.42) Synthesis of closo-monocarbon carborane-substituted natural porphyrins Valentina A. Ol¡�shevskaya,*a Rima P. Evstigneeva,b Valentina N. Luzgina,b Maya A. Gyul¡�malieva,b Pavel V. Petrovskii,a John H. Morrisc and Leonid I. Zakharkina a A. N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences, 117813 Moscow, Russian Federation.Fax: + 7 095 135 5085; e-mail: olshevsk@ineos.ac.ru b M. V. Lomonosov Moscow State Academy of Fine Chemical Technology, 117571 Moscow, Russian Federation. Fax: + 7 095 434 8711; e-mail: evstigneeva@httos.mitht.msk.ru c Department of Pure and Applied Chemistry, Strathclyde University, Glasgow, G1 1XL, UK 10.1070/MC2001v011n01ABEH001383 Previously unknown 1,3,5,8-tetramethyl-6,7-di[2'-(closo-monocarbon carborane-1''-yl caesium)methoxycarbonylethyl]porphyrin and 1,3,5,8-tetramethyl-2,4-divinyl-6,7-di[2'-(closo-monocarbon carborane-1''-yl caesium)methoxycarbonylethyl]porphyrin were synthesised in the reactions of deuteroporphyrin IX and protoporphyrin IX, respectively, with (1-hydroxymethyl-closomonocarbon carborane)caesium.Currently, considerable attention is paid to the synthesis of carboranyl-substituted heterocycles for the use as pharmaceuticals for the boron neutron-capture therapy (BNCT) of cancer.1 Among these compounds are carboranylporphyrins, which were synthesised more than two decades ago.2 Interest in the synthesis of boronated porphyrins is caused by the ability of these compounds to accumulate selectively and to persist in tumour cells for a long time.Previously,3.5 we described the syntheses of carboranyl-substituted porphyrins, in which the carborane polyhedron is bound to the porphyrin ring through the boron atom of carborane, which allows further functionalization at carbon atoms of the carborane polyhedron in order to decrease the lipophilicity of carborane substituents.Current progress in the carborane chemistry provides an opportunity to prepare new functionalised organic derivatives of monocarbon carborane,6 which are convenient synthons for the synthesis of a new type of monocarbon carborane-substituted porphyrins for BCNT. This work is devoted to the synthesis of novel monocarbon carborane-substituted porphyrins. Using natural deuteroporphyrin IX 1a, protoporphyrin IX 1b and (1-hydroxymethyl-closomonocarbon carborane)caesium 2, we obtained anionic monocarbon carborane derivatives of deuteroporphyrin IX 3a and protoporphyrin IX 3b, in which the closo-monocarbon carborane substituent is bound to the carboxylic groups of porphyrins 1a,b through the carbon atom of the closo-monocarbon carborane polyhedron (Scheme 1).¢Ó The reactions were performed in a methylene chloride.pyridine (1:1) mixture. Upon activation of carboxylic groups of porphyrins 1a,b with di-tert-butylpyrocarbonate (Boc2O) in the 1:2 ratio, compounds 3a and 3b were obtained as dark claret substances in 52 and 50% yields, respectively. Note that, although they are salts, compounds 3a and 3b are, nevertheless, poorly soluble in hydroxy-containing solvents.At the same time, they are readily soluble in THF, DMSO, DMF, MeCN and C5H5N. It is believed that the use of Na+, K+ or lipophilic organic cations instead of the Cs+ cation increases the water solubility of these compounds. The structures of 3a and 3b were confirmed by mass spectrometry and electronic absorption, IR and 1H NMR spectroscopy.¢Ô C HO NH N N HN Me R Me Me Me R HOOC COOH Cs+ Py.CH2Cl2 Boc2O DMAP 20 ¡ÆC NH N N HN Me R Me Me Me R O O C O O C 2 2Cs+ 1a,b 2 3a,b a R = H b R = CH=CH2 Scheme 1 ¢Ó General procedure for the synthesis of porphyrins 3a,b.To a solution of porphyrin 1a or 1b (0.196 mmol) in a mixture of 5 ml C5H5N and 5 ml CH2Cl2, Boc2O (0.22 mmol) was added, and the mixture was stirred for 10 min at 0 ¡ÆC.Then, compound 2 (0.392 mmol) and 4-dimethylaminopyridine (15 mg) were added, and the mixtiure was stirred for 1 h at 20 ¡ÆC. The reaction was monitored by TLC [Silufol plates, CHCl3. MeOH (9:1) as an eluent]. After completion of the reaction, the solvents were removed in vacuo, CHCl3 (5 ml) was added to the residue, and crystals of precipitated porphyrins 3a or 3b precipitated were filtered off.Recrystallisation from a DMSO.water mixture gave porphyrins 3a and 3b in 52 and 50% yields, respectively. ¢Ô Electronic absorption spectra were recorded on a Varian MAT 731 instrument. IR spectra were recorded on a UR-20 spectrometer as KBr pellets. 1H NMR spectra were recorded on a Bruker AMX-400 spectrometer at 400.13 MHz in [2H6]DMSO with TMS as a standard. 1,3,5,8-Tetramethyl-6,7-di[2'-(closo-monocarbon carborane-1''-yl caesium)methoxycarbonylethyl]porphyrin 3a: yield 52%. 1H NMR, d: 10.82 (s, 1H, meso-H), 10.31 (s, 1H, meso-H), 10.27 (s, 2H, meso-H), 9.33 (s, 1H, ¥â-pyrrole), 9.32 (s, 1H, ¥â-pyrrole), 4.35 (s, 4H, OCH2), 3.76 (s, 6H, Me), 3.73 (s, 6H, Me), 3.60 (m, 4H, CH2CH2CO), 2.92 (m, 4H, CH2CH2CO), .4.06 (br. s, 2H, NH). MS, m/z: 1086.45 (M+).Electronic spectrum, lmax/nm (e¡¿10.3) (DMSO): 399.4 (43.71), 496.8 (9.66), 528.4 (5.97), 564.8 (4.78), 618.8 (2.5). IR (n/cm.1): 3320 (NH), 2527 (BH), 1723 (C=O). Found (%): C, 37.93; H, 4.86; N, 5.27. Calc. for C34H54B22Cs2N4O4 (%): C, 37.58; H, 4.97; N, 5.16. 1,3,5,8-Tetramethyl-2,4-divinyl-6,7-di[2'-(closo-monocarbon carborane- 1''-yl caesium)methoxycarbonylethyl]porphyrin 3b: yield 50%. 1HNMR, d: 10.22 (s, 1H, meso-H), 10.12 (s, 2H, meso-H), 10.09 (s, 1H, meso-H), 8.42 (br. s, 1H, CH=CH2), 6.40 (d, 1H, =CHH, 3Jtrans 17.2 Hz), 6.19 (d, 1H, =CHH, 3Jcis 10.4 Hz), 4.29 (s, 4H, OCH2), 3.56 (m, 4H, CH2CH2CO), 3.08 (m, 4H, CH2CH2CO), 2.50 (s, 12H, Me), .4.23 (br. s, 1H, NH), .4.30 (br. s, 1H, NH). MS, m/z: 1138.53 (M+). Electronic spectrum, lmax/nm (e¡¿10.3) (DMSO): 397.8 (65.40), 495.6 (11.85), 527.6 (6.92), 563.8 (5.57), 617.8 (2.09).IR (n/cm.1): 3327 (NH), 2532 (BH), 1714 (C=O), 1657 (C=C). Found (%): C, 40.37; H, 4.98; N, 5.07. Calc. for C38H58B22Cs2N4O4 (%): C, 40.09; H, 5.10; N, 4.92.Mendeleev Communications Electronic Version, Issue 1, 2001 (pp. 1–42) Thus, the anionic nature of the compounds synthesised, as well as the effect of the cation, makes them more promising than the currently known carboranyl-substituted porphyrins for the preparation of water-soluble pharmaceuticals for BNCT.This work was supported by the Russian Foundation for Basic Research (grant nos. 00-03-3287-2a and 00-15-97866). References 1 A. H. Soloway, W. Tjarks. B. A. Barnum, F.-G. Rong, R. F. Barth, I. M. Codogni and J.G. Wilson, Chem. Rev., 1998, 98, 1515. 2 R. C. Hausholter and R. W. Rudolph, J. Am. Chem. Soc., 1978, 100, 4628. 3 R. P. Evstigneeva, V. N. Luzgina, V. A. Ol’shevskaya and L. I. Zakharkin, Dokl. Ross. Akad. Nauk, 1997, 357, 637 (Dokl. Chem., 1997, 357, 299). 4 L. I. Zakharkin, V. A. Ol’shevskaya, R. P. Evstigneeva, V. N. Luzgina, L. E. Vinogradova and P. V. Petrovskii, Izv. Akad. Nauk, Ser. Khim., 1998, 347 (Russ. Chem. Bull., 1998, 47, 340). 5 L. I. Zakharkin, V. A. Ol’shevskaya, S. Yu. Panfilova, P. V. Petrovskii, V. N. Luzgina and R. P. Evstigneeva, Izv. Akad. Nauk, Ser. Khim., 1999, 2337 (Russ. Chem. Bull., 1999, 48, 2312). 6 L. I. Zakharkin, V. A. Ol’shevskaya, P. V. Petrovskii and J. H. Morris, Mendeleev Commun., 2000, 71. Received: 13th October 2000; Com. 00/

ISSN:0959-9436     

出版商:RSC    

年代:2001

数据来源: RSC

摘要:

Mendeleev Communications Electronic Version, Issue 1, 2001 (pp. 1–42) Copper and iron hydroxides as new catalysts for redox reactions in aqueous solutions Galina L. Elizarova,* Lyudmila G. Matvienko, Andrei O. Kuzmin, Elena R. Savinova and Valentin N. Parmon G. K. Boreskov Institute of Catalysis, Siberian Branch of the Russian Academy of Sciences, 630090 Novosibirsk, Russian Federation. Fax: +7 3832 34 3056; e-mail: geliz@catalysis.nsk.su 10.1070/MC2001v011n01ABEH001379 Supported or colloidal CuII and FeIII hydroxides catalyse the oxidation of catechol to a muconic acid derivative and of benzene to phenol in aqueous hydrogen peroxide solutions at ambient temperature.Metal hydroxides are widely used as ion exchangers, adsorbents and collectors for impurities. However, their application as catalysts is rather scarce.Meanwhile, they are very attractive for catalysis: they exhibit a polynuclear structure and a high surface area, and they can be prepared in various forms (supported species, colloidal solutions and bulk materials). We found recently that copper and iron hydroxides can be successfully used as catalysts for the oxidation of water and light hydrocarbons1,2 and for H2O2 decomposition8,9 in aqueous solutions.In this work,† we found that copper and iron hydroxides catalyse benzene and catechol oxidation with H2O2; in the latter case, their catalytic performance is similar to that of dioxygenase enzymes. Recently,2 we found that H2O2 oxidises methane and ethylene to formic acid in the presence of a Cu(OH)2/SiO2 catalyst in aqueous solution.To clarify whether the oxidation of methane proceeds via the consecutive formation of methanol and formaldehyde, these compounds were used as substrates. Methanol was not oxidised, whereas formaldehyde was oxidised very slowly under the conditions of methane oxidation. This led us to an assumption that formic acid is formed from hydrocarbons via the transfer of two oxygen atoms to the substrate, likewise the operation of dioxygenases.To prove this assumption, catechol oxidation with H2O2 in the presence of copper and iron hydroxides was studied. Catechol oxidation was carried out in Ar at 295 K with vigorous stirring in the presence of either SiO2-supported hydroxides containing 2% FeIII or CuII ions or in their colloidal solutions.We found in a special experiment that the catalytic H2O2 decomposition followed by O2 formation begins only after catechol oxidation. To monitor the kinetics in the presence of supported catalysts, the samples taken from the reaction mixture were diluted with 0.1 M H2SO4 to stop the oxidation reaction and centrifuged; then, the spectra were measured. The semilogarithmic plots of the kinetic curves of the catechol consumption (ln Ccat vs.time) were linear in the concentration range from 0.005 to 0.02 M, thus proving the first reaction order with respect to the substrate. The influence of the concentrations of the substrate, H2O2 and NaOH and the amount of a catalyst on the rate of catechol oxidation was studied. Note that the behaviours of Fe- and Cucontaining catalysts were almost identical, except for a higher activity of the latter.An increase in the NaOH concentration from 0.001 to 0.2 M accelerated the reaction by a factor of about two; the reaction rate remained nearly constant upon a further increase in the alkali concentration. In a neutral medium, the reaction was very slow. A change in the catalyst amount from 25 to 100 mg in 20 ml of the reaction mixture lead to a less than twofold increase in the oxidation rate.When the concentration of either catechol (0.005–0.05 M) or H2O2 (0.01– 0.3 M) was varied, the reaction order changed from 1 to 0 for both of the reactants. Such orders are typical of nonradical oxidation reactions with H2O2. A study of catechol oxidation in the presence of starchstabilised hydroxide colloids supplemented these results. The reaction was studied spectrophotometrically in 0.05–0.1 M NaOH solutions in the presence of 1–5 mM catalyst.The molar ratio between catechol and a metal varied from 0.5 to 3.0, H2O2 concentrations changed from 0.005 to 0.025 M for each ratio. The reaction orders with respect to catechol and a catalyst equalled 1; the order with respect to H2O2 varied from 1 to 0 (in the same way as for the supported catalysts).Figure 1 demonstrates the UV-VIS spectra of the reaction mixture during the catalytic oxidation of catechol in colloidal Cu(OH)2. The absorption bands at 230 and 290 nm correspond to catechol absorption. The evolution of the absorption at 250 nm originates from the formation of a reaction product.The transformation of the catechol spectrum into the spectrum of the product through isosbestic points is indicative of the absence of stable intermediates. It is remarkable that an o-benzoquinone † Materials and methods. A UVIKON 923 spectrophotometer (USA), and a Kristall 2000M gas chromatograph with FID (Russia) were used; H2O2 was determined using TiIV.3 Catechol absorption bands at 275 and 290 nm were used for its detection in acidic and alkaline media, respectively.Supported FeO(OH)/SiO2, Cu(OH)2/SiO2 and starch-stabilised colloidal hydroxides were prepared as described elsewhere.1,2 In some experiments, hydroxides were obtained in situ by adding NaOH to copper and iron nitrates solutions. Table 1 Concentrations of phenol in aqueous benzene (ca. 0.02 M) solutions after 1–2 h of vigorous stirring at 295 K.Catalyst pH [H2O2]/mol dm–3 [PhOH]/104 mol dm–3 FeO(OH)/SiO2 12 0.025 0 7 0.025 7 in situ FeO(OH) 12 0.025 0 7 0.025 5 7 0.01 3 Colloid FeO(OH) 12 0.025 0 7 0.025 0 Cu(OH)2/SiO2 12 0.1 0 7 0.025 traces in situ Cu(OH)2 13 0.1 0 7 0.01 3 1 2 3 4 5 6 7 8 2.5 2.0 1.5 1.0 0.5 0.0 190 240 290 340 390 Absorbance l/nm Figure 1 UV-VIS absorption spectra of the reaction mixture during the oxidation of 2×10–3 M catechol with H2O2 (7×10–3 mol dm–3) in the presence of colloidal 1×10–3 mol dm–3 Cu(OH)2 stabilised with 0.5% starch in 0.1 M NaOH at 295 K.Reaction time/min: (1) 2; (2) 5; (3) 10; (4) 15; (5) 20; (6) 25; (7) 30 and (8) 40.Mendeleev Communications Electronic Version, Issue 1, 2001 (pp. 1�C42) absorption band at 380 nm4 was never observed. Figure 2 shows the intensity of the catechol absorption at 290 nm and the H2O2 concentration. Induction periods are observed in the kinetic curves, which increased with catechol concentration and decreased with H2O2 concentration. At a threefold excess of catechol over the catalyst and at a low H2O2 concentration, the oxidation rate was close to zero if catechol was added to the reaction mixture before H2O2, but it was rather high [especially in the case of Cu(OH)2] with the reverse order of the reagent addition.This suggests a competition between the substrate and the oxidant for the sites at the catalyst active centre. The peroxide intermediate formation is likely to play a key role. Note that the catechol absorption at 290 nm increases during the induction period (Figure 2, curve 1); this can result from the accumulation of a complex between catechol and the catalyst.At the same time, the H2O2 concentration does not change, the product is not formed and the spectra of the reaction mixture do not cross the isosbestic points (dotted lines in Figure 1). We suppose that an active intermediate is formed via the coordination of the substrate to either a peroxo complex or metal ions in high oxidation states (FeIV or CuIII).The UV-VIS spectrum of the product does not contain the absorption band at 270�C290 nm characteristic of a benzene ring, but contains a very intense absorption band at 250 nm (e > 104 dm3 mol�C1 cm�C1), which is characteristic of muconic acid and its lactone4 known as the products formed under the action of catechol dioxygenases.In acidic solutions, the product absorption band shifts to 225 nm, the addition of an alkali restores its position. This reversible shift of the absorption band with pH proves that the product is really an acid. Liquid chromatography (HPLC) of the working solutions and IR spectra of the samples obtained after filtration ofported catalyst and careful drying of the supernatant evidence that the reaction product is ¦Ã-lacton of ¦Á-hydro-¦Â-hydroxymuconic acid.The related product of di-tret-butylcatechol oxidation was observed previously.5,6 Thus, copper and iron hydroxides catalyse the cleavage of a benzene ring and the transfer of two oxygen atoms, similar to catechol dioxygenases.Chemical systems modelling these enzymes have been reported.5�C7 However, this work gives the first example of the simplest inorganic catalysts acting in aqueous solutions similarly to catechol dioxygenases. Previously,8,9 we found that H2O2 decomposition in the presence of Cu and Fe hydroxides proceeds via a nonradical mechanism. This is due to the formation of peroxo complexes of these hydroxides and FeIV upon the interaction with H2O2.The rates of formation and consumption of peroxo complexes and FeIV are strongly influenced by pH, reactant concentrations and the presence of an organic substrate.8�C10 It is likely that depending on the substrate nature and/or the reaction conditions different catalyst�CH2O2 intermediates may react with the substrate and transfer either one or two oxygen atoms to it.It was thus interesting to study the products of benzene oxidation in the presence of the hydroxide catalysts. We found that benzene is oxidised to phenol in aqueous solutions, i.e., the reaction proceeds via one oxygen atom transfer from the oxidant to the substrate. Table 1 lists the concentrations of phenol formed in 1�C2 h in aqueous benzene (ca. 0.02 M) solutions under different experimental conditions. Phenol concentrations were determined either from the absorption at l 286 nm or by GC. It is remarkable that phenol (as well as ethanol and methanol) is not oxidised in the systems under study. This is another evidence for the nonradical oxidation reaction catalysed by transition metal hydroxides.This study was supported in part by the Russian Foundation for Basic Research (grant no. 98-03-32410). We are grateful to L. A. Kozhanova for performing HPLC analysis. References 1 G. L. Elizarova, G. M. Zhidomirov and V. N. Parmon, Catal. Today, 2000, 58, 71. 2 A. O. Kuzmin, G. L. Elizarova, L. G. Matvienko, E. R. Savinova and V. N. Parmon, Mendeleev Commun., 1998, 210. 3 G.Charlot, Les Methodes de la Chimie Analytique, Masson et Cie, 1961. 4 Organic Electronic Spectral Data, ed. J. Kamlet, Wiley, New York, 1967. 5 H. Weiner and R. G. Finke, J. Am. Chem. Soc., 1999, 121, 9831. 6 T. Funabiki, A. Mizoguchi, T. Sugimoto, S. Tada, M. Tsuji, H. Sakamoto and S. Yoshida, J. Am. Chem. Soc., 1986, 108, 2921. 7 L. Que and R. Y. Ho, Chem. Rev., 1996, 96, 2607. 8 G. L. Elizarova, L. G. Matvienko, O. L. Ogorodnikova and V. N. Parmon, Kinet. Katal., 2000, 41, 366 [Kinet. Catal. (Engl. Transl.), 2000, 41, 332]. 9 G. L. Elizarova, L. G. Matvienko and V. N. Parmon, Kinet. Katal., 2000, 41, 839 (in Russian). 10 G. L. Elizarova, L. G. Matvienko, A. O. Kuzmin, E. R. Savinova and V. N. Parmon, Dokl. Ross. Akad. Nauk, 1999, 367, 640 [Dokl. Chem. (Engl. Transl.), 1999, 367, 188]. 1.0 0.8 0.6 0.4 1 2 1.0 0.6 0.2 10 20 30 D290 [H2O2]/102 mol dm�C3 t/min Figure 2 Kinetics of (1) the substrate and (2) H2O2 consumption during catechol oxidation in a colloidal FeO(OH) solution; 2¡Á10�C3 M catechol, 1¡Á10�C2 M H2O2, 1¡Á10�C3 M FeO(OH), 0.1 M NaOH, 295 K. Received: 26th September 20

ISSN:0959-9436     

出版商:RSC    

年代:2001

数据来源: RSC

摘要:

Mendeleev Communications Electronic Version, Issue 1, 2001 (pp. 1.42) New fluorinated nucleoside analogues with 2-butenolide rings prepared by nucleophilic vinylic fluorine displacement in 4,4-dialkyl-2,3-difluorobut-2-en-4-olides Old ich Paleta,*a Zden k Dudaa and Antonin Holyb a Department of Organic Chemistry, Institute of Chemical Technology, 16628 Prague, Czech Republic. Fax: +4202 2431 1082; e-mail: paletao@vscht.cz b Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, 16610 Prague, Czech Republic 10.1070/MC2001v011n01ABEH001377 Sodium salts of adenine, 2,6-diaminopurine, cytosine, 4-methoxypyrimidin-2-one and aliphatic or alicyclic amines reacted with 4,4-dialkyl-2,3-difluorobut-2-en-4-olides by vinylic substitution of fluorine to give 3-substituted butenolides as nucleoside analogues or enamines, while sodium and lithium salts of aliphatic and aromatic amines reacted as hard nucleophiles to attack the carbonyl group thus causing butenolide ring opening. A number of bioactive natural compounds contain butenolide rings.1 Some of them display HIV-enzyme inhibiting,2 anticancer, 3,4 anti-tumour5 and cytostatic6 properties.On the other hand, fluoro substituents are known as strong modifiers of bioactivity. 7.9 On this basis, it can be assumed that a combination of a fluorinated butenolide ring with a pharmacophore moiety, e.g., a nucleoside base, can create biological activity. Nucleoside analogues possessing a butenolide ring instead of a sugar part in the molecule have not been reported in the literature.As a general strategy for the synthesis of these compounds with potential bioactivity, we decided on a study of the modification of 4,4-dialkyl-2,3-difluorobut-2-en-4-olides 1 and 2 by vinylic displacement of fluorine with nitrogen nucleophiles. The reasons for this methodology have been accessible butenolides 110,11 and 2¢Ó and our recent observations11.14 in the chemistry of fluorinated butenolides.It has been observed11.14 that the reactivity of fluorinated but-2-en-4-olides possessing fluorine atoms attached to the double bond, as in compounds 1, 2, 314 and 413 (Scheme 1), is strongly dependent on their structure and character of a reagent: e.g., 1 and 2 reacted with various oxy anions by vinylic fluorine displacement,11,12 while the same reagents caused ring opening in fluorobutenolide13 3 or only tars formation in the reaction with chlorofluorobutenolide14 4.Different results have also been obtained in reactions of halobutenolides (including 2,3-dichlorobutenolide15) with nitrogen nucleophiles13,14 and hard or soft organometals.11.13 The literature data suggest that the following three types of reactions of nitrogen nucleophiles with butenolides 1 and 2 can be expected: displacement of ¥â-fluorine, nucleophilic addition to the double bond and ring opening by a carbonyl group attack. The N-nucleophiles employed in this study included aliphatic or aromatic amines, alkali salts of the amines and sodium salts of nucleoside bases as delocalised soft N-nucleophiles.Generally, the nucleophiles reacted in two different ways, i.e., with displacement of ¥â-fluorine or with a carbonyl group attack followed by butenolide ring opening.Aliphatic amines¢Ô and sodium salts of nucleoside bases¡× reacted with butenolides 1 and 2 by the displacement of vinylic fluorine (Scheme 2) with the formation of enamine-type products possessing neighbouring vinylic fluorine (5.11).It can be presumed that in the reaction mechanism 1,4-addition intermediates are formed primarily11,12 from which a ¥â-fluorine atom is expelled. The reactions with sodium salts of nucleoside bases were carried out at lower temperatures than those reported for non-fluorinated species16 and were completely regioselective to r e ¢Ó New spirocyclic butenolide 2 [2,3-difluoro-4,4-(pentane-1,5-diyl)but- 2-en-4-olide] was prepared analogously10 to compound 1.Cyclohexanol was added to methyl 2,3,3-trifluoroacrylate under photochemical or radical (dibenzoyl peroxide) initiation; the intermediate adduct [R2C(OH)CF2CHFCOOMe] cyclised spontaneously to butanolide during distillation (50.65% yield). The conversion of the intermediate butanolide to target butenolide 2 was performed by a novel procedure using triethylamine as a dehydrofluorinating agent (acetonitrile, room temperature, 10 h), 65.75% yield, bp 102.103 ¡ÆC (8 mmHg). 13C NMR (100.6MHz, CDCl3) d: 21.9 (s, CH2), 24.6 (s, CH2), 33.4 (s, CH2), 80.5 (s, C), 127.1 (d, CF, 1JCF 288 Hz), 160.0 (d, CF, 1JCF 299 Hz), 162.9 (s, C=O). 19F NMR (75.4 MHz, CDCl3) d: .166.4 (s, 1F), .127.4 (s, 1F).Found (%): C, 57.11; H, 5.55. Calc. for C9H10F2O2 (%): C, 57.45; H, 5.36. Table 1 Reactions of butenolides 1 and 2 with N-nucleophiles. Starting compound Nucleophile Product Yielda (%) aIsolated yields. bShifts d in ppm downfield from CFCl3. cComplete conversion, then reverse reaction to form 2. dCalculated from NMR spectra. 19F NMRb 2 EtNH2 5 80 .182.1 1 Et2NH 6 69 .186.8 2 Piperidine 7 70 .177.7 1 Nu(.)Na(+) Nu = adenin-9-yl 8 32 .145.7 1 Nu(.)Na(+) Nu = 4-methoxypyrimidin-2-on-1-yl 9 60 .142.6 2 Nu(.)Na(+) Nu = 2,6-diaminopurin-9-yl 10 51 .145.3 2 Nu(.)Na(+) Nu = cytosin-1-yl 11 81 .144.85 2 (Pri)2NLi 13 59 .135.1 (s) .144.9 (s) 2 PhEtNNa 14 (100)c .127.8 (s) .143.6 (s) 2 PhNHLi, Me3SiCl 15 43d .114.1 (s) .152.2 (s) O O F F O O F F 1 2 O O F 3 O O F Cl 4 Scheme 1 O O F F R R 1,2 Nu.H or Nu Na (.) (+) O O F Nu R R 5.11 5 Nu.H = EtNH.H 6 Nu.H = Et2N.H N H 7 Nu.H = 8 Nu = adenin-9-yl 9 Nu = 4-methoxypyrimidin-2-on-1-yl 10 Nu = 2,6-diaminopurin-9-yl 11 Nu = cytosin-1-yl Scheme 2 O O F N 7 O O F N N OMe O 9 O O F 10 N N N N NH2 H2NMendeleev Communications Electronic Version, Issue 1, 2001 (pp. 1–42) nucleoside bases. Examples of new enamino compounds and nucleoside analogues (7, 9, 10) are shown in Scheme 2.The 19F NMR spectra of new compounds 5–11 show singlet signals with a characteristic shift for each compound class (enamine or nucleoside analogue, Table 1). Aniline and N-ethylaniline, as well as free nucleoside bases, were completely unreactive even on heating to 80 °C. We observed no difference in the reactivity of butenolides 1 and 2 from the kinetic point of view during preparative reactions.This observation is in a sharp contrast to the reactions of butenolides with thiophenol or soft carbanions where butenolide 2 appeared to be completely unreactive.17 Sodium and lithium salts of aliphatic or aromatic amines reacted with butenolides 1 and 2, contrary to reactions of alkoxides,11,12 at the hard electrophilic centre of the carbonyl group with ring opening (Scheme 3).¶ This observation is also in contrast with the reactions15 of dichloro- or dibromobutenolides where vinylic displacement was observed.Hydroxyamides 13 and 14, obtained by quenching the mixture with trifluoroacetic acid, were unstable, and they were rapidly converted to starting butenolide 2 on distillation or slowly converted on storage (the process could be monitored by 19F NMR spectra); hydroxyamide 13 was more stable.To confirm the formation of intermediate 12, we trapped it as trimethylsilyl derivative 15 by silylation at –70 °C. The 19F NMR spectra of 15 and hydroxyamides 13 and 14 show two singlets (Table 1); the absence of mutual fluorine coupling as in starting butenolide 2 confirms (Z)-configuration for the propenamide structure.The structures of all the compounds synthesised were elucidated on the basis of 1H, 13C and 19F NMR spectra, the formulae of isolated products 5–11 were confirmed by microanalysis for carbon and hydrogen. The reported reactions of N-nucleophiles have extended the use of 2-fluoro-3-halogenobut-2-en-4-olides as new fluorinated synthons with a special interest in the preparation of a new type of nucleoside analogues. This work was supported by the Grant Agency of the Czech Republic (grant no. 203/96/1057) and by the Ministry of Education of the Czech Republic (project no. LB98233). References 1 D. W. Knight, Contemp. Org. Synth., 1994, 1, 287. 2 B. E. Roggo, P. Hug, S. Moss, F. Raschorf and H.H. Peter, J. Antibiot., 1994, 47, 143. 3 X.-P. Fang, J. E. Anderson, C.-J. Chang and J. L.McLaughlin, Tetrahedron, 1991, 47, 9751. 4 H. Mori, N. Yoshimi, S. Sugie, T. Tanaka, Y. Morishita, G. Jinlong, M. Torihara and J. Yamahara, Cancer Lett. (Shannon), 1992, 66, 93. 5 P. L. Triozze, J. Ailabouni, J. J. Rinehart and D. T. Witiak, Int. J. Pharm., 1993, 15, 47. 6 X. P. Fang, J.E. Anderson, D. L. Smith, J. L. McLaughlin and K. V.Wood, J. Nat. Prod., 1992, 55, 1655. 7 Organo-fluorine Compounds in Medicinal Chemistry and Biomedical Applications, eds. R. Filler, Y. Kobayashi and L. M. Yagupolskii, Elsevier, Amsterdam, 1993. 8 Fluorine in Medicine in the 21st Century (Conference Papers), eds. R. E. Banks and K. C. Lowe, UMIST, Manchester, 1994. 9 Cancer Chemotherapeutic Agents, ed.W. O. Foye, ACS, Washington D.C., 1995, pp. 49–55. 10 V. P. Šendrik, O. Paleta and V. D dek, Collect. Czech. Chem. Commun., 1977, 42, 2530. 11 O. Paleta, A. Pelter, J. Kebrle, Z. Duda and J. Hajduch, Tetrahedron, 2000, 56, 3197. 12 O. Paleta, A. Pelter and J. Kebrle, Tetrahedron Lett., 1994, 35, 9259. 13 J. Kví ala, J. Plocar, R. Vlasáková, O. Paleta and A.Pelter, Synlett, 1987, 986. 14 O. Paleta, A. Volkov and J. Hetflejš, J. Fluorine Chem., 2000, 102, 147. 15 V. Zikán, L. Vrba, B. Kaká and M. Semonský, Collect. Czech. Chem. Commun., 1973, 38, 1091. 16 P. Alexander and A. Holý, Collect. Czech. Chem. Commun., 1993, 58, 1151. 17 J. Hajduch and O. Paleta, unpublished results. ‡ Typical procedure for preparation of enamines 5–7.In an inert atmosphere, an amine (2.5 mmol) solution in dry and purified tetrahydrofuran (THF, 4 ml) was cooled at –20 to –30 °C and a solution of butenolide (1.2 mmol) in THF (5 ml) was added dropwise during 10–15 min. The mixture was stirred at –10 °C for 6 h and then allowed to warm to room temperature; next, volatile components were evaporated. The residue was purified by column chromatography (silica gel, dichloromethane); the product was recrystallised (chloroform–light petroleum).§ Typical procedure for preparation of nucleoside analogues 8–11. In an inert atmosphere, a mixture of sodium hydride (60% suspension in mineral oil, 1.9 mmol), dry dimethyl formamide (DMF, 10 ml) and a nucleoside base (1.6 mmol) was intensely stirred at room temperature (or elevated temperatures) for 1 h and then cooled at –20 to –40 °C.A butenolide (1.1 mmol) solution in DMF (5 ml) was added dropwise to the nucleoside base solution for 10–15 min, the solution was stirred at –20 to –40 °C for 1–2 h and then allowed to warm to room temperature. Volatile components of the reaction mixture were evaporated in a vacuum, and the solid residue was purified by column chromatography (silica gel), the product was once or twice recrystallised (methanol–light petroleum).¶ Typical reactions of butenolides with the alkali salts of amides. In an inert atmosphere, an amine (1.25 mmol) solution in dry and purified THF (2 ml) was cooled to ca. –70 °C and a butyllithium (1.3 mmol, 2.47 M solution) was added dropwise with intense stirring for 30 min. A solution of butenolide (1.1 mmol) in THF (2 ml) was added dropwise (10–15 min) to the cooled solution at ca. –60 °C, the mixture was stirred for 1 h and then warmed to room temperature for 2 h. The 19F NMR spectrum was measured (100% conversion of butenolide). Then, trifluoroacetic acid was added (equivalent to butyllithium), the mixture was neutralised with Na2CO3, volatile components were evaporated, and the residue was chromatographed (silica gel, dichloromethane) to obtain a mixture of the product and the starting butenolide. 2 NR1R2 O (–) M(+) F F O 12 M(+)NR1R2 (–) NR1R2 O F F O 13, 14 H CF3COOH D HN O F F O Me3Si 15 2 Me3SiCl M = Na, Li 13 R1 = R2 = Pri 14 R1 = Ph, R2 = H Scheme 3 e c c Received: 25th September 2000; Com. 00/1703

ISSN:0959-9436     

出版商:RSC    

年代:2001

数据来源: RSC

摘要:

Mendeleev Communications Electronic Version, Issue 1, 2001 (pp. 1.42) Intermolecular and intramolecular cycloaddition reactions of 1-ethyl-1,2,4-triazinium salts with alkynes Nataliya N. Mochulskaya, Anatoly A. Andreiko, Valery N. Charushin,* Boris V. Shulgin, Dmitry V. Raikov and Vladimir I. Solomonov Department of Organic Chemistry, Urals State Technical University, 620002 Ekaterinburg, Russian Federation.Fax: +7 3432 74 0458; e-mail: charushin@prm.uran.ru 10.1070/MC2001v011n01ABEH001370 Azomethyne ylides generated from 3-alkylthio substituted 1-alkyl-5-aryl-1,2,4-triazinium salts 4a.c on treatment with triethylamine undergo 1,3-dipolar cycloaddition with dimethyl acetylenedicarboxylate to give pyrrolo[2,1-f ][1,2,4]triazines, while 1-ethyl-5- phenyl-1,2,4-triazinium salts 1a,b bearing the C��C bond in the side-chain 3-alkynylthio substituent react with acetylenes to undergo either intermolecular 1,3-dipolar cycloaddition or intramolecular inverse electron demand Diels.Alder reactions.Inverse electron demand Diels.Alder reactions of ¥�-deficient azaaromatics is a powerful synthetic methodology.1 N-Alkyl-1,2,4- triazinium salts are appropriate substrates to be used in these (4 + 2) cycloaddition reactions.Indeed, we found that 1-ethyl- 5-phenyl-l,2,4-triazinium salts bearing acetylenic 3-butynylthio (compound 1a) or 4-pentynylthio (compound 1b) substituents at C-3 can undergo intramolecular (4 + 2) cycloaddition reaction under very mild conditions, thus being transformed into thieno- [2,3-b]- 3a or thiopyrano[2,3-b]pyridines 3b (Scheme 1).2 On the other hand, N-alkylpyridinium and other azinium salts, especially those bearing the CH2W fragment at the quaternary nitrogen (W is an electron-withdrawing group) are precursors of N-heterocyclic ylides, which can undergo 1,3-dipolar (3 + 2) cycloaddition reactions with both alkenes and acetylenes. The feature of N-alkyl-1,2,4-triazinium salts is that electron-withdrawing groups W in the N-alkyl fragment are not necessary to generate ylides, as found by the dimerisation into 4a,4b,9,10- tetrahydro-1,3,6,8,8a,10a-hexaazaphenanthrenes.3,4 In continuation of our studies on the behaviour of 1-alkyl-1,2,4-triazinium salts,5.7 we report that deprotonation of 1-ethyl-3-alkylthio-5- aryl-l,2,4-triazinium salts 4a.c with triethylamine (TEA) results in azomethine ylides 5a.c (non-stabilised species), which react in situ with dimethyl acetylenedicarboxylate (DMAD) to form pyrrolo[2,1-f ][1,2,4]triazines 6a.c in good yields (Scheme 2).¢Ó Attempts to use other alkynes, such as phenylacetylene, di(4-nitrophenyl) acetylene and di(pyridin-2-yl)acetylene, as dipolarophiles in the reaction with 4c were unsuccessful.When irradiated with UV light or pulsed electron beams, pyrrolo[2,1-f ][1,2,4]triazines 6a.c were found to exhibit intense luminescence giving emission in the region 450.650 nm with maxima at 500 nm and the light output comparable with that of stilbene.¢Ô It was interesting to examine the chemical behaviour of 3-alkynylthio-1,2,4-triazinium salts 1a,b on treatment with DMAD, i.e., when both types of cycloaddition reactions [(4 + 2) and (3 + 2)] can compete with each other.We found that, in case of a 4-pentynylthio substituent (n = 2), the intermolecular 1,3-dipolar cycloaddition reaction of 1b with DMAD leading to pyrrolotriazine 7 (47% yield) proceeds much faster than the intramolecular Diels.Alder reaction, while 3-butynylthio substituted 1-ethyl-1,2,4-triazinium salt 1a (n = l) undergoes predominantly the intramolecular ring transformation into thieno- [2,3-b]pyridine 3a in 44% yield (Scheme 3).Both reactions were carried out under identical conditions with triethylamine in absolute ethanol at room temperature. Although in both reactions we cannot exclude the formation of minor quantities of alternative products, moderate yields of 3a and 7 can be N N N Ph S (CH2)n BF4 N N N S (CH2)n H Ph BF4 .N2, CH2=CH2 . HBF4 N S (CH2)n Ph 1a,b a n = 1 b n = 2 2a,b 3a,b Scheme 1 ¢Ó All new compounds gave expected 1H NMR spectra, mass spectra and satisfactory elemental analyses. 3a: Dimethyl acetylenedicarboxylate (0.08 g, 0.56 mmol) was added to a suspension of 1-ethyl-3-(3-butynylthio)-5-phenyl-1,2,4-triazinium tetrafluoroborate 1a (0.18 g, 0.50 mmol) in 4 ml of absolute ethanol, and then triethylamine (0.06 g, 0.55 mmol) was added dropwise with stirring. The reaction mixture was stirred at room temperature for 36 h.After filtration, the solvent was removed in vacuo. Flash dry-column chromatography on silica gel (hexane.acetone, 4:1) gave 6-phenyl-2,3- dihydrothieno[2,3-b]pyridine (0.047 g, 44% yield) as white crystals, mp 82.83 ¡ÆC (lit.,2 mp 83 ¡ÆC). 6a: Dimethyl acetylenedicarboxylate (0.21 g, 1.46 mmol) was added to a suspension of 5-(4-bromophenyl)-1-ethyl-3-propylthio-1,2,4-triazinium tetrafluoroborate (0.52 g, 1.22 mmol) in 4 ml of absolute ethanol, and then triethylamine (0.14 g, 1.34 mmol) was added dropwise with stirring. The reaction mixture was stirred at room temperature for 72 h to precipitate a yellow crystalline product, which was collected by filtration and recrystallised from ethanol to yield 0.23 g (40%) of 4-(4-bromophenyl)- 5,6-dimethoxycarbonyl-7-methyl-2-propylthiopyrrolo[2,1- f ]- 1,2,4-triazine as a yellow product, mp 126.128 ¡ÆC. 1H NMR (CDCl3) d: 1.09 (t, 3H, SCH2CH2Me), 1.85 (m, 2H, SCH2CH2Me), 2.79 (s, 3H, Me), 3.20 (t, 2H, SCH2CH2Me), 3.47 (s, 3H, COOMe), 3.88 (s, 3H, COOMe), 7.54 (d, 2H, BrC6H4), 7.62 (d, 2H, BrC6H4).MS, m/z (%): 479 (58, [M + 1]+), 478 (16, M+), 477 (55), 464 (27), 462 (26), 446 (48), 444 (35), 438 (20), 437 (100), 436 (23), 435 (93). Compounds 6b and 6c were obtained analogously to 6a. 6b: yield 65%, yellow crystals, mp 108.110 ¡ÆC. 1H NMR (CDCl3) d: 1.48 (t, 3H, SCH2Me), 2.80 (s, 3H, Me), 3.21 (q, 2H, SCH2Me), 3.39 (s, 3H, COOMe), 3.87 (s, 3H, COOMe), 7.4.7.6 (m, 3H, Ph), 7.6.7.7 (m, 2H, Ph).MS, m/z (%): 386 (23, [M + 1]+), 385 (100, M+), 357 (21), 352 (41), 294 (32), 262 (20). 6c: yield 40%, yellow crystals, mp 165.167 ¡ÆC. 1HNMR ([2H6]DMSO) d: 2.61 (s, 3H, SMe), 2.76 (s, 3H, Me), 3.35 (s, 3H, COOMe), 3.82 (s, 3H, COOMe), 7.4.7.6 (m, 5H, Ph). MS, m/z (%): 372 (34, [M + 1]+), 371 (100, M+), 340 (22), 339 (35), 280 (35), 252 (22), 239 (21). 7: Dimethyl acetylenedicarboxylate (0.18 g, 1.26 mmol) was added to a suspension of 1-ethyl-3-(4-pentenylthio)-5-phenyl-1,2,4-triazinium tetrafluoroborate 1b (0.39 g, 1.05 mmol) in 5 ml of absolute ethanol, and then triethylamine (0.12 g, 1.16 mmol) was added dropwise with stirring.The reaction mixture was allowed to stand at room temperarure for 24 h.The solvent was removed in vacuo. Flash dry-column chromatography on silica gel (hexane.ethyl acetate, 4:1) gave 5,6-dimethoxycarbonyl-7-methyl- 2-(4-pentenylthio)-4-phenylpyrrolo[2,1-f ][1,2,4]triazine (0.208 g, 47%): yellow solid, mp 80.82 ¡ÆC. 1H NMR (CDCl3) d: 1.99 (t, 1H, C��CH, J 2.8 Hz), 2.07 (m, 2H, SCH2CH2, J 7.0 Hz), 2.42 (td, 2H, CH2C��CH, J 2.8 Hz, J 7.0 Hz), 2.80 (s, 3H, Me), 3.32 (t, 2H, SCH2, J 7.0 Hz), 3.39 (s, 3H, COOMe), 3.87 (s, 3H, COOMe), 7.4.7.6 (m, 3H, Ph), 7.6.7.7 (m, 2H, Ph).MS, m/z (%): 423 (24, M+), 396 (24), 395 (100), 384 (78), 371 (25), 364 (38), 357 (41), 267 (23).Mendeleev Communications Electronic Version, Issue 1, 2001 (pp. 1–42) explained by side reactions of starting 1,2,4-triazinium salts 1a,b, such as dequaternisation5 and dimerisation,3,4 as experimentally found by TLC.Thus, the conversion of 1-ethyl-3- alkynylthio-1,2,4-trazinium salts 1a,b into thieno[2,3-b]- pyridine 3a or pyrrolo[2,1-f ][1,2,4]triazine 7 depends on the length of the side chain bearing the acetylenic fragment. The found phenomenon is consistent with well-known features of the intramolecular Diels–Alder reactions of alkynyl-substituted pyrazines, pyrimidines and 1,2,4-triazines.2,8–11 In these ring transformations, the formation of bridged intermediates like 2 (Scheme 1) with an annelated five-membered ring is more favourable as compared to cycloadducts 2 condensed with a sixmembered ring.2,8–11 As a consequence, intramolecuh; Alder reactions leading to azines condensed with five-membered rings proceed much faster and require milder conditions. 2,8–11 The above results demonstrate a new interesting property of 1,2,4-triazinium salts to undergo two modes of cycloaddition reactions with alkynes. Evidence for the structures of 3a, 6a–c and 7 is provided by 1H NMR spectroscopy and mass spectrometry.† This work was supported by the US Civilian Research and Development Foundation (grant no.REC-005) and the Russian Foundation for Basic Research (grant nos. 00-03-32785a and 00-15-97390). References 1 D. L. Boger and S. M. Weinreb, Hetero Diels–Alder Methodology in Organic Syntheses, Academic Press, New York, 1987. 2 V. N. Charushin, A. van Veldhuizen, H. C. van der Plas and C.H. Stam, Tetrahedron, 1989, 45, 6499. 3 O. N. Chupakhin, B. V. Rudakov, S. G. Alexeev, V. N. Charushin and V. A. Chertkov, Tetrahedron Lett., 1990, 31, 7665. 4 B. V. Rudakov, S. G. Alexeev, V. N. Charushin, O. N. Chupakhin, V. A. Chertkov, G. G. Alexandrov and E. S. Klimov, Zh. Org. Khim., 1992, 28, 589 (Russ. J. Org. Chem., 1992, 28, 479). 5 O. N. Chupakhin, B. V. Rudakov, S. G.Alexeev, S. V. Shorshnev and V. N. Charushin, Mendeleev Commun., 1992, 85. 6 V. N. Charushin, S. G. Alexeev, O. N. Chupakhin and H. C. van der Plas, Adv. Heterocycl. Chem., 1989, 46, 73. 7 O. N. Chupakhin, S. G. Alexeev, B. V. Rudakov and V. N. Charushin, Heterocycles, 1992, 33, 931. 8 A. E. Frissen, Intramolecular Inverse Electron Demand Diels–Alder Reaction of Pyrimidines, Thesis, Wageningen, 1990, p. 117. 9 A. E. Frissen, A. T. M. Marcelis and H. C. van der Plas, Tetrahedron, 1987, 43, 1589. 10 A. E. Frissen, A. T. M. Marcelis and H. C. van der Plas, Tetrahedron, 1989, 45, 803. 11 A. E. Frissen, G. Geurtsen, A. T. M. Marcelis and H. C. van der Plas, Tetrahedron, 1990, 46, 595. ‡ For measuring the photoluminiscence spectra, compounds 6a–c and 7 were irradiated with monochromatic UV light at a wavelength of 310 nm followed by measuring emission with the second monochromator equipped with a photoelectric multiplier (1050 V) and an automatic potentiometer.The radioluminiscence and scintillation characteristics of compounds 6a–c and 7 were obtained using special nanosecond techniques. The test materials were excited by irradiation with pulsed electron beams at a high current density (pulse duration of 2 ns, electron energy of 100–200 keV, current density of 100–700 A cm–2) using a Radan electron accelerator. The spectra in the range 300–800 nm were measured by a charge-connecting detector (CCD) equipped with a computer. N N N Ar S R1 BF4 4a–c N N N Ar S R1 5a–c TEA DMAD N N N S R1 Ar Me MeOOC MeOOC 6a–c a R1 = Et, Ar = 4-BrC6H4 b R1 = Me, Ar = Ph c R1 = H, Ar = Ph Scheme 2 N N N Ph S (CH2)n BF4 1a,b N N N S Ph Me MeOOC MeOOC 7 COOMe COOMe n = 2 n = 1 3a Scheme 3 Received: 1st September 2000; Com. 00/1696

ISSN:0959-9436     

出版商:RSC    

年代:2001

数据来源: RSC

摘要:

Mendeleev Communications Electronic Version, Issue 1, 2001 (pp. 1–42) Influence of sulfite on radiolytic conversion of nitrate and nitrite in dilute aqueous solutions Hang-Sik Shin,a Yu-Ri Kimb and Alexandr V. Ponomarev*c a Department of Civil Engineering, Korean Advanced Institute of Science and Technology, Taejeon, 305-701, Republic of Korea b Central Research Institute, Samsung Heavy Industries Co., Ltd., Taejeon, 305-600, Republic of Korea c Institute of Physical Chemistry, Russian Academy of Sciences, 119991 Moscow, Russian Federation. Fax: +7 095 335 1778 10.1070/MC2001v011n01ABEH001403 Nitrate and nitrite ions are reduced in deaerated diluted aqueous solutions in the presence of sulfite under the action of electron beam.The removal of inorganic nitrogen compounds (nitrates, nitrites and ammonium ions) from wastewater is an important environmental problem.Such compounds are always present in industrial and municipal wastewater. Their high stability and solubility cause considerable difficulties for their removal by conventional methods of wastewater treatment. However, the environmental standards in many countries require that their residual concentrations in wastewaters were no higher than 10–40 ppm.It is well known1,2 that various pollutants can be removed from wastewater by electron-beam treatment. At the same time, the radiolytic decomposition of nitrogen-containing compounds in wastewater is inadequately studied. This work is devoted to the electron-beam removal of nitrates and nitrites at their simultaneous presence in aqueous solutions.As a rule, the simultaneous presence of nitrates, nitrites and ammonium is characteristic of municipal wastewater after anaerobic biological treatment. In this study, the main attention was paid to the radiolytic conversion of nitrates and nitrites, because their removal causes maximum difficulty in practice. The removal of ammonium ions (in the form of ammonia) is connected with smaller difficulties, because its effective blowing off as a typical stage of aerobic biological treatment is available.Model solutions were prepared using HNO3, KNO3, NaNO2, NH4OH and Na2SO3 of ‘extra pure’ grade. The optical measurements were carried out on Cary 1E and Specord M-40 spectrophotometers. The analysis for nitrate, nitrite and total nitrogen was performed by standard techniques.3,4 For the selective determination of nitrites, the Griss reagent and the formation of K3[Co(NO2)6]4 were used.An ELV-4 electron accelerator (1 MeV electron beam at a nominal beam power of 40 kW) was applied. The beam current was varied within the range 2–40 mA. The solutions were deaerated by bubbling pure nitrogen for 30–45 min or heating at 60–70 °C for 40 min.The solutions were moved through an electron beam as continuous jets with a flow rate of 3 m s–1 using a device described in ref. 5. For the removal of volatile nitrogen compounds, the irradiated solutions were kept in a thermostat at 50 °C for 40 min before the analysis. Computer simulation with the use of kinetic data6–8 and an algorithm9 was applied to explain the basic radiolysis stages. On the basis of published data,10 we can suggest that the removal of nitrate and nitrite from aerated aqueous solutions by electron-beam treatment does not occur at all or proceeds to a very low degree.The reason for high radiation stability of the test system is an opposite action of oxidising and reducing products of water radiolysis.The main processes causing the removal of nitrate are the reactions with hydrated electrons e– aq and H atoms: OH radicals play an insignificant role in nitrate degradation. Radical anions formed in reactions (1) and (2) cause partial conversion of NO3 – into NO2 –: However, the final conversion of nitrate into nitrite is mainly suppressed by back oxidation by OH radicals.Firstly, OH radicals react rapidly with the formed nitrite: Secondly, reaction (8) is possible: The additional pathway for the back formation of nitrate is the reaction of nitrite with hydrogen peroxide in an acidic medium: Hence, the high reactivity of OH radicals towards NO2 and nitrite ions in a combination with their low reactivity towards nitrate ions is the main obstacle for radiolytic degradation of nitrate.In the case of nitrite, H atom and e– aq reduce nitrite: Note that reactions (7)–(9) can occur in the presence of nitrite. Nitrogen oxide NO formed in reactions (11) and (12) seems to be the most stable among nitrogen oxides in deaerated solutions. 11 At the same time, the accumulation of NO in irradiated aqueous solutions is inhibited by its fast reactions with OH radicals and nitrogen dioxide with conversion into nitrite: At high doses, reactions (16) and (17) are possible in nitrate solutions: They not only promote the accumulation of NO but also interfere with the reformation of nitrate ions.In aerated solutions, oxygen can participate in the reactions and transform H atoms and e– aq into oxidising species (H2O2, HO2 and O2 – ).Because of this, we can conclude that the removal of nitrogen compounds upon irradiation of aerated NO2 – or NO3 – solutions is almost impossible. Thus, upon irradiation of a 10–4 mol dm–3 aqueous nitrate solution, its concentration remained unchanged even at a dose of 10 kGy. In turn, the radiolysis of an aqueous nitrite solution is accompanied by the effective conversion into nitrate, and the total removal of compounds is over 4% at doses up to 10 kGy. It is obvious that, for an increase in the efficiency of removal of nitrate and nitrite, it is necessary to use scavengers (S) of OH radicals under deaerated conditions.It is important that the scavenger should have a low reactivity towards reducing products NO3 – + e– aq ® NO3 2– NO3 – + H ® HNO3 – (1) (2) k = 9.7×109 dm3 mol–1 s–1 k = 1.4×106 dm3 mol–1 s–1 NO3 2– + H2O ® NO2 + 2OH– HNO3 – ® NO·2 + OH– 2NO·2 ® N2O4 N2O4 + H2O ® NO3 – + NO2 – + 2H+ k = 1.0×103 s–1 k = 2.3×102 s–1 k = 7.6×107 dm3 mol–1 s–1 k = 1.0×103 s–1 (3) (4) (5) (6) NO2 – + OH ® NO· 2 + OH– k = 1.0×1010 dm3 mol–1 s–1 (7) NO·2 + OH ® HNO3 k = 1.0×1010 dm3 mol–1 s–1 (8) NO2 – + H2O2 ® NO– 3 + H2O k = 4.0 dm3 mol–1 s–1 (9) NO2 – + e– aq ® NO2 2 – NO2 2– + H2O ® NO + 2OH– NO–2 + H ® NO + OH– k = 4.2×109 dm3 mol–1 s–1 k = 1.0×103 s–1 k = 7.1×108 dm3 mol–1 s–1 (10) (11) (12) NO + OH ® HNO2 NO2 · + NO ® N2O3 N2O3 + H2O ® 2NO2 – + 2H+ k = 2.0×1010 dm3 mol–1 s–1 k = 1.1×109 dm3 mol–1 s–1 k = 5.3×102 s–1 (13) (14) (15) NO2 + e– aq ® NO2 – NO2 + H ® H+ + NO2 – k = 1.0×1010 dm3 mol–1 s–1 k = 1.0×109 dm3 mol–1 s–1 (16) (17) NO3 2– + O2 ® NO3 – + O2 – NO2 2 – + O2 ® NO2 – + O2 – k = 2.0×108 dm3 mol–1 s–1 (18) (19)Mendeleev Communications Electronic Version, Issue 1, 2001 (pp. 1–42) of water radiolysis. On the other hand, taking into account the high rate constant of reaction (7), the value k(OH + S)×[S] should be higher at least by a factor of 2–3 than the value k(OH + NO2 –)×[ NO2 – ].Because of this, the sulfite ion can be used as the most suitable scavenger of OH radicals. The final product of its radiolytic conversions is the non-hazardous sulfate ion. The rate constant for reaction of OH radicals with sulfite is high, 1.5×109 dm3 mol–1 s–1 (near diffusion limit). At the same time, sulfite has a low reactivity towards reducing products of water radiolysis.An additional advantage of sulfite is its high reactivity towards nitrogen dioxide NO2 (k = = 3.5×107 dm3 mol–1 s–1). Figure 1 shows that the presence of sulfite in irradiated solution prevents the system from back radiolytic reactions. The presence of about 5×10–4 mol dm–3 sulfite provides virtually complete removal of nitrogen-containing compounds at a dose of 1.5 kGy from 10–4 mol dm–3 (curve 1) and an about twofold decrease in concentrations of these compounds in a 10–4 mol dm–3 nitrate solution (curve 3).The analysis testifies that, under these conditions, the residual compound in nitrate solution (curve 3) is mainly represented by nitrite (about 86%). The increase in sulfite concentration up to (8–9)×10–4 mol dm–3 provides virtually complete removal of nitrogen compounds from all the test solutions at an initial concentration of 10–4 mol dm–3.The same amount of sulfite causes 80% removal of the compounds from a 2×10–4 mol dm–3 nitrite solution (curve 4). Figure 1 also shows that the initial presence of nitrate in irradiated solution (curves 2 and 3) causes a lower sensitivity of the system upon increasing sulfite content.At a low concentration of sulfite [below (1–2)×10–3 mol dm–3], the radiolytic removal of nitrate from solution is virtually absent. However, in the case of nitrite solutions, a noticeable removal of these compounds is observed even at a low sulfite concentration. As follows from Figure 2, the maximum effect of sulfite additives is observed at comparatively low doses (1–2 kGy).At higher doses, the effect decreases. It is caused by an insufficient amount of the additive. Thus, at a 6×10–4 mol dm–3 sulfite concentration, the growth of dose from 0.5 to 1.5 kGy results in the effective removal of nitrogen compounds from a 10–4 mol dm–3 nitrate solution (G = 0.7 ion per 100 eV) up to the residual content ~17% (curve 5). However, at doses over 1.5 kGy the removal of the compounds is not observed.Other way, a slow growth of the residual concentration of nitrogen compounds with dose takes place. A decrease in the sulfite concentration to 4×10–4 mol dm–3 results in that a limiting degree of nitrate degradation considerably decreases. At a dose of 1.2 kGy, the degree of removal is not lower than 65%. A similar situation is also observed in 10–4 mol dm–3 nitrate–nitrite solutions.It is obvious that the change in the dose dependence is caused by a deficit of OH scavengers. However, under experimental conditions, an increase in the dose was reached by changing the dose rate, and this fact could have an effect on the observed dose dependence. The experimental results can be satisfactorily described by computer simulation of a set of the above reactions.Both experimental and calculated data show that, for the removal of comparatively small amounts of nitrogen compounds (~20 ppm of nitrate and nitrite) high doses and high concentrations of added sulfite are required. It is very difficult to say definitely to which compounds nitrate and nitrite degrade upon electronbeam treatment. It is not excluded that such compounds are N2 and N2O.These compounds were detected as radiolysis products of aqueous nitrate–acetate solutions.12 Therefore, the radiolytic degradation of nitrate and nitrite in aqueous solutions can be carried out in the presence of effective scavengers of OH radicals. A maximum effect was observed when the k(OH + S)×[S] value was higher than k(OH + NO2 – )× ×[NO2 – ] value by a factor of 2–3.The most suitable scavenger is sulfite. Anaerobic conditions are preferable for the radiolytic degradation of nitrate and nitrite. References 1 A.K.Pikaev, Khim. Vys. Energ., 2000, 34, 3 [High Energy Chem. (Engl. Transl.), 2000, 34, 1]. 2 A.K.Pikaev, Khim. Vys. Energ., 2000, 34, 83 [High Energy Chem. (Engl. Transl.), 2000, 34, 55]. 3 Standard Methods for the Examination of Water and Wastewater, eds.A. D. Eaton, L. S. Clesceri and A. E. Greenberg, American Public Health Association, 19th Edition, 1995, pp. 850–857. 4 A. P. Kreshkov and A. A. Yaroslavtsev, Analiticheskaya khimiya. Kachestvennyi analiz (Analytical Chemistry. The Qualitative Analysis), Khimiya, Leningrad, 1975, pp. 332–336 (in Russian). 5 A. V. Ponomarev, I.E. Makarov, A. V. Bludenko, A. K. Pikaev, V. N. Minin, D. K. Kim and B. Han, Khim. Vys. Energ., 1999, 33, 177 [High Energy Chem. (Engl. Transl.), 1999, 33, 145]. 100 80 60 40 20 0 0.3 0.6 0.9 C 1 2 3 4 [Sulfite]/10–3 M Figure 1 Influence of sulfite concentration on residual nitrate and nitrite content (C is the sum of ions, %) in irradiated aqueous solutions with initial concentration: (1) 10–4 mol dm–3 nitrite; (2) 5×10–5 mol dm–3 nitrite and 5×10–5 mol dm–3 nitrate; (3) 10–4 mol dm–3 nitrate; (4) 2×10–4 mol dm–3 nitrite (dose, 1.5 kGy; pH 7). 100 80 60 40 20 0 1.0 2.0 3.0 C Dose/kGy 1 2 3 4 5 Figure 2 Influence of dose on residual nitrate and nitrite content (C is the sum of ions, %) at pH 7 in the presence of (1)–(3) 4×10–4 mol dm–3 and (4), (5) 6×10–4 mol dm–3 sulfite in aqueous solutions with initial concentration: (1) 10–4 mol dm–3 nitrite; (2), (4) 5×10–5 mol dm–3 nitrite and 5×10–5 mol dm–3 nitrate; (3), (5) 10–4 mol dm–3 nitrate.Mendeleev Communications Electronic Version, Issue 1, 2001 (pp. 1–42) 6 G. V. Buxton and C. L. Greenstock, J. Phys. Chem. Ref. Data, 1983, 17, 886. 7 A. B. Ross and P. Neta, Rate Constants for Reactions of Inorganic Radicals in Aqueous Solution, NSRD-NBS 65, Washington, DC, 1979. 8 P. Neta, R. E. Huie and A. B. Ross, J. Phys. Chem. Ref. Data, 1988, 17, 1027. 9 A. V. Ponomarev, I. E. Makarov and A. K. Pikaev, Khim. Vys. Energ., 1991, 25, 311 (in Russian). 10 A. K. Pikaev, S. A. Kabakchi and I. E. Makarov, Vysokotemperaturnyi radioliz vody i vodnykh rastvorov (High-temperature Radiolysis of Water and Aqueous Solutions), Energoizdat, Moscow, 1988 (in Russian). 11 J. W. Mellor, A Comprehensive Treatise on Inorganic and Theoretical Chemistry, Longman, Green and Co., London, 1947, vol. VIII. 12 N. S. Stel’makh, B. E. Kritskaya, I. I. Byvsheva, G. N. Pirogova and I. M. Kosareva, Khim. Vys. Energ., 1997, 31, 405 [High Energy Chem. (Engl. Transl.), 1997, 31, 365]. Received: 30th November 2000; Com. 00/1729

ISSN:0959-9436     

出版商:RSC    

年代:2001

数据来源: RSC