摘要:

Mendeleev Communications Electronic Version, Issue 6, 1998 (pp. 207–248) Reactions of chelated PtII and PtIII imidoimino complexes: N-nitrosation involving transfer of an NO group from inorganic nitrites and nitrates Marina O. Ponina, Aleksei A. Sidorov, Sergei E. Nefedov, Igor L. Eremenko* and Ilya I. Moiseev N. S. Kurnakov Institute of General and Inorganic Chemistry, Russian Academy of Sciences, 117907 Moscow, Russian Federation.Fax: +7 095 952 1279; e-mail: ilerem@ionchran.msk.ru A bis-chelated imidoimino PtII complex, [(NPh)(N)C6H4]2Pt 1, was found to undergo N-nitrosation on reacting with AgNO2 or AgNO3 to form a product of formal HNO addition, [(NPh)(NNO)C6H4][(NPh)(NH)C6H4]Pt 3, that was characterised by X-ray analysis; similarly, an amidoimino binuclear PtIII complex was converted into 3 by reacting with NaNO2.Bis-chelated PtII imidoimino complexes [(NR)(N)C6H4]2Pt (1, R= Ph; 1a, R = H), having quinoid trans-NR-positioned ligands,1,2 are known to react with AgO3SCF3 with formation of binuclear PtIII–PtIII diamagnetic compounds {[(NR)(N)C6H4]2Pt}2+(O3SCF3)2 (2, R = Ph;2 2a, R = H3) (Scheme 1). Within the context of a program aimed at the investigation of coordinated imidoimino ligand reactivity we studied the interaction of the complexes 1 and 2 with inorganic nitrites and nitrates and observed N-nitrosation of the ligand leading to transfer of the NO group from NO2 – and NO3 – reagents under very mild conditions.No reaction between PtII complex [(NR)(N)C6H4]2Pt (1, R = Ph) and sodium nitrite/nitrate was observed at 20–60 °C in different solvents (THF, CH2Cl2, MeCN).However, 1 was found to react with AgNO2 in THF (20 °C)† giving rise to complex [(NPh)(NNO)C6H4][(NPh)(NH)C6H4]Pt 3 (Scheme 2). The reaction is accompanied by silver powder precipitation suggesting the involvement of a redox step in the process. Nevertheless, no formal change in the platinum atom oxidation state takes place in the course of the reaction.A possible explanation for the facts observed could be the presence of an intermediate binuclear complex, an analogue of 2, which is formed during the reaction. Within this proposal, complex 1 should first undergo oxidation by the Ag+ in the AgNO2 reagent to give a binuclear dication similarly to the oxidation 1 ® 2 observed under the conditions where AgO3SCF3 is used as an oxidant.2,3 Complex 2 is supposed to further react with NO2 – ion giving rise to the observed product 3.It is worth † Complex 1 (200 mg, 0.36 mmol) was dissolved in 50 ml of THF to form a dark blue solution. Solid AgNO2 (60 mg, 0.39 mmol) was added to the solution at 20 °C. The colour of the reaction mixture changed to brown-green in 30 min and the formation of grey metallic silver as an amorphous powder was observed.The solvent was removed at 25–30 °C (0.1 Torr) to dryness and the solid was extracted with diethyl ether (100 ml). The extract was filtered through a layer of silica gel (2×5 cm). The solution afforded brown prisms of 3 upon concentrating and cooling (–15 °C). Yield 89 mg (0.14 mmol, 39%). IR (KBr, n/cm–1) 1574 (m), 1487 (m), 1442 (m), 1392 (m), 1286 (m), 1256 (m), 1140 (m), 1064 (m), 920 (w), 907 (w), 870 (w), 832 (w), 802 (m), 742 (m), 688 (m), 658 (m), 598 (w), 588 (m), 564 (w).Found (%): C, 48.79; H, 3.01; N, 11.94. Calc. for C24H19N5OPt (%): C, 48.98; H, 3.23; N 11.90. noting that complex 2 contains unusually long Pt–Pt distances [3.260(1) Å in 2 and 3.031(4) Å in 2a, while the distance between the PtII atoms of the neighbouring molecules in the initial complexes 1 and 1a is equal to 4.8 Å].In order to verify this scheme, we studied the reaction of complex 2 with potassium nitrite. By reacting 1 and AgNO3 in acetone at 20 °C a dimer of low solubility {[(NPh)(N)C6H4]2Pt}2(NO3)2 4 was obtained‡ and the precipitation of metallic silver was observed. This complex reacts very easily at 20–50 °C with inorganic (KNO2) nitrite under heterophasic conditions leading to complex 3.‡ The data available are therefore consistent with the scheme assuming that the first stage of the reaction is the oxidation of PtII and formation of the dimers {[(NPh)(N)C6H4]2Pt}2+X2, where X = NO2 or NO3.It should be noted that complex 4 also gives compound 3 and a new unidentified complex upon heating (100 °C, xylene).The binuclear complex 2 is stable at 100–140 °C. However, it reacts with KNO2 at 50–80 °C forming complex 3 and the initial compound 1 in the ratio 1:2. ‡ Complex 1 (200 mg, 0.36 mmol) and AgNO3 (65 mg, 0.38 mmol) were ground in an agate mortar with 2 ml of acetone. The resulting brown-black solid was extracted with chloroform (200 ml).After cooling of this brown solution to –18 °C a microcrystalline powder of 4 [115 mg, 0.09 mmol, 50%. Found (%): C, 22.98; H, 1.54, N, 6.76. Calc. for C24H18N6O6Pt2 (%): C, 23.26; H, 1.45; N, 6.79.] was separated by decantation, washed with diethyl ether (10 ml) and dried in vacuo. Further reaction between 4 (100 mg, 0.08 mmol) and KNO2 (25 mg, 0.16 mmol) in 2 ml of acetone was performed in the same manner affording 35 mg (0.06 mmol, 37.5%) of 3.Complex 3 can also be prepared in one stage by the grinding of 1 with an excess of AgNO3 and KNO2 in 2–3 ml of acetone. N N R N N R Pt N N N N R Pt AgO3SCF3 R N N N N R Pt R 2+ (O3SCF3)2 1 R = Ph 1a R = H 2 R = Ph 2a R = H Scheme 1 N N Ph N N Ph Pt N N N N Ph Pt AgNO3 Ph N N N N Ph Pt Ph 2+ (NO3)2 1 4 N N N N Ph Pt Ph 3 N O H AgNO2 KNO2 at 20–50 ºC or thermolysis of 4 at 100 ºC Scheme 2Mendeleev Communications Electronic Version, Issue 6, 1998 (pp. 207–248) The monomeric and diamagnetic compound [(NPh)(NNO)- C6H4][(NPh)(NH)C6H4]Pt 3 contains a PtII atom, as in starting compound 1. According to the X-ray data§ (Figure 1), the phenyl substituents of the ligands in 3 [C(Ph)–N 1.43(1) and 1.44(1) Å; the N atoms of the NPh moieties for both ligands § Rhombohedral crystals, space group R3, a = 22.970(3), c = 21.594(4) Å, V = 9867(5) Å3, Z = 18, R1 = 0.042, Rw = 0.058 for 2315 reflections with F > 4.0s.Bond lengths, bond angles, atomic coordinates and thermal parameters have been deposited at the Cambridge Crystallographic Data Centre (CCDC). For details, see ‘Notice to authors’, Mendeleev Communications, 1998, Issue 1.Any request to the CCDC for data should quote the full literature citation and the reference number 1135/29. have a trigonal-planar configuration] are cis-positioned, unlike the trans-configuration of these groups in the starting material. The H atom and NO group are attached to another two N atoms of molecule 3 [N–H distance 1.09(5) Å; the NNO fragment has a bent configuration with distances N–N 1.34(1) Å, N–O 1.30(2) Å, �N–N–O 115(1)°].The NH and NNO groups are bound together via a hydrogen bond H···O [1.76(3) Å] to form a six-membered metallacycle. The N–O and N–N bond distances in the N–N=O group are in the range between single and double bonds probably indicating the delocalisation of the electron density over this fragment.It is interesting to note that the interatomic distances in the chelate (NPh)(NNO)C6H4 group of 3 are close to those expected for the benzoid form [N(Ph)–C(C6H4) 1.40(1) Å, N(NO)–C(C6H4) 1.43(1) Å]. Meanwhile, the ligand moiety with the protonated group (NPh)(NH)C6H4 features a quinodiimine geometry [N(Ph)– C(C6H4) 1.37(1) Å, N(H+)–C(C6H4) 1.32(1) Å, a six-membered carbon ring containing two short and four long C–C bonds (see Figure 1)].In addition, the metal-to-metal distance in 3 is obviously non-bonding [Pt···Pt length for the neighbouring molecules is equal to 4.947(1) Å]. The mechanistic aspects of the reactions will be discussed in a full paper. We are thankful to the Russian Foundation for Basic Research (grant no. 96-03-33171) for financial support. The X-ray structural investigation was perform at the X-Ray Structural Centre (INEOS, RAS). References 1 A. A. Sidorov and S. B. Katser, Zh. Neorg. Khim., 1994, 39, 860 (Russ. J. Inorg. Chem., 1994, 39, 900). 2 I. L. Eremenko, S. E. Nefedov, A. A. Sidorov, M. O. Ponina, P. V. Danilov, T. A. Stramnova, I. P. Stolarov, S. B. Katser, S. T.Orlova, M. N. Vargaftik, I. I. Moiseev and Yu. A. Ustynyuk, J. Organomet. Chem., 1998, 551, 171. 3 A. A. Sidorov, M. O. Ponina, S. E. Nefedov, I. L. Eremenko, Yu. A. Ustynyuk and Yu. A. Lusikov, Zh. Neorg. Khim., 1997, 42, 853 (Russ. J. Inorg. Chem., 1997, 42, 952). 4 F. A. Allen, O. Kennard, D. G. Watson, L. Brammer, A. Guy Orpen and R. Taylor, J. Chem. Soc., Perkin Trans. 2, 1987, S1.O(1) N(1) N(2) N(3) N(4) N(5) C(1) C(2) C(3) C(4) C(5) C(6) C(7) C(8) C(9) C(10) C(11) C(12) C(13) C(14) C(15) C(16) C(17) C(18) C(19) C(20) C(21) C(22) C(23) C(24) Pt(1) H(1) Figure 1 Crystal structure of compound 3. Selected bond lengths (Å): Pt(1)–N(1) 2.027(8), Pt(1)–N(2) 1.973(9), Pt(1)–N(3) 1.981(8), Pt(1)–N(4) 2.004(8), O(1)–N(5) 1.303(16), N(1)–C(1) 1.367(14), N(1)–C(7) 1.436(14), N(2)–C(6) 1.325(14), N(3)–C(13) 1.403(14), N(3)–C(19) 1.434(14), N(4)– N(5) 1.338(14), N(4)–C(18) 1.429(14), C(1)–C(2) 1.412(15), C(1)–C(6) 1.443(16), C(2)–C(3) 1.358(17), C(3)–C(4) 1.412(19), C(4)–C(5) 1.342(17), C(5)–C(6) 1.435(17), C(13)–C(18) 1.385(16), C(14)–C(15) 1.403(17), C(15)–C(16) 1.401(19), C(16)–C(17) 1.379(19), C(17)–C(18) 1.374(16); selected bond angles (°): N(1)–Pt(1)–N(2) 79.1(3), N(1)–Pt(1)–N(3) 104.4(3), N(2)–Pt(1)–N(3) 176.3(4), N(1)–Pt(1)–N(4) 175.4(4), N(2)– Pt(1)–N(4) 96.4(4), N(3)–Pt(1)–N(4) 80.1(3), Pt(1)–N(4)–N(5) 132.1(8), O(1)–N(5)–N(4) 115.5(10). Received: Moscow, 5th August 1998 Cambridge, 11th September 1998; Com. 8/06232C

ISSN:0959-9436     

出版商:RSC    

年代:1998

数据来源: RSC

摘要:

Mendeleev Communications Electronic Version, Issue 6, 1998 (pp. 207–248) The first example of the catalytic activity of ( -H)Os3( -OCNR1R2)(CO)10 clusters in the double bond migration reactions of allylic systems functionalised with an amido group Victoriya A. Ershova,* Sergei V. Tkachev, Anatoly V. Golovin and Leonid Ya. Al’t Institute of Inorganic Chemistry, Siberian Branch of the Russian Academy of Sciences, 630090 Novosibirsk, Russian Federation.Fax: +7 3832 34 4489; e-mail: ers@hydro.nsc.ru As exemplified by the isomerisation of N-allylacetamide in the presence of hydridocarbonyl complexes (m-H)Os3(m-OCNR1R2)(CO)10 (R1 = H, Alk; R2 = Alk), it has been demonstrated for the first time that they are effective catalysts for the [1,2]-double bond shift under mild conditions in allylic compounds functionalised with an amido group.Allylic isomerisation of various olefinic molecules is the key step in many preparations. The choice of a means and conditions to start this process depends on the type of functional substituent present in the allylic fragment. In particular, even such strong bases as potassium tert-butoxide are known to be ineffective in the transformation of N-allylamides into enamides important for organic synthesis, but the [1,2]-double bond shift can be carried out in rather severe conditions in the presence of metallocomplex catalysts.The modest list of these complexes includes, to our knowledge, only the complexes of iron, Fe(CO)5 under UV irradiation,1 ruthenium, HRuCl(PPh3)3 2 and rhodium, HRh(PPh3)4,2 RhI–BINAP†,3 and polymer-supported RhI-DIOP‡,2,4 under heating.As regards the cluster complexes, any data on the isomerisation of alkenes with an amido function are still lacking in the literature while a sufficiently large number of papers is devoted to other types of allylic substrates (mainly to hydrocarbons and alcohols) (see review 5 and corresponding references). The pioneering work of a A. J.Deeming and S. Hasso6 was the first example of a metal cluster-catalysed isomerisation of an unfunctionalised olefin. The high activity under mild conditions of unsaturated complex (m-H)2Os3(CO)10 was demonstrated. At the same time it was shown that another triosmium hydride (m-H)- Os3(m-Br)(CO)10 does not catalyse alkene isomerisation at room temperature (m-Br is a 3e-donor).In the present paper we consider the ability of the coordinatively saturated triosmium complexes (m-H)Os3(m-OCNR1R2)(CO)10, (R1 = H, Alk; R2 = Alk) to catalyse the isomerisation of N-allylamides under rather mild conditions. We have recently described7,8 the isomerisation of the hydridocarbonyl allyl-containing clusters (m-H)Os3(m-OCNRCH2CH=CH2)- (CO)10 (1 R =H, 2 R =Me) to the propenyl-carboxamido clusters (m-H)Os3(m-OCNRCH=CHMe)(CO)10 (3 R =H, 4 R =Me) under mild conditions (Scheme 1).This reaction seemed to occur for no apparent reason and was obscure. Here we show that this process is a catalytic interaction. Each of the compounds 1 and 2 can be considered as a derivative of N-allylamide with the corresponding clustercontaining substituent.To clarify the role of this cluster-containing substituent in the allylic isomerisation comparative tests of † BINAP = 2,2'-bis(diphenylphosphino)-1,1'-binaphthyl. ‡ DIOP = 2,3-isopropyliden-2,3-dihydroxy-1,4-bis(diphenylphosphino)- butane. N-allylacetamide 5 and cluster 1 were performed under the same conditions. The reaction was monitored by 1H NMR spectroscopy.It was found that the N-allylacetamide, consumed in a ~30-fold molar excess with respect to 1, is completely converted in its presence into N-propenylacetamide 6§ which is a ~1:3.5 mixture of cis- and trans-isomers (CDCl3, 18 °C, ~500 h). Cluster 1 itself is also almost fully isomerised to 3.¶ A similar transformation of 5 (full or partial) is observed in solutions containing 3–10 mol% of the other carboxamido complexes (m-H)Os3(m-OCNR1R2)(CO)10, including those without either double bond or NH hydrogen atom (Scheme 2,†† Figure 1).No detectable spectral changes for the complexes in either form or intensity of resonances were observed during the reaction. Compound 5 appeared to be unaffected by other types of complexes such as amido (m-H)Os3(m-NHCH2CH=CH2)(CO)10 ‡‡ 10 or pure carbonyl Os3(CO)12 under the same conditions.The above data demonstrate that the cluster fragment plays no significant role as the substituent in the convertible allylcontaining molecule (double bond migration occurs in compound 5 lacking this substituent but only in the presence of any carboxamido cluster), and the allylic isomerisation in itself is not a monomolecular process.We are obviously dealing with a catalytic type of reaction, in which the cluster fragment (m-H)Os3(m-OCN) takes part. To confirm these findings, comparative estimates (1H NMR) for 2 to 4 conversion rates have been obtained, depending on § trans-6: 1H NMR (250 MHz, CDCl3) d: 8.67 (br. s, 1H, =NH), 6.72 (ddq, 1H, =N–CH=, 3J 14.2, 10.3 Hz, 4J 1.7 Hz), 5.12 (dq, 1H, =CH–, 3J 14.2 Hz, 3J 6.8 Hz), 2.02 [s, 3H, –C(O)Me], 1.66 (dd, 3H, Me, 3J 6.8 Hz, 4J 1.7 Hz).cis-6: 1H NMR (250 MHz, CDCl3) d: 8.29 (br. s, 1H, =NH), 6.70 (ddq, 1H, =N–CH=, 3J 9.0, 10.7 Hz, 4J 1.8 Hz), 4.80 (dq, 1H, =CH–, 3J 9.0 Hz, 3J 7.1 Hz), 2.09 [s, 3H, –C(O)Me], 1.63 (dd, 3H, Me, 3J 7.1 Hz, 4J 1.8 Hz). ¶ Like 1, complex 3 may also exhibit catalytic activity. However, a decrease in the reaction rate with time indicates that the activity of 3 cannot be higher than that of 1.†† Syntheses of 7, 9: see ref. 9 and of 8, see ref. 10. ‡‡ Synthesis of 10: sealed tube, a mixture of (m-H)Os3(m-OH)(CO)10 and NH2CH2CH=CH2 (1:2) in THF, 90 °C, 1 h. Yield 80%. 1H NMR (200 MHz, CDCl3) d: 5.85 (ddt, 1H, =CH–, 3Jtrans 16.1 Hz, 3Jcis 10.3 Hz, 3J 6.5 Hz), 5.30 (dd, 1H, =CHHcis, 3J 10.3 Hz, Jgem 1.1 Hz), 5.24 (dd, 1H, =CHHtrans, 3J 16.1 Hz, Jgem 1.1 Hz), 3.95 (br. s, 1H, =NH), 3.46 (dd, 2H, =NCH2–, 3J 6.5 Hz, 3JCH–NH 6.9 Hz), –14.90 (d, 1H, m-H, 3J 2.7 Hz).IR data are analogous to those described in the literature.11 m m H (OC)3Os Os(CO)3 O C Os(CO)4 RNCH2CH=CH2 H (OC)3Os Os(CO)3 O C Os(CO)4 RNCH=CHMe Scheme 1 1 R = H 2 R = Me 3 R = H 4 R = Me O=CMeNHCH2CH=CH2 O=CMeNHCH=CHMe catalyst = (m-H)Os3(m-OCNR1R2)(CO)10 catalyst 5 6 1 R1 = H, R2 = Allyl 2 R1 = Me, R2 = Allyl 7 R1 = H, R2 = Me 8 R1 = H, R2 = (CH2)4Me 9 R1 = R2 = Me Scheme 2Mendeleev Communications Electronic Version, Issue 6, 1998 (pp. 207–248) both the concentration of 2 and the presence in its solution of any other Os3 cluster having a carboxamido bridging ligand.It was found that the reaction rate, as expected, increases as the general cluster concentration grows and depends on the kind of m-ligand present. Specifically, for a solution of 2 in CDCl3 0.015 mol dm–3 (a) at 20 °C the reaction halftime t1/2 ª 536 h, while for 0.045 mol dm–3 (b) the estimated t1/2 value is ~317 h, which is approximately 1.7 times less. After the addition of complex 7 to the solution (a) and reaching the same overall concentration as for (b) (i.e. 0.03 mol dm–3 for 7), t1/2 (~177 h) decreases [1.8 times with respect to (b) and 3 times with respect to (a)]. Similarly, the halflife decreases by approximately 3.2 times (from ~863 h to ~266 h) when passing from solution 2 (0.023 mol dm–3 in C6D6) to a mixture of 2 with complex 9 (0.047 mol dm–3).Hence the examples of isomerisation of (m-H)Os3(m-OCNRCH2CH= CH2)(CO)10 clusters (R = H, Me) and N-allylacetamide in the presence of hydridocarbonyl complexes (m-H)- Os3(m-OCNR1R2)(CO)10 (R1 = H, Alk; R2 = Alk) demonstrate that a [1,2]-double bond shift, at least of a monosubstituted bond, in the allylic systems functionalised with an amido group is invoked by these complexes, even at room temperature.This study was supported by the Russian Foundation for Basic Research (grant no. 97-03-33046). We are grateful to Dr. V. A. Maksakov for useful discussions in the initial phase of this work. References 1 A. J. Hubert, P. Moniotte, G. Goebbels, R. Warin and P. Teyssie, J. Chem. Soc., Perkin Trans. 2, 1973, 1954. 2 J. K. Stille and Y. Becker, J. Org.Chem., 1980, 45, 2139. 3 (a) S. Otsuka and K Tani, Synthesis, 1991, 665; (b) K. Tani, Pure Appl. Chem., 1985, 57, 1845. 4 S. Fritschel, J. J. H. Acherman, T. Keyser and J. K. Stille, J. Org. Chem., 1979, 44, 3152. 5 G. Süss-Fink and G. Meister, Transition Metal Clusters in Homogeneous Catalysis, in Adv. Organomet. Chem., 1993, 35, 41. 6 A. J. Deeming and S. Hasso, J. Organomet.Chem., 1976, 114, 313. 7 V. A. Maksakov, V. A. Ershova, V. P. Kirin and A. V. Golovin, J. Organomet. Chem., 1997, 532, 11. 8 V. A. Ershova, V. A. Maksakov, A. V. Golovin, S. V. Tkachev and L. A. Sheludyakova, Izv. Akad. Nauk, Ser. Khim., 1998, 158 (Russ. Chem. Bull., 1998, 47, 160). 9 Y.-X. Lin, A. Mayr, C. B. Knobler and H. D. Kaesz, J. Organomet. Chem., 1984, 272, 207. 10 V. A.Maksakov, V. A. Ershova, V. P. Kirin, N. V. Podberezskaya and L. A. Sheludyakova, in Blagorodnye metally: khimiya i tekhnologiya (Noble Metals: Chemistry and Technology), Nauka, Novosibirsk, 1989, p. 125 (in Russian). 11 V. A. Maksakov, V. P. Kirin, S. N. Konchenko, N. M. Bravaya, A. D. Pomogailo, A. V. Virovets, N. V. Podberezskaya, I. G. Barakovskaya and S. V. Tkachev, Izv. Akad. Nauk, Ser. Khim., 1993, 1293 (Russ. Chem. Bull., 1993, 42, 1236). =CH– =C =NCH2– =NMe –C(O)Me m-H –Me trans-6 cis-6 =NCH= A B C D –C(O)Me cis-6 trans-6 cis-6, trans-6 =CH– trans-6 cis-6 =NMe Hcis =C Htrans Figure 1 Changes in the 1H NMR spectra over 1 week for the main resonances from N-allylacetamide 5 mixed with 3 mol% of (m-H)Os3- (m-OCNHMe)(CO)10 7 in CDCl3 solution (250 MHz, room temperature). The mole fraction of N-propenylacetamide 6 increases gradually from zero (A) through 30% (B) and 85% (C) to 100% (D). 6.9 6.6 6.0 5.7 5.3 5.0 4.6 4.0 3.7 2.8 2.5 2.2 2.0 1.5 –14.3 d/ppm 5 5 5 5 7 7 7 7 m-H Received: Moscow, 8th April 1998 Cambridge, 18th August 1998; Com. 8/02795A

ISSN:0959-9436     

出版商:RSC    

年代:1998

数据来源: RSC

摘要:

Mendeleev Communications Electronic Version, Issue 6, 1998 (pp. 207–248) Partial oxidation of light paraffins with hydrogen peroxide in the presence of peroxocomplexes of copper(II) hydroxide Andrei O. Kuzmin, Galina L. Elizarova,* Ludmila G. Matvienko, 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 Methane, ethane and ethylene are oxidised by hydrogen peroxide in aqueous solutions at room temperature and atmospheric pressure in the presence of peroxocomplexes of copper(II) hydroxide; the reaction presumably proceeds by a non-radical mechanism. Activation of light paraffins under mild conditions is a challenge for many scientists working in the field of modern catalysis. It is known that the most active and selective catalysts for the low-temperature oxidation of light paraffins are enzymes of the (mono)oxygenase type.1 It is now well established that the catalytic cycles of Fe- and Cu-containing enzymes of the oxygenase type usually include intermediate formation of peroxocomplexes. 2,3 Numerous bi- and polynuclear complexes of Fe and Cu with rather sophisticated organic ligands have been synthesised (see, e.g., review4) for the structural modelling of these enzymes.However, only some of these proved to be capable of forming peroxocomplexes under mild conditions. It was recently shown that simple compounds, such as copper and iron hydroxides with polynuclear structures, can form peroxocomplexes active in the oxidation of hydrazine derivatives.5 The present work demonstrates for the first time the oxidation of methane, ethane and ethylene by hydrogen peroxide under mild conditions in the presence of copper(II) peroxocomplexes in a simple heterogeneous system based on Cu(OH)2 deposited on SiO2.Equipment. A Shimadzu UV 300 spectrophotometer, a Bruker MSL 400 NMR spectrometer, a Tsvet 530 gas chromatograph with a flame ionisation detector (a 3 m column with 2% diglycerol on Carbopack) and a I-135 pH-meter were used in this work.The reaction was carried out in 10 ml of aqueous solution in the presence of 0.5 g of a catalyst at 298 K under atmospheric pressure. The gas phase of the reactor was formed by 150 cm3 of either air or a hydrocarbon.The volume of oxygen evolved was measured with a volumetric set-up. The catalyst Cu(OH)2/SiO2 was prepared according to the method reported by Elizarova et al.5 50 cm3 of water were added to 5 g of a KSKG silica gel (Dzerzhinsk, Russia) (Ssp = 300 m2 g–1), ground to a powder, and then a 1 M solution of NaOH was added to adjust to pH 10–11.Then 7.8 cm3 of 0.2 M Cu(NO3)2 was added with vigorous stirring. The precipitate was filtered, rinsed repeatedly with water and dried first at 383 K and then at 530 K for 30–40 min. The catalyst obtained contained 2% Cu (w/w). It should be stressed that the nature of the support and the procedure used for the hydroxide preparation are of key importance for the catalytic activity of the resulting sample.Thus, considerably less active catalysts were obtained when Aerosil or TiO2 was used as a support. Comparison of the diffuse reflection spectrum of the catalyst with the spectrum of bulk Cu(OH)2, which was prepared by the standard procedure,6 indicated that all the copper in the catalyst system was in the hydroxide form (Figure 1). Addition of H2O2 to an aqueous suspension of Cu(OH)2/SiO2 rapidly turns the blue colour of the latter into brown.The diffuse reflection spectrum of the H2O2-treated and filtered sample exhibits a charge transfer band at 26000 cm–1 (Figure 1), which points to the coordination of H2O2 by Cu ions. This is also confirmed by the characteristic reaction with TiIV. Thus, treatment of the catalyst with a solution of TiIV in 1 M H2SO4 results in decomposition of the copper peroxide (disappearance of brown colour) and binding of the H2O2 released to TiIV with the appearance of the yellow colour of TiIV peroxocomplex.7 Decomposition of hydrogen peroxide in the presence of light hydrocarbons.Cu(OH)2/SiO2 is an active catalyst for the decomposition of H2O2 in the pH range 7–11 (dissolution of copper hydroxide takes place below pH 7).The kinetics of H2O2 decomposition and dioxygen evolution at pH 10.5 are shown in Figures 2 and 3, respectively. Part of the experimental evidence proves a non-radical mechanism of H2O2 decomposition in the presence of CuII hydroxide.8 In particular, in the presence of radical inhibitors (a- and b-naphthols), neither an induction period nor a decrease in the hydrogen peroxide decomposition rate are observed in the range of inhibitor concentrations from 1.0×10–5 to 5×10–4 M.When the hydrogen peroxide decomposition proceeds in an atmosphere of ethane or ethylene, the reaction rate is considerably lower than that in air (Figures 2 and 3). The amount of oxygen evolved also decreases. Meanwhile, the catalyst has a brown colour and thus remains in the form of peroxocomplex both in a hydrocarbon and in an air atmosphere.It is thus likely that peroxocomplexes of copper hydroxide, active in the H2O2 decomposition reaction, can also interact with ethane and 80 70 60 50 40 30 20 10 0 42 38 34 30 26 22 18 14 10 1 2 3 n/10–3 cm–1 1 – R• (%) Figure 1 The diffuse reflection spectra of (1) bulk Cu(OH)2, (2) Cu(OH)2/ SiO2 catalyst and (3) the catalyst after interaction with H2O2. Table 1 Products of methane, ethane and ethylene oxidation by hydrogen peroxide in the presence of Cu(OH)2/SiO2.Substrate pH Concentration of H2O2/M Products/10–3 M (in the liquid phase) Ethane 10.6 0.15 acetaldehyde (0.63) ethanol (traces) Ethane 8.0 0.15 acetaldehyde (1.0) ethanol (0.13) Ethane 10.8 0.5 acetaldehyde (0.65) ethanol (traces) Ethane 8.0 0.5 acetaldehyde (0.9) ethanol (0.11) Ethylene 10.5 0.15 formic acid (14) Methane 8.0 0.15 formic acid (0.08) Methane 10.5 0.15 formic acid (0.07)Mendeleev Communications Electronic Version, Issue 6, 1998 (pp. 207–248) ethylene. In a methane atmosphere, the H2O2 decomposition in the presence of Cu(OH)2/SiO2 proceeds as fast as it does in air.Analysis of the oxidation products. Gas chromatographic analysis of the liquid phase after complete decomposition of H2O2 in the presence of ethane (duration of experiment ca. 1 h) revealed acetaldehyde and ethanol which were undetectable in the absence of any of the reaction mixture components (catalyst, hydrocarbon or H2O2). The amount of products depends on the reaction conditions (Table 1).The maximum level of the ethane oxidation products in the solution shown in Table 1 corresponds to a 1.4% conversion of H2O2. Upon ethylene oxidation, traces of ethylene oxide were detected in the gas phase. 1H NMR spectroscopy of the liquid phase after C2H4 oxidation in D2O revealed a narrow singlet at 8.43 ppm, belonging to HCOO–. The latter is confirmed by spectrophotometric analysis with chromotropic acid.9 The formate concentration was found to be 1.4×10–2 M and corresponded to a 36% conversion of H2O2.In addition, the NMR spectrum showed a strong signal from water protons (Dd = 0.8 ppm) which could mask the signals from other products, e.g., alcohols. However, no ethanol was detected by gas chromatography. It is noteworthy that a remarkable isotope effect is observed in D2O (Figure 3).Despite the fact that the presence of methane has no effect on the kinetics of H2O2 decomposition, its oxidation does take place, since formic acid (ca. 8×10–5 M) is detected in the solution by its reaction with chromotropic acid (the sensitivity of this method is 1×10–5 M HCOOH).9 According to preliminary data, the catalysts based on iron hydroxide are also active in the oxidation of the above-mentioned hydrocarbons.They are, however, characterised by much lower reaction rates and yields of the oxidation products. In conclusion, it is worth mentioning that hydroxides of transition metals seem to be very promising catalysts for redox reactions in aqueous solutions. This is due to their simple synthesis, polynuclear structure and an absence of organic ligands, which are usually oxidised together with an organic substrate.Taking into account the non-radical mechanism of H2O2 decomposition in the presence of Cu and Fe hydroxides, one may assume that hydrocarbons are also oxidised without intermediate formation of free radicals. Although the mechanisms of the hydrocarbon oxidation reactions described in the present paper are not quite clear yet, and the yields of the of light paraffin oxidation products are not sufficiently high, the very fact of their formation and the absence of a wide range of oxidation products are remarkable, and this is another argument in favour of the non-radical mechanism of oxidation.This fact distinguishes the above-mentioned systems from the radicalchain oxidation of hydrocarbons in acidic media in the presence of Fenton (H2O2 + Fe2+/Fe3+) reagent (see review10 and references therein).The authors thank M. A. Fedotov and L. A. Pinaeva for their assistance with the analysis of the oxidation products. References 1 G. A. Kovalenko, Usp. Khim., 1996, 65, 676 (Russ. Chem. Rev., 1996, 65, 625). 2 L. Shu, J. C. Nesheim, K. Kauffmann, E. Munck, J. D. Lipscomb and L. Que Jr., Science, 1997, 275, 515. 3 W. Shin, U. M. Sundaram, J. L. Cole, H. H. Zhang, B. Hedman, K. O. Hodgson and E. I. Solomon, J. Am. Chem. Soc., 1996, 118, 3202. 4 P. Vigato, S. Tamburini and D. Fenton, Coord. Chem. Rev., 1990, 106, 25. 5 G. L. Elizarova, L. G. Matvienko, O. P. Pestunova, D. E. Babushkin and V.N. Parmon, Kinet. Katal., 1998, 39, 49 [Kinet. Catal. (Engl. Transl.), 1998, 39, 44]. 6 U. V. Karyakin and I. I. Angelov, Chistye khimicheskie veshchestva (Pure Chemical Substances), Khimiya, Moscow, 1974, p. 232 (in Russian). 7 G. Charlot, Les Methodes de la Chimie Analytique. Analyse Quantitative Minerale, Masson et Cie, 1961 (in French). 8 G. L. Elizarova, L. G. Matvienko, O. L. Ogorodnikova and V. N. Parmon, Kinet. Katal., submitted. 9 W. M. Grant, Anal. Chem., 1948, 20, 267. 10 C. Walling, Acc. Chem. Res., 1975, 8, 125. 100 80 60 40 20 0 5 10 15 20 25 30 35 40 Time/min Amount of H2O2 (%) 1 2 3 Figure 2 Kinetics of H2O2 (10 ml, 0.15 M) decomposition at 293 K in the presence of Cu(OH)2/SiO2 (0.5 g) at pH 10.5 in an atmosphere of: (1) air, (2) ethane and (3) ethylene. H2O2 content is given as a percentage of its initial concentration. V/ml 16 14 12 10 8 6 4 2 0 Time/min 1 2 3 4 5 10 15 20 25 30 35 40 Figure 3 Kinetics of the gas evolution from 10 ml of 0.15 M H2O2 solution in the presence of Cu(OH)2/SiO2 (0.5 g) at pH 10.5 and 293 K in H2O in an atmosphere of: (1) air, (2) ethane, (3) ethylene and (4) the same as (3) but in D2O. Received: Moscow, 2nd July 1998 Cambridge, 11th September 1998; Com. 8/05567J

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Mendeleev Communications Electronic Version, Issue 6, 1998 (pp. 207–248) Appearance of the supercritical state of carbon in the laser evaporation of low-density graphite foil Sergei I. Kudryashov,* Sergei G. Ionov, Alexander A. Karabutov and Nikita B. Zorov Department of Chemistry, M. V. Lomonosov Moscow State University, 119899 Moscow, Russian Federation. Fax: +7 095 932 8846; e-mail: serg@laser.chem.msu.su A high concentration of nonequilibrium defects in crystallites and a low bulk density of the graphite foil obtained from thermally expanded graphite favour the explosive decomposition of the laser-heated surface layer of the substance in the supercritical state.Low-density carbon materials such as graphite foil are of considerable interest because of the possibility of generating various high-temperature states of carbon by the action of intense laser radiation.Due to the high (up to 80%) porosity of the low-density graphite foil, quasi-equilibrium evaporation into the pores occurs in the near-surface region of laser radiation absorption with a thickness greater than 100 nm. The average size of the pores, according to small-angle X-ray back scattering data, is 10–20 nm (less than the free path length of vapour species).Depending on the ratio between the material density r and the density of carbon in the critical state rcr = 0.64 g cm–3,1 the critical state of the substance (r = rcr), the labile state of the liquid phase with pre-critical parameters (r < rcr), or the supercritical state of the substance (r > rcr) in the immediate vicinity of the critical point can be formed.The structure of graphite foil is metastable2 due to the presence of nonequilibrium chemically induced defects; therefore, the heats of laser-induced phase transitions in graphite foil can differ from similar parameters for polycrystalline graphite (PCG) chosen for the study as the reference sample. In this work, for studying the mechanism of the laser-induced decomposition of graphite foil, we used the method of photoacoustic spectroscopy, which is widely used for the investigation of phase transitions occurring in the bulk and on the surface of condensed matter under the action of laser radiation.3 Previously, in the study of laser evaporation of dense PCG (bulk density r = 1.7 g cm–3) by the photoacoustic procedure, we have observed the threshold-like (by laser power density, I0 ª 0.3 GW cm–2) formation of the surface layer of the liquid phase of carbon at the thermodynamically unstable (labile) state, which is decomposed due to hydrodynamic removal of the products of spinodal decomposition of this state: nuclei of the liquid and gas phases.4 The disappearance of the thermoacoustic pulse of rarefaction of negative polarity in the acoustic signal detected by the photoacoustic procedure was used as a criterion of formation and hydrodynamic decomposition of the labile state of the liquid phase of carbon.In fact, the compression wave of the thermoacoustic nature (with a positive polarity) on the free surface of the labile liquid phase of carbon is not reflected with the appearance of the following rarefaction wave (with a negative polarity), but is transformed into a directed flow wave of the gas–liquid mixture of the products of spinodal decomposition.Thus, the recoil pressure of the substance evaporated on the target surface is equal to the thermoacoustic pressure in the labile phase (Figures 1 and 2) and is approximately half the pressure of saturated carbon vapour at the given temperature, provided its value is not greater than the critical temperature of carbon.4 In this work, we chose a graphite foil sample, which differs from a PCG sample in bulk density (0.7 g cm–3) and high concentration of nonequilibrium structural defects, as the object of photoacoustic studies. In experiments, we used a photoacoustic setup similar to that described in ref. 4. An Nd:YAG laser (l = 532 nm, t = 10 ns, f = 0.9 Hz) heated and evaporated the graphite target with a thickness of 600 mm. The absorption of radiation in the thin (less than 10–7 m) surface layer of the target, followed by thermalization of the absorbed energy to the energy of the phonon subsystem and evaporation of the substance, created surface thermoacoustic and evaporation sources of longitudinal acoustic waves, which were detected on the back side of the target by a ‘thick’ piezoelectric ceramic PZT-19 detector (thickness d = 1.5±0.1 mm, time constant ca. 500 ms) and an S8-12 oscilloscope with an input resistance of 1 MW. The thickness of the acoustic detector provided a time ‘window’ with a duration of 400–500 ns for the direct detection of the acoustic signal without reflection in the piezocrystal.The acoustic detector worked in the idling regime, i.e., the signal detected was proportional to the displacement amplitude (the integral value for the vibrational velocity). However, a path length Lpath of about 4 mm for the acoustic wave in the graphite target and a protective brass disk in the acoustic detector were Figure 1 Dependence of the thermoacoustic pressure ( ), recoil pressure for PCG ( ) and thermoacoustic pressure for graphite foil ( ) on I0 (RSD £ 10% for each acoustic pressure value).Acoustic pressure (arbitrary units) Power density/GW cm–2 200 150 100 50 0 0.5 1.0 1.5 2.0 2.5 Figure 2 Dependence of normalised values (divided into I0) of the thermoacoustic pressure ( ), recoil pressure for PCG ( ) and thermoacoustic pressure for graphite foil ( ) on I0 (RSD £ 16% for each normalised value).Normalised acoustic pressure (arbitrary units) Power density/GW cm–2 200 100 20 0.0 0.5 1.0 1.5 2.0 2.5Mendeleev Communications Electronic Version, Issue 6, 1998 (pp. 207–248) chosen in such a way that the detector was localized in the far diffraction zone [Lpath >> Ldiffr = (d2 source f )/Vsound £ 200 mm for sizes of the acoustic source dsource ª 150 mm, sound velocity Vsound ª 450 m s–1, and a frequency of the main spectral component of the acoustic signal f ª 5 MHz].Due to this arrangement of the acoustic detector, when the acoustic signal was propagated in the target, diffraction exerted a differentiating effect on the signal shape.As a result of the successive action of differentiating effects (due to diffraction) and integration (idling regime), the detected signal presents the real spatial and temporal distribution of thermoelastic stresses in the region of acoustic generation predicted by the photoacoustic theory.5 The signal observed upon laser irradiation of the graphite foil target takes the form of a single compression pulse (with a positive polarity) over the whole studied range of laser power density (I0 = 0.06–2.5 GW cm–2), i.e., it is formed under conditions of hydrodynamic removal of the substance.The direct experimental evidence for the explosive and bulk character of formation of the acoustic compression pulse during laser decomposition of the graphite foil sample was obtained by scanning electron microscopy (SEM), studying the shape of the crater in the graphite foil target irradiated with a power density of 0.003–1 GW cm–2.The structure of partially torn off packets of crystallites is observed on the target surface only beginning from the threshold value I0 = 0.006 GW cm–2 corresponding to the deposition of radiation energy of ca. 200 kJ mol–1 to the absorption layer on the target surface (Figure 3). For incident power density I0 > 0.015 GWcm–2, a smooth crater surface is observed, which indicates complete removal of the laser-heated layer of the substance. It is likely that the hydrodynamic mechanism of acoustic generation during laser evaporation of graphite foil (r > rcr) can be related to the expansion of the laser-heated layer of carbon in the supercritical state (thickness to 100 nm for the given sample of graphite foil with a bulk density of 0.7 g cm–3).In fact, the amplitude of the acoustic compression pulse generated in the graphite foil target (Figures 1 and 2), taking into account greater dissipation of the longitudinal acoustic wave in the foil as compared to the PCG target (thickness of the targets 600±25 mm, correction coefficient for graphite foil 1.3±0.2), is two to three times greater than the amplitude of the acoustic compression pulse appeared during the spinodal decomposition of the labile liquid phase of carbon in the PCG target at I0 = 0.3–2.5 GW cm–2.This implies that the internal quasistatic vapour pressure in closed cavities of graphite foil exceeds by 2–3 times the value of the recoil pressure during the nonequilibrium hydrodynamic decomposition of the surface layer of the labile liquid phase in the PCG target and, hence, exceeds by 1–1.5 times the value of the equilibrium pressure of saturated carbon vapour at the same evaporation temperature, and corresponds to the formation of the supercritical state of carbon. Taking into account the calibration of the acoustic detector during laser evaporation of PCG,6 the maximum pressure in the graphite foil target volume occupied by the substance in the supercritical state is 3400±500 bar at I0 = = 2.5 GWcm–2, which considerably exceeds the value of the critical carbon pressure (2210 bar1).As follows from the SEM and photoacoustic spectroscopy data, the supercritical state of carbon appears in the graphite foil target at I0 < 0.06 GW cm–2 (for PCG at I0 > 0.3 GWcm–2), which indicates a significant decrease in the total heat of formation of the supercritical state of carbon from 2707 to 200 kJ mol–1 due to the contribution of the energy of nonequilibrium chemically induced defects of the crystallites (more than 70 kJ mol–1).The authors are grateful to the Russian Foundation for Basic Research for support (grant no. 98-03-32679). References 1 H. R. Leider, O. H. Krikorian and D. A. Young, Carbon, 1973, 11, 555. 2 S. I. Kudryashov, S. G. Ionov, A. A. Karabutov and N. B. Zorov, Mendeleev Commun., 1998, in press. 3 I. A. Veselovskii, B. M. Zhiryakov, A. N. Korotchenko and A. A. Samokhin, Kvantovaya Elektronika, 1985, 12, 381 (Sov. J. Quantum Electronics, 1985, 15, 246). 4 S. I. Kudryashov, A. A. Karabutov and N. B. Zorov, Mendeleev Commun., 1998, 6. 5 V. E. Gusev and A. A. Karabutov, Lazernaya Optoakustika (Laser Photoacoustic), Nauka, Moscow, 1991 (in Russian). 6 S. I. Kudryashov, A. A. Karabutov, M. A. Kudryashova, V. I. Beketov and N. B. Zorov, Mendeleev Commun., 1998, 29. 7 Termodinamicheskie svoistva individual’nykh veshchestv (Thermodynamic Properties of Individual Substances), ed. V. P. Glushko, Nauka, Moscow, 1979, vol. 2, p. 10 (in Russian). Figure 3 SEM image of the surface of the graphite foil sample laser irradiated with a power density greater than 0.006 GW cm–2. 10 mm Received: Moscow, 25th May 1998 Cambridge, 6th August 1998; Com. 8/04727H

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Mendeleev Communications Electronic Version, Issue 6, 1998 (pp. 207–248) The role of crystalline defects and the density of a graphite foil in the laser-induced degradation Sergei I. Kudryashov,* Sergei N. Borisov, Sergei G. Ionov and Nikita B. Zorov Department of Chemistry, M. V. Lomonosov Moscow State University, 119899 Moscow, Russian Federation. Fax: +7 095 932 8846; e-mail: serg@laser.chem.msu.su The differences in the efficiency of laser-induced degradation of foil samples of thermally expanded graphite are determined by differences in the density of the foil and in the concentration of nonequilibrium crystallite defects in the starting thermally expanded graphite and depend on the thermodynamics of carbon evaporation in the vicinity of the critical point.Under conditions of laser vaporisation, low-density carbon materials are promising sources of large carbon clusters.1,2 However, the thermodynamics and mechanisms of laser-induced vaporisation of these materials have scarcely been studied until now.For systematic studies of the behaviour of low-density carbon materials under the action of laser radiation, it is of interest to use the graphite foil (GF) obtained from thermally expanded graphite (TEG), because its physicochemical properties (density, microstructure, texture and concentration of nonequilibrium chemically and thermally induced crystallite defects) can be varied. We have studied the physicochemical properties of graphite foil in recent years.3,4 We found that GF is a lowdensity carbon material consisting of separate weakly bound crystallites (with a thickness of about 0.01 mm) oriented nearly parallel to the foil surface and possessing, at a density of 0.5–0.7 g cm–3, 70–80% porosity (according to the low-angle X-ray scattering data, the average pore size is 10–20 nm).Because of the high porosity of the structure, the GF absorbance A(629 nm) = 0.9 in the near-surface region (up to 100 nm in thickness at a density of 0.7 g cm–3) approaches this parameter for the ideal black body, and the velocities of propagation of acoustic and thermal waves in the material dramatically decrease.3 In the region of radiation absorption, quasi-equilibrium evaporation into the pores of the foil (the average pore diameter is shorter than the free path length of vapour particles) occurs, and depending on the ratio between the material density r and the density of carbon in the critical state (rcr = 0.64 g cm–3),5 the subcritical (r £ rcr), critical, and supercritical (r > rcr)6 states of the substance can occur in the pores. Due to the presence of nonequilibrium defects, the GF structure is metastable; therefore, the heats of laser-induced phase transitions in GF can differ from similar characteristics for crystalline graphite.In this work, the effects of the bulk density of GF and the concentration of nonequilibrium defects on the thermodynamics of laser evaporation of GF were studied by the optoacoustic procedure of measuring the average depth of the crater X per laser pulse.7 Graphite foil was vaporised in air by focused radiation of the second harmonic of an Nd:YAG laser [wavelength 532 nm, pulse energy 5 mJ, pulse width (FWHM) 25 ns, and pulse repetition rate 12.5 Hz] in the laser power density range I0 0.01–3 GW cm–2.The GF samples with densities of 0.5 g cm–3 (nos. 1–3, r < rcr) and 0.7 g cm–3 (nos. 4 and 5, r > rcr) obtained by rolling (without binders) of TEG that was prepared by thermal treatment of hydrolysed intercalated graphite compounds with sulfuric acid at 1200–1300 K8 were examined.The GF samples with different concentrations of nonequilibrium defects were obtained by variations in the conditions of the synthesis of graphite bisulfate and the temperature of the thermal treatment. The previously studied9 sample of polycrystalline graphite (PCG, 1.7 g cm–3) was chosen as reference sample no. 6. Since the mechanism of substance removal under the action of pulsed laser radiation on GF samples was not known beforehand, we considered the overall process as sample degradation taking into account the entire set of related processes (heating, melting, evaporation, vapour absorption, etc.). The specific depth of a crater X/(rI0) [Figure 1(a)], which takes into account the difference in the densities of different graphite samples (r is the ratio of the sample density to the density of crystalline graphite 2.2 g cm–3), was considered as the efficiency of the degradation at different I0 values.Using laser time-offlight mass spectroscopy, we obtained other characteristics of the degradation of graphite materials, viz., temperatures of the substance in the region of the hot core and in the expansion zone of the laser plume.These values were determined by Saha’s equation from the ratio of intensities of multiply charged atomic carbon ions (up to triply charged) and from the expression for the half-width of the Maxwell distribution of velocities for the laser plume particles, respectively. The experimental dependences of X/(rI0) on I0 [Figure 1(a)] show that there are two characteristic ranges of I0 in which the behaviour of the graphite materials is fundamentally different.At I0 > 1GWcm–2, the degradation proceeds similarly for all of the graphite materials: the efficiency of degradation X/(rI0) 100 10 1 0.1 0.01 0.1 1 300 250 200 150 0.2 1 (a) (b) X/(rI0) Ed/kJ mol–1 Power density/GW cm–2 Figure 1 (a) Dependences of the specific depth of a crater X/(rI0) [mm(GW cm–2)–1] on the laser power density for different graphite samples (GF sample numbers are indicated); (b) dependence of the degradation energy per mole of the substance on I0 for GF sample no. 5. 1 2 3 4 5 6 T/K Power density/GW cm–2 105 104 103 0.01 0.1 1 Figure 2 Maximum temperature of laser plume particles as a function of I0 for GF sample nos. 5 ( ) and 1 ( ) and a PCG sample ( ).Mendeleev Communications Electronic Version, Issue 6, 1998 (pp. 207–248) decreases gradually. Judging from the increase in the maximum plume temperature in the hot core and expansion zone (Figure 2), this is due to substantial absorption of radiation by the degradation products and screening of the target.By contrast, in the region of moderate values I0 < 1 GW cm–2, differences in the properties of the test materials appear [Figures 1(a) and 2]. These materials can be subdivided into two groups by the efficiency of decomposition X/(rI0). The group with higher efficiency of decomposition contains the GF sample nos. 4, 5 (0.7 g cm–3) and 3 (0.5 g cm–3) with high defect concentrations.The second group with low efficiency consists of the low-defect GF sample nos. 1 and 2 with a bulk density of 0.5 g cm–3 as well as PCG sample. The comparison of the GF sample nos. 1–3 with the same density and different defect concentrations shows that it is the latter factor that plays the determining role in the laser-induced degradation of these materials.It has been shown in ref. 6 that the degradation of the lowdensity high-defect GF sample no. 5 proceeds via hydrodynamic removal of the substance (carbon in the supercritical state) from the laser-heated surface layer of the target. A similar process of hydrodynamic removal of a vapour–liquid mixture of the products of spinodal decomposition of the labile liquid carbon phase takes place in the surface vaporisation of the PCG sample.9 Therefore, differences in the efficiency of degradation likely appear during the formation of the final (before degradation) state of carbon rather than at the stage of removal (due to plasma formation and screening of the target surface).In order to study the energetics of degradation of the GF samples, we calculated the deposited energy per mole of removed substance (degradation energy Ed) resulting from the absorption of laser radiation in the target: where Vm and A are the molar volume and the absorbance of the samples, respectively.When the GF absorbance is about 0.9, the degradation energies Ed are approximately 50 kJ mol–1 for GF sample nos. 3 and 4 in the I0 range 0.1–1 GW cm–2 and 193±8 kJ mol–1 for sample no. 5 [Figure 1(b), 0.2–0.7 GWcm–2]. For the PCG sample and GF sample nos. 1 and 2, the degradation energy is as high as 500 kJ mol–1 in the I0 range 0.1– 0.3 GWcm–2, and it is approximately halved at I0 > 0.3GWcm–2. Thus, it can be noted that the heat of formation of the supercritical state of carbon (� 270 kJ mol–1)10 that is formed by laser vaporisation of high-defect GF sample nos. 4 and 5 (r > rcr) decreases to the degradation energies of these samples resulting from the contribution of the energy of nonequilibrium defects of crystallites (about 220 and 80 kJ mol–1, respectively). The degradation energies of low-density GF sample nos. 1 and 2 (r < rcr) and the PCG sample correspond to the enthalpy of formation of carbon vapour with subcritical parameters (ca. 500 kJ mol–1)10,11 in the laser power density range 0.1– 0.3 GW cm–2 and to the enthalpy of formation of the liquid carbon phase in the labile state (� 270 kJ mol–1)10 at I0 > 0.3GWcm–2. An anomalously low (about 50 kJ mol–1) value of the degradation energy for the low-density high-defect GF sample no. 3 (r < rcr) in the I0 range 0.1–0.5 GW cm–2 is explained by fast transition of the liquid carbon phase to the labile state almost without consumption of energy for evaporation (265 kJ mol–1),11 which is favoured by a decrease in the heat of formation of the labile state (ca. 270 kJ mol–1)10 by the energy of nonequilibrium defects (ca. 220 kJ mol–1). This work was supported by the Russian Foundation for Basic Research (grant no. 98-03-32679).References 1 H. Y. So and C. L. Wilkins, J. Phys. Chem., 1989, 93, 1184. 2 I. J. Dance, K. J. Fisher and G. D. Willet, J. Phys. Chem., 1991, 95, 8425. 3 S. I. Kudryashov, S. V. Sokolov, N. B. Zorov, A. A. Karabutov and Yu. Ya. Kuzyakov, Mendeleev Commun., 1997, 25. 4 L. A. Monyakina, V. V. Avdeev, I. V. Nikol’skaya and S. G. Ionov, Zh. Fiz. Khim., 1995, 69, 926 (Russ. J. Phys. Chem., 1995, 69, 842). 5 H. R. Leider, O. H. Krikorian and D. A. Young, Carbon, 1973, 11, 555. 6 S. I. Kudryashov, S. G. Ionov, A. A. Karabutov and N. B. Zorov, Mendeleev Commun., 1998, 212. 7 S. I. Kudryashov, A. A. Karabutov, N. B. Zorov and Yu. Ya. Kuzyakov, Mendeleev Commun., 1996, 96. 8 V. A. Kulbachinskii, S. G. Ionov, S. A. Lapin and A. G. Mandrea, Phys. Chem. Solids, 1996, 57, 893. 9 S. I. Kudryashov, A. A. Karabutov and N. B. Zorov, Mendeleev Commun., 1998, 6. 10 Termodinamicheskie svoistva individual’nykh veshchestv (Thermodynamic Properties of Individual Substances), ed. V. P. Glushko, Nauka, Moscow, 1979, vol. 2, p. 10 (in Russian). 11 A. V. Kirillin, M. D. Kovalenko and M. A. Sheindlin, Teplofizika Vysokikh Temperatur, 1985, 23, 699 (in Russian). Ed = òI(t)dt AVm X (1) Received: Moscow, 8th June 1998 Cambridge, 10th August 1998; Com. 8/04

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Mendeleev Communications Electronic Version, Issue 6, 1998 (pp. 207–248) A new family of stable 2-imidazoline nitroxides Sergei F. Vasilevsky,*a Eugene V. Tretyakov,a Oleg M. Usov,a Yuri N. Molin,a Sergei V. Fokin,b Yuri G. Shwedenkov,b Vladimir N. Ikorskii,b Galina V. Romanenko,b Renad Z. Sagdeevb and Victor I. Ovcharenko*b a Institute of Chemical Kinetics and Combustion, Siberian Branch of the Russian Academy of Sciences, 630090 Novosibirsk, Russian Federation. Fax: +7 3832 342350; e-mail: vasilev@ns.kinetics.nsc.ru b International Tomography Centre, Siberian Branch of the Russian Academy of Sciences, 630090 Novosibirsk, Russian Federation.Fax: +7 3832 331399; e-mail: ovchar@tomo.nsc.ru Methods of synthesising stable 2-imidazoline nitroxides linked to a pyrazole moiety either directly or through a phenylethynylic bridge have been developed; an unusually strong temperature dependence of meff for 2-(1-methylpyrazolyl-5)-4,4,5,5-tetramethyl- 1-oxyl-2-imidazoline-3-oxide is observed.Polyfunctional stable nitroxides are very effective in the design of n-dimensional heterospin systems susceptible to magnetic ordering.1–4 This circumstance prompted us to synthesise a new family of stable nitroxides — pyrazole and acetylenylpyrazole derivatives of 2-imidazoline nitroxides — and to investigate the heterospin systems based on metal complexes with these spin-labelled ligands.Donor nitrogen atoms of the pyrazole ring are favourable for coordination by metal ions. The use of an acetylene fragment in the molecular structure allows one to reach specific distances between functional groups that is very desirable in the design of high dimensional molecular systems.Noteworthy is the fact that only a few papers5–8 were devoted to the development of the synthesis of acetylenic derivatives of 2-imidazoline nitroxides due to their low stability. We synthesised a series of new nitronyl- and iminonitroxides 1–9 using a classical Ullman approach9 based on condensation of the corresponding aldehydes with 2,3-dimethyl- 2,3-bis(hydroxylamino)butane or its sulfate derivative† and subsequent oxidation of the cyclic adducts with sodium periodate.‡ Acetylene-containing starting materials have been prepared by the cross-coupling reaction of the corresponding iodopyrazoles10 with p-ethynylbenzaldehyde in the presence of Pd(PPh3)2(OAc)2, CuI and NEt3.Nitroxides 1–9 were obtained in a good yield and are quite stable in solid and in solution at ambient temperature. They have EPR spectra intrinsic to 2-imidazoline nitroxides. Figures 1 and 2 exemplify the EPR spectra for nitroxides 6 and 7. The † Synthesis of formylpyrazoles and (1,3-dihydroxy-4,4,5,5-tetramethylimidazolinyl- 2)pyrazoles will be published elsewhere. ‡ General procedure for the synthesis of 2-imidazoline nitroxides 1–9.To a suspension of the anhydro adduct (0.01 mol) of 2,3-bis(hydroxylamino)- 2,3-dimethylbutane and the corresponding aldehyde in chloroform (50 ml) at 10–15 °C was added an aqueous solution (50 ml) of sodium periodate (0.015 mol), and the reaction mixture was stirred for 50 min to 4 h.The organic layer was immediately separated, dried over CaCl2 and concentrated in vacuo. The residue was chromatographed on a silica gel column (‘KSK’, Russia, 100–200 mech, air dried) with chloroform as the eluent. After evaporation of the solvents from the eluate the remaining solid was twice recrystallized from an appropriate solvent to afford nitroxides 1–9.All compounds were identified by elemental analyses and spectroscopic data which was consistent with the assigned structures. 1: mp 100–101 °C (from benzene–hexane), yield 85%. 2: mp 71–72 °C (from hexane), yield 9%. 3: mp 139–140 °C (from benzene–hexane), yield 65%. 4: mp 143–144 °C (from benzene–hexane), yield 39%. 5: mp 114–115 °C (from hexane), yield 14%. 6: mp 130.5–131 °C (from benzene–hexane), yield 71%. 7: mp 106.5–107 °C (from hexane), yield 15%. 8: mp 144–145 °C (from benzene–hexane), yield 56%. 9: mp 117– 118 °C (from benzene–hexane), yield 63%. N N N N O O N N N N O N N N N O O N N N N O O N N N N O N N N N O O N N N N O N N N N O O N N N N O O 1 2 3 4 5 6 7 8 9 0.1 mT Figure 1 Central component of the EPR spectrum of radical 6. Oxygenfree hexane solution (5×10–5M) of radical 6 at room temperature.Mendeleev Communications Electronic Version, Issue 6, 1998 (pp. 207–248) spectrum of radical 6 is a quintet (1:2:3:2:1), caused by hyperfine interaction between two equivalent nitroxide nitrogen nuclei (aN = 0.74 mT), each line of the quintet being additionally split due to hyperfine interaction with 12 protons of the a-methyl groups [aH(Me) = 0.021 mT] and with ortho-protons of the benzene ring (aortho = 0.054 mT).This is illustrated by Figure 1, where a central component of the quintet is depicted. The EPR spectrum of radical 7 presented in Figure 2 is caused by HFI with two non-equivalent nitrogen of the imidazoline moiety, the hyperfine coupling constants differing by a factor about two (aN1 = 0.907 mT and aN3 = 0.432 mT).g-Factors of radicals 6 and 7 are 2.0065 and 2.0059, respectively. Nitroxides 1–9 have effective magnetic moments at room temperature corresponding to the values usual for one unpaired electron per molecule (1.71±0.05 B.M.). The values of the effective magnetic moments of 1–3 and 5–9 hardly change in the temperature range 5– 300 K.§ As a typical example of the experimental meff(T) dependence for this group of nitroxides the meff(T) plot for 5 (filled) is shown in Figure 3.Special attention should be given to the magnetic behaviour of 4. We revealed an unexpectedly strong temperature dependence of meff for solid 4 (Figure 3, empty). The experimental temperature dependence of the magnetic susceptibility of 4 (Figure 3, insert) is very well fitted (solid line) by the Bleaney–Bowers model11 for isolated two-centre exchange clusters with spin 1/2 (g = 2.0, J = –39 K).This correlates well with an X-ray structure investigation of a single crystal of 4, which revealed packing by pairs of molecules in solid 4.¶ However, the mechanism of such a strong exchange interaction in nitroxide pairs needs an in § Magnetic measurements were made using a Quantum Design SQUID magnetometer over the temperature range 2–300 K.EPR spectra were recorded on a Bruker EMX EPR spectrometer. ¶ Crystal data for 4: C11H17N4O2, M = 237.29, monoclinic, space group P21/c, 293(2) K, a = 7.0846(9), b = 17.447(2), c = 12.763(1) Å, b = 126.72(1)°, V = 1264.5(2) Å3, Z = 4, Dc = 1.246 g cm–3. 1587 Ihkl were measured on a four-circle automated Enraf Nonius CAD4 diffractometer (lMoKa, graphite monochromator, q/2q-scan, 2.34 < q < 24.96°).The structure was solved by the program SIR97 and refined by a fullmatrix least-squares technique in anisotropic approximation for all nonhydrogen atoms. Positions of all hydrogen atoms were located in a difference Fourier map and then refined in isotropic approximation.The final R-indexes are: R1 = 0.0316, wR2 = 0.0803 for 1431 unique Ihkl > 2sI, GOOF = 0.868. Crystal data for Ni2(hfacac)422(C6H6): C25H24F12N4NiO6, M = 763.19, monoclinic, space group P21/c, 293(2) K, a = 16.442(2), b = 13.500(2), c = 15.858(2) Å, b = 115.50(1)°, V = 3177.1(7) Å3, Z = 4, Dc = 1.596 g cm–3. 3124 Ihkl were measured on a four-circle automated Enraf Nonius CAD4 diffractometer (lMoKa, graphite monochromator, q/2q-scan, 1.37 < q < 22.47°).The structure was solved by the automated Patterson interpretation program and refined by a full-matrix least-squares technique in anisotropic approximation for all non-hydrogen atoms. The positions of all hydrogen atoms were located in a difference Fourier map and than refined in an isotropic approximation.The final R-indexes are: R1 = 0.0485, wR2 = 0.0666 for 3001 unique Ihkl > 2sI, GOOF = 0.674. All calculations for both compounds were carried out using the SHELXL97 program. 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., 1998, Issue 1.Any request to the CCDC for data should quote the full literature citation and the reference number 1139/31. Figure 2 EPR spectrum of radical 7 (5×10–5 M) in an oxygen-free hexane solution at room temperature. 0.1 mT meff/B.M. T/K c/10–3 cm3 mol–1 1.6 1.2 0.8 0.4 0 50 100 150 200 250 300 0 50 100 150 200 250 300 3 2 1 T/K Figure 3 Experimental dependences meff(T) for 5 ( ) and 4 ( ).Insert: plot c versus T for 4. The solid lines represent the optimal theoretical curves. C(1) C(2) C(3) C(4) C(5) C(6) O(1) O(2) N(1) N(2) N(3) N(4) C(41) Figure 4 General view of molecule 4. Selected bond lengths (Å): N(1)–O(1) 1.279(2), N(1)–C(3) 1.340(2), N(1)–C(1) 1.496(2), C(1)–C(2) 1.536(3), C(2)–N(2) 1.507(2), O(2)–N(2) 1.277(2), N(2)–C(3) 1.344(2), C(3)–C(4) 1.446(2), C(4)–N(4) 1.353(2), C(4)–C(5) 1.370(3), C(5)–C(6) 1.384(3), C(6)–N(3) 1.327(3), N(3)–N(4) 1.348(2); selected bond angles (°): O(1)–N(1)–C(3) 126.0(2), O(1)–N(1)–C(1) 123.0(1), C(3)–N(1)–C(1) 111.0(1), N(1)–C(1)–C(2) 100.5(2), N(2)–C(2)–C(1) 100.4(1), O(2)–N(2)– C(3) 126.4(1), O(2)–N(2)–C(2) 122.5(1), C(3)–N(2)–C(2) 110.6(1), N(1)– C(3)–N(2) 109.3(2), N(1)–C(3)–C(4) 125.0(2), N(2)–C(3)–C(4) 125.4(2).O(01) O(02) C(02) C(061) C(05) C(04) C(01) C(03) C(041) N(4) N(3) N(1) N(2) O(1) O(2) O(4) O(3) C(06) Figure 5 General view of binuclear molecule Ni2(hfacac)422(C6H6). Selected bond lengths (Å): Ni–O(1) 2.008(1), Ni–O(4) 2.016(1), Ni–O(01)' 2.052(1), Ni–O(3) 2.058(2), Ni–O(2) 2.090(1), Ni–N(3) 2.093(2), O(01)– N(1) 1.302(2), N(1)–C(03) 1.282(3), N(1)–C(01) 1.562(2), C(01)–C(02) 1.537(4), C(02)–N(2) 1.527(2), N(2)–O(02) 1.245(2), N(2)–C(03) 1.344(3), C(03)–C(04) 1.471(2); selected bond angles (°): O(4)–Ni–O(3) 85.92(6), O(1)–Ni–O(2) 87.76(6), N(1)–O(01)–Ni' 124.0(1), C(03)–N(1)–O(01) 127.5(2), C(03)–N(1)–C(01) 112.3(2), O(01)–N(1)–C(01) 118.4(2), N(2)– C(02)–C(01) 103.4(2), N(2)–C(02)–C(021) 107.9(2), O(02)–N(2)–C(03) 128.1(1), O(02)–N(2)–C(02) 123.7(2), C(03)–N(2)–C(02) 108.1(2), N(1)– C(03)–N(2) 111.8(2), N(1)–C(03)–C(04) 123.6(2), N(2)–C(03)–C(04) 124.7(2).Mendeleev Communications Electronic Version, Issue 6, 1998 (pp. 207–248) depth quantum-chemical analysis. This is of particular interest because there are no intermolecular contacts shorter then 3 Å in the crystal structure of 4. A general view of the separate nitronyl nitroxide molecule is given in Figure 4, with some selected bond lengths and bond angles.In Figure 5 are given additionally some selected data for binuclear complex Ni2(hfacac)422(C6H6). The structure of the molecule of this (first structurally characterised) metal complex with spin-labelled pyrazole, shown in Figure 5, demonstrates (as mentioned in the introduction) the possibility of pyrazole 2-imidazoline derivatives behaving as a bridge function. Full details of this investigation will be published elsewhere.The authors express their gratitude to the Russian Foundation for Basic Research (grant nos. 96-03-32229 and 98-03-32908a). The authors also thank the Siberian Branch of the RAS (grant no. 97-N35 and grant no. 473-1997 for young scientists) for financial support.References 1 A. Caneschi, D. Gatteschi and P. Rey, Progr. Inorg. Chem., 1991, 39, 331. 2 O. Kahn, Molecular Magnetism, VCH, New York, 1993. 3 K. Inoue, T. Hayamizu, H. Iwamura, D. Hashizume and Y. Ohashi, J. Am. Chem. Soc., 1996, 118, 1803. 4 V. I. Ovcharenko, A. B. Burdukov and R. N. Musin, Mol. Cryst. Liq. Cryst., 1995, 273, 89. 5 E. F. Ullman, L. Call and J. H. Osiecki, J. Org. Chem., 1970, 35, 3623. 6 E. F. Ullman, J. H. Osiecki, D. G. B. Boocock and R. Darcy, J. Am. Chem. Soc., 1972, 94, 7049. 7 L. Dulog and J. S. Kim, Makromol. Chem., 1989, 190, 2609. 8 P. Wautelet, A. Bieber, P. Turek, J. Moigne and J. J. Andre, Mol. Cryst. Liq. Cryst.,1997, 305, 55. 9 E. F. Ullman, J. H. Osiecki, D. G. B. Boocock and R. Darcy, J. Am. Chem. Soc., 1972, 94, 7049. 10 S. F. Vasilevsky and M. S. Shvartsberg, Izv. Akad. Nauk SSSR, Ser. Khim., 1980, 1071 (Bull. Acad. Sci. USSR, Div. Chem. Sci., 1980, 29, 778). 11 B. Bleaney and K. D. Bowers, Proc. Roy. Soc., 1952, A214, 451. Received: Moscow, 9th June 1998 Cambridge, 23rd July 1998; Com. 8/04737E

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年代:1998

数据来源: RSC

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Mendeleev Communications Electronic Version, Issue 6, 1998 (pp. 207–248) Modeling structure and spectra of silver complexes in condensate films of polar liquid crystals Natalia V. Ozhegova, Aleksandr V. Nemukhin,* Tatiana I. Shabatina and Gleb B. Sergeev Department of Chemistry, M. V. Lomonosov Moscow State University, 119899 Moscow, Russian Federation. Fax: +7 095 939 0283; e-mail: anem@ecc.chem.msu.su By performing ab initio quantum chemistry calculations, including partial geometry optimization and vibrational analysis for the sandwich-like cyanobenzene–silver complexes, it is shown that the observed red shifts in the CN stretching region of the IR spectra of silver–cyanobiphenyl condensate films should be assigned to the formation of the p-complexes.The materials formed by co-condensation of metal atoms and organic mesogen molecules exhibit interesting properties which promise important technological applications.1 The reactions of metals with the molecules composing liquid crystals, in particular, cyanobiphenyl derivatives, are carried out under low-temperature conditions by condensing the molecular beams into thin films, and IR and UV spectral techniques are used to characterize the reaction products.2,3 However, little is known about the structure of these intriguing substances and the experimental spectral patterns deserve theoretically motivated interpretations.The studies of silver complexes with the 4-pentyl-4'-cyanobiphenyl (5CB) molecules described in refs. 2 and 3 showed that (1), the strong IR band at 2230 cm–1 assigned to the CN stretching vibration characterised the spectrum of the pure 5CB film and (2), two new bands at 2080 and 2030 cm–1 appeared in the samples obtained upon co-condensation of 5CB with silver.The tentative assignment of these spectral features was carried out following the trends in chemistry of the transition metal complexes with unsaturated organic molecules.4 The vibrational spectral shifts due to such complexation may amount by up to several hundred wavenumbers,5 therefore, the red shifts of 150 and 200 cm–1 in the silver–5CB condensates compared to the pure 5CB have been qualitatively explained by the formation of p-type complexes.3 The aim of this work is to perform a theoretical analysis of the complexes which can be formed in condensate films and to suggest a model consistent with the observed IR spectral shifts.Presently, the modern methods of ab initio quantum chemistry can be applied for fairly extended molecular systems, however, the standard approaches of quantum chemistry molecular modeling, namely, a search of the global minimum on the potential energy surface with subsequent vibrational analysis have limited value in this case, since we intend to simulate properties of the bulk, but not of the gas phase system.Moreover, the only vibrational degrees of freedom indicative in the spectrum, namely, the vibrations of the CN groups of the ligands, are directly probed in the experiments, and the modeling should be oriented on these particular features. Therefore, we apply here the following strategy.The complete ab initio geometry optimization and vibrational analysis based on quantum chemistry calculations is performed for the 5CB molecule and for its most important fragment, cyanobenzene PhCN. The reference value of the strong IR band assigned to the CN vibrations is deduced by comparison to that in the silver complexes. A series of calculations was then carried out for the sandwich-like complex Ag(PhCN)2 with the majority of geometry parameters fixed.An analysis of the electron density distributions as well as the curvatures of the potential energy surfaces along the C–N coordinates allows us to estimate the spectral shifts for the CN vibrations and to formulate a structural model consistent with the observed spectral patterns of the Ag/5CB films.We have used the GAMESS quantum chemistry package6 operational on an Intel-based Pentium Pro workstation. The conventional Stevens–Bash–Krauss (SBK) pseudopotentials on all heavy atoms with the corresponding basis sets7 were employed. Figure 1 shows the stucture of the 5CB molecule referring to the minimum of the potential surface in the Hartree–Fock approximation.This structure is very close to that predicted by the density functional calculations,8,9 and even such a delicate parameter as the torsional angle between the benzene rings (44°) is nicely reproduced by our calculations. The frequency of the normal vibration easily recognized as the CN stretch equals 2497 cm–1. The same treatment of the cyanobenzene molecule PhCN gives for this vibration the frequency 2501 cm–1.If the usual scaling procedure to improve the Hartree–Fock harmonic frequencies is employed with a scaling factor of 0.9, then the vibrational band predicted for both 5CB and PhCN molecules at about 2250 cm–1 is in excellent agreement with the observed value of 2230 cm–1. An additional check of the approach is provided by a series of calculations for the PhCN molecule with different basis sets [DZV, TZV, 6-311G, 6-311G*(1d1p)] which give consistent values of the CN vibrational frequency ranging from 2500 to 2585 cm–1 (cf. 2501 cm–1 with the SBK option). Complete geometry optimization and vibrational analysis of the free, i.e. not embedded into the liquid crystal matrix, species (PhCN)Ag, (PhCN)Ag+ and (PhCN)Ag2 lead to the conclusion that the global minima correspond to the s-type complexes with the linear arrangements C–N···Ag with the N···Ag distances (in Å) shown in the picture, and the C–N vibrational frequencies shifted from the reference value for PhCN by +9, –7 and +20 cm–1, respectively.Therefore, such configurations cannot be expected in the Ag/5CB films, since experimentally shifts of –150 and –200 cm–1 have been observed.The structures corresponding to the p-complexes were considered next. According to the X-ray investigations10–12 the cyanobiphenyl molecules in the films are arranged in pairs C5H11 CN 5CB Figure 1 The stucture of the 5CB molecule corresponding to the minimum on the potential energy surface. Ag C N C N (1) (2) R Figure 2 Model for the silver–cyanobenzene complex.Mendeleev Communications Electronic Version, Issue 6, 1998 (pp. 207–248) by the ‘head-to-tail’ principle. Therefore, we have considered a model for the silver–cyanobenzene complex shown in Figure 2. The system possesses planar symmetry with the silver atom placed at equal distances from the ligands, namely, from the centre of the CN fragment of ligand (1) and from the centre of the ring of ligand (2).In calculations, almost all the geometry parameters were fixed at the values of the free PhCN molecule, and the distance R between the planar ligands (1) and (2) was varied. Partial geometry optimization was performed with the use of the Hilderbrandt type internal coordinates. Pilot calculations showed that two Hartree–Fock solutions could compete for the ground state, one corresponding to (PhCN)2Ag and another to the charge-transfer (PhCN)2 –Ag+ configurations.Therefore, the multiconfigurational self-consistent field (MCSCF) method was used in order to take into account such a pronounced effect of electron distributions in the complex. In calculations, the orbitals were obtained by using the state averaging technique over both contributing electronic configurations.The computed dependence of total energy on the interligand distance R is shown in Figure 3. This graph, together with the view of the charges on atoms computed according to the natural population analysis,13 clearly illustrate the changes in the structure of the complex when the distance between the matrix molecules is varied.At large R (R > 4.7 Å), the neutral silver atom is embedded into the cavity between the ligands. In the vicinity of R = 4.7 Å a sharp change in shape of the energy curve (Figure 3) indicates a drastic modification in the electron density distribution: an electron from the silver atom jumps to the ligands, and the chargetransfer (PhCN)2 –Ag+ configuration dominates at R < 4.7Å.This observation is confirmed by direct calculations of the natural electronic charges13 on the fragments of the complex: Ag, PhCN (1) and PhCN (2). It is important to notice that almost all electron density borrowed from silver flows into the p* system of the benzene ring of the (lower in Figure 2) ligand PhCN (2), while only a small fraction of the electron charge is donated to the p* orbitals of CN of the (upper in Figure 2) ligand PhCN (1).Qualitatively, the red shifts in vibrational frequencies of the CN groups in the cyanobiphenyl–silver complexes are understood. Upon formation of the films, the silver atoms enter the cavities between the pairs of organic ligands in such a manner that asymmetric arrangements with respect to the CN groups are accomplished (a simplified picture is presented in Figure 2).Within the solid phase, the occurrence of distances between the ligands close enough to account for the chargetransfer complexes (in our simplified model for R £ 4.7 Å) is justified, in particular, by the X-ray investigations.8,9 Donation of the smaller fraction of electron density of silver to the antibonding orbitals of CN of one ligand results in an increase in the corresponding internuclear C–N distance and a decrease in the curvature of the potential surface along this coordinate, i.e.a decrease in the vibrational frequency. Donation of the larger fraction of the charge on Ag to the p* system of another ligand leads to a redistribution of the electron density in the thus formed negative ion, with a decrease in the corresponding CN frequency by another value. In particular, in our calculations the CN vibrational frequency of pure anion PhCN– is shifted to the red compared to the neutral molecule PhCN by 220 cm–1.We attempted to reproduce the vibrational matrix shifts at the quantitative level. For this goal again the model pictured in Figure 2 was employed. We selected 3 representative values of the interligand distances R, namely, R = 4.4 Å (charge-transfer configuration), R = 4.8 Å (neutral configuration) and R = 4.7Å (critical point for the electron jump) and analysed the cuts through the potential energy surfaces corresponding to the C–N coordinates.First, partial non-gradient geometry optimization was performed with respect to the C–N and C–C (between the closest carbon atoms of the cyano groups and of the benzene ring) distances while keeping all other parameters fixed.Then the points on the potential surfaces around the found equilibrium C–N coordinates were computed and numerical estimates of the energy curvatures and the vibrational frequencies of the CN groups were obtained. Table 1 shows the results of these simulations. Clearly, the conclusions of the qualitative picture described above is confirmed by the numerical data.In the case of the charge-transfer complex (R = 4.4 Å) the simulated red shifts in the CN vibrations (–150 and –175 cm–1) correlate well with those observed experimentally for the Ag/5CB films (–150 and –200 cm–1). Of course, it is difficult to expect complete agreement between values computed for the model system and those measured for the real system, however, their correspondence is good enough to confirm our understanding of the phenomena.This work was supported by the Russian Foundation for Basic Research (grant no. 98-03-33168). References 1 A. P. Polishchuk and T. V. Timofeeva, Usp. Khim., 1993, 62, 319 (Russ. Chem. Rev., 1993, 62, 291). 2 T. I. Shabatina, E. V. Vovk, T. V. Khasanova, G. N. Andreev and G. B. Sergeev, Supramolecular Science, 1997, 4, 485. 3 E. V. Vovk, T. I. Shabatina, A. V. Vlasov and G. B. Sergeev, Supramolecular Science, 1997, 4, 509. 4 K. Nakamoto, Infrared and Raman Spectra of Inorganic Compounds, Wiley-Interscience, New York, 1986. 5 T. S. Kurtikyan, G. M. Kuzyanz and V. T. Aleksanyan, Koord.Khim., 1977, 3, 1482 [J. Coord. Chem. (Engl. Transl.), 1977, 3, 1152]. 6 M. W. Schmidt, K. K. Baldridge, J. A. Boatz, S. T. Elbert, M. S. Gordon, J. H. Jensen, S. Koseki, N. Matsunaga, K. A. Nguyen, S. J. Su, T. L. Windus, M. Dupuis and J. A. Montgomery, J. Comput. Chem., 1993, 14, 1347. 7 W. J. Stevens, H. Basch and M. Krauss, J. Chem. Phys., 1984, 81, 6026. 8 C. J. Adam, S.J. Clark, G. J. Ackland and J. Crain, Phys. Rev. E, 1997, 55, 5641. 9 S. J. Clark, C. J. Adam, G. J. Ackland, J. White and J. Crain, Liq. Cryst., 1997, 22, 469. 10 W. Haase, H. Paulus and R. Pendzialek, Mol. Cryst. Liq. Cryst., 1983, 100, 211. C N Ag 2.81 C N Ag 2.24 C N Ag 2.46 Ag Table 1 Computed harmonic frequencies of the CN vibrations in the complex (PhCN)2Ag depending on the interligand distance R and the corresponding frequency shifts with respect to the value 2501 cm–1 in the free molecule PhCN. R/Å Frequencies and shifts/cm–1 w in PhCN (1) Dw w in PhCN (2) Dw 4.4 2351 –150 2326 –175 4.7 2392 –109 2412 –89 4.8 2416 –85 2471 –30 –246.92 –246.94 –246.96 –246.98 –247.00 –247.02 –247.04 –247.06 3.8 4.0 4.2 4.4 4.6 4.8 5.0 5.2 5.4 5.6 (PhCN)2 –Ag+ (PhCN)2Ag R/Å E (a.e.) Figure 3 Energy dependence of (PhCN)2Ag on the interligand distance R.Mendeleev Communications Electronic Version, Issue 6, 1998 (pp. 207–248) 11 L. Walz, H. Paulus and W. Haas, Z. Kristallogr., 1987, 180, 97. 12 S. Paul and P. Mandal, Mol. Cryst. Liq. Cryst., 1985, 131, 223. 13 A. E. Reed, L. A. Curtiss and F. Weinhold, Chem. Rev., 1988, 88, 899. Received: Moscow, 10th June 1998 Cambridge, 23rd July 1998; Com. 8/04739A

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出版商:RSC    

年代:1998

数据来源: RSC

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Mendeleev Communications Electronic Version, Issue 6, 1998 (pp. 207–248) The formation of neptunium peroxo complexes upon reduction of neptunium(VI) by hydrogen peroxide in concentrated solutions of alkalis Vladimir P. Shilov, Andrei V. Gogolev and Alexei K. Pikaev* Institute of Physical Chemistry, Russian Academy of Sciences, 117915 Moscow, Russian Federation. Fax: +7 095 335 1778 Kinetic studies have shown that the formation of NpV peroxo complexes upon reduction of NpVI by hydrogen peroxide in concentrated solutions of alkalis occurs via the intermediate appearance of NpVI peroxo complexes.In our previous work,1 it was shown that for reactions of hydrogen peroxide with NpVI and AmVI in 0.1 mol dm–3 solutions of HClO4, or with NpVII within the pH range 9–14, there is a linear dependence of lgk (k is the reaction rate constant) on potential difference DE = E(Ann + 1/Ann) – E(O2/H2O2) (An = = actinide).These reactions proceed via an outer sphere mechanism. However, rate constants for reactions of hydrogen peroxide with NpVI in solution at pH 5 or in alkaline medium are higher by 4 orders of magnitude than those expected from the respective DE values. Such behaviour indicates an intrasphere reaction mechanism, i.e., the formation of an NpVI peroxo complex.Note that peroxo complexes were also described in the case of UVI.2 Earlier3 we investigated the kinetics of the reaction between NpVI and hydrogen peroxide in slightly alkaline solutions (pH 9.2–13.7). It was found that the reaction rate decreased with increasing pH value.Continuing the study with concentrated solutions of alkalis (1–8.4 mol dm–3), we observed that in these solutions, the product of reduction is NpV peroxo complex. The respective data are briefly described in the present paper. A solution of 237NpO2(ClO4)2 in perchloric acid prepared via a standard procedure was used as a stock solution. A solution of NpV was also utilized.The neptunium concentration in the solutions was determined by a complexonometric method with its preliminary reduction to tetravalent state.4 Hydrogen peroxide was produced by decomposition of BaO2 (high-purity grade) by 1 mol dm–3 perchloric acid solution. The addition of concentrated K2SO4 solution was used to precipitate BaSO4 and KClO4. The analysis of H2O2 was conducted by a permanganatometric method. The LiOH and NaOH used were high-purity grade (the content of iron in the 17 mol dm–3 NaOH solutions supplied was less than 3×10–5%).The solutions were prepared with twice distilled water. The study on the reaction of NpVI with hydrogen peroxide was carried out by recording the change in the intensity of its wide charge-transfer band of optical absorption in the near UV region using spectrophotometers SF-46 (Russia) and ‘Shimadzu UV-3100’ (Japan).To investigate this reaction, the solution of alkali was placed in a quartz cell (optical path lengths 1 or 5 cm), the spectrum was recorded, an aliquot of the stock NpVI solution was added upon vigorous stirring, and the spectrum was recorded again. The solution of hydrogen peroxide was then inserted, and the spectrum or absorbance at the chosen wavelength (usually at 320 nm) were periodically measured. Note that hydrogen peroxide in alkaline solutions exists in the form of HO2 – or O2 2–.For simplicity, the designation HO2 – is used in this paper. It was found that alkaline NpVI solutions became yellowbrown as a result of the addition of hydrogen peroxide.Optical absorption spectra of ~ 8 mol dm–3 NaOH solutions containing various amounts of NpVI and hydrogen peroxide which were recorded 20–40 s after mixing the solutions are analogous to the spectrum obtained by us upon the addition of hydrogen peroxide to alkaline NpV solutions and coincide with those described in the literature5–7 for NpV peroxo complex. The molar absorption coefficient of the complex obtained from the measurements of absorbance of ~ 8 mol dm–3 NaOH solution at different ratios of NpV and HO2 – concentrations is equal to 3.8×102 m2 mol–1 at 320 nm.To determine the stoichiometry of reaction between HO2 – and NpVI, HO2 – solution was added to a 1 mol dm–3 solution of LiOH, containing 1×10–3 mol dm–3 NpVI, up to a concentration 4×10–4 mol dm–3.The solution became turbid over several minutes, and a precipitate was formed. The latter was separated by centrifugation, then it was dissolved in a 0.1 mol dm–3 solution of HClO4. HClO4 was added to the supernatant to adjust the pH to approximately 1. Absorption spectra were recorded in both solutions. They showed the presence of NpV. The total content of NpV in both solutions allowed us to conclude that ratio D[NpVI] / [HO2 –]0 ~ 1.8, where D[NpVI] designates the difference between initial and final NpVI concentrations, i.e., the total reaction that took place in the solution can be described as: The stoichiometry of reaction (1) was also studied for NaOH solutions.In this case, excess NpVI was also used, and alkaline NpVI solutions, stored for 1–2 days in the dark to finish the partial reduction of NpVI by organic impurities present in stock NaOH solution (it was supplied from the manufacturer in a polyethylene vessel), were utilized.The data obtained are shown in Table 1, where n = D[NpVI] / [HO2 –]0. It is evident that hydrogen peroxide is consumed in NpVI reduction and also in side reactions; their fraction increases with increasing NaOH concentration.The dependence of absorbance of 8.4 mol dm–3 NaOH solutions, containing 1×10–4 mol dm–3 NpVI and different HO2 – amounts, at 320 nm (A320) on time was investigated. The data obtained are shown in Figure 1. The analysis of the data allows us to draw the following conclusions. At [HO2 –]0/[NpVI]0 > 1, absorbance for 23–25 s reaches 93–95% of the maximal value, i.e., 4t1/2 (t1/2 is the half-life of one of the reagents, for example, NpVI) elapsed to this moment, and t1/2 = 6 s.The constancy of t1/2 within the range of HO2 – concentrations from 1×10–4 to 1×10–3 mol dm–3 requires us to accept the following reduction mechanism at these concentration ratios. Initially, the complex of NpVI with HO2 – of 1:m composition where m > 1 is formed. The increase in A320 values for the next 30–40 s at [HO2 –] = 10–3 mol dm–3 obeys the rate law for a first-order reaction but t1/2 = 12 s.At present, we can not 2NpVI + HO2 – + OH– 2NpV + O2 + H2O (1) 2.0 1.6 1.2 0.8 0.4 0 10 20 30 40 50 A320 t/min 1 2 3 4 5 Figure 1 Dependence of A320 on time for an 8.4 mol dm–3 NaOH solution containing 1×10–4 mol dm–3 NpVI and various HO2 – concentrations (mol dm–3): 1, 4.2×10–5; 2, 1×10–4; 3, 2.04×10–4; 4, 3.97×10–4; 5, 1.03×10–3 (temperature 25 °C, optical path length 5 cm).Mendeleev Communications Electronic Version, Issue 6, 1998 (pp. 207–248) explain the increase in t1/2 value. After reaching the maximum, A320 decreases. At [HO2 –]0/[NpVI]0 = 1–10, the absorbance tends to the value corresponding to the equilibrium value for a NpV and HO2 – solution of a concentration that is equal approximately to [HO2 –]0 – 0.5[NpVI]0.Hence, the ligand HO2 – is already present in the coordination sphere, and a complex NpV(HO2 –) appears via reduction of NpVI(HO2 –) complex by the species attacking from outside. At [HO2 –]0/[NpVI]0 > 0.5, A320 decreases to a value corresponding to NpVI concentration minus the amount consumed in reaction with hydrogen peroxide.At HO2 – excess, the NpV(HO2 –) concentration calculated via molar absorption coefficient is equal to 90–95% of the initial neptunium concentration. If reactions: proceed, the NpV(HO2 –) concentration after reduction should be equal to about 0.5[NpVI]0, and then an increase in absorbance should occur because of reaction between NpV and HO2 –. Special experiments showed that the NpV peroxo complex in the reaction of NpV with hydrogen peroxide is formed slowly.For instance, at [HO2 –]0/[NpV]0 = 10:1, the duration of this reaction is 70 min. Since an increase is not observed, it is most probable that reactions (2), (4), (6), (7) and (5) take place: At NpVI excess, reaction (8) should be added to the reactions considered: At [HO2 –]0/[NpVI]0 < 0.5, it is necessary to propose as an explanation of the obtained kinetic data (the initial rate linearly decreases with increasing NaOH concentration but slightly depends on NpVI concentration and increases with increasing [HO2 –]0) that the formed complex NpV(HO2 –) participates in reaction (9): In addition, dissociation of NpV(HO2 –) to NpV and HO2 – occurs, and released hydrogen peroxide reacts with NpVI.As mentioned above, HO2 – is consumed not only in NpVI reduction but also in side reactions. Reactions (10) and (11) can belong to such processes: Radical ion O– formed oxidizes NpV to NpVI. In reaction (11), radical ion O– can appear in the NpV coordination sphere and in the same place can perform its oxidation.References 1 V. P. Shilov, A. V. Gogolev and A. K. Pikaev, Khim. Vys. Energ., 1998, 32, 395 (in Russian). 2 Kompleksnye soedineniya urana (Uranium Complex Compounds), ed. I. I. Chernyaev, Nauka, Moscow, 1964 (in Russian). 3 A. V. Gogolev, V. P. Shilov and A. K. Pikaev, Khim. Vys. Energ., 1996, 30, 255 [High-Energy Chem. (Engl. Transl.), 1996, 30, 229]. 4 A. P. Smirnov-Averin, G. S. Kovalenko, N. P. Ermolaev and N. N. Krot, Zh. Anal. Khim., 1966, 21, 76 [J. Anal. Chem. USSR (Engl. Transl.), 1966, 21, 62]. 5 C.Musikas, Radiochem. Radioanal. Lett., 1970, 4, 347. 6 C.Musikas, J. Chim. Phys. Phys.-Chim. Biol., 1974, 71, 197. 7 A. V. Gogolev, V. P. Shilov and A. K. Pikaev, Mendeleev Commun., 1996, 127. NpVI + HO2 – NpVI(HO2 –) NpVI(HO2 –) NpV+ HO2 HO2 + OH– O2 – + H2O NpVI(HO2 –) +O2 – NpV(HO2 –) +O2 (2) (3) (4) (5) NpVI(HO2 –) +HO2 – NpVI(HO2 –)2 NpVI(HO2 –)2 NpV(HO2 –) +HO2 (6) (7) NpVI + O2 – NpV + O2 (8) NpV(HO2 –) +NpVI 2NpV + HO2 (9) Table 1 Influence of NaOH concentration and initial NpVI and HO2 – concentrations on the stoichiometry of reaction NpVI + HO2 –. [NaOH]/ mol dm–3 [NpVI]0 / 10–4 mol dm–3 [HO2 –]0 / 10–4 mol dm–3 D[NpVI]0 / 10–4 mol dm–3 n 1.0 1.98 0.74 1.29 1.74 1.0 2.48 1.08 1.97 1.82 2.1 2.20 1.01 1.58 1.56 4.1 3.85 1.80 2.73 1.52 4.2 3.50 1.67 2.38 1.43 8.2 8.12 3.28 4.66 1.42 8.2 3.84 1.82 2.36 1.30 HO2 – + O2 – O– + OH– + O2 NpV(HO2 –) + O2 – NpV + O– + OH– + O2 (10) (11) Received: Moscow, 23rd April 1998 Cambridge, 17th July 1998; Com. 8/03092H

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年代:1998

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Mendeleev Communications Electronic Version, Issue 6, 1998 (pp. 207–248) A simple preparation of -hydroxydienoic fatty acids with double-bond positional isomerism Igor V. Ivanov,*a,b Galina I. Myagkovaa and Hartmut Kühnb a M. V. Lomonosov State Academy of Fine Chemical Technology, 117571 Moscow, Russian Federation. Fax: +7 095 434 8711; e-mail: myagkova@httos.mitht.msk.ru b Institute of Biochemistry, University Clinics Charité, Humboldt University, D-10115 Berlin, Germany A set of new regioisomeric w-hydroxydienoic fatty acids has been prepared via a three-step procedure involving the methylation of w-carboxydienoic fatty acids followed by the NaBH4 reduction of a mixture of the resulting monomethyl esters and HPLC separation.Lipoxygenases are lipid peroxidising enzymes which oxygenate polyenoic fatty acids containing a (1Z,4Z)-pentadienoic system to their corresponding 1-hydroperoxy-(2E,4Z)-derivatives.1 Mammalian 15-lipoxygenase (LOX) is unique among other LOX due to its ability to oxidise polyunsaturated fatty acids incorporated in complex membrane lipids.2,3 Although the first X-ray structure of mammalian 15-LOX has recently been solved, the structural features of the substrate binding cage are not completely understood.4 Based on the theory1,4–7 of ‘hydrophobic binding cavity’ we suggested that the incorporation of a polar (hydroxy) or evenly charged (carboxy) group at the w-position of a fatty acid molecule could hinder the proper substrate alignment at the substrate binding site of 15-LOX.In order to prove this suggestion and test the substrate specificity of LOX we synthesised a set of isomeric w-carboxydienoic fatty acids.8,9 To avoid total synthesis in the preparation of w-hydroxydienoic acids we propose an original three-step procedure which provides access to both possible regioisomeric w-hydroxy acids (4a–e and 5a–e) from dicarboxylic acid 1a–e (Scheme 1).The methylation of dicarboxylic acid 1a–e with a small molar excess of diazomethane in diethyl ether leads to a mixture of two monomethyl esters, 2a–e and 3a–e.The sequential reduction of this mixture with an ethanol solution of sodium borohydride produced two w-hydroxy acids 4a–e and 5a–e.† Both isomeric products were eluted in reverse phase HPLC as a single peak when the chromatogram was developed with the solvent system methanol–water–acetic acid (85:15:0.1, v/v) at a flow rate of 1 ml min–1.However, when the mixture of w- hydroxydienoic acids was analysed by normal phase HPLC the isomeric compounds, 4a–e and 5a–e, were resolved (Figure 1). In carrying out the isomer separation we prepared both product isomers with a degree of purity exceeding 99%. The yield of the entire preparation procedure calculated for the mixture of 4 and 5 varied between 61–65%.The analysis of the ratio of isomeric products 4a–e and 5a–e (Scheme 1) shows that the methylation of dienedicarboxylic acids 1b–e with diazomethane occurs without any significant preference for either one or the other carboxylic group. Although the data observed were reproducible and the ratio of isomeric products 4a–e and 5a–e, and hence, that of monomethyl esters 3a–e and 4a–e in the starting mixture varied slightly, compound 1a failed to follow the trend.Whether methylation of one of the carboxylic groups has any preference or the predominant formation of one of the methyl esters in the case of 1a was accidental, should be studied further. † In a typical experiment, the dicarboxylic acid 1a–e (0.10 mmol) dissolved in 1 ml diethyl ether was methylated with a small molar excess of diazomethane (0.12 mmol).The ether was removed by argon flow and 7 ml of a 0.5 M ethanol solution of sodium borohydride (the solution was prepared as described by Brown et al.,10 and the concentration of borohydride was determined by the hydrolysis method) was added to the residue at room temperature under argon.The reaction mixture was stirred for 6–16 h at 24 °C. After the organic solvent was evaporated under vacuum, the reaction mixture was quenched with 2 ml of water and then acidified to pH 3. The fatty acid derivatives were extracted twice with 5 ml of ethyl acetate, the combined organic extracts were concentrated under vacuum and the resulting products 4 and 5, preliminary purified by RP-HPLC, were separated by normal phase HPLC.w 4a:5a = 3:17 4b:5b = 1:1 4c:5c = 3:2 4d:5d = 2:3 4e:5e = 1:1 Scheme 1 CO2H HO2C n m CO2Me HO2C n m CH2N2 CO2H MeO2C n m 2a–e 3a–e i, NaBH4, EtOH ii, HPLC separation CO2H HO n' m' OH HO2C m' n' 1a n = 3, m = 8 1b n = 3, m = 7 1c n = 6, m = 7 1d n = 5, m = 7 1e n = 5, m = 6 4a n' = 9, m' = 3 4b n' = 8, m' = 3 4c n' = 8, m' = 6 4d n' = 8, m' = 5 4e n' = 7, m' = 5 5a n' = 4, m' = 8 5b n' = 4, m' = 7 5c n' = 7, m' = 7 5d n' = 6, m' = 7 5e n' = 6, m' = 6 aOnly the early eluting compound in SP-HPLC (Figure 2) was analysed. A Nucleosil 100-7 column (250×5 mm, 7 mm particle size; Machery and Nagel, Germany) with the solvent system hexane–isopropanol–acetic acid (100:10:0.1, v/v) was used, flow rate 1 ml min–1.The oxygenated products were analysed by GC-MS as the corresponding trimethylsilylmethyl ester derivatives. b(C) is the minor intensity fragmentation. Table 1 Analytical data for the oxygenated w-hydroxydienoic fatty acid isomers.a,b w-Hydroxyacid Oxygenation product Retention time/min Key ion fragmentation, m/z 4a (n' = 9, m' = 3) 5.84 470 (M+), 255 (A), 317 (B) 4b (n' = 8, m' = 3) 6.57 456 (M+), 255 (A), 303 (B) 4c (n' = 8, m' = 6) 6.72 498 (M+), 355 (C), 297 (A), 303 (B) 4d (n' = 8, m' = 5) 7.98 484 (M+), 355 (C), 283 (A), 303 (B) 4e (n' = 7, m' = 5) 8.63 470 (M+), 341 (C), 283 (A), 289 (B) 5a (n' = 4, m' = 8) 13.78 470 (M+), 325 (A), 247 (B) 5b (n' = 4, m' = 7) 12.63 456 (M+), 311 (A), 247 (B) 5c (n' = 7, m' = 7) 7.58 498 (M+), 341 (C), 311 (A), 289 (B) 5d (n' = 6, m' = 7) 9.28 484 (M+), 327 (C), 311 (A), 275 (B) 5e (n' = 6, m' = 6) 9.00 470 (M+), 327 (C), 297 (A), 275 (B) COOMe TMSO OTMS n' m' A B CMendeleev Communications Electronic Version, Issue 6, 1998 (pp. 207–248) Unfortunately, neither 1H NMR spectra nor GC-MS data of the trimethylsilylmethyl ester provided sufficient information to localise the position of the double bond system in products 4 and 5, especially when the difference between n' and m' is less then 2 carbon atoms.‡ To solve this problem the w-hydroxylated fatty acids 4a–e and 5a–e were oxygenated to their corresponding hydroperoxy derivatives in the presence of 2,2'-azobis- (amindiopropane)hydrochloride which induces peroxy radical mediated lipid peroxydation.§,11 This procedure involves a double bond conjunction associated with a Z–E isomerisation of the double bond shifted.HPLC analysis of the reaction mixture indicated the formation of four oxygenation products (Figure 2) containing conjugated diene chromophores with absorbance maxima between 230 and 235 nm (inset). The UV spectra of the fraction eluting early from the oxygenated products, with absorbance maxima at 235 nm, indicated the geometry,12 and the GC-MS data in Table 1 indicated the position of the double bonds.The data observed confirmed the position of the double bond system in compounds 4a–e and 5a–e. This work was supported in part by a DAAD fellowship awarded to I. V. Ivanov (A/96/28729), a grant from the Russian Foundation for Basic Research (grant no. 96-03-327-68a) awarded to G. I. Myagkova and I. V. Ivanov and a grant awarded by the Deutsche Forschungsgemeinschaft [Ku 961(2-2)] to H. Kühn. References 1 W. D. Lehman, Free Radical Biol. Med., 1994, 16. 241. 2 H. Kühn and A. Brash, J. Biol. Chem., 1990, 265, 1454. 3 T. Schewe, W. Halangk, C. Hiebsch and S. M. Rapoport, FEBS Lett., 1975, 60, 149. 4 S. A. Gillmor, A.Villasenor, R. Fletterick, E. Sigal and M. F. Browner, Natur. Struct. Biol., 1997, 4, 1003. 5 Q.-F. Gan, M. F. Browner, D. L. Sloane and E. Sigal, J. Biol. Chem., 1996, 271, 25412. ‡ All the compounds 4 and 5 gave satisfactory analytical data and were characterised by 1H NMR spectroscopy and GC-MS analysis. 4a (n' = 9, m' = 3): 1H NMR (CDCl3) d: 1.25–1.35 (m, 12H, CH2), 1.56–1.70 (m, 4H, 3-CH2 and 17-CH2), 2.04 (m, 2H, 10-CH2), 2.09 (m, 2H, 4-CH2), 2.35 (t, 2H, CH2COO, J 7 Hz), 2.78 (m, 2H, 7-CH2), 3.67 (t, 2H, 18-CH2, J 2.5 Hz), 5.30–5.38 (m, 4H, CH=CH).GC-MS, m/z: 382 (M+), 367 (M+ – Me), 351 (M+ – MeO). 4b (n' = 8, m' = 3): early eluting product in normal phase HPLC (see Figure 1); 1H NMR (CDCl3) d: 1.30–1.40 (m, 10H, CH2), 1.55–1.65 (m, 4H, 3-CH2 and 16-CH2), 2.04 (m, 2H, 10-CH2), 2.10 (m, 2H, 4-CH2), 2.37 (t, 2H, CH2COO, J 7 Hz), 2.77 (m, 2H, 7-CH2), 3.67 (t, 2H, 17-CH2, J 2.5 Hz), 5.35–5.42 (m, 4H, CH=CH).GC-MS, m/z: 368 (M+), 353 (M+ – Me), 337 (M+ – MeO). 4c (n' = 8, m' = 6): 1H NMR (CDCl3) d: 1.30–1.40 (m, 16H, CH2), 1.60 (m, 2H, 3-CH2), 1.65 (m, 2H, 19-CH2), 2.07 (m, 4H, 7-CH2 and 13-CH2), 2.37 (t, 2H, CH2COO, J 7 Hz), 2.79 (m, 2H, 10-CH2), 3.67 (t, 2H, 18-CH2, J 2.5 Hz), 5.35–5.45 (m, 4H, CH=CH).GC-MS, m/z: 410 (M+), 395 (M+ – Me), 379 (M+ – MeO). 4d (n' = 8, m' = 5): 1H NMR (CDCl3) d: 1.30–1.40 (m, 14H, CH2), 1.60 (m, 2H, 3-CH2), 1.66 (m, 2H, 18-CH2), 2.06 (m, 2H, 12-CH2), 2.10 (m, 2H, 6-CH2), 2.35 (t, 2H, CH2COO, J 7 Hz), 2.78 (m, 2H, 9-CH2), 3.64 (t, 2H, 19-CH2, J 2.5 Hz), 5.30–5.40 (m, 4H, CH=CH).GC-MS, m/z: 396 (M+), 381 (M+ – Me), 365 (M+ – MeO). 4e (n' = 7, m' = 5): early eluting product in normal phase HPLC (see Figure 1); 1H NMR (CDCl3) d: 1.30–1.40 (m, 12H, CH2), 1.60 (m, 2H, 3-CH2), 1.65 (m, 2H, 17-CH2), 2.07 (m, 4H, 6-CH2 and 12-CH2), 2.35 (t, 2H, CH2COO, J 7 Hz), 2.78 (m, 2H, 9-CH2), 3.65 (t, 2H, 18-CH2, J 2.5 Hz), 5.30–5.40 (m, 4H, CH=CH). GC-MS, m/z: 382 (M+), 367 (M+ – Me), 351 (M+ – MeO). 5a (n' = 4, m' = 8): early eluting product in normal phase HPLC (see Figure 1); 1H NMR (CDCl3) d: 1.25–1.35 (m, 12H, CH2), 1.59 (m, 2H, 3-CH2), 1.72 (m, 2H, 17-CH2), 2.05 (m, 2H, 9-CH2), 2.14 (m, 2H, 15-CH2), 2.35 (t, 2H, CH2COO, J 7 Hz), 2.78 (m, 2H, 12-CH2), 3.67 (t, 2H, 18-CH2, J 2.5 Hz), 5.30–5.38 (m, 4H, CH=CH). GC-MS, m/z: 382 (M+), 367 (M+ – Me), 351 (M+ – MeO). 5b (n' = 4, m' = 7): 1H NMR (CDCl3) d: 1.30–1.40 (m, 10H, CH2), 1.57 (m, 2H, 3-CH2), 1.73 (m, 2H, 16-CH2), 2.05 (m, 2H, 8-CH2), 2.15 (m, 2H, 14-CH2), 2.37 (t, 2H, CH2COO, J 7 Hz), 2.78 (m, 2H, 11-CH2), 3.68 (t, 2H, 17-CH2, J 2.5 Hz), 5.30–5.38 (m, 4H, CH=CH). GC-MS, m/z: 368 (M+), 353 (M+ – Me), 337 (M+ – MeO). 5c (n' = 7, m' = 7): early eluting product in normal phase HPLC (see Figure 1); 1H NMR (CDCl3) d: 1.30–1.40 (m, 16H, CH2), 1.57 (m, 2H, 3-CH2), 1.64 (m, 2H, 19-CH2), 2.05 (m, 4H, 8-CH2 and 14-CH2), 2.37 (t, 2H, CH2COO, J 7 Hz), 2.79 (m, 2H, 11-CH2), 3.64 (t, 2H, 20-CH2, J 2.5 Hz), 5.30–5.40 (m, 4H, CH=CH).GC-MS, m/z: 410 (M+), 395 (M+ – Me), 379 (M+ – MeO). 5d (n' = 6, m' = 7): early eluting product in normal phase HPLC (see Figure 1); 1H NMR (CDCl3) d: 1.30–1.40 (m, 14H, CH2), 1.57 (m, 2H, 3-CH2), 1.65 (m, 2H, 18-CH2), 2.05 (m, 4H, 8-CH2 and 14-CH2), 2.35 (t, 2H, CH2COO, J 7 Hz), 2.79 (m, 2H, 11-CH2), 3.64 (t, 2H, 19-CH2, J 2.5 Hz), 5.30–5.40 (m, 4H, CH=CH). GC-MS, m/z: 396 (M+), 381 (M+ – Me), 365 (M+ – MeO). 5e (n' = 6, m' = 6): 1H NMR (CDCl3) d: 1.30–1.40 (m, 12H, CH2), 1.59 (m, 2H, 3-CH2), 1.66 (m, 2H, 17-CH2), 2.05 (m, 4H, 7-CH2 and 13-CH2), 2.35 (t, 2H, CH2COO, J 7 Hz), 2.78 (m, 2H, 10-CH2), 3.65 (t, 2H, 18-CH2, J 2.5 Hz), 5.30–5.40 (m, 4H, CH=CH).GC-MS, m/z: 382 (M+), 367 (M+ – Me), 351 (M+ – MeO). § The w-hydroxylated acids 4a–e or 5a–e (0.01 mmol) were incubated at 40 °C for 2 h with 100 mmol of 2,2'-azo-bis(2-amindiopropane)- hydrochloride in 2 ml of 0.1 M borate buffer (pH 9.0) containing 10% (v/v) of methanol.Then the reaction was stopped and hydroperoxides were reduced to the corresponding hydroxides by addition of an equimolar amount of sodium borohydride. The mixture was acidified to pH 3.5, the fatty acids were extracted with 2 ml of ethyl acetate, concentrated under vacuum and analysed by normal phase HPLC and GC-MS as their thrimethylsilylmethyl ester derivatives [the carboxylic group was methylated with diazomethane, the hydroxylic groups were silylated with bis(trimethylsilyl)trifluoroacetamide in pyridine]. Absorbance at 210 nm Retention time/min 5c 4c 4e 5e 4b 5b 16.3 17.2 16.9 18.4 18.8 20.5 15 20 20 20 Figure 1 SP-HPLC separation of the products formed by NaBH4 reduction of a mixture of monomethyl esters of 1c (I), 1e (II) and 1b (III).[The compounds were separated on an analytical Nucleosil 100-7 column (250×5 mm, 7 mm particle size; Machery and Nagel, Germany) with the solvent system hexane–isopropanol–acetic acid (100:2:0.1, v/v), flow rate 1 ml min–1.] I II III Absorbance at 235 nm Retention time/min 13-OH(Z,E) 20 200 240 Absorbance l/nm (E,E) (Z,E) 17.7 19.5 22.9 24.2 13-OH(E,E) 9-OH(E,E) 9-OH(E,Z) Figure 2 Analytical SP-HPLC of non-enzymatically oxidised 17-hydroxy- (9Z,12Z)-heptadecadienoic acid 5b [this HPLC run was performed with the solvent system hexane–isopropanol–acetic acid (100:7.5:0.1, v/v)].(E,Z)Mendeleev Communications Electronic Version, Issue 6, 1998 (pp. 207–248) 6 S. Bongräber, R. J. Kuban, M. Anton and H. Kühn, J. Mol. Biol., 1996, 264, 1145. 7 H. Kühn, H. Sprecher and A. R. Brash, J. Biol. Chem., 1990, 265, 16300. 8 I. V. Ivanov, N. V. Groza, G.M. Malchenko, G. I. Myagkova and T. Schewe, Bioorg. Khim., 1997, 23, 519 (Russ. J. Bioorg. Chem., 1997, 23, 481). 9 I. V. Ivanov, N. V. Groza, H. Kühn and G. I. Myagkova, Bioorg. Khim., 1998, 24, 454 (Russ. J. Bioorg. Chem., 1998, 24, 398). 10 N. C. Brown, S. Narasimhan and Y. M. Choi, J. Org. Chem., 1988, 47, 4702. 11 C. D. Ingram and A. R. Brash, Lipids, 1998, 23, 340. 12 V. W. Bowry and R. Stocker, J. Am. Chem. Soc., 1993, 115, 6029. Received: Moscow, 3rd August 1998 Cambridge, 29th September 1998; Com. 8/06230G

ISSN:0959-9436     

出版商:RSC    

年代:1998

数据来源: RSC

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Mendeleev Communications Electronic Version, Issue 6, 1998 (pp. 207–248) Kinetics of hydrolysis of p-nitrophenyl ethyl chloromethyl phosphonate in a sodium bis(2-ethylhexyl)sulfosuccinate–decane–water reverse micellar system, below and above the percolation threshold Lucia Ya. Zakharova,*a Farida G. Valeeva,a Lyudmila A. Kudryavtseva,a Nataliya L. Zakhartchenkob and Yuri F. Zuevb a A. E. Arbuzov Institute of Organic and Physical Chemistry, Russian Academy of Sciences, 420088 Kazan, Russian Federation.Fax: +7 8432 75 2253; e-mail: vos@iopc.kcn.ru b Kazan Institute of Biochemistry and Biophysics, Russian Academy of Sciences, 420503 Kazan, Russian Federation A kinetic study of the basic hydrolysis of the substrate in a sodium bis(2-ethylhexyl)sulfosuccinate–decane–water reverse micellar system has shown a change in the reactivity of p-nitrophenyl ethyl chloromethyl phosphonate above the percolation threshold.The applicability of the pseudophase model of micellar catalysis, below and above the percolation threshold, is shown. Reverse micelles and water-in-oil microemulsions have drawn wide attention as biomimetic systems.1,2 The most typical anionic surfactant capable of forming reverse micellar aggregates without any co-surfactant is sodium bis(2-ethylhexyl)sulfosuccinate (AOT).† The structural behaviour of reverse systems depends on several parameters, such as temperature, water content, ionic strength, etc.3 Although the pseudophase model of micellar catalysis4 does not take into account the geometry of the particles, it is reasonable to assume that altering the above parameters, resulting in the modification of aggregates, will affect the reaction rate in micelles.When either the volume fraction of dispersed phase f or the temperature is varied percolation phenomenon can take place in the AOT-based reverse micellar systems.5–7 The occurrence of percolation reveals that the process of micellar clustering increases very rapidly.Percolation can be manifested by a rapid increase, by 3–4 orders of magnitude, of the electric conductivity of the system. The structure of the micellar system is assumed7 to be unaffected by percolation, i.e. as before it is formed by isolated water droplets surrounded by an AOT monolayer. It is undoubtedly of interest to study the influence of clustering phenomena on the reaction rate in micelles.† AOT or Aerosol OT is a trivial name for bis(2-ethylhexyl)sulfosuccinate. In this work the kinetics of the basic hydrolysis of p-nitrophenyl ethyl chloromethyl phosphonate 1 in AOT–decane–water reverse micelles at various molar ratios W = [H2O]/[AOT] and Z = [decane]/[AOT] has been investigated (Scheme 1). An analysis of the kinetic data in terms of the pseudophase model and a test of the model under different experimental conditions with high concentrations of the ionic reagent and a variation in temperature and W, Z parameters have been carried out.NaOH 0.01 M W = 9.8 W = 12.0 W = 15.1 W = 20.0 55 50 45 40 35 30 25 20 15 10 5 0.25 0.30 0.35 0.40 0.45 0.50 0.55 Tp/°C CAOT/M 104 103 102 101 100 0 10 20 30 40 50 60 70 T/°C s/mS cm–1 Figure 1 Dependence of the percolation threshold temperature on AOT concentration in the AOT–decane–water reverse micellar system at various W values.The insert gives an example of the electric conductivity change vs. temperature for W = 15.1, CNaOH = 0.01M, the AOT concentrations: 0.26 M, 0.30 M, 0.35 M, 0.42 M, 0.49 M. O NO2 P O ClH2C EtO + OH P O O ClH2C EtO O NO2 Scheme 1 –1.0 –1.2 –1.4 –1.6 –2.0 –2.2 –2.4 –2.0 –2.2 –1.6 –1.8 –2.0 –2.2 lg kobs 103T–1/K–1 water W = 26.6 W = 20.0 W = 15.1 Tcr = 25.5 °C Tcr = 26 °C Tcr = 27.5 °C 3.1 3.2 3.3 3.4 3.5 Figure 2 The Arrhenius dependence of the observed rate constant for the basic hydrolysis of 1 in the AOT–decane–water reverse micellar system at various W values (CNaOH = 0.01 M, CAOT = 0.42 M ).Mendeleev Communications Electronic Version, Issue 6, 1998 (pp. 207–248) Substrate 1 was prepared according to the previously reported procedure.8 The surfactant AOT was from ‘Sigma’ and used without further purification. Sodium hydroxide and decane were obtained commercially and decane was distilled prior to use. Solutions were made up in twice-distilled water.Microemulsions were prepared by mixing AOT, decane and water, in the appropriate proportions, and shaking vigorously until a transparent solution was obtained. Under experimental conditions the reverse micellar systems always exist in accordance with the AOT phase diagram.9 The reaction was monitored by observing the p-nitrophenolate absorption at 400 nm. A spectrophotometer ‘Specord UV VIS’ equipped with temperature-controlled cell holders was employed.The substrate concentration (5×10–5 M) was much less than the nucleophile concentration, and the kinetic data always fitted the first order equation with correlation r � 0.999. The electrical conductivity was measured using a OK 102/1 conductivity meter (Radelkis, Hungary), operating at 80 Hz and 3 kHz. The temperature was controlled in a parallelplane cell with ±0.2 °C accuracy. The temperature of the percolation threshold was determined as the point at which the first derivative of conductivity with respect to temperature changes its sign.Figure 1 plots the dependence of the percolation threshold temperature (Tp) on the AOT concentration at various W values. The occurrence of the percolation threshold reveals that cluster size, attractive interactions and the rate of exchange of material between micelles through collisions all increase. The appearance of a percolation threshold corresponds to the formation of the first ‘infinite’ cluster.Based on the electric conductivity measurements the conditions for the kinetic study below and above the percolation threshold were chosen.The kinetic data are shown in Figures 2–4. In Figure 2 the lg kobs vs. 1/T plot at various W values is represented (CAOT = 0.42 M, CNaOH = 0.01 M). The Arrhenius dependence changes its slope at definite critical temperatures (Tcr). At W = 26.6 a decrease in the slope occurs, which is in line with a reduction in activation energy (Ea), whereas at W = 20.0 and 15.1 a transition to negative Ea values is observed.It is evident that the values Tcr (Figure 2) and Tp (Figure 1) for the same W value are nearly identical, which makes it possible to assume that the change of the slope in the Arrhenius dependence is connected with the clustering phenomenon. At the same time, it should be assumed that a decrease in Ea above the percolation threshold is not directly due to the acceleration of the dynamic processes resulting from clustering. Such a direct effect would be expected in the case of fast reactions, in which the rate is controlled by diffusion of reagents.10 The reaction in this study does not belong to these fast processes, so the basic assumption of the pseudophase model should be observed, suggesting that the exchange of materials between droplets is much faster than the reaction in this study, and therefore has no effect on the kinetics.We can assume that clustering and acceleration of the dynamic processes result in the alteration of some characteristics of the micellar microenvironment of the reagents (i.e. micropolarity, surface potential, etc.), thus influencing their reactivity.The kinetic data were treated in terms of the pseudophase model4 with the assumption that there is competition between reactions in different microphases of the reverse micelles. The problems and approximations involved in these definitions have been discussed previously.11 For the reaction occurring at the interface the first order rate constant is given by equation (1): where ki/s–1 is a bimolecular interfacial rate constant, expressed in terms of the molar ratio [OH]/[AOT]; it is connected to the conventional pseudo first order constant k'i/s–1 and the second order constant k2,i/M–1 s–1 as foows: V is the molar volume of AOT, [OH]t is the total OH concentration and KS and KOH are partition coefficients, which are defined as where the molar concentrations of substrate (S), decane and AOT are given in square brackets; subscripts i, o, w are related to the interface, oil and water, respectively.Figure 3 plots the kobs vs. CAOT dependence for the various W values at 25 °C. As one can see from Figure 1 the experimental conditions for the kinetic study are as follows. The micellar system is below the percolation threshold for W = 15.1 and 20.0 whereas for W = 9.8 the clustering process is very active.The kinetic data in Figure 4 suggest that in the system studied a 2–2.5-fold retardation of the hydrolysis of 1 takes place by comparison with the reaction in water but the observed rate constant still depends linearly on the NaOH concentration. An increase in the AOT concentration results in some inhibition of the reaction (Figure 3) evidently due to dilution of the reagents with increasing volume fraction of the dispersed phase.The observed rate constant is reduced with the increase in W (Figure 3, insert). Equation (1) can be linearized in the 1/kobsCAOT vs. Z coordinates, which makes it possible to determine the values KOH, KS and ki. In this work our task was to test the pseudophase model during the clustering process of reverse micelles.A comparison of the experimental and calculated kinetic data shown in Figure 3 demonstrates a rather good agreement between them both below and above the percolation threshold. The calculated parameters are KOH = 2.6 and ki = 5.8 s–1. Assuming V = 0.37 lmol–1,12 we can calculate k2,i = 2.15 M–1 s–1 (for the sake of comparison k2,w = 4.0 M–1 s–1).From the analysis of the calculated parameters some conclusions can be drawn with respect to the factors responsible for the micellar rate effects in the system studied. The observed effect kobs/kw ª 0.4–0.5 is mainly determined by two factors. The first results from a change in the microenvironment of the reagents and the second results from concentrating the reagents in the microdroplets and has some resemblance to interfacial catalysis. The first effect can be expressed via the k2,i/k2,w ratio.It is evident that this value is comparable with the observed ratio kobs/kw, i.e. it is a fundamental contribution to the total 7 6 5 4 3 2 1 0 0.20 0.30 0.40 0.50 0.60 kobs/10–2 s–1 CAOT/M 3 2 1 0 10 15 20 25 30 35 40 W kobs/10–2 s–1 W = 9.8 W= 15.1 W = 20.0 Figure 3 The AOT concentration dependence of the observed rate constant for the basic hydrolysis of 1 at various W values (CNaOH = 0.01M, 25 °C).The insert shows the observed rate constant vs. W. The solid lines are related to the calculated kobs values. kobs = kiKSKOH[OH]t (KS + Z)(KOH + W)[AOT] (1) ki = k'i ; k2,i = kiV [OH] [AOT] (2) KS= ;KOH = [S]i[decane] [S]0[AOT] [OH]i[H2O] [OH]w[AOT] (3)Mendeleev Communications Electronic Version, Issue 6, 1998 (pp. 207–248) micellar rate effect. It can be connected with changes in the reactivity of the substrate due to changes in the micropolarity, solvation or orientation of the reagents. According to Ingold’s theory,13 lowering the polarity of the microenvironment should favour the ion–molecular reaction, in particular, the reaction of phosphorus acid esters with OH–.14 One can therefore assume that inhibition of the reaction probably results from the loss in entropy due to the lowered mobility of the substrate rather than to a change in the micropolarity.The effect of concentrating the reagents in microdroplets plays a minor role in the catalytic mechanism due to the low value of the partition coefficient of the nucleophile (KOH = 2.6) connected with its high hydrophilicity and electrostatic repulsion from the negatively charged micellar surface.In conclusion, in this work the kinetics of 1 in AOT-based reverse micelles and the influence of droplet clustering have been studied. A change in the reactivity of 1 above the percolation threshold was observed, which is reflected in the alteration of the slope in the Arrhenius plot.This anomalous behaviour can be caused by a reduction in the area of micellar contact with the oil and the alteration of some properties of the surface layer due to micelle clustering, both of which influence the reactivity. It has been found that the pseudophase model is adequate both below and above the percolation threshold. This work was supported by the Russian Foundation for Basic Research (grant no. 97-03-32372). References 1 Yu. L. Khmel’nitsky, A. V. Levashov, N. L. Klyachko and K. Martinek, Usp. Khim., 1984, 53, 545 (Russ. Chem. Rev., 1984, 53, 319). 2 Microemulsions: Structure and Dynamics, eds. S. E. Friberg and P. Bothorel, CRC Press, Inc. Boca Raton, Florida, USA, 1987. 3 E. B. Leodidis and T. A. Hatton, Langmuir, 1989, 5, 741. 4 L. Garsia-Rio, J. R. Leis, M. E. Pena and E. Iglesias, J. Phys. Chem., 1993, 97, 3437. 5 A. Jada, J. Lang and R. Zana, J. Phys. Chem., 1989, 93, 10. 6 C. Cametti, P. Codastefano, P. Tartaglia, R. Rouch and S. H. Chen., Phys. Rev. Lett., 1990, 64, 1461. 7 Y. Feldman, N. Kozlovich, I. Nir, N. Garti, V. Archipov, Z. Idiyatullin, Yu.Zuev and V. Fedotov, J. Phys. Chem., 1996, 100, 3745. 8 V. E. Bel’skii, L. A. Kudryavtseva, O. M. Il’ina and B. E. Ivanov, Zh. Obshch. Khim., 1970, 49, 2470 [J. Gen. Chem. USSR (Engl. Transl.), 1970, 49, 2180]. 9 S. Perez-Casas, R. Castillo and M. Costas, J. Phys. Chem., 1997, B, 101, 7043. 10 M. Almgren and R. Johannsson, J. Phys. Chem., 1992, 96, 9512. 11 P. Stilbs, J. Colloid Interface Sci., 1982, 87, 385. 12 K. Martinek, A. K. Yatsimirsky, A. V. Levashov and I. V. Beresin, Micellization, Solubilization, and Microemulsions, ed. K. L. Mittal, Plenum Press, New York–London, 1977, p. 489. 13 C. K. Ingold, Structure and Mechanism in Organic Chemistry, Cornell University Press, Ithaca–London, 1969. 14 N. A. Loshadkin, in Toksichnye efiry kislot fosfora (Toxic Ethers of Phosphorus Acids), ed. P. O’Brain, Mir, Moscow, 1964, p. 460 (in Russian). water 0.26 M 0.30 M 0.35 M 0.42 M 0.49 M 12 10 8 6 4 2 0 0.00 0.01 0.02 0.03 0.04 CNaOH/M kobs/10–2 s–1 Figure 4 Dependence of the observed rate constant for the basic hydrolysis of 1 on the NaOH concentration in the system at various AOT concentrations. W = 15.1, 25 °C. Received: Moscow, 7th July 1998 Cambridge, 9th September 1998; Com. 8/05577G

ISSN:0959-9436     

出版商:RSC    

年代:1998

数据来源: RSC