摘要:

Mendeleev Communications Electronic Version, Issue 4, 1998 (pp. 129–168) Direct X-ray confirmation of the possible use of magnetochemical criteria for binuclear structural isomers of copper(II) complexes based on acylhydrazones of salicylic aldehyde-substituted derivatives Victor A. Kogan,a Vladimir V. Lukov,*a Sergei I. Levchenkov,a Mikhail Yu. Antipinb and Oleg V. Shishkinc a Department of Chemistry, Rostov State University, 344090 Rostov-on-Don, Russian Federation. Fax:+7 8632 28 5667 b A.N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences, 117813 Moscow, Russian Federation. Fax: +7 095 135 5085 c Institute for Single Crystals, National Academy of Sciences of the Ukraine, 310001 Khar’kov, Ukraine. Fax:+7 057 232 0273 X-Ray structural investigations and magnetic measurements of binuclear copper(II) complexes with salicylic aldehyde acylhydrazone have demonstrated the possible use of magnetochemical criteria for the identification of structural isomers in the given class of compounds.It was shown earlier1–3 that complex formation between acylhydrazones of salicylic aldehyde-substituted derivatives and copper(II) acetate leads to two possible isomeric structures 1a or 1b whereas copper(II) perchlorate gives a binuclear analogue of the type 1b'.The difference between these structures lies in the different electronic nature of the bridging oxygen atoms. In fact the bridging atom in 1a is the a-oxyazinic atom of the hydrazide moiety while in 1b and 1b' it is the phenoxide oxygen atom of the salicylic moiety. We believe that the types of hybridization of these two oxygen atoms are quite different, so as a consequence the bond angles Cu–O–Cu in the exchange fragment are different too.The systematic magnetochemical study carried out by us revealed that the antiferromagnetic exchange interaction for the complexes 1b and 1b' is always much stronger (the exchange parameters 2J lie in the range –300–500 cm–1) than for the binuclear complexes 1a (2J lie in the range –20–130 cm–1).3,4 This can be explained by the greater degree of planarity of the exchange fragment including the phenoxide oxygen atom (types 1b, 1b').A geometrical model which explains these differences has been developed earlier,5 and the experimental data in this field were also systematized.These data point to a possible use of magnetochemical criterion in the identification of given structural isomers. The present paper is devoted to the first confirmation of the above hypothesis using X-ray diffraction data.† The type 1b' binuclear copper(II) complex (R1 = H, R2 = C12H25) has been used as an object of investigation; its magnetic properties have been compared with the properties of the type 1a complex (R1 = H, R2 = C12H25) which has been especially synthesized for the first time.It can easily be seen that in this particular case the exchange parameters 2J (calculated in terms of the HDVV model6) for the 1a type complex are much lower (in absolute value) than for 1b'. This can be explained3 by the geometrical differences between the exchange fragments.Indeed, the structure of the † Crystal data for 1b': C42H70N4O6Cu2 2+ · 2ClO4 – , monoclinic, space group P21/c, a = 17.528(5) Å, b = 18.087(7) Å, c = 7.812(2) Å, b = = 94.54(2)°, V = 2469(1) Å3, F(000) = 1108, Dc = 1.416 g cm–3, Z = 2. Data were measured using a Syntex P21/PC diffractometer (T = 193 K, graphite-monochromated MoKa radiation, l = 0.71073 Å, q/2q scan, 2qmax = 50°).The structure was solved by direct methods using the SHELXTL PLUS program package. Refinement against F2 in an anisotropic approximation (the hydrogen atoms isotropic in the riding model) by a full matrix least-squares method for 2888 reflections was carried out to R1 = 0.077 [for 1754 reflections with F > 4s(F), wR2 = 0.244, S = 1.02]. Atomic coordinates, bond lengths and bond angles 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 this material should quote the full literature citation and the reference number 1135/28. Cu O O Cu A R1 O N Cu O N R2 R1 O N Cu O N R2 1a R1 O N Cu O N R2 R1 O N Cu O N R2 R1 O N Cu O NH R2 R1 O N Cu O HN R2 · 2ClO4 2+ 1b 1b' aMean square error. bMole part of paramagnetic impurity.cThe value of meff is calculated per one copper ion in the binuclear molecule. Table 1 Magnetic properties of type 1a and 1b' binuclear complexes. T/K meff /B.M. (exp.) meff /B.M. (calc.) 1a: 2J = –118 cm–1, g = 2.02, r = 0.66%,a f = 0b 85.4 1.12 1.11 102 1.24 1.24 119 1.33 1.33 137 1.40 1.40 150 1.44 1.44 171 1.50 1.49 230 1.59 1.59 242 1.60 1.60 263 1.62 1.62 293 1.65 1.64 1b': 2J = –349 cm–1, g = 2.00, r = 1.47%,a f = 0.03b 77.4 0.38 0.38 101 0.46 0.47 136 0.66 0.66 160 0.78 0.78 190 0.93 0.93 216 1.04 1.04 232 1.10 1.10 254 1.17 1.16 271 1.22 1.21 299 1.27 1.28Mendeleev Communications Electronic Version, Issue 4, 1998 (pp. 129-168) complex (Figure 1) has confirmed this assumption; the exchange fragment A is strictly planar. The small displacement (0.06 Å) of the copper atom from the plane O(2), O(2A), O(1), N(2) to the O(1M) atom is possibly caused by the small differences in the Cu(1)–O (perchlorate-ion) [2.600(6) Å] and Cu(1)–O (methanol) [2.320(6) Å] bond lengths.As shown earlier the type 1b' complexes are ionic in organic solvents so Cu(1)–O (perchlorate) coordinative bonds are not strong and the anions are out of the coordination sphere in solution.Nevertheless in contrast to other types of complexes7 the type 1b' complexes, according to magnetochemical data, remain dimeric in solution. All these results confirm the high stability of the complex molecules due to their high symmetry. The following brief description of complex structure confirms this.In the crystal the molecule 1b' (R1 = H, R2 = C12H25) is arranged in the centre of symmetry which is situated at the intersection of the Cu(1)–Cu(1A) and O(2)–O(2A) lines. The copper atom is six-coordinate (taking into account weak coordination of the metal with ClO4 – ). The organic ligand is almost planar. The atom deviations from the mean plane are less than 0.04 Å.The bond length values in the O=C–NH– N=C–Car fragment indicate considerable delocalization of electron density. The five-membered metallocycle is planar. The atomic deviations from the mean plane are less than 0.05 Å. The six-membered metallocycle has a flattened sofa conformation. The deviation of the Cu(1) atom from the N(2), C(14), C(15), C(18), O(2) plane is 0.18 Å.The alkyl substituent has a trans-conformation with regard to all C(sp3)–C(sp3) bonds, excluding the C(2)–C(3) bond. This substituent is directed almost orthogonally to the plane of the organic ligand. The angle between their mean planes is 110.4°. The methanol molecule is turned, with respect to the Cu(1)–O(1) bond, by –30.0(7)° [the O(1)–Cu(1)–O(1M)–C(1M) torsion angle]. Unfortunately, the position of the hydroxy group hydrogen could not be determined. In the crystal complex molecules form infinite chains due to H-bonding H(1N)···O(25)' (1 – x, 0.5 + y, 1.5 - z) (O···H 2.06 Å, O···H–N 163.9°).Thus, the X-ray confirmation discussed in this paper allows one to use with great confidence the magnetic exchange parameters for binuclear copper(II) complexes based on acylhydrazones as the magnetochemical criterion of structural isomerism. References 1 V.A. Kogan and V. V. Lukov, Abstracts of the XXIXth Intl. Congress on Coord. Chem., Lausanne, Switzerland, 1992, p. 708. 2 E. V. Bogatyreva, V. A. Kogan, V. V. Lukov and V. A. Lokshin, Zh. Neorg. Khim., 1990, 35, 2010 (Russ. J. Inorg. Chem., 1990, 35, 1145). 3 V. V. Lukov, S. I. Levchenkov and V. A. Kogan, Koord. Khim., 1995, 21, 402 (Russ. J. Coord. Chem., 1995, 21, 385). 4 V. A. Kogan, V. V. Zelentsov, G. M. Larin and V. V. Lukov, Kompleksy perekhodnykh metallov s gidrazonami. Fiziko-khimicheskie svoistva i struktura (Transition metal complexes with hydrazones. Physicalchemical properties and structure), Nauka, Moscow, 1990, p. 112 (in Russian). 5 V. A. Kogan and V. V. Lukov, Koord. Khim., 1993, 19, 476 (Russ. J. Coord. Chem., 1993, 19, 545). 6 R.Carlin, Magnetochemistry, Springer–Verlag, Heidelberg, 1986. 7 S. I. Levchenkov, V. V. Lukov and V. A. Kogan, Koord. Khim., 1996, 22, 557 (Russ. J. Coord. Chem., 1996, 22, 523). C(13) C(12) C(11) C(10) C(9) C(8) C(7) C(6) C(5) C(4) C(3) C(2) C(1) C(14) C(15) C(16) C(17) C(18) C(19) C(20) N(1) N(2) O(1) O(2) C(1M) O(1M) Cu(1) Figure 1 Structure of complex 1b' (R1 = H, R2 = C12H25), ClO4 – anions are not shown. Selected bond lengths (Å) and bond angles (°): Cu(1)–N(2) 1.918(7), Cu(1)–O(2) 1.971(5), Cu(1)–O(2A) 1.974(5), Cu(1)–O(l) 2.011(5), O(2)–Cu(1A) 1.974(5), Cu(1)–O(1M) 2.320(6), Cu(1)–Cu(1A) 2.885(8); N(2)–Cu(1)–O(2) 90.5(3), N(2)–Cu(1)–O(2A) 170.2(2), O(2)–Cu(1)–O(2A) 80.5(2), N(2)–Cu(1)–O(1) 81.1(3), O(2)–Cu(1)–O(1) 171.2(2), O(2A)–Cu(1)– O(1) 107.6(2), Cu(1)–O(2)–Cu(1A) 99.5(2). Cu(1A) O(2A) Received: Moscow, 24th April 1998 Cambridge, 24th June 1998; Com. 8/03516D

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年代:1998

数据来源: RSC

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Mendeleev Communications Electronic Version, Issue 4, 1998 (pp. 129–168) 1,2-Asymmetric induction in nucleophilic Michael addition reactions of amines under microwave irradiation Nelly N. Romanova,* Alexander G. Gravis, Irina F. Leshcheva and Yuri G. Bundel’ Department of Chemistry, M. V. Lomonosov Moscow State University, 119899 Moscow, Russian Federation. Fax: +7 095 932 8846 1,2-Asymmetric induction of up to 76% is observed in the reactions of several amines with the b-substituted acrylic acid ester (S)-1 containing a g-asymmetric carbon atom in the absence of solvent after 12 min microwave irradiation.The development of methods for preparing b-amino acids and their derivatives1 which have biological activity dependent on the stereochemistry of the isomers, is one of the most urgent problems in fine organic synthesis.Stereocontrolled Michael addition of amines to the double bond of a,b-unsaturated carboxylic acids could be a convenient and cheap method for the solution of this chemical problem, which is simultaneously associated with the selection of conditions for asymmetric induction and control of stereochemistry at the newly formed chiral centres.2 We have shown for the first time that microwave irradiation (MW) can be successfully used to activate the reactions of amines with esters of crotonic acid.3 Under these conditions, the chemical yields of target esters of b-aminobutyric acid reach 84%, the rate of their formation increases by several orders of magnitude, and the reaction duration is 10–25 min (cf. 50 h in ref. 4). An insignificant stereoselectivity was observed when either the amine or the ester group contained a chirality source. In the reaction with methyl crotonate, the action of the a-ethylphenyl chiral centre of the amine through two s-bonds resulted in a weak asymmetric induction (diastereoisomer ratio 54:46); 1,5-asymmetric induction in the reactions of achiral amines (piperidine, morpholine and benzylamine) with sec-butyl crotonate is completely absent.3 In this work, we studied (under MW conditions) the stereoselectivity of conjugated addition of amines to esters of an a,b-unsaturated carboxylic acid with a stereogenic centre in the g-position.The ethyl ester of b-substituted acrylic acid trans-(S)-1,5 which is widely used as a starting object along with the methyl ester of trans-(S)-2 and which can easily be obtained from D-(+)-mannitol, was used as a substrate with a chiral source in various addition reactions at the double bond.4,6–8 The reactions of the ester of trans-(S)-1 with amines 3–5 were carried out in a commercial microwave oven (Funai MO 785 VT) in the absence of solvent for 12 min at a power of 510 W and the temperature of the reaction mixture not higher than 60 °C.The reaction run was monitored by thin layer chromatography on silica gel, and reaction products were isolated by column chromatography on silica gel using a heptane–ethyl acetate (2:1) mixture as the eluent. The chemical and optical yields of amino esters 6–8 are presented in Table 1. The syn- and trans-diastereoisomers of b-amino esters 6–8 obtained were isolated as mixtures, and the analysis of their 1H NMR† spectra made it possible to determine the ratio of diastereoisomers in amino esters 6–8.It is shown in ref. 4 that the observed syn-stereoselectivity of the conjugated addition of benzylamine 3 to the methyl ester of trans-(S)-2 depends on the reaction temperature: a diastereoisomeric excess of syn-isomer 9 reaches a maximum (100%) at –50 °C and decreases to 80% when the temperature increases to 0 °C and the reaction duration is 50 h.The published data on the stereoselectivity of the reactions of esters of trans-(S)-1 and trans-(S)-2 with N-6 and Cnucleophiles7 performed under conditions different from those used in the current work indicate that in these cases, the predominant diastereoisomers have a syn-configuration. For example, in the reaction with hydroxylamine (room temperature, 24 h, ZnCl2, 79%), the syn:anti ratio is 20:1;6 in the reaction with nitromethane (temperature from –30 °C to 34 °C, 12–4 h, TBAF, yield ca. 70%), the syn:anti ratio varies from 19:1 to 7:1.7 † The 1H NMR spectra were recorded on a VXR-400 Varian spectrometer (400 MHz) in a CDCl3 solution at 28 °C using TMS as the internal standard.Protons in the 1H NMR spectra are numbered as follows: The reverse assignment of the signals of H-A and H-A' is also possible. The spectra of predominantly formed diastereoisomers are given. For 6, d: 1.25 (t, 3H, Me-1, JMe-1,CH2-2 7.18 Hz), 1.33 (s, 3H, Me-7), 1.39 (s, 3H, Me-8), 2.45 (dd, 1H, H-3, JH-3,H-3' 14.93 Hz, JH-3,H-4 6.20 Hz), 2.49 (dd, 1H, H-3', JH-3',H-3 14.93 Hz, JH-3',H-4 6.20 Hz), 3.14 (q, 1H, H-4, JH-4,H-3 = JH-4,H-3' = JH-4,H-5 6.20 Hz), 3.81 (dd, 1H, H-6, JH-6,H-6' 8.40 Hz, JH-6,H-5 6.78 Hz), 3.99 (dd, 1H, H-6', JH-6',H-6 8.40 Hz, JH-6',H-5 7.13 Hz), 4.13 (q, 2H, CH2-2, JCH2-2,Me-1 7.18 Hz), 4.20 (ddd, 1H, H-5, JH-5,H-6 6.78 Hz, JH-5,H-6' 7.13 Hz, JH-5,H-4 6.20 Hz); R1: 1.8 (s, 1H, NH); R2: 3.90 (s, 2H, CH2), 7.20–7.35 (m, 5H, Ph).For 7, d: 1.31 (t, 3H, Me-1, JMe-1,CH2-2 7.15 Hz), 1.34 (s, 3H, Me-7), 1.40 (s, 3H, Me-8), 2.33 (dd, 1H, H-3, JH-3,H-3' 14.53 Hz, JH-3,H-4 6.32 Hz), 2.52 (dd, 1H, H-3', JH-3',H-3 14.53 Hz, JH-3',H-4 8.79 Hz), 3.20 (dt, 1H, H-4, JH-4,H-3 = JH-4,H-5 6.32 Hz, JH-4,H-3' 8.79 Hz), 3.75 (dd, 1H, H-6, JH-6,H-6' 7.91 Hz, JH-6,H-5 6.32 Hz), 3.96 (t, 1H, H-6', JH-6',H-6 = = JH-6',H-5 7.91 Hz), 4.17 (dq, 1H, H-2, JH-2,H-2' 14.0 Hz, JH-2,Me-1 7.15 Hz), 4.19 (dq, 1H, H-2', JH-2',H-2 14.0 Hz, JH-2',Me-1 7.15 Hz), 4.25 (dt, 1H, H-5, JH-5,H-6 = JH-5,H-4 6.32 Hz, JH-5,H-6' 7.91 Hz); R1 + R2: 1.38 (m, 2H), 1.48 (m, 4H), 2.48 (m, 4H).For 8, d: 1.25 (t, 3H, Me-1, JMe-1,CH2-2 7.19 Hz), 1.30 (s, 3H, Me-7), 1.37 (s, 3H, Me-8), 2.41 (dd, 1H, H-3, JH-3,H-3' 15.16 Hz, JH-3,H-4 5.19 Hz), 2.52 (dd, 1H, H-3', JH-3',H-3 15.16 Hz, JH-3',H-4 6.29 Hz), 2.84 (ddd, 1H, H-4, JH-4,H-3 5.19, JH-4,H-3' 6.29 Hz, JH-4,H-5 5.10 Hz), 3.76 (dd, 1H, H-6, JH-6,H-6' 7.39 Hz, JH-6,H-5 6.61 Hz), 3.90 (dd, 1H, H-6', JH-6',H-6 7.39 Hz, JH-6',H-5 6.61 Hz), 4.08 (dt, 1H, H-5, JH-5,H-6 = JH-5,H-6' 6.61 Hz, JH-5,H-4 5.10 Hz), 4.12 (q, 2H, CH2-2, JCH2-2,Me-1 7.19 Hz); R1: 1.89 (s, 1H, NH); R2: 1.33 (d, 3H, Me, JMe–CH 6.7 Hz), 3.88 (q, 1H, CH, JCH–Me 6.7 Hz), 7.20–7.35 (m, 5H, Ph).O O ROOC O O ROOC R2R1N O O ROOC R2R1N R1R2NH trans-(S)-1,2 3–5 syn-6–9 anti-6–9 1 R = Et 2 R = Me 3,6 R = Et, R1 = H, R2 = CH2Ph 4,7 R = Et, (R1 + R2) = –(CH2)5– 5,8 R = Et, R1 = H, R2 = (S)-CH(Me)Ph 9 R = Me, R1 = H, R2 = CH2Ph O O O R2R1N O 1 2 3 4 5 6 7 8 Table 1 Chemical and optical yields of esters of b-amino acids 6–8.Time/min Reaction conditions Yield (%) Diastereoisomer ratio (%) 6 12 MW 79 88:12 7 12 MW 95 64:36 8 12 MW 28 85:15Mendeleev Communications Electronic Version, Issue 4, 1998 (pp. 129-168) The comparison of the stereochemical results obtained in refs. 4, 6 and 7 with the preliminary data obtained in this work suggests that in the variant of the Michael reaction used, MW has no effect on the order of magnitude of 1,2-asymmetric induction and the predominantly formed diastereoisomers of amino esters 6–8 most likely have the syn-configuration as well.Thus, the diastereoselectivity of the Michael addition of amines under MW conditions is due (as in the absence of MW4,6,7) to asymmetric induction of the g-chiral centre in the starting ester of trans-(S)-1, which is located near the prochiral centre in the b-position, and the stereochemistry of nucleophilic addition is determined by the structure of the amine used.A high level of asymmetric induction was achieved when benzylamine 3 was used as the nucleophile. It is noteworthy that the stereoselectivity of reaction of the cyclic amine, piperidine 4, as compared to the primary benzylamine 3, in the reaction with ester 1 under MW conditions is approximately four times lower, which is most likely related to the relatively higher nucleophilicity of piperidine.This decreases the role of steric preference of the nucleophilic attack of amine from the pro-S or pro-R side of the double bond of ester 1 to the prochiral centre at the b-position.The diastereoisomeric excess (70%) in the case of amine 8 is most likely the result of the overall stereochemical effect of two chirality sources: in the g-position of the starting trans-(S)-ester-1 (1,2-asymmetric induction) and in amine (S)-5 (1,3-asymmetric induction). This work was financially supported by the Russian Foundation for Basic Research (grant no. 96-03-32157) and MOPO RF (grant no. 01.0170f from the Interuniversity Science Technical Program ‘General and Technical Chemistry’). References 1 M. Fernandez-Suarez, L. Munoz, R. Fernandez and R. Riguera, Tetrahedron Asymm., 1997, 8, 1847. 2 N. N. Romanova, A. G. Gravis and Yu. G. Bundel’, Usp. Khim., 1996, 65, 1170 (Russ. Chem. Rev., 1996, 65, 1083). 3 N. N. Romanova, A. G. Gravis, G. M. Shaidullina, I. F. Leshcheva and Yu. G. Bundel’, Mendeleev Commun., 1997, 235. 4 H. Matsunaga, T. Sakamaki, H. Nagaoka and Y. Yamada, Tetrahedron Lett., 1983, 24, 3009. 5 S. Tanako, A. Kurotaki, M. Takahashi and K. Ogasawara, Synthesis, 1986, 403. 6 Y. Xiang, H.-J. Gi, D. Nin, R. F. Schinazi and K. Zhao, J. Org. Chem., 1997, 62, 7430. 7 V. L. Patrocinio, P. R. R. Costa and C. R. D. Correia, Synthesis, 1994, 474. 8 Y. Hirai, T. Suga and H. Nagaoka, Tetrahedron Lett., 1997, 38, 4997. Received: Moscow, 23rd April 1998 Cambridge, 21st May 1998; Com. 8/03093F

ISSN:0959-9436     

出版商:RSC    

年代:1998

数据来源: RSC

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Mendeleev Communications Electronic Version, Issue 4, 1998 (pp. 129–168) Cross-coupling of copper arylacetylides with N-(o-iodoaryl)hydrazines as a new method of synthesising 2-substituted indoles Tat’yana A. Prikhod’ko and Sergey F. Vasilevsky* Institute of Chemical Kinetics and Combustion, Siberian Branch of the Russian Academy of Sciences, 630090 Novosibirsk, Russian Federation. Fax: +7 3832 34 2350; e-mail: vasilev@ns.kinetics.nsc.ru A new method is proposed for synthesising 2-substituted indoles by cross-coupling of copper(I) arylacetylides with N-(o-iodophenyl)hydrazines in DMF.We have already reported on the cyclocondensation of activated o-chloroarylacetylenes with hydrazine which results in substituted indazoles.1 This method is, however, limited by the necessity of using both aryl halides and acetylenic components which possess only electron-withdrawing substituents.In addition, the cyclocondensation of o-chloro-substituted arylacetylenes with NH2NH2·H2O fails to give the intermediate compounds, N-(o-acetylenylaryl)hydrazines (substitution of a chlorine atom by a hydrazine group is the rate determining stage). Thus, it is impossible to study the cyclization of intermediates in a ‘pure form’ depending on the experimental conditions.It is also known that the direction of cyclization of (o-acetylenylaryl)carboxylic acid hydrazides, also containing two nitrogen atoms of differing nucleophilicity, may be controlled by varying the reaction conditions.2 We assume that an alternative way of synthesising N-(o-acetylenylaryl)hydrazines by interaction of N-(o-iodoaryl) hydrazines with either terminal acetylenes or their acetylide allows us not only to isolate intermediates but also to study the direction of N-(o-arylethynyl)hydrazine cyclization in the absence of acceptor substituents or even in the presence of donors.This, in turn, would make it possible to determine more precisely the influence of both internal (character of substituents) and external (conditions of cyclization) factors on the route of cyclization, its generality and limitations, and to synthesise other condensed heterocyclic systems.The interaction between N-(o-iodophenyl)hydrazine 1 and p-nitrophenylacetylene 2 under standard cross-coupling conditions (Scheme 1) gives rise to 3-substituted indazole 3 in 38% yield.We have failed to isolate the expected intermediate 4. Using chloride (1·HCl) as a more stable substrate, we managed to increase the yield of 3† to 43%. All attempts to condense 1 with p-methoxyphenylacetylene failed, since the reaction was followed by resinification. These results and the comparatively low yield of 3 are attributed to † All compounds synthesised have satisfactory analytical and spectral data. 3: mp 117–118 °C (from benzene–hexane); 1H NMR (CDCl3) d: 4.45 (s, 2H, CH2), 7.0–8.2 (m, 8H, arom. H), 10.6 (br. s, 1H, NH); IR (CHCl3, n/cm–1): 1350 and 1530 (NO2), 3480 (br., NH). both the lability of initial iodohydrazine 1 and the low reactivity of halide atom due to the +M-effect of the hydrazine group. A similar result was observed for the reaction of arylacetylenes with vicinal iodoaminopyrazoles.To avoid complications, the authors used acylic protection of the amino group and replaced the catalytic variant of cross-coupling by the acetylide method of synthesis.3 We used this method in the present work. The acetylation of hydrazine 1 does indeed cause substrate stabilization and makes it possible to carry out cross-coupling of copper(I) p-nitrophenyl- 5a, phenyl- 5b and even of p-methoxyphenylacetylide 5c with a-N-(o-iodophenyl)-b-N-(acetyl)hydrazine 6 (Scheme 2, Table 1).However, we failed to isolate intermediates 7a–c upon condensation. The reaction leads to the 2-substituted indoles 8a–c‡ (30–75%). As expected, the reaction with 5a proceeds most smoothly. It is interesting that compounds 8a–c exist in a tautomeric equilibrium 8a–c 8'a–c in solution (see NMR spectra).The formation of the pyrrole rather than the pyrazole ring is related to the greater nucleophilicity of the amine nitrogen atom as compared with the amide nitrogen. The application of pyridine as a solvent in the reaction of iodide 6 with 5a changes the route of cyclocondensation. The I NHNH2 C C NO2 NHNH2 i N N H H2C NO2 1 C NO2 HC 2 3 4 Scheme 1 Reagents and conditions: i, N2, Pd(PPh3)2Cl2–CuI, Et3N, 80 °C, 4.5 h.I NHNHCOMe C C R NHNHCOMe N NHCOMe R 6 C R CuC 5a–c 9 7a–c N N H2C NO2 COMe i ii 8a–c N N R 8'a–c C OH Me Scheme 2 Reagents and conditions: i, N2, DMF, 155 °C, 3–7 h; ii, N2, Py, 110 °C, 3.5 h. Table 1 Cyclocondensation of copper arylacetylides CuCºC–C6H4–R-p with a-N-(o-iodophenyl)-b-N-(acetyl)hydrazine 6.Acetylide 5 R Indole 8 DMF, 155 °C Yield (%) a NO2 a 3 h 74.7 b H b 5 h 32.0 c OMe c 7 h 41.0Mendeleev Communications Electronic Version, Issue 4, 1998 (pp. 129-168) formation of isoindazole 9§ (30%) is probably related to the generation of a stronger N-anion nucleophile from the ‘acidic’ MeCONH group in the presence of base (Py).All our attempts to carry out condensation of iodohydrazine 6 with copper(I) acetylide 5c under similar conditions (Py) failed, probably due to the opposing polarization of a triple bond in intermediate 7c (compared to 7a) and due to the impossibility of forming an aromatic system. We have managed to synthesize intermediate 7a from 6 and 2 by using a catalytic variant of cross-coupling and decreasing the temperature to 80 °C.The yield of 7a¶ reached 68%. The interaction between iodide 6 and p-methoxyphenylacetylene under similar conditions fails to give the corresponding product 7c (the reaction mass still contains initial 6) and the reaction is accompanied by strong resinification. We assume that this is caused by the lower CH-acidity of p-methoxyphenylacetylene compared to that of p-nitrophenylacetylene.4 In attempting to remove the acylic protection in 7a by boiling in n-butanol in the presence of K2CO3 we failed to isolate the expected intermediate 4 because the reaction was followed by cyclization into indazole 3 (48%).We therefore suggest the direction of heterocyclization to be different in the absence of the base because the amine nitrogen atom is a stronger nucleophile than the amide one.Indeed, heating of 7a in DMF in the presence of CuI at 120 °C gives indole 8a in 75% yield (Scheme 3). Thus, we have demonstrated the possibility of cross-coupling 1-alkynes and their acetylides with N-(o-iodophenyl)hydrazine and a-N-(o-iodophenyl)-b-N-(acetyl)hydrazine to produce condensed heterocyclic systems in a one-pot reaction: 1.The condensation of a-N-(o-iodophenyl)-b-N-(acetyl)- hydrazine with substituted copper(I) arylacetylides in DMF proceeds with the formation of a pyrrole ring and leads to the corresponding indoles. This is a new method for synthesising 2-substituted indoles. The same compounds are obtained by the cyclization of a-N-[(o-arylacetylenyl)phenyl]-b-N-(acetyl)- hydrazine in DMF in the presense of CuI.‡ 8a: mp 287.5–288 °C (from EtOH); 1H NMR (CDCl3) d: 1.52 and 2.22 [s, 3H, =C(OH)CH3 and COCH3], 6.83 and 6.95 (s, 1H, H-3 and H-3'), 7.2–8.45 (m, 8H, arom. H); IR (CHCl3, n/cm–1): 1340 and 1510 (NO2), 1680 (C=O), 3200, 3380 (br., NH, OH). 8b: mp 216–217 °C (from EtOAc); 1H NMR (CDCl3) d: 1.55 and 2.10 [s, 3H, =C(OH)CH3 and COCH3], 6.65 and 6.75 (s, 1H, H-3 and H-3'), 7.10–8.25 (m, 9H, arom.H); IR (CHCl3, n/cm–1): 1710 (C=O), 3230, 3400 (br., NH, OH). 8c: mp 193–194 °C (from EtOAc); 1H NMR (CDCl3) d: 1.53 and 2.12 [s, 3H, =C(OH)CH3 and COCH3], 3.83 and 3.85 (s, 3H, OCH3 and OCH3 ' ), 6.55 and 6.65 (s, 1H, H-3 and H-3'), 6.9–8.1 (m, 8H, arom. H); IR (CHCl3, n/cm–1): 1040 (OCH3), 1705 (C=O), 3250, 3390 (br., NH, OH).§ 9: mp 123–125 °C (from EtOAc); 1H NMR (CDCl3) d: 2.75 (s, 3H, CH3), 4.41 (s, 2H, CH2), 7.3–7.6 [m, 5H, H(b,b',4,5,6)], 8.17 [d, 2H, H(a,a'), J 11.25 Hz], 8.46 (d, 1H, H-7, J 8.4 Hz); IR (CHCl3 n/cm–1): 1350 (and 1330) and 1530 (NO2), 1720 (and 1710) (C=O). ¶ 7a: mp 165–166 °C (from EtOH–benzene); 1H NMR (CDCl3) d: 2.15 (s, 3H, CH3), 6.8–7.62 (m, 6H, H-2,3,4,5,2',6'), 8.20 (d, 2H, H-3',5', J 8.6 Hz); IR (CHCl3, n/cm–1): 1350 and 1530 (NO2), 1710 (C=O), 2220 (CºC), 3450 (br., NH). 2. The cyclocondensation of a-N-(o-iodophenyl)-b-N-(acetyl)- hydrazine with copper(I) acetylides with electron-withdrawing substituents gives 3-substituted isoindazoles under the effect of bases. 3. The Pd–Cu-catalysed cross-coupling of N-(o-iodophenyl) hydrazine with 1-alkynes bearing electron-withdrawing substituents in the presence of base is followed by cyclization to 3-substituted indazoles. This work was supported by the Russian Foundation for Basic Research (grant no. 95-03-08928a).References 1 S. F. Vasilevsky and T. A. Prikhod’ko, Mendeleev Commun., 1996, 98. 2 S. F. Vasilevsky, A. V. Pozdnyakov and M. S. Shvartzberg, Izv. Akad. Nauk SSSR, Ser. Khim., 1985, 1367 (Bull. Acad. Sci. USSR, Div. Chem. Sci., 1985, 34, 1250). 3 E. V. Tretyakov, PhD Thesis., Inst. Chem. Kinetics and Combustion, SB RAS, Novosibirsk, 1997, p. 130. 4 M. I. Terekhova, E. S. Petrov, S. F. Vasilevsky, V. F. Ivanov and M. S. Shvartzberg, Izv. Akad. Nauk SSSR, Ser. Khim., 1984, 923 (Bull. Acad. Sci. USSR, Div. Chem. Sci., 1984, 33, 850). C C NO2 NHNHCOMe N NHCOMe NO2 6 + 2 3 7a N N H2C NO2 i 8a H K2CO3 BunOH CuI DMF Scheme 3 Reagents and conditions: i, N2, Pd(PPh3)2Cl2–CuI, Et3N, 80 °C, 4.5 h. Received: Moscow, 9th April 1998 Cambridge, 11th May 1998; Com. 8/02798F

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Mendeleev Communications Electronic Version, Issue 4, 1998 (pp. 129–168) Thermodynamic state of the laser-induced liquid phase and position of the triple point of carbon Sergei I. Kudryashov,* Aleksander A. Karabutov and Nikita B. Zorov Department of Chemistry, M. V. Lomonosov Moscow State University, 119899 Moscow, Russian Federation. E-mail: serg@laser.chem.msu.su Quasi-equilibrium and metastable (overheated) liquid phases of carbon are formed in the initial stage of the laser irradiation of a graphite target in air and in a vacuum, respectively, with an approximate position of the solid–liquid–vapour triple point of carbon at 1 bar, 4000 K.The problem of the thermodynamic state of carbon, in particular, its liquid phase, under high-power pulsed laser irradiation has hardly been studied to date.Meanwhile, for nonequilibrium laser-induced melting and evaporation of a substance, the thermodynamic theory of stability predicts the appearance of a metastable (overheated) liquid phase1 and, hence, the results of studying physical (optical, thermophysical) properties of a laser-induced graphite melt2,3 should be, albeit cautiously, related to the parameters of the equilibrium liquid phase.Under laser irradiation of a graphite target a liquid phase of carbon is formed through a sequence of heating, melting and evaporation processes as well as oxidation. Our estimates of oxidation (burning) front velocity at the surface of the laserheated graphite target in air were performed using gas dynamics formulae (1) for a collision frequency of gas molecules with the target surface where a is the sticking coefficient of oxygen molecules on a graphite surface (a = 1), b is the oxygen content in air (21%), s is the cross section of a carbon atom on a graphite surface (1.5×10–20 m2), L is the surface atomic layer thickness (3.35×10–10 m), N is the air density at 4000 K (2.5×1024 m–3), V is the average velocity of air species at 4000 K (103 m s–1), and M is the average mass of air species (5×10–26 kg).These estimates exhibited a negligible effect due to the oxidation process (the oxidation velocity value is less than the atomic layer per laser pulse of duration 25 ns). On opposite, heating, melting and evaporation processes are dominant at the laserinduced formation of a liquid phase of carbon occurring via different routes in the phase diagram of carbon depending on the value of external pressure P0 on the target surface (residual gas in vacuum or in air) (Figure 1). Therefore, at the present time, the ambiguity in the determination of the parameters of the solid–liquid–vapour triple point of carbon presented in the literature is the most significant problem for describing the route of formation of the liquid phase of carbon (in the phase diagram of the substance) under conditions of pulse laser irradiation.The points (100 atm, 5000 K)4–7 and (1 atm, 4000 K)8,9 in the phase diagram of carbon are presently assigned to the most probable points of the triple point. We suppose that the graphite target in a vacuum exists under an external pressure P0 of residual gas (i.e. 10–7 torr) and the recoil pressure Prec of laser-evaporated carbon species (in the absence of a ‘graphite–carbon vapour’ equilibrium). The residual gas pressure remains constant with laser heating of the target surface under high vacuum conditions but the recoil pressure, which is equal to approximately one half of the saturated carbon vapour pressure Psat at the given surface temperature T,10 rapidly increases according to the Clausius– Clapeyron equation with growth of evaporation temperature on the target surface.Hence, the graphite target is hardly evaporated on heating with laser radiation, up to the intersection point of the sublimation curve with the P(T) curve; the P(T) curve describes the total pressure of the residual gas in the Knudsen layer and the recoil pressure Prec of carbon vapour at the temperature of the target surface T (Figure 1, curve 1).On further heating of the graphite target with laser radiation, starting from the sublimation curve, one cannot neglect the evaporation of the target, which produces a considerable recoil pressure of carbon vapour on the target surface. The temperature dependence P(T) of the overall pressure of the residual pressure and recoil pressure of carbon vapour is presented in the phase diagram below the sublimation curve.It therefore corresponds to the absence of mechanical equilibrium on the target surface and the co-existence of a metastable (overheated) solid in the gas phase with a nonequilibrium composition (Figure 1, curve 1).When the representative point for the thermodynamic state of the graphite target surface layer moves along the P(T) curve, it asymptotically reaches the curve 0.5Psat(T). The last curve at certain pressure and temperature values crosses the curve of co-existence of the metastable (overheated) phases of solid and liquid for carbon, which continues the corresponding curve of co-existence of the equilibrium phases of the solid and liquid to a region lower than the triple point.Thus the metastable (overheated) phase of liquid carbon is formed on the target surface and its evaporation under laser irradiation follows along the 0.5Psat(T) curve to the spinodal curve of the carbon liquid phase (Figure 1). Different routes of formation of the carbon liquid phase in the case of evaporation in air (P0 = 1 bar) may occur depending on the position of the solid–liquid–vapour triple point for carbon (1 or 100 bar) since the residual gas (air) pressure in the Knudsen layer can exceed the corresponding pressure Ptr of carbon vapour in the triple point.We assume the pressure of the heated air in the near-surface layer of 10–6 m thickness remains constant (1 bar) with the surface temperature growth due to fast (10–9 s) acoustic off-loading of the layer and the increase of the P(T) is mainly concerned with the recoil pressure growth [the P/Pa T/K solid liquid spinodal curve triple point vapour 1 2 Figure 1 The trajectories of the surface layer state in the schematic phase P,T-diagram for the laser heating, melting and evaporation of graphite in a vacuum (1) and in air (2).Voxid = a2bsLN0.25V = absL P0 0.5pMkT (1) P(T) = P0 + Prec = P0 + 0.5Psat(T) (2)Mendeleev Communications Electronic Version, Issue 4, 1998 (pp. 129-168) 0.5Psat(T) term in the expression (2)]. In this case, laser heating and evaporation of the graphite target results in the formation of a quasi-equilibrium phase of the carbon melt on the target surface under an external pressure P(T) > 1 bar.The intersection of the P(T) curve with the curve of liquid–vapour equilibrium takes place near the triple point of carbon [at P(T) = 2 bar according to equation (2)]. Further laser evaporation processes follow the P(T) curve in the region of the metastable (overheated) liquid phase of carbon [P(T) ª 0.5Psat(T) < Psat(T)] up to the spinodal curve for the liquid phase (Figure 1, curve 2).At the present time, it is established that laser-irradiated graphite begins to melt in air at the threshold power density I0 = 0.02 GW cm–2 of laser radiation with a nanosecond duration.3,11 The chaotic arrangement of crystallites in the melting/recrystallisation region of highly-oriented pyrolytic graphite was identified by transmission electron microscopy.11 Interference of the heating (probing) laser radiation observed for angular dependence of the reflection coefficient of the polycrystalline graphite target at power density values above the melting threshold value has also confirmed production of the surface graphite melt layer under the laser irradiation.3 The published data on the parameters of the thermodynamic state of the graphite surface (4000 K, 10 bar)12 within the laser pulse at I0 = 0.02 GW cm–2 are in reasonable agreement with our estimates of the total gas pressure P(T) at this temperature of the target surface (1–2 bar) obtained according to equation (2).The facts presented indicate that laser heating of the graphite target passes through a quasi-equilibrium melting stage of the material at the parameters of the triple point of carbon Ttr ª 4000 K, Ptr < 10 bar.In the present study of the composition of positively charged products of laser thermal evaporation of polycrystalline graphite using a laser setup [laser radiation wavelength 532 nm, pulse energy 5 mJ, pulse duration (FWHM) 25 ns, repetition rate 12.5 Hz] and a time-of-flight mass spectrometer described previously,13 we determined the evaporation temperature of carbon in a vacuum as 4000±1200 K (Figure 2) from the half-width of the Maxwell distribution of primary ion velocities.The thermal emission mechanism of the primary ion yield and the effusive movement of the charged species under a carbon plume pressure lower than 1 bar were assumed for the temperature calculations.The range of I0 (0.01–0.1 GW cm–2) in which the evaporation temperature values were calculated undoubtedly covers the threshold value of the laser power density for the transition of the overheated solid to the overheated liquid in a vacuum, because the last one is close to the I0 value for graphite melting in air (0.02 GW cm–2).Since the curve of co-existence of the overheated solid with the overheated liquid moves (in the phase diagram of carbon) from the triple point almost vertically down, the established value of the evaporation temperature of the overheated substance at 4000±1200 K can be considered as a reasonable estimate for the temperature of the triple point of carbon. Thus, the analysis of the experimental data on the thermodynamic parameters of the laser melting of graphite suggests that the parameters of the triple point of carbon (4000 K, 1 atm) given9 as the result of statistical processing of the whole mass of available published data agree satisfactorily with the data presented in this work.Regarding the method of formation of the liquid carbon phase under the the pulsed laser irradiation of graphite, this position of the triple point of carbon implies that on laser heating of graphite in air the liquid phase is formed under quasi-equilibrium conditions, and when graphite is evaporated in a vacuum, it is formed from the metastable (overheated) solid phase of carbon. References 1 V.P. Skripov, E. N. Sinitsyn, P. A. Pavlov and G.V. Ermakov, Termodinamicheskie svoistva zhidkostei v metastabil’nom sostoyanii (Thermodynamic Properties of Liquids in Metastable State), Atomizdat, Moscow, 1980, ch. 1 (in Russian). 2 D. H. Reitze, H. Ahn and M. C. Downer, Phys. Rev. B, 1992, 45, 2677. 3 S. I. Kudryashov, A. A. Karabutov, V. I. Emelyanov and N. B. Zorov, Mendeleev Commun., 1997, 224. 4 M. J. Basset, J. Phys. Radium., 1939, 10, 217. 5 L.F. Vereschagin and N. S. Fateeva, Zh. Eksp. Teor. Fiz., 1968, 55, 1145 (in Russian). 6 N. S. Fateeva and L. F. Vereschagin, PZhTF, 1971, 13, 157 (in Russian). 7 G. J. Schoessow, Phys. Rev. Lett., 1968, 21, 738. 8 Z. Roshan, Thesis D. Sc. Phys., 1935, Fac. de Paris, no. 2442, Rodstein (in French). 9 E. I. Asinovskii, A. V. Kirillin and A. V. Kostanovskii, Teplofizika Vysokikh Temperatur, 1997, 35, 716 (in Russian). 10 S. I. Anisimov, Ya. A. Imas and G. S. Romanov, Deistvie moshchnogo lazernogo izlucheniya na metally (Effect of High-power Laser Radiation on Metals), Nauka, Moscow, 1970 (in Russian). 11 T. Venkatesan, D. C. Jacobson and J. M. Gibson, Phys. Rev. Lett., 1984, 53, 360. 12 R. Srinivasan, J. Chem. Phys., 1988, 126, 453. 13 S. I. Kudryashov, A. A. Karabutov, N. B. Zorov and Yu. Ya. Kuzyakov, Mendeleev Commun., 1997, 22. Evaporation temperature/K Power density/GW cm–2 104 103 0.01 0.1 1 Figure 2 Evaporation temperature of the polycrystalline graphite versus laser power density. Received: Moscow, 3rd April 1998 Cambridge, 10th June 1998; Com. 8/02793E

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Mendeleev Communications Electronic Version, Issue 4, 1998 (pp. 129–168) On the nature of the intermediate in the Lewis acid-promoted synthesis of dihydroisoquinolines from nitriles and -phenylethyl chloride Electron A. Mistryukov* and Olga N. Sorokina N. D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences, 117913 Moscow, Russian Federation. Fax:+7 095 135 5328 In addition to Lewis acidity, the ability to co-ordinate both reactants is a prerequisite for catalyst activity in the cyclisation reaction of b-phenylethyl chloride and alkyl- or aryl nitriles to dihydroisoquinolines.The known cyclisation reaction of b-phenylethyl chloride to dihydroisoquinolines with nitriles and SnCl4 presents a useful synthetic method.1 In this communication we present our efforts to elucidate the connection between the structure of the nitrile component and the nature of the Lewis acid.Based on the experimental evidence, an attempt is made to rationalize some mechanistic aspects of the reaction, namely, the nature of the intermediate. Two variants of the experimental conditions were used to obtain the results presented below.† (A) Low-boiling acetonitrile was used as excess reactant and solvent and (B) the solvent was phosphorus oxychloride for high-boiling nitriles.As shown in preliminary experiments, the literature procedure for 1 ® 3 conversion is more convenient when run in the solvent POCl3 (Scheme 1). Apart from the ease of end product separation this solvent significantly activates the Lewis acid and may be recovered for repeated use.The results are presented in Table 1. So, the acidity of Lewis catalysts is not directly related to the yield of cyclized products. To explain why some moderately strong acids are active and give cyclic products (entries 1, 2 and 5), but some do not (entries 3, 4, 6) — including the strongest of the acids tested AlCl3 — it is helpful also to consider the specific structure of the ‘reactive’ (entries 1 and 2) and ‘unreactive’ (entries 3 and 4) nitriles.To the same end, also informative are the mechanistic considerations of another synthetic approach to dihydroisoquinolines via b-phenylethylamines (Bishler–Napiralski procedure, Scheme 1, 1 ® 4 ® 3 and 6 ® 5 ® 4 ® 3).2 Obviously, it may be assumed that both synthetic pathways have the same intermediate, nitrilium cation 4, which originates either by dechlorination of imidoyl chloride or alkylation of alkyl nitrile on nitrogen.But this assumption is an oversimplification of the actual process. In fact, in this line of reasoning the best catalyst for conversion of 1 and 2 to nitrylium 4 should be the strongest Lewis acid AlCl3, which, if it bound chlorine to complex anion AlCl4 and thus facilitated the formation of carbonium ion intercepted by nitrile, would immediately give the cyclized product.† Method A. To 20 ml of acetonitrile was added SnCl4 (0.04 mol) gradually with cooling followed by chloride 10 (0.04 mol). After heating at 60–70 °C for 6 h and overnight at room temperature, the reaction mixture was decomposed by water with cooling (40 ml).Pentane was added (40 ml) and then, with cooling, the aqueous layer was saturated with solid KOH. The organic extract (after drying over KOH, filtration through Al2O3 and evaporation) was converted into chloride by the action of 5 ml of trimethyl chlorosilane in 5 ml BuiOH and 10 ml ethyl acetate. After filtration and washing with 10×2 ml of EtOAc the recovered yield was 6.67 g (79%) of 11 as the hydrochloride,2 mp 176– 177 °C. 1H NMR (D2O) d: 1.58 (s, 6H, gem Me), 2.90 (s, 3H, Me), 3.28 (s, 2H, CH2), 7.55–8.13 (m, 4H, aromatic). Method B. To a mixture of 1.16 mol b-phenylethyl chloride (163.5 g, 150 ml) and 1.16 mol acetonitrile (47.6 g, 61 ml) was added 1.16 mol of POCl3 (177.5 g, 105 ml) and, gradually with cooling, 1.16 mol (303.2 g, 133 ml) SnCl4.After gentle reflux for 5 h and overnight at room temperature, 300 ml of ethyl acetate was added. The complex salt was filtered off and washed with 500 ml of the same solvent and 100 ml of diethyl ether. Yield was 465.4 g (95%); to a suspension of this complex in 800 ml of water was added, with cooling, 800 ml of 10 M sodium hydroxide. The base after extraction with diethyl ether and drying over solid NaOH was distilled, bp 100–105 °C/5 mmHg, yield 104.6 g (62%).Chloride mp 198–200 °C. 1H NMR (base, CDCl3) d: 2.23 (s, 3H, Me), 2.47 (t, 2H, Ar–CH2), 3.50 (t, 2H, N–CH2), 7.14 (m, 4H, aromatic); 13C NMR (CDCl3) d: 19.19 (t, Me), 24.87 (t, Ar–CH2), 40.78 (t, N–CH2), 128.57 (q, Ar–C), 136.76 (t, C=N). b Cl N H R + RCN SnCl4 SnCl5 1 2 3 1 + 2 – Cl– (MCln) N C R N Cl– – Cl– (MCln) C(Cl)R 4 5 NHCOR 6 Cl 7 SnCl4 RCN CN O Me SnCl4 8 Cl 9 Me 10 NCR SnCl4 Cl Me N HCl·SnCl4 Me 11 Me Me SnCl4 MeCN a R = Me b R = CH2Ph c R = CH2Cl d R = CH2CH2OMe Scheme 1 ax is the anion in the complex salt.bNo organic basic fraction was isolated after aqueous work-up. cExtensive chlorination of the end product and intermolecular condensation of the starting chloride are the main side reactions.Table 1 The yield of isoquinoline as a function of nitrile structure and Lewis acid. Entry Nitrile Lewis acid Productsa Yield (%) 1 2a SnCl4 3a x = SnCl5 85 2 2b SnCl4 3b x = SnCl5 80 3 2c SnCl4 — 0b 4 2d SnCl4 — 0b 5 2a TiCl4 3a x = TiCl4 + n 60 6 2a ZnCl2 — 0b 7 2a SbCl5 3a x = SbCl6 60c 8 2a AlCl3 — 0bMendeleev Communications Electronic Version, Issue 4, 1998 (pp. 129-168) In reality, this catalyst is completely inactive and the starting chloride 1 may be recovered almost quantitatively after standard work-up. At the same time, AlCl3 smoothly converts amide 6a into isoquinoline 3a, presumably via 4. Thus, it is not only the Lewis acidity of the catalyst which is of importance, but also some other intrinsic property of the metal chlorides used for 1 ® 3 conversion.We believe that this crucial factor is the metal coordination number and the ease of ligand exchange in the transition complex. A logical assumption is that all components of the reaction, i.e., nitrile and chloride, are incorporated into the inner sphere of the metal (7, Scheme 1). Within such a framework, the aluminium chloride complex with nitrile is unable to add another ligand, b-phenyethyl chloride, or to exchange it for one of the chlorides.Also, following the same line of reasoning, the unreactivity of nitrile 2d may be explained by coordination as in 8 or 9. Nitrile 2c is inactive (see entry 3) also by virtue of this ‘wrong’ coordination (on chlorine) or not coordinating at all (reduced nucleophilicity of nitrogen). Interestingly, if the two important parts of the isoquinoline molecule are assembled together as in 4, aluminium chloride and all the other chlorides in Table 1 are effective as cyclisation catalysts. References 1 M. Lora-Tamayo, R. Madronerob and G. G. Munoz, Chem. Ber., 1960, 93, 289. 2 V. C. Schclyaev, B. B. Alexandrov, M. I. Vihrin and G. I. Lagotkina, Khim. Geterotsikl. Soedin., 1987, 806 (in Russian). Received: Moscow, 27th March 1998 Cambridge, 11th May 1998; Com. 8/02403K

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Mendeleev Communications Electronic Version, Issue 4, 1998 (pp. 129–168) Dechlorination of carbon tetrachloride in water on an activated zinc surface Tatiana N. Boronina,*a Kenneth J. Klabundeb and Gleb B. Sergeeva a Department of Chemistry, M. V. Lomonosov Moscow State University, 119899 Moscow, Russian Federation. Fax: +7 095 939 0283; e-mail: tbor@cryo.chem.msu.su b Department of Chemistry, Kansas State University, KS 66506 Manhattan, USA.Fax: +1 913 532 6666; e-mail: kenjk@ksu.edu Bimetallic enhancement with Pd, Ag and Au, or mechanical and cryochemical treatment, are shown to increase Zn(0) surface reactivity towards carbon tetrachloride in water and to promote both dechlorination and conversion into methane and other hydrocarbons. The use of zero-valent metals for in situ conversion of onerous water contaminants, such as carbon tetrachloride (CCl4), trichloroethylene (TCE), etc., into hydrocarbon and other non-toxic products has emerged lately as an important area of environmental chemistry.1–4 Chlorocarbon dechlorination in water by zero-valent metals is a heterogeneous processes in which the surface plays an important role.1,2,5–8 Commercial Zn(0) dust converts CCl4 via chloroform and methylene dichloride into methyl chloride and methane, though methylene dichloride degrades about two orders of magnitude slower than CCl4.9,10 Mechanical grinding or striking,11 preparation of metal particles by cryo-condensation,12 or doping with a second metal13,14 are known to create a chemically active surface.Herein we employed Zn(0) activated by cryochemical or mechanical treatment or doping with Pd, Ag and Au in an attempt to enhance the surface performance toward CCl4 in water and to promote dechlorination and conversion into methane and other hydrocarbons.† Activated zinc surface reactivity towards CCl4 in water.The observed first-order kinetic constant kI obs for CCl4 degradation and the CCl4 :methane ratio were used to compare zinc particle reactivity in reactions with identical initial conditions (Table 1).The kI obs value is known to increase with the amount of metal, specific surface area and active site concentration.2,4 CCl4 was shown to degrade in water in the presence of Zn dust.9,10 The methane concentration was gradually increased over time.10 Methane evolution was dramatically enhanced on the activated metal particles during the first few hours.The CCl4 degradation rate was also significantly raised by doping with Pd or Ag and cryo treatment. Cryo zinc exhibited a lower reactivity † Experimental. Distilled, argon-purged water, carbon tetrachloride of spectranalytical grade and Zn(0) dust of certified grade (Fisher) were used.Mechanically activated zinc was prepared by pressing zinc dust at 2000 psi into pellets 5 mm in diameter and 0.025 g in weight. Zinc cryoparticle (cryo) was obtained by co-deposition of zinc and pentane vapours at 77 K, followed by warming to room temperature and solvent evaporation.12 Bimetallic enhancement was performed by deposition of silver, palladium or gold from the salts AgNO3, 99.9% (Fisher), K2PdCl4 and AuCl3 99.99% (Aldrich) on a zinc surface via the red-ox reaction in water.14 Kinetics of CCl4 dechlorination by zinc systems in water were studied using a 1–1.5 fold excess of metal.Experiments were carried out in 40 ml glass amber vials, capped with Teflon Mininert valves. Each vial contained 28 ml of 0.9–1.0 mM CCl4 water solution. The initial pH (no buffer) ranged from 6.10 to 6.20.Zinc dust, 0.1–2.2 g (cryo or pellets, 0.11 g) was added to the cooled solution. To achieve the required loading of silver or palladium, ca. 2.14 and 1.1 mol%, zinc dust was followed by an aliquot of aqueous AgNO3 or K2PdCl4. Vials were mixed at 60 rpm at room temperature and sampled at certain intervals of time. The reaction time varied from 10 to 120 h.Chlorocarbons were analysed with a direct water or headspace injection on a Perkin-Elmer Auto System Gas Chromatograph/Q-Mass 910 Mass Spectrometer and methane on a GOW-MAC GC.6 Hydrocarbon identification was performed on a Headspace Analyser Varian Star 3600CX GC (FID) Automatic System and a PLOT capillary column.10 Experiments were carried out in 22 ml vials for the Headspace analysis, containing 0.5 g of zinc dust or cryo in 5 ml of 0.5 mM CCl4 water solution at 32 °C without mixing.Deposition of ca. 0.1 mol% of Ag, Pd or Au was carried out before injecting CCl4 stock solution. which one would expect, given its large specific surface area: 5.23 m2 g–1 compare to 0.243 m2 g–1 for dust. We put the surface active site deactivation down to oxide formation, and/or a parallel reaction with water.10 Pellets showed a lower kI obs value than dust, although it is not clear how to account for a pellet mass which actually participates in the reaction.Products and possible reaction pathways of CCl4 degradation in water by activated zinc. The reaction products are summarized in Table 2. Chloroform and methylene dichloride were intermediate products in all reactions studied.This, together with methyl chloride and methane as the final products, pointed towards stepwise CCl4 dechlorination. This pathway was proposed to be similar to the reductive hydrogenolysis initiated by electron transfer.2,15 However, the following experimental facts suggested a multiple parallel– sequential reaction pathway: i, methane evolution overtook methyl chloride; ii, acetylene formed on the dust; iii, traces of DCEs (0.5 mol% of the initial CCl4 concentration) appeared on the dust resulting from a parallel methylene dichloride degradation pathway; iv, TCE, 1,1-DCE and 1,2-DCE formed on cryo zinc and pellets (up to 5%), where DCEs might be the products from either TCE sequential dechlorination and/or from another reaction pathway; v, ethane, ethylene, acetylene C4–C6 hydrocarbons (1–3%), and TCE and DCEs (5%) were observed on bimetallic systems.The results reported here have shown that bimetallic enhancement and cryo and mechanical treatment affect the zinc surface reactivity, increase the reduction rate and alter the priority of the reaction pathways in a favour of those leading to C2 compounds and methane.The methods of surface activation used in the present study facilitate the initial electron transfer step which we believe is rate determining. As regards the pathways, C–Zn bond formation and a possible catalytic effect of Pd, Au and Ag might be considered, since the high reactivity of cryo metals in organometallic synthesis, and successful chlorocarbon dehydrohalogenation using a Pd/H2 catalyst,12,15 have previously been reported.Direct chlorocarbon hydrogenolysis on a zinc surface with metal or metal/H2 serving as a reactant or, in bimetallic systems, as a catalyst, could yield methane and C2 hydrocarbons, or carbide formation followed by hydrolysis would yield acetylene. The latter on Zn/Pd appeared to be an intermediate product and was subsequently reduced to ethylene and ethane or underwent coupling reactions yielding C4–C6 hydrocarbons. Table 1 Zinc system reactivity towards carbon tetrachloride in water. Zinc particle kind and mass CCl4 degradation rate, kI obs /h–1 CCl4 conversion into methane (%) dust 0.1 g 0.026±0.003 14.5 (120 h) 1.2 (2.5 h) cryo 0.1 g 0.084±0.006 27.3 (120 h) 18.0 (2.5 h) pellets 0.1 g 0.015±0.001 31.3 (120 h) dust 2.2 g 0.538±0.081 2.5 (4 h) dust 2.2 g/0.1 mol% Pd 4.2±0.3 12.0 (4 h) dust 2.2 g/2.1 mol% Ag 2.5±0.2 24.0 (4 h)Mendeleev Communications Electronic Version, Issue 4, 1998 (pp. 129-168) The support of the Hazardous Substance Research Centre at Kansas State University is acknowledged. References 1 R. W. Gillham and S. F. O’Hannesin, Ground Water, 1994, 32 (6), 958. 2 L. J. Matheson and P. G. Tratnyek, Environ. Sci. Technol., 1994, 28, 2045. 3 E. L. Appleton, Environ. Sci. Technol./News, 1996, 30, 536A. 4 T. L. Jonson, M. M. Scherer and P. G. Tratnyek, Environ. Sci. Technol., 1996, 30, 2634. 5 D. R. Burris, T. J. Campbell and V. S. Manoranjan, Environ. Sci. Technol., 1995, 29, 2850. 6 W. S. Orth and R. W. Gillham, Environ. Sci.Technol., 1996, 30, 66. 7 R. M. Allen King, R. M. Halket and D. R. Burris, Environ. Toxicol. Chem., 1997, 16, 424. 8 T. J. Campbell, D. R. Burris, A. L. Roberts and J. R. Wells, Environ. Toxicol. Chem., 1997, 16, 625. 9 T. N. Boronina, K. J. Klabunde and G. B. Sergeev, Environ. Sci. Technol., 1995, 29, 1511. 10 T. N. Boronina, I. Lagadic and K. J. Klabunde, Environ. Sci. Technol., 1998, in press. 11 V. A. Radzig, Kinet. Katal., 1978, 19, 713 [Kinet. Catal. (Engl. Transl.), 1978, 563]. 12 K. J. Klabunde, Free Atoms, Clusters, and Nanoscale Particles, Academic Press, New York, 1994. 13 C. G. Schreier and M. Reinhard, 209th Natl Meet.-Am. Chem. Soc., Div. Environ. Chem., Anaheim, CA, April 1995, 35 (1), 745. 14 R. Muftikian, K. Nebesny, Q. Fernando and N. Korte, Environ. Sci. Technol., 1996, 30, 3593. 15 L. T. Bryndzia, Environ. Sci. Technol., 1996, 30, 3642. a1,2-Dichloroethylene. bEthane, ethylene, acetylene and solid products were not analysed. c1,1-Dichloroethylene. Table 2 Products identified upon CCl4 dechlorination in water by zinc (in all reactions CHCl3 and CH2Cl2 were intermediate products). Zinc metal system Products identified Dust CH4, C2H2, CH3Cl, ZnCl2, Zn(OH)2, traces of trans-, cis- 1,2-DCEa Cryo the same + H2, TCE Pelletsb the same + H2, TCE, 1,1-DCEc Dust/Pd H2, CH4, C2H6, C2H4, C2H2, C4, CH3Cl, ZnO Dust/Ag CO2, CH4, C2H6, C2H4, C2H2, CH3Cl, 1,1-DCE, TCE, ZnO Dust/Aub CH4, C2H6, C2H4, C2H2, CH3Cl Pellets/Pdb H2, CH4, CH3Cl Pellets/Agb CO2, CH4, traces of 1,1-DCE, CH3Cl Received: Moscow, 24th March 1998 Cambridge, 1st May 1998; Com. 8/02399I

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年代:1998

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Mendeleev Communications Electronic Version, Issue 4, 1998 (pp. 129–168) Enzymatic determination of - and -naphthols using peanut peroxidase Nailya A. Bagirova,a Tatyana N. Shekhovtsova,*a Elena A. Shopovaa and Robert B. van Huysteeb a Department of Chemistry, M. V. Lomonosov Moscow State University, 119899 Moscow, Russian Federation. Fax: +7 095 939 4675; e-mail: shekhov@chromat.chem.msu.su b Department of Plant Sciences, University of Western Ontario, London, N6A 5B7 Ontario, Canada.Fax: +1 519 661 3935; e-mail: huystee@julian.uwo.ca Novel cationic peanut peroxidase has been used for developing a technique for the determination of a- and b-naphthols based on their differing effect towards enzyme activity in the o-dianisidine oxidation reaction. Cationic peanut peroxidase (CPP) belongs to those plant peroxidases (alfalfa, tobacco) whose isolation and investigation has only been started relatively recently.1–4 We began a systematic study of the inhibitors and substrates of this enzyme and a development of procedures for their determination only 2 years ago;5,6 until that time CPP had not been used in chemical analysis.The data obtained from our recent research has shown that the catalytic activity of CPP in the reactions of aryldiamine (and o-dianisidine, in particular) oxidation with H2O2 is inhibited by phenols (phenol and resorcinol, for example) with redox potentials higher than that of o-dianisidine (1.08, 1.04 and 0.85 V, respectively),7 and phenols with potentials less than that of o-dianisidine (such as pyrocatechol, hydroquinone and pyrogallol with potentials 0.74, 0.71 and 0.61 V, respectively) are the second substrates of the enzyme.The aim of this work is to study the effect of condensed phenols (a- and b-naphthols, in particular) on the catalytic activity of CPP, and to show the possibility of applying this enzyme in chemical analysis for the determination of these phenols.Studying the influence of a- and b-naphthols on CPP catalytic activity. The reaction of o-dianisidine (3,3'-dimethoxybenzidine) oxidation with H2O2 catalysed by CPP was selected as an indicator for studying the possibility of determining a- and b-naphthols.† The rate of the enzymatic reaction was monitored spectrophotometrically by an increase in solution absorbance because of the formation of coloured products. Studying the effect of naphthols on the CPP catalytic activity has shown that the introduction of b-naphthol causes a decrease in the indicator reaction rate which is inversely proportional to b-naphthol concentration.Kinetic curves of the reaction in the presence of a-naphthol are characterised by the occurrence of an induction period, whose duration is directly proportional to the concentration of a-naphthol, and the slope of the second part of the kinetic curves does not change at different concentrations of a-naphthol (Table 1).So, it has been shown that in spite of the similar structure of the condensed phenols studied, the nature of their effect was different, and might be explained in terms of their redox properties as well as in the case of polyphenols.Thus, b-naphthol having a redox potential higher than that of † Experimental details. Cationic peanut peroxidase (1.11.1.7) was isolated from a medium of cultured cells.8 Aqueous enzyme solutions were obtained by dissolving the enzyme preparation in Tris buffer (pH 7.5). Solutions of o-dianisidine and naphthols (analytical grade reagents from ‘Soyuz Reactive’, Moscow, Russia) were prepared daily by dissolution of accurately weighed amounts in ethanol (working naphthol solutions of lower concentration were prepared by diluting an ethanol solution with water), solutions of H2O2 (Merck) in water.Double distilled and demineralized water was used. Optimum conditions of the indicator reaction:5 Tris-HCl buffer pH 5.0, concentrations of CPP 0.15 nM, o-dianisidine 0.12 mM, H2O2 0.15 mM.The absolute value of the initial rate of the indicator reaction (V0, mMmin–1) was calculated according to the formula: V0 = Dc/Dt = = DA·l/Dt·l·e = tg a/e·l, where c is the concentration of the reaction product; t is the time of the reaction; e is the molar absorbance coefficient; l is the cuvette length, tg a is the slope of a kinetic curve plotted as absorbance vs.time. o-dianisidine (1.09 and 0.85 V, respectively)7 belongs to the CPP inhibitors, and a-naphthol, which is more readily oxidised than o-dianisidine (E = 0.80 V), acts as the second substrate of CPP in the indicator reaction. Using the dilution method9 we have shown that b-naphthol is a reversible inhibitor of CPP. The results of studying the interaction of the inhibitor and enzyme over time have also confirmed the reversible character of the inhibition: the preliminary incubation10 of a b-naphthol solution (3 mM) with CPP for 1 h does not change the extent of its inhibitory effect.The presentation of the experimental data obtained in the coordinates of Lineweaver–Buerck and Dixon11,12 confirmed the mixed nature of the CPP inhibition with b-naphthol.The values of the Michaelis constant are (10.4±0.5)×10–5, (11.3±0.3)×10–5, (13.0±0.3)×10–5 and (14.2±0.3)×10–5 M (at b-naphthol concentrations 2, 4, 6 and 8 mM, respectively), and the inhibition constant is (1.2±0.3) mM. Optimisation of the determination conditions of naphthols. To obtain the optimum conditions for the naphthol determination the dependences of the rate of the indicator reaction on pH and concentrations of o-dianisidine and H2O2 in the presence of a- and b-naphthols were studied. The conditions were considered to be optimum if the inhibitory effect of b-naphthol was a maximum and the duration of the induction period in the presence of a-naphthol was sufficiently long, but did not exceed 3 min.At the same time, the rate of o-dianisidine oxidation starting after the induction period needed to be high enough in the case of a-naphthol.The choice of optimum peroxidase concentration was conditioned by the necessity to maintain a reaction rate convenient for spectrophotometric monitoring. These conditions are as follows: Tris-HCl buffer a b aNaphthol concentration. bThe initial indicator reaction rate.cThe duration of the induction period. Table 1 Dependence of the indicator reaction rate on a- and b-naphthol concentration (n = 3). Naphthol Ca/mM V0 b/mM min–1 tind c /s In the absence of naphthol — 4.27±0.03 — a-Naphthol 0.5 4.30±0.03 36±2 2.5 4.20±0.07 92±5 5.0 4.17±0.07 155±3 b-Naphthol 1.0 3.87±0.07 — 5.0 3.43±0.03 — 10.0 2.83±0.03 — aThe lower limit of analytical concentration. bThe relative standard deviation for naphthol determination at a concentration equal to C1.cThe duration of the induction period/s. dThe naphthol concentration. eThe initial indicator reaction rate/mM min–1. Table 2 Analytical characteristics of the enzymatic determination of naphthols using oxidation of o-dianisidine catalysed by peanut peroxidase.Compound Applicable concentration range/mM Equation of calibration graph C1 a/mM RSDb (%) (n = 3, P = 95%) a-Naphthol 0.5–5.0 tc = 25.52xd + 23.41 0.5 20 b-Naphthol 1.0–10.0 V0 e = –0.08x + 3.81 1.2 15Mendeleev Communications Electronic Version, Issue 4, 1998 (pp. 129-168) pH 4.5–5.0 for b-naphthol and pH 5.0–5.5 for a-naphthol, concentrations: CPP 0.15 nM, o-dianisidine 0.25 mM, H2O2 75 mM.Analytical characteristics of the proposed procedures for the determination of naphthol are presented in Table 2. As the effect of the nature of the naphthol on the catalytic activity of CPP was different, their combined action (at various ratios due to the concentration ranges applicable) on the indicator process was studied. It has been found that the reaction rate in the presence of both a- and b-naphthols (in 1:1–1:10 ratio) was the same as that in the presence of b-naphthol alone, while the induction period was the same as that with a-naphthol alone (Table 3).If the ratio of the naphthol concentrations is more than 1:10 (1:15, for instance), the reaction rate decreases significantly and it is difficult to measure the duration of the induction period.It has therefore been shown that a- and b-naphthols might be determined together in ratios 1:1–1:10. Determination of b-naphthol and a-naphthol using the o-dianisidine oxidation reaction. 7 ml of a 0.05 M Tris-HCl buffer (pH 5.0), 0.05 ml of 30 nM CPP solution and the required volume of standard b-naphthol (or a-naphthol) solution over the concentration range 0.1–1 mM (or 0.05–0.5 mM) were placed sequentially in a glass test-tube fitted with a ground-glass stopper. 0.1 ml of a 25 mM o-dianisidine solution and H2O up to10 ml volume of the reaction mixture in all cases were then added into the same test-tube. Finally, 0.1 ml of a 7.5 mM H2O2 solution was introduced. At the moment when the H2O2 was added and the reaction solution was mixed a stop-watch was started and the absorbance at 440 nm was measured at 15 s intervals for 2 min (or 5 min).The initial rate of the reaction (V0) in the presence of b-naphthol was characterised by the slope of a kinetic curve plotted as absorbance vs. time. The calibration graph for the determination of b-naphthol was plotted as V0 (mM min–1) vs. concentration. In the case of a-naphthol determination the duration of the induction period (tind /s) was determined. The calibration graph for the determination of a-naphthol was plotted as tind vs.concentration. Thus, it can be stated that the nature of the effect of the condensed phenols (as well as polyphenols studied earlier) on the catalytic activity of peanut peroxidase is mainly governed by their redox properties. The fact that a- and b-naphthols belong to different groups of phenols — substrates or inhibitors of CPP — made it possible to elaborate a sensitive procedure not only for their individual determination, but also for the determination of one of them in the presence of the other in different ratios (1:1–1:10). The data obtained show the potential for the application of CPP in chemical analysis for the determination of phenols and isomers, and in particular, inhibitors and substrates (such as a- and b-naphthols) in mixtures of them, without preliminary separation.This work was partially supported by the Russian Foundation for Basic Research (grant no. 97-03-33578a). References 1 R. B. van Huystee, Y. Xu and J. P. O’Donnel, Plant Physiol. Biochem., 1992, 30, 293. 2 M. J. Rodriguez-Maranon, M. J. Stillman and R. B. van Huystee, Biochem. Biophys. Res. Commun., 1993, 194, 326. 3 Y. Xu and R. B. van Huystee, J. Plant Physiol., 1993, 141, 141. 4 M. J. Rodriguez-Maranon, D. Mercier, R. B. van Huystee and M. J. Stillman, Biochem. J., 1994, 301, 335. 5 T. N. Shekhovtsova, N. A. Bagirova and I. G. Gazaryan, International Congress on Analytical Chemistry, Moscow, 1997, p. 16. 6 T. N. Shekhovtsova, N. A. Bagirova, N. V. Tabatchikova and R. B. van Huystee, International Workshop on Peroxidase Biotechnology and Application, St. Petersburg, 1997, p. 13. 7 L. F. Fieser, J. Am. Chem. Soc., 1930, 52, 5204. 8 P. A. Sesto and R. B. van Huystee, Plant Science, 1989, 61, 163. 9 M. Dixon and E. Webb, Enzymes, London Group Limited, London, 1979, p. 550. 10 C. Tran-Minh, Ion-selective Electrode Rev., 1981, 7, 41. 11 T. Keleti, Basic Enzyme Kinetics, Academia Kiado, Budapest, 1990, p. 234. 12 I. V. Berezin and K. Martinec, Mol. Biol., 1971, 5, 347 (in Russian). aThe naphthol concentration. bThe initial indicator reaction rate. cThe duration of the induction period. Table 3 Combined effect of a- and b-naphthol (ratio 1:5) on the indicator reaction rate (n = 3, P = 95%). Naphthol Ca/mM V0 b/mM min–1 tind c /s In the absence of naphthol — 4.20±0.07 — a-Naphthol 0.7 4.07±0.09 40±3 b-Naphthol 3.5 3.67±0.07 — a-Naphthol + b-Naphthol 0.7 3.70±0.08 38±1 3.5 Received: Moscow, 16th March 1998 Cambridge, 16th April 1998; Com. 8/02196A

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Mendeleev Communications Electronic Version, Issue 4, 1998 (pp. 129–168) Synthesis and unusual rearrangement of 2-organyl-4,4,6,6-tetramethyl-5-chloro- 6 5-sila- 2-dihydro-1,3,4 4-oxadiazinium chlorides Boris A. Gostevskii, Ol’ga B. Kozyreva, Vadim A. Pestunovich,* Yurii A. Chuvashev, Valentin A. Lopyrev and Mikhail G. Voronkov Irkutsk Institute of Chemistry, Siberian Branch of the Russian Academy of Sciences, 664033 Irkutsk, Russian Federation.Fax: + 7 3952 35 6046; e-mail: vadim@irioch.irk.ru The reactions of O-TMS derivatives of 1,1-dimethylhydrazides of trifluoroacetic and benzoic acids with Me2Si(CHCl2)Cl give 2-organyl-4,4,6,6-tetramethyl-5-chloro-6l5-sila-D2-dihydro-1,3,4l4-oxadiazinium chlorides which in CDCl3 solution exhibit unexpected decomposition with the formation of Me2SiCl2, DMF and the corresponding organylcyanide.A recent study of 2-organyl-4,4,6,6-tetramethyl-6l5-sila-D2- dihydro-1,3,4l4-oxadiazinium chlorides 1 showed that these six-membered silaheterocycles, of unusual zwitterionic structure with coordinative Si�Cl bonds, are unstable and isomerize on melting or heating and prolonged storage in solution to fivemembered (O–Si)chelate dimethyl[2-(1,1-dimethyl-2-acylhydrazino) methyl]chlorosilanes 2 via a Vavzonec-type rearrangement1 –3 (Scheme 1): We have now succeeded in preparing two 5-chloroderivatives of compounds 1, 2-trifluoromethyl- and 2-phenyl- 4,4,6,6-tetramethyl-5-chloro-6l5-sila-D2-dihydro-1,3,4l4-oxadiazinium chlorides 3a,b, from the reactions of dimethyl- (dichloromethyl)chlorosilane with an equimolar amount of the O-TMS derivative of 1,1-dimethylhydrazides of trifluoroacetic and benzoic acids, respectively† (Scheme 2): Hypervalent silicon chiral heterocycles 3a,b gave satisfactory elemental analyses and the expected NMR spectra.‡ Thus, pentacoordination at the silicon atom in 3a,b is revealed by a strong (by 58 ppm) high field shift of their 29Si NMR signals with respect to those observed in the spectrum of the parent tetracoordinated compound, ClMe2SiCHCl2. The chirality of the C-5 atom results in diastereotopy of the methyl groups at the N-4 and Si atoms, as detected by 1H and 13C NMR † Synthesis of 2-trifluoromethyl- and 2-phenyl-4,4,6,6-tetramethyl- 5-chloro-6l5-sila-D2-dihydro-1,3,4l4-oxadiazinium chlorides.A mixture of 1,1-dimethylhydrazone of trimethylsiloxy-2,2,2-trifluoroethanone4 (3.82 g, 16.7 mmol) and dimethyl(dichloromethyl)chlorosilane (3.35 g, 18.9 mmol) in 30 ml of dry diethyl ether was kept for 8 h in an evacuated sealed ampoule at room temperature.The solvent and volatile compounds were then evaporated in vacuo and the residue was recrystallized from dry diethyl ether and dried in vacuo.The yield of 3a was 2.76 g (55.5%), mp 93 °C (evacuated capillary). Compound 3b was prepared similarly from the reaction of ClMe2SiCHCl2 with O-trimethylsilylated 1,1-dimethyl-2-benzoylhydrazine5 in dry Et2O in 89% yield, mp 101.5 °C (evacuated capillary). spectroscopy, though two Me2Si proton singlets are broadened at ambient temperature and coalesce at higher temperature perhaps due to dissociation–association and pseudorotation at trigonal-bipyramidal silicon.6 Finally, the ammonium character of the N-4 atom provides high values of the 1H and 13C NMR chemical shifts in the NMe2 fragments.Heterocycles 3a,b are also thermodynamically unstable but the direction of their spontaneous transformation in solution differs drastically from that observed for the progenitor compounds 1a,b which have no C–Cl bond.In CDCl3 5-chlorosubstituted derivatives 3a,b undergo an unusual rearrangement decomposition to yield dimethyldichlorosilane, N,N-dimethylformamide (DMF) and the nitrile of the corresponding carboxylic acid. These compounds were detected by NMR and GLC-MS spectroscopy§ as the exclusive and major (70% yield) products of the decay of heterocycles 3a and 3b, respectively.From the NMR monitoring data, the half-life of compounds 3a,b at room temperature is about 3 days. The mechanism of the decomposition of compounds 3a,b cannot be established unambiguously at this time. It can be preliminary described as a total combination of various concerted acts (Scheme 3): These involve the heterolytic cleavage of the N–N+ and C–O bonds, formation of a covalent Si–C bond and insertion of the oxygen atom into the endocyclic Si–C bond leading to formation of the corresponding organonitrile and unobserved, transient dimethyl[(N,N-dimethylamino)chloromethoxy]chlorosilane 4 which yields DMF and dimethyldichlorosilane from a fast ‡ The NMR spectra were run for 20% solutions of compounds in CDCl3 in evacuated sealed NMR tubes on a JEOL FX 90Q spectrometer.TMS was used as internal standard. 13C and 29Si NMR spectra were recorded with proton decoupling, the latter being obtained by use of the INEPT pulse sequence. Compound 3a: 1H NMR (–20 °C) d: 0.74 and 0.90 (s, 6H, Me2Si), 3.57 and 3.62 (s, 6H, NMe2), 5.61 (s, 1H, CHCl); 13C NMR d: 8.4 and 8.8 (Me2Si), 52.7 and 55.5 (NMe2), 80.4 (CHCl), 116.9 (q, CF3, 1JCF 283.7 Hz), 159.1 (q, CO, 1JCF 37.7 Hz); 29Si NMR d: –40.2.Compound 3b: 1H NMR d: 0.86 and 1.05 (s, 6H, Me2Si), 3.67 and 3.73 (s, 6H, NMe2), 6.06 (s, 1H, CHCl), 7.4–8.0 (m, 5H, Ph); 13C NMR d: 6.9 and 8.0 (Me2Si), 52.4 and 57.3 (NMe2), 77.4 (CHCl), 127.5 (C-2',6'), 128.0 (C-3',5'), 131.1 (C-1'), 132.0 (C-4'), 164.5 (CO); 29Si NMR d: –36.1. § Mass spectra of the products of decomposition of 3a,b were detected on a Hewlett-Packard instrument equipped with a HP 5890 chromatograph and a HP 5971A mass-selective detector. l D l N Me2N Si O R Me Me Cl 1 Me2NN Si O R Me Me Cl 2 Scheme 1 N Me2N Si O R Me Me H Cl N Me3SiO R Me2N + ClMe2SiCHCl2 – Me3SiCl Cl 3a R = CF3 3b R = Ph Scheme 2 N Me2N Si O R Me Me H Cl Cl 3 RCN 4 Scheme 3 Me2NCHClOSiMe2Cl Me2NCHO + Me2SiCl2Mendeleev Communications Electronic Version, Issue 4, 1998 (pp. 129-168) b-decomposition. However, the rearrangement of the transition species, Me2NCHClSi(O+)Me2Cl–, into 4 raises doubts. Owing to the more nucleophilic nature of the methyl carbon than that of an endocyclic Ca, this rearrangement should instead lead to a stable product, Me2NCHClSiMe(OMe)Cl. The second and more probable scheme for the decomposition of 3a,b might involve the double migration of an O atom from Si to Ca and a Cl atom from Ca to Si with the aid of chloride ion, with concerted or subsequent heterolytic cleavage of the N–N+ and C–Si bonds in the resulting transition complex (Scheme 4): The proposed 1,2-sigmatropic shift resembles the well-known fluorine-induced relay of the nucleophile from silicon to its adjacent carbon in thermodynamically controlled reactions of the nucleophilic substitution of ClSiMe2CH2Cl with PhEH (E = O or NMe).7 A more detailed study of compounds 3 is in progress.The authors are grateful to the Russian Foundation for Basic Research (grant no. 96-03-32718) and the International Science and Technology Centre (grant no. 427) for financial support. References 1 I. D. Kalikhman, V. A. Pestunovich, B. A. Gostevskii, O. B. Bannikova and M. G. Voronkov, J. Organomet. Chem., 1988, 338, 169. 2 A. A. Macharashvili, V. E. Shklover, Yu. T. Struchkov, B. A. Gostevskii, I. D. Kalikhman, O. B. Bannikova, V. A. Pestunovich and M. G. Voronkov, J. Organomet. Chem., 1988, 340, 23. 3 A. A. Macharashvili, V. E. Shklover, Yu.T. Struchkov, B. A. Gostevskii, I. D. Kalikhman, O. B. Bannikova, V. A. Pestunovich and M. G. Voronkov, J. Organomet. Chem., 1988, 356, 23. 4 I. D. Kalikhman, E. N. Medvedeva, O. B. Bannikova, N. G. Fabina, M. F. Larin, V. A. Lopyrev and M. G. Voronkov, Zh. Obshch. Chem., 1984, 54, 477 (Chem. Abstr., 1984, 101, 55156). 5 I. D. Kalikhman, O. B. Bannikova, L. I. Volkova, B. A. Gostevskii, T. I. Yushmanova, V. A. Lopyrev and M. G. Voronkov, Izv. Akad. Nauk SSSR, Ser. Khim., 1988, 460 (Bull. Acad. Sci. USSR, Div. Chem. Sci., 1988, 37, 378). 6 Vad. V. Negrebetsky, A. G. Shipov, E. P. Kramarova, V. V. Negrebetsky and Yu. I. Baukov, J. Organomet. Chem., 1997, 530, 1 and references cited therein. 7 J. Eisch and C. S. Chiu, J. Organomet. Chem., 1988, 358, C1. N Me2N Si O R Me Me H Cl Cl 3 Scheme 4 N O R Me2N Cl Si H Me Me Cl RCN + Me2NCHO + Me2SiCl2 Received: Moscow, 12th March 1998 Cambridge, 1st May 1998; Com. 8/02184H

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摘要:

Mendeleev Communications Electronic Version, Issue 4, 1998 (pp. 129–168) Low-temperature radiation polymerization of cyanogen bromide Galina A. Kichigina,* Pavel S. Mozhaev, Dmitriy P. Kiryukhin and Igor M. Barkalov Institute for Problems of Chemical Physics, Russian Academy of Sciences, 142432 Chernogolovka, Moscow Region, Russian Federation. Fax: +7 096 515 3588 The absence in crystalline cyanogen bromide of intermolecular chains with strong N···H hydrogen bonds typical of the HCN crystal causes a difference in cryopolymerization in these monomers.Heat release is observed during defrosting of radiolysed cyanogen bromide, connected with its polymerization at 220–230 K. There is another heat release due to polymerization of cyanogen bromide in the melting region.The dependence of the yield of the polymer forming in the melting regions on the irradiation dose has an extreme character. We assume that the suppression of the polymerization of cyanogen bromide in the melting region is connected with progressive destruction of the matrix structure during irradiation. Radiation-induced cryochemical conversion of solid hydrogen cyanide, its polymerization and copolymerization are described in refs. 1–3. Hydrogen cyanide is converted into a polymer more effectively in its copolymerization with acetaldehyde and ethylene oxide.4,5 Radiolysis of solid HCN at 77 K leads to stabilization of the active centres of the radical and its ionic nature (for more details see refs. 6–9). Further heating of the system in the solid phase leads to formation of a conjugate polymer of the –[HC=N]n– type8,9 and tetramer crystals (1,2-diaminomaleinodinitrile).3 The forming polymer gives a singlet EPR spectrum typical of polyconjugate systems, its molecular mass being M = 1540±50.7,9 According to the literature,10 the tetragonal crystal structure of HCN possesses intermolecular chains bound by strong N···H hydrogen bonds of the ‘head-to-tail’ type, which leads to a weakening of the C···N interactions.In this connection it is assumed that the most probable reaction during radiolysis of HCN crystals is elimination of a proton and formation of a complex with a neighbouring molecule, [HCN···H]+. An electron settling on this complex results in the formation of a H2C=N· radical. We thus assume that the main intermediate particle that is stabilized during low-temperature radiolysis of the HCN crystal is a complex cation of the [HCN···H]+ type.6 This probably determines the main direction for all subsequent cryochemical conversions.Since there are no hydrogen bonds in cyanogen bromide, it would be of interest to compare the tendency to cryopolymerization of this compound and hydrogen cyanide.The aim of the present work is to investigate the lowtemperature radiation-induced polymerization of cyanogen bromide.† Radiolysis of crystalline cyanogen bromide at 77 K leads to an accumulation of stabilized active centres in it. The radiation yield of these centres, determined from the initial section of the accumulation curve, is G = 7.8 which almost coincides with the radiation yield for the accumulation of paramagnetic centres in hydrogen cyanide under the same conditions.8 The calorimetric curve for cyanogen bromide heating from 80 K shows only an endothermic peak due to the monomer crystals melting at 324 K (Figure 1, curve 1).The melting heat is DH = 11.6 kJ mol–1. A small heat release peak is observed during defrosting of radiolysed cyanogen bromide, which is connected with its polymerization in the temperature range 220–230 K.In the course of further heating in the premelting and melting regions, the calorimeter also shows heat release † Experimental details. The preparation and purification of cyanogen bromide has been described.11 Its major characteristics are as follows: mp 50–51 °C, bp 61 °C. The phase state of the system and the kinetics of cryopolymerization were studied by a calorimetric technique.12 Radiolysis of the samples examined was performed in a vacuum in calorimetric sealed ampoules at 77 K using a ‘Gamma-tok’ set-up with 60Co g-rays, dose rate 1.4 Gy s–1.The dose rate was measured by an ionisation chamber and the ferrosulfate method. The EPR spectra of the free radicals were recorded on an EPR-21 radiospectrometer at 77 K.IR absorption spectra in the range 400–3600 cm–1 were recorded on a UR- 20 spectrometer. The IR samples were prepared as KBr pellets. due to polymerization of cyanogen bromide (Figure 1, curve 2). Such a picture emerges only for doses of preirradiation £ 1 MGy. At larger doses heat release is observed only in the range 220–230 K, while the heat release in the premelting region is lost.After defrosting, the unreacted cyanogen bromide is removed in vacuo, and the polymer yield is determined gravimetrically. A series of calorimetric measurements of the sort given in Figure 1 and gravimetric measurements of the polymer yield after defrosting give a mean specific heat for polymerization of cyanogen bromide, DH = 86±2 kJ mol–1.This value is close to that for the cryopolymerization of hydrogen cyanide, DH = 85 kJmol–1.5 The isolated polymer is orange–red in colour, which is typical of conjugated systems. The polymer is unstable and decomposes during storage at room temperature. The IR spectrum of the cyanogen bromide polymer, as distinct from the IR absorption spectra of the initial monomer, has no absorption band ns CºN at 2180 cm–1, while a band due to the C=N bond vibration appears at 1700 cm–1.The dependence of the polymer yield on the preirradiation dose is given in Figure 2. It has an unusually extreme view. In the dose range 0–980 kGy, the polymer yield increases monotonously reaching a maximum value of ~9% at 980 kGy. The polymer yield of hydrogen cyanide under the same conditions is considerably lower, ~2.5% at a dose of 800 kGy.1 Further increase of the dose leads to a yield reduction down to ~4% at 1.2 MGy, which remains practically unchanged up to a dose of 2 MGy (Figure 2).Assuming that all the isolated 1 0 –1 –2 –3 –4 –5 –6 200 250 300 350 T/K Heat power/10–2 W g–1 Figure 1 Calorimetric heating curves for cyanogen bromide: (1) unirradiated and (2) g-irradiated at 77 K with a dose of 980 kGy. 1 2Mendeleev Communications Electronic Version, Issue 4, 1998 (pp. 129-168) polymer forms in a subsequent stage during further defrosting of the irradiated sample, the extreme character of the dependence of the polymer yield on the dose should be connected with a superposition of the two different polymerization processes. As seen from Figure 1, cyanogen bromide polymerizes in two significantly different temperature regions, which may be caused by different types of initiating centres.The fact that the calorimetric measurements are performed for the sample preirradiated with different doses of g-radiation makes it possible to obtain the dependence of the polymer yield on the dose against the measured heat release in different temperature regions (regions of the proposed phase transition and melting).The dependences obtained so far are given in Figure 2 (curves 2 and 3). It is evident that with an increase in the preirradiation dose, the yield of the polymer forming in the low-temperature region quickly reaches its maximum value of ~1.5%, which does not change even at very high doses (Figure 2, curve 2).The dependence of the yield of the polymer forming in the premelting and melting regions on the irradiation dose has an extreme character (Figure 2, curve 3). It should be noted that a maximum value of the polymer yield and then a decrease are observed in the region of very high doses when the crystal matrix structure is already sufficiently disturbed.We assume that the suppression of the polymerization of cyanogen bromide in the melting region is connected with destruction of the crystal matrix during the radiation. Such radiation-induced destruction may lead to a sufficiently sharp increase in the molecular mobility in this temperature region.13 The result of such changes may be an increased rate of termination of the polymer chains, which leads to a degradation of the chain process, hence to a decrease in the polymer yield. Thus, the absence in the cyanogen bromide crystal of intermolecular chains with strong N···H hydrogen bonds typical of the HCN crystal causes a difference in the cryopolymerization dynamics between these two monomers.It is very probable that the low thermal stability of the polymer, as distinct from the polymer of hydrogen cyanide, is also connected with the absence of ‘reinforcing’ hydrogen bonds between macromolecules in the polymer of cyanogen bromide.This work was financially supported by the Russian Foundation for Basic Research (grant no. 96-03-32271). References 1 P. S. Mozhaev, D. P. Kiryukhin, G. A. Kichigina and I. M. Barkalov, Mendeleev Commun., 1994, 17. 2 P. S. Mozhaev, G. A. Kichigina, D. P. Kiryukhin and I. M. Barkalov, Khim. Vys. Energ., 1995, 29, 19 [High Energy Chem. (Engl. Transl.), 1995, 29, 15]. 3 P. S. Mozhaev, G. A. Kichigina, Z. G. Aliev, D. P. Kiryukhin, L. O. Atovmyan and I. M. Barkalov, Dokl. Ross. Akad. Nauk, 1994, 335, 747 [Dokl. Phys. Chem. (Engl. Transl.), 1994, 335, 77]. 4 D. P. Kiryukhin, G.A. Kichigina, P. S. Mozhaev and I. M. Barkalov, Vysokomol. Soedin., Ser. A, 1997, 39, 1109 (Polym. Sci. A, 1997, 39, 727). 5 D. P. Kiryukhin, G. A. Kichigina and I. M. Barkalov, Vysokomol. Soedin., Ser. A, 1998, in press. 6 S. I. Kuzina, D. P. Kiryukhin, A. P. Pivovarov, P. S. Mozhaev, A. I. Mikhailov and I. M. Barkalov, Khim. Vys. Energ., 1998, in press. 7 S. I. Kuzina, P.S. Mozhaev, D. P. Kiryukhin, A. I. Mikhailov and I. M. Barkalov, Mendeleev Commun., 1996, 34. 8 S. I. Kuzina, P. S. Mozhaev, D. P. Kiryukhin, A. I. Mikhailov and I. M. Barkalov, Khim. Vys. Energ., 1996, 30, 295 [High Energy Chem. (Engl. Transl.), 1996, 30, 267]. 9 S. I. Kuzina, P. S. Mozhaev, D. P. Kiryukhin, A. I. Mikhailov and I. M. Barkalov, Izv. Akad. Nauk, Ser. Khim., 1996, 859 (Russ. Chem. Bull., 1996, 45, 814). 10 J. A. Platts and S. T. Howard, J. Chem. Phys., 1996, 105, 4468. 11 D. H. Gein, Ber., 1934, 67, 1028. 12 I. M. Barkalov and D. P. Kiryukhin, Int. Rev. Phys. Chem., 1994, 13, 337. 13 D. P. Kiryukhin, O. I. Barkalov and I. M. Barkalov, Khim. Vys. Energ., 1995, 29, 271 [High Energy Chem. (Engl. Transl.), 1995, 29, 247]. 10 8 6 4 2 0 500 1000 1500 2000 Polymer yield (%) Dose/kGy Figure 2 Dependence of the polymer yield on the preirradiation dose at 77 K: (1) integral, (2) in the temperature region of premelting and melting for cyanogen bromide and (3) in the temperature region 220–230 K. 1 2 3 Received: Moscow, 20th February 1998 Cambridge, 1st May 1998; Com. 8/01641K

ISSN:0959-9436     

出版商:RSC    

年代:1998

数据来源: RSC

摘要:

Mendeleev Communications Electronic Version, Issue 4, 1998 (pp. 129–168) Drop-spark discharge: an atomization and excitation source for atomic emission sensors Vladimir V. Yagov,* Andrei S. Korotkov, Boris K. Zuev and Boris F. Myasoedov V. I. Vernadsky Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences, 117975 Moscow, Russian Federation. Fax: +7 095 938 2054 Drop-spark discharge (DSD) arising after breakdown in the air gap between two approaching free electrolyte surfaces may be used as an atomization and excitation source for a new optic sensor.Despite the well-known advantages of atomic emission spectroscopy (AES) it is not the usual technique for sensors: routine atomization sources are too large and powerful, and nebulizers are too complicated for the purpose.Nonetheless, due to the high selectivity of AES the possibility of making AES sensors is very attractive. In our opinion, low energy electrical discharges on a free water electrolyte surface are promising sources for this goal. In this case a discharge provides both light emission and sample introduction by sputtering of the electrolyte cathode. Cherfalvi and Mezei1,2 described an analytical application of continuous glow discharge with an electrolyte cathode (ELCAD) and a metal anode.Here we discuss unidirectional discharge in the air gap between a lowering drop and a free water surface. In contrast to ELCAD, drop-spark discharge (DSD) is an impulse source and has no solid/plasma interface. A discharge cell contains two 2.5 mm i.d.glass tubes, one above the other (see Figure 1). Analysing solution (catholyte) was delivered through the lower tube at a flow rate of ca. 3 ml min–1. The anolyte (usually 0.4 M HCl) was added dropwise from the upper tube (3–10 drops per minute). The cell was open to the ambient air. The plates of a 2 mF capacitor were connected with two platinum wire electrodes immersed in catholyte and anolyte, respectively.During discharge the voltage was reduced from 800 V to ca. 600 V; a low power high voltage supplier restored the initial value of the capacitor voltage during a few seconds of intermittence. The emission intensity was detected in the range from 370 to 800 nm with two photomultiplier tubes. Spectral selection was achieved with a monochromator for the first one and with a 589 nm interference filter (band pass 2 nm, transmittance 64%) for the second one. Current and light pulses were recorded with a PC data acquisition board.Time resolution was ca. 30 ms. A scheme of drop motion and light/current response are presented in Figure 1. The discharge started when the distance between the lower surface of a drop and the upper surface of liquid in the lower tube became small enough for breakdown.The latter was accompanied by current and light emission pulses. Thereafter, in a few milliseconds the current was almost constant, whereas light intensity (in particular, the Pb 405.8 nm line in Figure 1) strongly oscillated. The circuit was then shorted out by an elecrolyte bridge, leading to a strong increase in current and termination of light emission (step II).There are at least three kinds of emitters with specific kinetics in DSD: metal atoms, products of water decomposition (H· and HO· radicals) and atmospheric gases. The behaviour of atmospheric gases in DSD is too complex and varied to be described in detail. They create rather intense background emission in the range from 370 to 500 nm.As distinct from other species, N2 and N2 + bands give a very strong short pulse during breakdown. It is an N2 band with a peak at 405.9 nm that is reponsible for the first peak on the light intensity curve in Figure 1. Only the most intense atomic lines can be used for metal determination with DSD, in particular Na 589.0 and 589.6 nm, Ca 422.7 nm, Pb 405.8 nm, Ga 417.2 nm, K 766.4 and 769.9 nm, In 451.1 and 410.2 nm, Tl 535.1 nm, Mg 516–519 nm, Li 670.8 nm.As Figure 2(a) indicates, the intensities of the Na 589 nm and In 451 nm lines pulsed strongly and synchronously, which is common for other metals. The intensity of the H 656, 486 and 434 nm lines do not oscillate as strongly as for metal lines. As Figure 2(b) illustrates, there is no obvious correlation between the pulsations of the H 656 nm and Na 589 nm lines.The difference in emission kinetics for metals and hydrogen appears to be connected with the values of the excitation potential. For hydrogen this value exceeds 12 eV while for the Table 1 Reproducibility of atomic emission intensity, conditions as in Figure 2, n = 55. Integrated intensity Relative standard deviation, sr Na 589 nm 0.048 In 451 nm 0.046 H 656 nm 0.036 Na 589 nm/In 541 nm 0.018 Na 589 nm/H 656 nm 0.048 dilute acid sample current 100 mA light intensity (arbitrary units) I II III 0.1 1.0 10.0 100.0 t/ms + – anode cathode + – Figure 1 Circuit diagram, steps for drop motion (I – discharge, II – short, III – intermittence) and time dependence of current and light intensity. Conditions: 405.8 nm, band pass 2 nm, catholyte 5 mM PbII in 0.4 M HCl.Mendeleev Communications Electronic Version, Issue 4, 1998 (pp. 129-168) above-mentioned metal lines it is < 5 eV. Therefore, hydrogen emits only in the thin cathode layer where excitation conditions are very difficult. It is likely that emission of another species with a high excitation potential may be detected if their concentrations are sufficiently great.In contrast, metals may emit in the positive column which is probably many times greater in size than a cathode layer. The oscillations of metal emission intensity appear to be connected with electrolyte sputtering that leads to a synchronism of the kinetic curves of different metals [see Figure 2(a)]. The fine structure of the kinetic emission curves is clearly not reproducible but the integrated intensity has a modest relative standard deviation, as seen from Table 1.The flow rate and its pulses, breakdown and sputtering instabilities affect the intensity deviations. To minimize these influences it is reasonable to use internal standardization. The most convenient way is to use the hydrogen line, since it is a constant part of the DSD spectrum independent of the content of dissolved salts. Unfortunately the difference between the nature of the metal and hydrogen emission reduces the usefulness of such a standardization.As shown in Table 1, sr does not reduce in this case. A greater effect can be achieved by the use of indium as an internal standard. Table 1 indicates that in this case the relative standard deviation sr does not exceed 0.02.The dependence of integrated intensity on metal concentration for alkaline metals is not linear. As seen from Figure 3, the curves may be straightened in a log-log scale in the concentration range from 10–4 to 10–2 M. The gradient is ca. 0.8 in all instances. That the gradient is less than one may be related to reabsorption.Since the electrostatic energy of the condenser is CU2/2, where C and U are capacity and voltage, respectively, a simple calculation shows that in the case of 10 s intermittence time, C = 2 mF and U = 1000 V, power consumption does not exceed 0.1 W. The estimation is suitable for the DSD source described here with a certain margin (we use U = 800 V). The source can be used for alkaline metal determination, with current detection limits 10–4 M for Li, 2×10–5 M for K and 5×10–7 M for Na.It is possible to reduce the capacity and consequently the power consumption by one order of magnitude, at least for the very intense D-line of sodium. As illustrated in Figure 3, calibration plots for sodium with C = 2 mF (curve 1) and C = 0.25 mF (curve 3) differ only by the shift along the vertical axis. A DSD source with C = 0.25 mF and power consumption of ca. 0.01 W may be used for sodium determination with a detection limit of 10–5 M. Reasonable reproducibility and low power consumption allow us to hope that DSD may be used as a source in AES sensors. The source is not bright and obviously it is not appropriate for trace analysis. One possible application of DSD lies in the monitoring of Na, K, Mg and Ca, which are the major metal components of water in most cases.There are some features of DSD which make it more appropriate for sensors than other kinds of discharges with electrolyte surfaces. Firstly, the absence of solid/plasma interfaces enables the memory effect to be avoided, which is usually caused by erosion and contamination of electrodes.Secondly, the breakdown apparently provides more effective electrolyte sputtering than in the case of continuous discharges. References 1 T. Cherfalvi and P. Mezei, J. Anal. Atom. Spectrom., 1994, 9, 345. 2 T. Cherfalvi and P. Mezei, Fresenius’ J. Anal. Chem., 1996, 355, 813. (a) (b) Intensity (arbitrary units) t/ms 0 4 Intensity (arbitrary units) t/ms 0 4 1 2 1 2 Figure 2 Simultaneously-recorded light pulses. (a): 1, Na 589 nm and 2, In 451 nm; (b): 1, Na 589 nm and 2, H 656 nm. Catholyte 1 mM InIII and 0.05 mM NaI in 0.4 mM HCl. 10000 1000 100 Intensity (arbitrary units) 0.1 1.0 10.0 C/mM 1 2 3 4 Figure 3 Calibration curves for Na 589 nm (1 and 3), K 767 nm (2) and Li 671 nm (4) lines, with capacity 2 mF (1, 2 and 4) and 0.25 mF (3). Received: Moscow, 10th February 1998 Cambridge, 12th May 1998; Com. 8/01633J

ISSN:0959-9436     

出版商:RSC    

年代:1998

数据来源: RSC