摘要:

Mendeleev Communications Electronic Version, Issue 1, 1998 (pp. 1–42) Reaction of acylisothiocyanates with 5-isopropoxy-4-methyloxazole Anton V. Dudin,* Nicolai E. Agafonov and Viktor M. Zhulin N. D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences, 117913 Moscow, Russian Federation. Fax: +7 095 135 5328 Formal [3+2]-cycloaddition of acylisothiocyanates to 5-isopropoxy-4-methyloxazole gives derivatives of 5-acylimino-3-thiazoline.In recent years, extensive studies have been carried out on the formal [3+2]-cycloaddition to oxazoles 1 accompanied by opening of the oxazole ring and formation of another heterocycle 3 (Scheme 1). A series of ‘ene’ components 2 of this reaction, such as C=C,1 C=N,2 N=N,2,3 C=O2,4 and N=O5 bonds have been studied; the addition of oxazoles to the C=S group of thioaldehydes generated in situ has also been reported.6 We found that acylisothiocyanates 4a–c reacted with 5-isopropoxy- 4-methyloxazole 5 to give hitherto unknown 5-acylimino- 2-isopropoxycarbonyl-2-methyl-3-thiazolines 6a–c, i.e.the transformation occured via formal [3+2]-cycloaddition of the C=S bond of acylisothiocyanate to the 2nd and 4th atoms of the oxazole ring (Scheme 2).Thus, we show for the first time that oxazoles react by the above mechanism not only with heteroolefins but also with heterocumulenes.† The structure of adduct 6a was confirmed by X-ray diffraction analysis‡ (Figure 1), while the structures of compounds 6b,c were established by comparing their 1H and 13C NMR and mass spectra with those of compound 6a.The authors express their gratitude to L. G. Vorontsova and M. G. Kurella who performed the X-ray diffraction analysis. References 1 (a) G. Ya. Kondrat’eva, M. A. Aitzhanova, V. S. Bogdanov and O. S. Chizhov, Izv. Akad. Nauk SSSR, Ser. Khim., 1979, 1313 (Bull. Acad. Sci. USSR, Div. Chem. Sci., 1979, 28, 1228); (b) T. Ibata, Y. Isogami, H. Nakawa, H. Tamura, H. Suga, X.Shi and H. Fujieda, Bull. Chem. Soc. Jpn., 1992, 65, 1771. 2 A. Hassner and B. Fischer, Tetrahedron, 1989, 45, 3535. 3 (a) T. Ibata, H. Suga, Y. Isogami, H. Tamura and X. Shi, Bull. Chem. Soc. Jpn., 1992, 65, 2998; (b) T. Ibata, Y. Isogami and H. Tamura, Chem. Lett., 1988, 1551. 4 H. Suga, X. Shi, H. Fujieda and T. Ibata, Tetrahedron Lett., 1991, 32, 6911. 5 H. Suga and T.Ibata, Chem. Lett., 1991, 1221. 6 E. Vedejs and S. Fields, J. Org. Chem., 1988, 53, 4663. 7 R. A. Firestone, E. E. Harris and W. Reuter, Tetrahedron, 1967, 23, 943. † 5-Benzoylimino-2-isopropoxy-2-methyl-3-thiazoline 6a was obtained by refluxing oxazole 57 (1.0 g, 7.1 mmol) and isothiocyanate 4a (1.16 g, 7.1 mmol) in toluene for 7 h under argon. The resulting mixture was chromatographed on a column with SiO2 using benzene as an eluent to give 1.50 g of compound 6a as large yellow prisms, mp 84–85.5 °C (from hexane), Rf (Silufol, Et2O–benzene, 1:1) 0.53–0.56.Found (%): C 59.00, H 5.36, N 9.29, S 10.30. Calc. for C15H16N2O3S (%): C 59.19, H 5.30, N 9.21, S 10.53. 1H NMR (300 MHz, CDCl3) d: 1.23 [m, 6H, CH(CH3)2], 2.00 (s, 3H, CH3), 5.04 [m, 1H, CH(CH3)2], 7.51 (m, 3H, Ph), 8.30 (t, 3H, Ph and N=CH). 13C NMR (75.5 MHz, CDCl3) d: 21.3 [q, CH(CH3)2], 24.7 (q, CH3), 70.7 [d, CH(CH3)2], 93.7 (s, S–C–CH3), 128.5 and 130.4 (d, Ph, o- and m-CH), 133.7 (d, Ph, p-CH), 134.4 (s, Ph, quaternary C), 163.7 (d, N=CH), 167.1 (s, N=C–S), 177.6 and 178.3 (s, N–C=O and O–C=O). MS (EI, 70 eV) m/z 304 [M]+. Adducts 6b [bp 144–145 °C (1 mmHg)] and 6c (mp 99–101.5 °C) were synthesized similarly to adduct 6a. ‡ X-ray diffraction analysis.Crystals of compound 6a in the form of tetrahedral prisms were grown from pentane, triclinic, a = 10.164(1) Å, b = 9.732(1) Å, c = 7.877(1) Å, a = 96.40(1)°, b = 93.30(1)°, g = 98.92(1)°, Z = 2, space group P , C15H16N2O3S. A complete set of 1295 independent reflections with I > 2s(I) was obtained on a RED-4 four-circle automatic diffractometer (l Cu-Ka, graphite monochromator, w–q/2q scanning, q £ 60°).The structure of compound 6a was solved by a direct method. The coordinates of non-hydrogen atoms were refined by the least-squares method in an anisotropic approximation; the hydrogen atom coordinates were refined isotropically. The final value of R was 0.07. Atomic coordinates, bond lengths and thermal parameters have been deposited at the Cambridge Crystallographic Data Centre (CCDC).For details, see Notice to Authors, Mendeleev Commun., 1998, issue 1. Any request to the CCDC should quote the full literature citation and the reference number 1135/23. N O R2 R3 R1 X Y + N X Y R1 R2 COR3 Scheme 1 1 2 3 C(19) C(18) C(20) O(3) C(17) C(21) O(4) C(9) N(6) S(1) C(7) C(8) N(5) C(10) O(2) C(11) C(12) C(13) C(14) C(15) C(16) Figure 1 The structure of compound 6a.Bond lengths (Å): S(1)–C(7) 1.763(5), S(1)–C(9) 1.859(6), O(2)–C(10) 1.227(8), O(3)–C(17) 1.345(7), O(3)–C(18) 1.461(7), O(4)–C(17) 1.226(8), N(5)–C(7) 1.283(8), N(5)–C(10) 1.421(7), N(6)–C(8) 1.292(9), N(6)–C(9) 1.401(7), C(7)–C(8) 1.429(9), C(9)–C(17) 1.492(10), C(9)–C(21) 1.513(8), C(10)–C(11) 1.519(10), C(11)–C(12) 1.341(8), C(12)–C(13) 1.391(10), C(13)–C(14) 1.363(9), C(14)–C(15) 1.417(10), C(15)–C(16) 1.435(10), C(16)–C(11) 1.383(8), C(18)–C(19) 1.527(8), C(18)–C(20) 1.512(10).Bond angles (°): C(7)– S(1)–C(9) 89.3(3), S(1)–C(7)–C(8) 107.5(5), S(1)–C(7)–N(5) 128.5(5), N(5)–C(7)–C(8) 124.0(6), C(7)–C(8)–N(6) 120.6(6), C(8)–N(6)–C(9) 112.0(6), S(1)–C(9)–N(6) 110.0(5), S(1)–C(9)–C(17) 104.0(5), S(1)–C(9)– C(21) 110.9(5), N(6)–C(9)–C(17) 109.9(5), N(6)–C(9)–C(21) 111.0(5), C(17)–C(9)–C(21) 110.8(6), C(7)–N(5)–C(10) 115.7(5), O(2)–C(10)–N(5) 125.6(7), O(2)–C(10)–C(11) 120.1(7), N(5)–C(10)–C(11) 114.3(5), C(10)– C(11)–C(12) 118.9(6), C(10)–C(11)–C(16) 119.6(7), C(12)–C(11)–C(16) 121.4(7), C(11)–C(12)–C(13) 121.3(6), C(12)–C(13)–C(14) 119.3(8), C(13)–C(14)–C(15) 121.5(8), C(14)–C(15)–C(16) 117.0(6), C(15)–C(16)– C(11) 119.2(7), C(9)–C(17)–O(4) 124.9(7), O(3)–C(17)–O(4) 120.7(6), O(3)–C(17)–C(9) 114.4(5), O(3)–C(18)–C(19) 104.6(3), O(3)–C(18)–C(20) 105.8(6), C(17)–O(3)–C(18) 119.4(5), C(19)–C(18)–C(20) 110.2(6).R C O N C S + N O Me PriO N S Me COOPri CON R 4a–c 5 6aR = Ph (69%) 6b R = Me (25%) 6c R = p-NO2C6H4 (75%) Scheme 2 1 2 3 4 5 1 Received: Moscow, 18th November 1997 Cambridge, 8th January 1998; Com. 7/08938D

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年代:1998

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Mendeleev Communications Electronic Version, Issue 1, 1998 (pp. 1–42) Unexpected synthesis of 2-(3-hydroxymethyl-3,3-pentamethyleneacetonyl)- 2-trifluoromethylimidazolidine Vyacheslav Ya. Sosnovskikh* and Michail Yu. Mel’nikov Department of Chemistry, A. M. Gor’ky Urals State University, 620083 Ekaterinburg, Russian Federation. Fax: +7 3432 615 978; e-mail: Vyacheslav.Sosnovskikh@usu.ru The reaction of 2-amino-6-hydroxy-5,5-pentamethylene-1,1,1-trifluoro-2-hexen-4-one with ethylenediamine, in contrast to the similar reaction involving 2-amino-6-hydroxy-5,5-dimethyl-1,1,1-trifluoro-2-hexen-4-one, leads to 2-(3-hydroxymethyl-3,3-pentamethyleneacetonyl)- 2-trifluoromethylimidazolidine.It is known1 that ethylenediamine reacts with b-amino-b-polyfluoroalkylvinylketones at two electrophilic centres simultaneously to produce 2,3-dihydro-1,4-diazepines. In an attempt to synthesize diazepines containing such substituents as the trifluoromethyl and hydroxyalkyl groups, we found that 2-amino-6-hydroxy-5,5-dimethyl(pentamethylene)-1,1,1-trifluoro- 2-hexen-4-ones 1,2, obtained by the condensation of 4-hydroxy- 3,3-dimethyl(pentamethylene)butan-2-ones with trifluoroacetonitrile, 2 react with ethylenediamine in quite different ways although their structures are very similar.For instance, aminoenone 1 gives the expected diazepine 3 in a 75% yield, while aminoenone 2 gives imidazolidine 4 in the same yield under these conditions.† In the latter case, double nucleophilic attack at the b-carbon atom with elimination of an ammonia molecule takes place, while the carbonyl group is retained, most likely due to steric factors.The formation of 2-trifluoromethyl-2-ethoxycarbonylmethylimidazolidine from the reaction of ethylenediamine with ethyl trifluoroacetoacetate has been reported previously,3 but the † 2,3-Dihydro-5-trifluoromethyl-7-(2-hydroxy-1,1-dimethylethyl)-1,4-diazepine 3. Aminoenone 1 (300 mg, 1.4 mmol) was dissolved in 400 ml (360 mg, 6.0 mmol) of ethylenediamine, and the reaction mixture was kept for three days at room temperature.The resulting crystals of diazepine 3 were recrystallised from hexane, yield 250 mg (75%), mp 130–131 °C. Found (%): C 50.87, H 6.53, N 11.73. Calc. for C10H15F3N2O (%): C 50.84; H 6.40; N 11.86. IR (vaseline oil, n/cm–1): 3345, 3140 (NH, OH), 1620, 1570, 1550 (C=N, C=C, NH). 1H NMR (80 MHz, CDCl3) d: 1.19 (s, 6H, 2CH3), 2.9 (br. s, 2H, OH, NH), 3.50 (br. s, 2H, CH2N), 3.57 (s, 2H, CH2O), 3.78 (t, 2H, CH2N=), 5.07 (s, 1H, =CH). 2-(3-Hydroxymethyl-3,3-pentamethyleneacetonyl)-2-trifluoromethylimidazolidine 4 was obtained from 200 mg of aminoenone 2 under the same conditions as diazepine 3. Yield 180 mg (76%), mp 85–86 °C (hexane).Found (%): C 53.26; H 7.32; N 9.59. Calc. for C13H21F3N2O2 (%): C 53.05; H 7.19; N 9.52. IR (vaseline oil, n/cm–1): 3360 , 3315, 3195 (NH, OH), 1705 (C=O), 1645 (NH). 1H NMR (80 MHz, CDCl3) d: 1.2–2.0 [m, 10 H, (CH2)5], 2.90 (s, 2H, CH2), 3.02 (s, 4H, CH2CH2), 3.4 (br. s, 3H, OH, 2NH), 3.72 (s, 2H, CH2O). literature contains no data regarding this reaction pathway involving b-amino-b-polyfluoroalkylvinylketones.At present, we are trying to clarify whether the formation of imidazolidine 4 revealed here is a characteristic property of b-amino-b-polyfluoroalkylvinylketones or if this reaction presents a specific case caused by the structural features of aminoenone 2. This work was supported by the Russian Foundation for Basic Research (grant no. 96-03-33373). References 1 K. I. Pashkevich, A. Ya. Aizikovich and I. Ya. Postovskii, Izv. Akad. Nauk SSSR, Ser. Khim., 1981, 455 (Bull. Acad. Sci. USSR, Div. Chem. Sci., 1981, 30, 420). 2 V. Ya. Sosnovskikh and M. Yu. Mel’nikov, Zh. Org. Khim., 1998, in press. 3 G. M. J. Slusarczuk and M. M. Joullie, J. Org. Chem., 1971, 36, 37. OH O NH2 CF3 R1 R2 + (CH2NH2)2 –NH3 –H2O –NH3 OH N CF3 NH Me Me OH O HN NH CF3 1,2 3 4 1 R1 = R2 = Me 2 R1 + R2 = (CH2)5 Received: Moscow, 3rd October 1997 Cambridge, 28th November 1997; Com. 7/07584G

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年代:1998

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Mendeleev Communications Electronic Version, Issue 1, 1998 (pp. 1–42) First synthesis of 5-hydroxycyclohexane-1,3-dione Vladimir G. Zaitsev* and Fedor A. Lakhvich Institute of Bioorganic Chemistry, Academy of Sciences of Belarus, 220141 Minsk, Belarus. Fax: +375 172 637 132; e-mail: prostan@ns.iboch.ac.by A simple synthetic scheme for 5-hydroxycyclohexane-1,3-dione 1, existing in solution mainly in the enolic form 1a, is proposed for the first time.Recently, we described the synthesis and utilization of 4-hydroxycyclohexane- 1,3-dione.1 Here, we propose a simple preparative synthesis of a regioisomer, 5-hydroxycyclohexane-1,3-dione 1, by the Ni/Ra-catalysed hydrogenation of phloroglucinol in an alkaline methanolic solution. Hydroxy diketone 1 is stable in the form of its sodium salt, but dehydrates in strongly acidic solution affording resorcinol. The 1H NMR spectrum of diketone 1 in [2H5]pyridine solution shows only the enolic form of dione 1.In contrast, the 1H NMR spectrum in [2H6]acetone shows that dione 1 exists predominantly as the enolic tautomer 1a, with only 15–20% of the diketo tautomer. 5-Hydroxycyclohexane-1,3-dione 1 was found earlier2 in the products of metabolism of phloroglucinol by Pseudomonas sp.Nevertheless, a chemical synthesis of the compound 1 was thought to be problematic due to the known instability of b-hydroxy ketones, and the authors3 had proposed a complex and multistage scheme for a synthetic equivalent of 1, 5-phenyldimethylsilylcyclohexane- 1,3-dione 2. Dione 1, synthesised by us,† yields esters or ethers from its enolic or hydroxy group, easily and with good chemoselectivity, depending on the reaction conditions.The use of dione 1 in the synthesis of natural polyketides will be reported separately. References 1 (a) V. G. Zaitsev, G. I. Polozov and F. A. Lakhvich, Tetrahedron, 1994, 50, 6377; (b) V. G. Zaitsev and F. A. Lakhvich, Mendeleev Commun., 1995, 224; (c) F.A. Lakhvich and V. G. Zaitsev, XI International Conference on Organic Synthesis (IUPAC), Amsterdam, The Netherlands, 1996, OC-47, p. 87. 2 (a) T. R. Patel, K. G. Jure and G. A. Jones, Appl. Environ. Microbiol., 1981, 42, 1010; (b) S. M. Armstrong and T. R. Patel, Can. J. Microbiol., 1993, 39, 899. 3 J. E. Oliver, R. M. Waters and W. R. Lusby, Tetrahedron, 1990, 46, 1125.† 5-Hydroxycyclohexane-1,3-dione 1. A mixture of 1.05 g (6.5 mmol) of phloroglucinol dihydrate, 0.29 g (7.2 mmol) of NaOH in 10 ml methanol and 0.5 g of freshly prepared Ni catalyst was stirred for 2 h at 100 bar H2 and room temperature. Catalyst was then filtered off and the filtrate was passed through a column containing 5 g sulfoacidic cationite in H+ form. The column was additionally washed with 50 ml MeOH.The combined effluents were evaporated in vacuo giving 0.95 g (~100%) of the monohydrate of 5-hydroxycyclohexane-1,3-dione 1, a viscous oil, which crystallised when cooling. Mp 44–45 °C. 1H NMR ([2H5]pyridine) d: 2.93, 2.99 (2dd, 4H, 4,6-H, J 4.5, 17 Hz and 7, 17 Hz), 4.65 (septet, 1H, 5-H, J 4.5, 7 Hz), 5.87 (s, 1H, 2-H), 7.45 (br. s, >1H, enolic H). 1H NMR ([2H6]acetone) d: 2.39 (ddd, 1.7H, 4-H for 1a, J 4, 7 and 17 Hz), 2.62 (dt+d, 2.1H, 6-H for 1a and 4-H for 1, J 4.5, 17 + 16 Hz), 2.95 (d, 0.4H, 4-H for 1, J 16 Hz), 3.16 and 3.65 (2m, 0.4H, 2-H for 1), 4.29 (m, 0.85H, 5-H for 1a), 4.52 (m, 0.15H, 5-H for 1), 5.39 (m, 0.7H, 2-H for 1a). IR (KBr, n/cm–1): 3440 (br), 2680 (br), 1710 (weak), 1620, 1230, 1165, 1060. Found (%): C, 49.23; H, 6.96. Calc. for C6H10O4 (%): C, 49.31; H, 6.85. OH OH HO i, H2 (Ni/Ra) NaOH, MeOH ii, H+ O O HO OH O HO O O PhMe2Si 1 1a 2 Received: Moscow, 20th May 1997 Cambridge, 25th June 1997; Com. 7/03874G

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年代:1998

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Mendeleev Communications Electronic Version, Issue 1, 1998 (pp. 1–42) 2,4,4,6-Tetrabromocyclohexa-2,5-dienone in the presence of triphenylphosphine as a regiospecific and stereoselective reagent for the nucleophilic substitution of bromine for hydroxyl Elena D. Matveeva,* Tatyana A. Podrugina and Nikolai S. Zefirov Department of Chemistry, M. V. Lomonosov Moscow State University, 119899 Moscow, Russian Federation Fax: +7 095 939 0290 A highly reactive, regio- and stereo-specific reagent, a 2,4,4,6-tetrabromocyclohexa-2,5-dienone–triphenylphosphine complex, has been used for the first time in the nucleophilic substitution of bromine for hydroxyl in alcohols. 2,4,4,6-Tetrabromocyclohexa-2,5-dienone I is known to be a useful reagent for the cation radical bromination of a broad range of organic compounds and for the electrophilic bromination of phenols and dialkylanilines.1,2 However, no examples of its application as a donor of nucleophilic bromine have been reported to date.We found that tetrabromide I can successfully be used in the nucleophilic substitution of bromine for hydroxyl, i.e., serve as a source of nucleophilic halogen. In our previous work3,4 we studied complexes of triphenylphosphine with esters of trichloro- and tribromo-acetic acids and with trichloroacetonitrile.When these complexes are used, nucleophilic substitution in alcohols occurs in high yields and highly regio- and stereospecifically. It should be noted that esters of tribromoacetic acid are less readily available synthetically than esters of trichloroacetic acid.To broaden the range of halophilic compounds that allow one to perform nucleophilic substitution of bromine for the hydroxyl group, we resorted to the readily available tetrabromide I.2 Based on literature data,3–5 we assume that the reaction of aDetermined by GLC. b37% olefin. c13% olefin. dexo-Bromonorbornane is the only product. eDetermined by 1H NMR spectroscopy.f(E)-1-p-Tolyl- 4-bromobut-1-ene is the only product. Table 1 Optimum conditions for various substrates in the substitution reaction. Starting compounds T/°C t/h Solvent Yield (%) Isomeric puritya (%) –10 0.25 MeCN 99 100 –5 0 0.5 0.5 MeCN MeCN 90 90 99.9 99.9 00 11 MeCN CH2Cl2 55 55 63b 87c 0 2 C6 H3 Cl3 98 99 00 12 12 CH2Cl2 MeCN 60 40 99d 99d 00 12 12 CH2Cl2 MeCN 85 67 99d 99d 0 2 CH2 Cl2 80 98e 0 2 CH2 Cl2 80 98.9e –10 2 CH2Cl2 70 99f OH 1 OH 2 OH 3 OH 4 OH 5 OH 6 Me OH 7 OH O Me 8 Me OH 9Mendeleev Communications Electronic Version, Issue 1, 1998 (pp. 1–42) triphenylphosphine with tetrabromide I starts with attack of the nucleophilic phosphorus atom on an electrophilic centre, a halogen atom, i.e. a halophilic interaction.6 Unlike the previously studied reactions of CCl3X (where X = COOR; CN) with triphenylphosphine, the reaction of the latter with tetrabromide I occurs exothermically and at a high rate.In the presence of alcohols, oxyphosphonium intermediates II are formed. It is obviously in intermediate II that nucleophilic substitution occurs to give the corresponding bromides (Scheme 1). The substitution reaction has general applicability, and this complex reacts with primary, secondary, sterically hindered and cage alcohols under sufficiently mild conditions to give high yields of the corresponding bromides. We found that the optimum conditions of substitution are as follows: a polar solvent (acetonitrile), temperature from –10 °C to 0 °C, reagent ratio alcohol:triphenylphosphine:tetrabromide I = 1:1:1 (Table 1).It was shown for octan-1-ol 1 as an example that the replacement of the hydroxyl group in primary alcohols occurs in 15 min in an almost quantitative yield. This reagent was found to be regiospecific, which was demonstrated for the replacement of the hydroxyl group in secondary and especially in branched secondary alcohols. For example, octan-2-ol 2 is transformed into 2-bromooctane in 90% yield and with an isomeric purity of 99.9%.In spatially hindered alcohols, such as 2-methyloctan-3-ol 3, substitution occurs in 40% yield, which is the best yield for such alcohols. Usually nucleophilic substitution in such alcohols is accompanied by rearrangements and elimination if classical reagents or even reagents based on triphenylphosphine are used.5 It should be emphasised that in the case studied, the yield of the olefin is only 13% and no rearrangement products are formed. (Literature data for the PPh3·CBr4 complex for an analogous structure, 3-methylbutan-2-ol:7 the reaction yield is 30%, 8% of which is an isomerised product). Even the reaction with neopentyl alcohol 4 occurs without isomerisation of the carbon skeleton under very mild conditions (0 °C) in a quantitative yield and with high isomeric purity (99%) (for the PPh3·CBr4 complex, the yield of neopentyl bromide is 42%8).The replacement of hydroxyl in cage alcohols occurs under similar conditions (0 to +5 °C), and the process is strictly regiospecific. For example, the replacement in both endo-5 and exo-6 norborneols results in exo-bromonorbornane in high yield (60%), the isomeric purity of the product being over 99%.This is a very high yield for such systems.9 Exo- and endo-isomers differ in the chemical shift of the methine proton at the C2 atom in the 1H NMR spectra. In both cases the chemical shift of this proton in the product is 3.95 ppm (lit.,10 3.9 ppm). The high regio- and stereo-specificity of the reagent was also shown for alcohols such as analogues of natural carbinols. For example, alcohols 7 and 8 react with the complex under study to give exclusively regio-substitution products, whose structure was confirmed by 1H NMR spectroscopy.The substitution in secondary carbinols containing cyclopropane substituents occurs through stereospecific opening of the cyclopropane ring. The reaction of p-tolylcyclopropylcarbinol 9 gives (E)-1-p-tolyl-4-bromobut-1-ene as the only product.The data presented above suggest the high reactivity, regiospecificity and stereoselectivity of 2,4,4,6-tetrabromocyclohexa- 2,5-dienone in the presence of triphenylphosphine in the nucleophilic substitution of bromine for a hydroxyl group. The proposed method looks extremely promising for fine organic syntheses.This study was financially supported by the Russian Foundation for Basic Research (grant no. 96-03-33395). References 1 G. H. Markgraf, G. T. Marshall, M. A. Greeley and F. Michael, Chem. and Ind. (London), 1987, 298. 2 M. Tsubota, M. Iso and K. Suzuki, Bull. Chem. Soc. Jpn., 1972, 45, 1252. 3 E. D. Matveeva, A. L. Kurts, A. I. Yalovskaya, N.G. Nikishova and Yu. G. Bundel’, Zh. Org. Khim., 1989, 25, 716 [J. Org. Chem. USSR (Engl. Transl.), 1989, 25, 642]. 4 E. D. Matveeva, A. I. Yalovskaya, I. A. Cherepanov, Yu. G. Bundel’ and A. L. Kurts, Zh. Org. Khim., 1991, 27, 1611 (Russ. J. Org. Chem., 1991, 27, 1409). 5 B.R.Castro, Org. React., 1982, 29, 1. 6 N. S. Zefirov and D. I. Makhon’kov, Chem. Rev., 1982, 82, 615. 7 R. A. Arain and M. K. Hargreaves, J. Chem. Soc. C, 1970, 67. 8 R. G. Weiss and E. I. Snyder, J. Org. Chem., 1971, 36, 403. 9 P. Hodge and E. Khoshdel, J. Chem. Soc., Perkin Trans. 1, 1984, 195. 10 W. C. Wong and C. C. Lee, Can. J. Chem., 1954, 42, 1245. Br Br Br Ph Br PPh3 + ROH Br Br Br OH [Ph3P+OR]Br– + II Ph3PO + RBr II Scheme 1 I OH Br Br O Br Br PPh3, 0 °C Br Received: Moscow, 28th November 1997 Cambridge, 5th December 1997; Com. 7/01983A

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年代:1998

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Mendeleev Communications Electronic Version, Issue 1, 1998 (pp. 1–42) Synthesis of arylmethylenecyanothioacetamides in a Michael reaction Vladimir D. Dyachenko,a Sergey G. Krivokolyskoa and Victor P. Litvinov*b a T. G. Shevchenko Lugansk State Pedagogical Institute, 348011 Lugansk, Ukraine. Fax: +7 0642 517 518 b N. D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences, 117913 Moscow, Russian Federation.Fax: +7 095 135 5328 Interaction of arylmethylenecyanoacetic esters and cyanothioacetamide in the presence of N-methylmorpholine leads to formation of arylmethylenecyanothioacetamides, which have been used in the synthesis of substituted thiazoles. It is known that arylmethylenecyanothioacetamides may be obtained by the condensation of an aromatic aldehyde and cyanothioacetamide in the presence of amines.1–3 We found that the interaction of arylmethylenecyanoacetic esters 1 and cyanothioacetamide 2 in ethanol at room temperature in the presence of an equimolar quantity of N-methylmorpholine leads to formation of arylmethylenecyanothioacetamides 3 (method A),† also obtained by the condensation of aromatic aldehydes 4 with cyanothioacetamide 2 (method B).This type of transformation involving exchange of methylene components is already known,4 but exchange of cyanoacetic ester for cyanothioacetamide is novel. It is known that the reaction of arylmethylenecyanoacetic esters (Ar = 4-ClC6H4, 4-BrC6H4, Ph) with cyanothioacetamide leads to formation of 4-aryl-6-oxy-3,5-dicyanopyridin- † Arylmethylenecyanothioacetamides 3a–d. Method A.A mixture of 10 mmol of compound 1, 10 mmol of cyanothioacetamide 2 and 10 mmol of N-methylmorpholine in 15 ml of ethanol was stirred at 20 °C during 40 min. The precipitate was filtered and washed with ethanol and hexane. Compounds 3a–d were obtained and recrystallized from ethanol (Table 1). Method B. To a mixture of 10 mmol of aldehyde 4 and 10 mmol of cyanothioacetamide 2 in 15 ml of ethanol was added one drop of N-methylmorpholine, and the resulting mixture was stirred at 20 °C during 30 min.The precipitate was filtered and washed with ethanol and hexane (Table 1). Compound 3d is known.1 Its yield by method A was 84%, and 86% by method B, mp 232–233 °C. 2(1H)-thiones.5,6 The above-mentioned exchange of methylene components in a Michael reaction may be accounted for by the presence of electron-donating groups in the aromatic ring, which promotes deactivation of the double bond in the compounds 1.This leads to disintegration of the hypothetical adduct 5 by means of formation of a new C=C bond with elimination of the less nucleophilic anion. In addition, arylmethylenecyanothioacetamides 3 are less soluble in ethanol than compounds 1.This leads, according Le Chatelier’s principle, to displacement of the reaction equilibrium towards formation of products 3. The structure of the compounds 3 was confirmed by 1H NMR spectral data and by involvement of the compounds 3 in a Hantzsch-type condensation, from which substituted thiazoles 6 were obtained.‡ References 1 V. Y. Grinstein and L.A. Serina, Izv. Akad. Nauk Latv. SSR, Ser. Khim., 1963, 4, 469 (in Russian). 2 J. S. A. Brunskill, A. De and D. F. Ewing, J. Chem. Soc., Perkin Trans. 1, 1978, 629. 3 V. G. Brunton, M. J. Lear, D. J. Robins, S. Williamson and P. Workman, Anti-Cancer Drug Design, 1994, 9, 291. 4 A. Michael and A. Ross, J. Am. Chem. Soc., 1930, 52, 4598. 5 G. E. H. Elgemeie, S. M. M. Mohamed, S.M. Sherif and M. H. Elnagdi, Heterocycles, 1985, 23, 3103. 6 Yu. A. Sharanin, A. M. Shestopalov, V. Yu. Mortikov, S. N. Melenchuk, V. K. Promonenkov, B. M. Zolotaryov and V. P. Litvinov, Izv. Akad. Nauk SSSR, Ser. Khim., 1986, 153 (Bull. Acad. Sci. USSR, Div. Chem. Sci., 1986, 35, 139). ‡ 3-Aryl-2-(4-R-thiazol-2-yl)acrylonitriles 6a–m. To a solution of 10 mmol of the compound 3 in 10 ml of dimethylformamide at 20 °C was added 10 mmol of a-bromoketone 7 and the mixture was stirred during 3 h.The resulting precipitate was filtered and washed with water, ethanol and hexane (Table 1). Ar COOEt NC NCCH2CSNH2, B 2 method A EtOOC NC Ar CN CSNH2 N S NC Ar R Ar CSNH2 NC ArCHO BrCH2COR 7 2, B method B 1 5 6 3 4 B = N-methylmorpholine a 2,4-(EtO)2C6H3 b 3,4-(MeO)2C6H3 c 4-BuOC6H4 d 4-Me2NC6H4 1,3,4 Ar 6 Ar R a 2,4-(EtO)2C6H3 4-ClC6H4 b 2,4-(EtO)2C6H3 4-MeC6H4 c 2,4-(EtO)2C6H3 4-BuC6H4 d 2,4-(EtO)2C6H3 Ph e 2,4-(EtO)2C6H3 3-cumarinyl f 2,4-(EtO)2C6H3 4-PhC6H4 g 2,4-(EtO)2C6H3 3,4-Cl2C6H3 h 2,4-(EtO)2C6H3 4-BrC6H4 i 4-Me2NC6H4 4-BuC6H4 j 4-BuOC6H4 4-BrC6H4 k 3,4-(MeO)2C6H3 4-PhC6H4 l 3,4-(MeO)2C6H3 2-thienyl m 3,4-(MeO)2C6H3 4-BuC6H4 7 R a 4-BuC6H4 b 2-thienyl c 3-cumarinyl d 4-PhC6H4 e 4-BrC6H4 f Ph g 4-MeC6H4 Scheme 1 Received: Moscow, 28th July 1997 Cambridge, 8th January 1998; Com. 7/03149AMendeleev Communications Electronic Version, Issue 1, 1998 (pp. 1–42) Table 1 Characteristics of compounds 3a–c and 6a–m.Compound Yield (%) method A/B Mp/°C 1H NMR spectra (d, [2H6]DMSO) 3a 76/82 178–180 9.94 and 9.37 (s, 2H, NH2), 8.43 (s, 1H, CH=), 8.10 and 6.71 (d, 2H, C6H3), 6.67 (s, 1H, C6H3), 4.16 (q, 4H, 2CH2), 1.38 (t, 3H, CH3), 1.36 (t, 3H, CH3) 3b 82/83 198–200 9.95 and 9.43 (s, 2H, NH2), 8.08 (s, 1H, CH=), 7.69 (s, 1H, C6H3), 7.58 and 7.15 (d, 2H, C6H3), 3.88 and 3.83 (s, 6H, 2CH3) 3c 85/94 131–132 9.98 and 9.46 (s, 2H, NH2), 8.07 (s, 1H, CH=), 7.97 and 7.13 (d, 4H, C6H4), 4.09 (t, 2H, OCH2), 1.15–1.85 [m, 4H, (CH2)2], 0.94 (t, 3H, CH3) 6a 77 143–145 8.40 (s, 1H, CH=), 8.22 (s, 1H, thiazolyl), 8.15 and 6.75 (d, 2H, C6H3), 6.66 (s, 1H, C6H3), 8.02 and 7.53 (d, 4H, C6H4), 4.15 (m, 4H, 2CH2), 1.41 and 1.36 (t, 6H, 2CH3) 6b 81 135–137 8.43 (s, 1H, CH=), 8.20 (s, 1H, thiazolyl), 8.07 and 6.71 (d, 2H, C6H3), 6.67 (s, 1H, C6H3), 7.89 and 7.27 (d, 4H, C6H4), 4.18 (m, 4H, 2CH2), 2.35 (s, 3H, CH3), 1.41 and 1.36 (t, 6H, 2CH3) 6c 72 94–95 8.40 (s, 1H, CH=), 8.13 (s, 1H, thiazolyl), 8.06 and 6.72 (d, 2H, C6H3), 6.63 (s, 1H, C6H3), 7.88 and 7.26 (d, 4H, C6H4), 2.59 (t, 2H, OCH2), 1.42 and 1.37 (t, 6H, 2CH3), 1.60 [m, 4H, (CH2)2], 0.89 (t, 3H, CH3) 6d 84 134–135 8.38 (s, 1H, CH=), 8.15 (s, 1H, thiazolyl), 8.02 and 6.71 (d, 2H, C6H3), 6.61 (s, 1H, C6H3), 7.44 (m, 5H, Ph), 4.10 (m, 4H, 2CH2), 1.38 and 1.32 (t, 6H, 2CH3) 6e 85 194–196 8.68 (s, 1H, cumarinyl), 8.38 (s, 1H, CH=), 8.18 (s, 1H, thiazolyl), 8.02 and 6.70 (d, 2H, C6H3), 6.61 (s, 1H, C6H3), 7.37–7.79 (m, 4H, Harom), 4.14 (m, 4H, 2CH2), 1.44 and 1.37 (t, 6H, 2CH3) 6f 90 174–176 8.45 (s, 1H, CH=), 8.19 (s, 1H, thiazolyl), 8.11 and 6.85 (d, 2H, C6H3), 6.67 (s, 1H, C6H3), 7.46–7.75 (m, 9H, Harom), 4.16 (m, 4H, 2CH2), 1.42 and 1.37 (t, 6H, 2CH3) 6g 77 129–131 8.30 (s, 1H, CH=), 8.15 (s, 1H, thiazolyl), 8.11 and 6.67 (d, 2H, C6H3), 6.56 (s, 1H, C6H3), 7.64–7.89 (m, 3H, Harom), 4.10 (m, 4H, 2CH2), 1.42 and 1.35 (t, 6H, 2CH3) 6h 91 145–146 8.40 (s, 1H, CH=), 8.24 (s, 1H, thiazolyl), 8.15 and 6.74 (d, 2H, C6H3), 6.66 (s, 1H, C6H3), 7.94 and 7.66 (d, 4H, C6H4), 4.16 (m, 4H, 2CH2), 1.41 and 1.36 (t, 6H, 2CH3) 6i 74 128–130 8.10 (s, 1H, CH=), 7.91 (s, 1H, thiazolyl), 7.85 (m, 4H, Harom), 7.26 and 6.82 (d, 4H, C6H4), 3.07 (s, 6H, 2CH3), 2.62 (t, 2H, CH2), 1.15–1.70 [m, 4H, (CH2)2], 0.92 (t, 3H, CH3) 6j 75 109–111 8.27 (s, 1H, CH=), 8.21 (s, 1H, thiazolyl), 8.00 and 7.09 (d, 4H, C6H4), 7.95 and 7.64 (d, 4H, C6H4), 4.05 (t, 2H, OCH2), 1.25–1.84 [m, 4H, (CH2)2], 0.92 (t, 3H, CH3) 6k 80 187–189 8.30 (s, 1H, CH=), 8.15 (s, 1H, thiazolyl), 8.10 and 7.70 (d, 4H, C6H4), 7.80 (s, 1H, C6H3), 7.45 and 7.15 (d, 2H, C6H3), 3.89 and 3.87 (s, 6H, 2CH3) 6l 71 159–161 8.19 (s, 1H, CH=), 8.06 (s, 1H, thiazolyl), 7.74 (m, 4H, Harom), 7.15 (m, 2H, thienyl), 3.87 and 3.84 (s, 6H, 2CH3) 6m 84 103–104 8.26 (s, 1H, CH=), 8.13 (s, 1H, thiazolyl), 7.93 and 7.22 (d, 4H, C6H4), 7.75 (m, 2H, Harom), 7.15 (d, 1H, Harom)

ISSN:0959-9436     

出版商:RSC    

年代:1998

数据来源: RSC

摘要:

Mendeleev Communications Electronic Version, Issue 1, 1998 (pp. 1–42) A novel stationary phase for the high performance liquid chromatographic separation and determination of phenols Natalia A. Penner,* Pavel N. Nesterenko, Andrey V. Khryaschevsky, Tatiana N. Stranadko and Oleg A. Shpigun Department of Chemistry, M. V. Lomonosov Moscow State University, 119899 Moscow, Russian Federation. Fax: +7 095 939 4675; e-mail: group@chromat.chem.msu.su A novel type of hyper-crosslinked polystyrene resin has been used as a stationary phase in the high performance liquid chromatographic separation of phenol and its derivatives; a simplified procedure for their quantitative determination on a ppb level, based on preconcentration and separation using a single chromatographic column, is proposed.The use of polymer resins as a stationary phase in reversedphase high-performance liquid chromatography (RP HPLC) has grown dramatically since an increasing number of polymer columns became commercially available. The reason for this growth is connected with the low stability of the most frequently used octadecylsilica (ODS) in alkaline media and undesirable interactions between polar solutes and residual silanol groups that influence the peak shape and column performance.1–5 The main area of application of polymer resins in RP HPLC is the separation of different biomolecules such as peptides and proteins. However, they can also be efficient for the preconcentration and separation of other organic molecules, e.g.hyper-crosslinked polystyrene has been successfully used for preconcentration prior to HPLC-determination of phenol traces in aqueous solutions.6 The high degree of crosslinking and new approach to the synthesis of polystyrene networks provide a reasonable mechanical stability that allows a narrow fraction of fine (down to 3–5 mm diameter) particles to be obtained.These sorbents are biporous (have a bimodal pore size distribution) and possess highly developed micropore structures.They demonstrate good kinetics and reversibility of adsorption and desorption process,6–8 allowing their use not only as sorbents for solid-phase extraction but also as column packing for HPLC.9 It is interesting that hypercrosslinked polystyrene has a hydrophobic, but at the same time wettable by water, surface.7 As mentioned before, biporous hyper-crosslinked polystyrenetype sorbents show an unique affinity towards non-substituted phenol, a very high dynamic adsorption capacity (80 mg g–1 on a 20×1.4 cm column with a linear flow rate over 4 cm min–1) and an exceptionally high recovery of phenols from water solutions at a low concentration level (phenol 96±5%, p-nitrophenol 99±4%, 2,4-dinitrophenol 95±5%, o-nitrophenol 96±6%, 2,4-dichlorophenol 96±5%).6 Thus, the unique combination of physico-mechanical and chemical properties of hyper-crosslinked polystyrene opens up new facilities in the determination of phenol and its derivatives by using a single chromatographic column for preconcentration and separation.There is a growing demand for a simple trace-level determination of ecotoxicants, such as phenol and its derivatives, in natural waters.Determination of phenols usually includes preconcentration (extraction, solid-phase extraction) followed by chromatographic separation;10–12 therefore, this process is time-consuming and not too efficient. Moreover, in most cases the possibilities of a common preconcentration procedure are limited because only a small part of the preconcentrate is used for further analysis.The procedure would be more efficient if the whole volume of preconcentrate were served as a sample for chromatographic analysis. Probably, the application of HPLC columns packed with hyper-crosslinked polystyrene would allow the combination of both preconcentration and separation, which would result in a decrease in analysis time and increased accuracy, and moreover, to a decreased volume of original water sample.Because the preconcentration of phenols by neutral noncharged hyper-crosslinked polystyrenes has already been investigated and optimal conditions chosen,13 we studied the chromatographic behaviour of phenol and its chloro-, nitro- and methyl-derivatives on a column packed with this sorbent as well as the possibility of carrying out both preconcentration and separation with a single column.Retention of phenols on a chromatographic column strongly depends on the pH of the buffer solution in the mobile phase, because of partial dissociation of the molecules of phenol and its derivatives with pH change. Due to the high hydrolytic stability of hyper-crosslinked polystyrene,1,6–8 the retention of phenols over a broad range of mobile phase pH was investigated.Increase of buffer pH in the eluent results in dissociation of phenol molecules, and consequently, their capacity factor k' [k' = (tR – t0)/t0] decreases due to the lower affinity of the ionic form of phenol towards the stationary phase in comparison with the molecular form (Figure 1).The sharp change of retention corresponds to equality of the concentrations of the ionic and molecular form of phenols or their pKa. It should be noted that at pH 5.4–6.5 a some increase in retention was observed. This effect is thought to be connected with the increasing role of salting out under a significantly increasing ionic strength of 5 mM phosphate buffer over this pH range.An approximate estimation has shown it to increase from a value of 0.05 at pH 5.4 to 0.075 at pH 6.5. With polystyrene resin as a stationary phase the retention of organic molecules in the reversed phase mode of HPLC depends on the nature and concentration of an organic modifier much stronger as compared to ODS packings because the surface of the polymer stationary phases is more sensitive to solvation by organic solvents.1,7 In the case of polymer sorbents retention is generally defined by hydrophobic solute–sorbent interactions; therefore, the addition of strong solvents such as acetonitrile and THF to the mobile phase usually considerably improves the peak shape.In this work we used acetonitrile as an organic modifier of the mobile phase.The dependence of retention (k') obtained from the acetonitrile content is described well by equation (1), proposed by Jandera14 over the range of acetonrile concentration from 40 to 90% v/v. Table 1 Parameters [equation (1)] describing the retention of phenols on hyper-crosslinked polystyrene as a function of acetonitrile concentration in the mobile phase. Chromatographic column: hydrophobic cross-linked polystyrene (15 mm), 150×3 (i.d.) mm; eluent: a mixture of acetonitrile with 5 mM phosphate buffer (pH 6.5).Substances a m×102 d×104 r Phenol 1.74 4.39 2.43 0.990 2,4-Dichlorophenol 3.34 7.04 3.97 0.997 4-Chloro-3-methylphenol 3.08 6.72 3.80 0.996 Pentachlorophenol 3.24 6.33 3.21 0.996 2,6-Dimethylphenol 2.79 5.92 3.14 0.999 2,4,6-Trichlorophenol 4.05 8.51 5.02 0.988 p-Nitrophenol 2.81 6.99 4.20 0.998 2,4-Dinitrophenol –0.23 2.80 0.63 0.850 o-Nitrophenol 2.63 5.45 2.98 0.974 2-Chlorophenol 2.23 4.66 2.40 0.988 lg k' = a – mX + dX2 (1)Mendeleev Communications Electronic Version, Issue 1, 1998 (pp. 1–42) In equation (1), X is the concentration of an organic solvent in the mobile phase in % v/v; a is a parameter corresponding to retention of phenol in water and m and d are parameters describing the change of retention with growth of X.It should be noted that for many sorbates the value of coefficient d is negligible over the investigated range of concentration of an organic solvent and consequently, the dependence of lg k' from X is close to linear. However, the deviation of this dependence from a linear one for phenols should not be ignored. The parameters of equation (1) describing the retention of the phenols under investigation on hyper-crosslinked polystyrene are presented in Table 1. The elution order of phenol and its derivatives is in accordance with their distribution coefficients obtained earlier for adsorption on hyper-crosslinked polystyrene in static conditions.13 The mechanism of retention of phenols on polymer sorbents is complex because their retention is influenced by many factors, namely: hydrophobic interactions of phenols with the surface of polymer particles, p–p interactions between phenols and the polystyrene matrix, the size-exclusion effect of micropores, the formation of relatively stable adducts with molecules of organic solvent in eluent, etc.Some of the secondary equilibria taking place in this chromatographic system, and which are responsible for the loss of separation in the resulting chromatographic performance, can be suppressed by increasing the concentration of the common electrolyte in the eluent. So, the addition of KCl to the mobile phase at a concentration ca. 0.01 M markedly improves the peak shape.At the same time the retention of phenols remains practically unchanged. It should be pointed out that under the conditions chosen (Figure 2) the performance of a column (150×3 mm) packed with hyper-crosslinked polystyrene is comparatively high (11100 plates per metre, calculated based on retention of phenol). Thus, an eluent consisting of a 45:55 (v/v) mixture of acetonitrile with 5 mM phosphate buffer (pH 5.4) containing 0.01 M KCl has been found to be optimal for the separation of phenol and its two chloro- and three nitroderivatives.Because hyper-crosslinked polystyrene has both a high affinity to phenol and its derivatives and a reasonable selectivity in their chromatographic separation, a simple and rapid procedure for their quantitative determination at a ppb level in water using a single chromatographic column for preconcentration and separation can be proposed.As an example, the determination of phenol, 2-chlorophenol, 4-chloro-3-methylphenol and 2,4-dichlorophenol was demonstrated. The determination includes the following steps: 1. sample preparation (adjusting pH of sample to 2–3, filtration, degassing); 2. column conditioning by consecutive flushing with a mixture of acetonitrile and water; 3.preconcentration (pumping of the sample prepared as described in step 1 through the column); 4. pre-separation involving washing the column with an eluent containing 5–10 v/v acetonitrile (if necessary) to remove any components preceding the phenol peak; 5. separation of phenols (separation conditions found earlier15 to be optimal for the separation of phenol and three of its chloro-derivatives mentioned above are presented in Figure 3) Figure 1 Plot of capacity factors of phenols versus pH of buffer solution in the mobile phase. Chromatographic column: hydrophobic cross-linked polystyrene (15 mm), 62×2 mm i.d.; eluent: a 1:1 (v/v) mixture of acetonitrile with 5 mM phosphate buffer; flow rate: 0.2 ml min–1; detection, wavelength: 274 nm.Phenols: phenol (1), p-nitrophenol (2), 2,6-dimethylphenol (3), o-nitrophenol (4), 2,4-dinitrophenol (5), 2-chlorophenol (6), 4-chloro-3-methylphenol (7), 2,4-dichlorophenol (8), 2,4,6-trichlorophenol (9), pentachlorophenol (10). 6 5 4 3 2 1 0 4 6 8 10 pH k' k' 35 30 25 20 15 10 5 0 4 6 8 10 pH 1 2 3 4 5 6 7 8 9 1 10 Figure 2 Chromatogram of a mixture of 2,4-dinitriphenol (1), phenol (2), p-nitrophenol (3), o-nitrophenol (4), 2,4-dichlorophenol (5), 2,4,6-trichlorophenol (6).Chromatographic column: hydrophobic cross-linked polystyrene (15 mm), 150×3 (i.d.) mm; eluent: a 45:55 (v/v) mixture of acetonitrile with 5 mM phosphate buffer (pH 5.4) containing 0.01 M KCl; flow rate: 1 mlmin–1; detection wavelength: 274 nm.(1) (2) (3) (4) (5) (6) 0 10 20 30 t/minMendeleev Communications Electronic Version, Issue 1, 1998 (pp. 1–42) and recording of the chromatogram; 6. washing the column with an eluent of increased acetonitrile content to remove strongly retained substances from the sample. It should be noted that chromatographs equipped with a syringe-type pump [Phoenix 20 CU (Carlo Erba) and Milichrom] are more convenient for the determination of phenols by the procedure described above.The technique proposed is quick (analysis duration including sample preparation does not exceed 30 min) and sensitive, because it avoids losing sample at the preconcentration stage and allows additional peak broadening in the chromatographic column.The chromatogram obtained after percolating 2.0 ml of water sample with a concentration of phenols at the ppb level through the chromatographic column is presented in Figure 3. It was found that loading 2 ml of water sample onto the column and separation under the conditions as stated in Figure 3 provides quantitative determination over the following ranges: 3–100 ppb for phenol, 3–100 ppb for 2-chlorophenol, 8–200 ppb for 4-chloro-3-methylphenol and 50–1000 ppb for 2,4-dichlorophenol.Thus, the use of hyper-crosslinked polystyrene allows a simple and quick HPLC determination of phenols in water based on their preconcentration and separation with a single chromatographic column. References 1 N. Tanaka and M. Araki, Polymer-based Packing Materials for RPLC, in Advances in Chromatography, VCH, New York, 1989, vol. 30, p. 81. 2 L. D. Bowers and S. Pedigo, J. Chromatogr., 1986, 371, 243. 3 T. Sasagawa, L. N. Ericsson, D. C. Teller, K. Titani and K. A. Walsh, J. Chromatogr., 1984, 307, 29. 4 D. J. Pietrzyk, E. P. Kroeff and T. D. Rotsch, Anal. Chem., 1978, 50, 497. 5 Y.-B. Yang and M. Verzele, J. Chromatogr., 1987, 387, 197. 6 M. P. Tsyurupa, M.M. Ilyin, A. I. Andreeva and V. A. Davankov, Fresenius J. Anal. Chem., 1995, 352, 673. 7 M. P. Tsyurupa, L. A. Maslova, A. I. Andreeva, T. A. Mrachkovskaya and V. A. Davankov, React. Polym., 1995, 25, 69. 8 V. A. Davankov and M. P. Tsyurupa, React. Polym., 1990, 13, 27. 9 M. Beth, K. K. Under, M. P. Tsyurupa and V. A. Davankov, Chromatographia, 1993, 16, 351. 10 V. Piangelerelli, F. Nerini and S. Cavalli, Ann. Chim., 1993, 83, 331. 11 B. Gawdzik, J. Gawdzik and U. Czerwinska-Bil, J. Chromatogr., 1990, 509, 135. 12 M. W. Jung, D. W. Lee, J. S. Rhee and K. J. Paeng, Anal. Sci., 1996, 12, 981. 13 A. V. Khryaschevsky, M. B. Podlovchenko, P. N. Nesterenko and O. A. Shpigun, Vestn. Mosk. Univ., Ser. 2. Khim., 1998, 39, in press. 14 V. D. Shatz and O. V. Sachartova, Vysokoeffektivnaya zhidkostnaya khromatografiya (High performance liquid chromatography), Zinatne, Riga, 1988 (in Russian). 15 C. W. Klampfl and E. Spanos, J. Chromatogr. A, 1995, 715, 213. Figure 3 The chromatogram resulting after percolating 2.0 ml of a water sample spiked with phenol (25 mg l–1), 2-chlorophenol (25 mg l–1), 4-chloro- 3-methylphenol (25 mg l–1), 2,4-dichlorophenol (100 mg l–1) through the chromatographic column. Eluent: a 49.5:49.5:1 (v/v) mixture of acetonitrile, distilled water and acetic acid; for other conditions, see Figure 1. (1) (2) (3) (4) 0 10 t/min 5 Received: Moscow, 31st October 1997 Cambridge, 9th December 1997; Com. 7/07981H

ISSN:0959-9436     

出版商:RSC    

年代:1998

数据来源: RSC

摘要:

Mendeleev Communications Electronic Version, Issue 1, 1998 (pp. 1–42) Optical feedback in laser-induced phase transitions of carbon Sergei I. Kudryashov,* Alexander A. Karabutov, Vladimir I. Emel’yanov, Mariya A. Kudryashova, Raissa D. Voronina and Nikita B. Zorov Department of Chemistry, M. V. Lomonosov Moscow State University, 119899 Moscow, Russian Federation. Fax: +7 095 431 3063; e-mail: serg@laser.chem.msu.su Owing to interference of laser radiation in a film of liquid carbon on the surface of graphite, the change in the film thickness apparently controls the dynamics of laser-induced phase transitions (melting and evaporation) of carbon.In the light of the latest data about the dielectric character of the optical properties of liquid metals,1,2 the theory of laser-induced phase transitions (LIPT) in metals and metal-like materials seems far from being well developed.Up to date, a number of important functions of the liquid phase in LIPT have been established. The necessity to take into account the surface melt made it possible to disprove the view3 that the surface of a target can be heated monotonically above critical temperature Tcr up to T ~ DevapH ~ 10Tcr; it was found that temperatures T > Tcr can be achieved only in vapours as a result of efficient absorbance of radiation.1 The film of the melt also plays a crucial role in the feedback mechanism of the velocity of propagation of phase transition fronts, the particular mechanism of the influence of properties of the melt being determined by the a/c ratio assumed in the model.If the melt is characterised by a ‘metallic’ type of properties (large a/c values), a liquid phase with thickness c/Vevap 2 of up to 10–3 cm is formed as a result of propagation of the heat wave deep into the target,1 and thermal resistance of the liquid layer acts as the key factor in the feedback mechanism.4 This parameter determines the heat flux directed at the melting front in the bulk of the target and thus controls the temperature of the surface and the rate of evaporation.When this feedback mechanism operates during a free-generation laser pulse, the LIPT dynamics reach a steady-state regime with constant velocities Vevap and Vmelt and a constant thickness of the melt Yst.4 The role of optical feedback in dielectric oxide melts during laser-induced oxidation of metals has been noted previously.5 It was found that due to interference of the radiation in the metal oxide film, its reflectance and transmittance vary as a function of the film thickness, and instantaneous values of these parameters control the chemical transformation.For LIPT in metals, the optical feedback has been considered in the context of ‘metal–dielectric’ phase transitions.1 In the case where formation of the dielectric phase during metal– dielectric transition is characterised by a threshold Tmd (Imd), the reflectance coefficient of the medium sharply diminishes at I = Imd; this causes an acceleration of the evaporation front propagation followed by a flattening out of the dependence of Vevap, since the temperature of the surface of a transparent dielectric cannot markedly exceed the temperature of the metal–dielectric transition, Tmd £ Tcr.The predominant part of the energy flux is at the ‘transparency’ wave front deposited in the melt. In the present study, we consider the mechanism of optical feedback in the LIPT dynamics in relation to graphite characterised by ‘metal-like’ thermal and optical properties.This specific feature of graphite made it possible to apply some elements of the theory of the ‘thermal’ mechanism of destruction of materials to the description of the LIPT dynamics in the 0.01–0.3 GW cm–2 range of radiation intensity.3 A significant point in the description of the LIPT dynamics is that carbon melt is a dielectric material over the optical region [n(532 nm) = 1, k(532 nm) < 0.5,6 n(532 nm) = 0.84±0.01, k(532 nm) = 0.45±0.152], i.e.it is characterised by a small a/c value. Therefore, the role of heat conduction of the liquid film is insignificant compared to that of the change in the optical properties of the air–melt–graphite layered medium, which depends on the velocities of propagation of the melting and evaporation fronts via individual optical characteristics of liquid carbon and the instantaneous thickness of the melt film.When a carbon surface is heated by laser radiation up to the temperature of the graphite–liquid–vapour triple point Ttr (ca. 5000 K), phase transition fronts, melting and evaporation, start to propagate deep into the material. In the case of a moderately absorbing graphite melt [a(532 nm) = (8±3)×104 cm–1] with a low heat conductivity, the movement of the melting front deep into the target is maintained as a result of heating and melting of graphite at the phase interface, owing to absorbance of the radiation that has passed through the melt by the solid phase, whereas the movement of the evaporation front is maintained owing to the absorbance of radiation in the melt phase.Since the velocities of propagation of the fronts depend on the heats of the transition [DH(liq., Ptr, Ttr) = 200 kJ mol–1 and DevapH(P, T) = 265 kJ mol–1],7,8 the melting front overtakes the evaporation front, and the film of liquid carbon appears. In turn, owing to interference of the radiation, the thickness of the melt film Y determines the reflectance (R), transmittance (T) and absorbance (A) of the air–melt–graphite layered medium and has an influence on the velocities of propagation of the phase transition fronts.In this study, we describe the variation of the film thickness during the laser pulse with a power density much higher than the threshold value needed for graphite to melt (0.02 GW cm–2) by equation (1).According to the overall balance of the fluxes on the surface of the material, the light flux coming from the gas phase is partially reflected by the melt film; it warms up and evaporates the liquid film with a heat of DHeff(P, T) [DevapH(P, T) + DH(liq.; Ptr, Ttr ® P, T)], whereas that part of the flux that passes through the film is spent in maintaining the movement of the melting front and heat wave in the solid.Thus, the boundary condition for the Stefan problem for the melting front velocity has the following form (Vm is the molar volume of graphite) and the velocity of the evaporation front can be expressed as follows Taking into account equations (2) and (3), equation (1) can be written as equation (4): We can find a particular solution for this equation for the initial condition Y(0) = 0 if we express the R(Y) and T(Y) dependences for a moderately absorbing film in terms of the theory of multiple reflections in layered media,9 i.e.by the dY dt = Vmelt(t) – Vevap(t) (1) Vmelt(t) = T(Y)I(t)Vm DH(liq.; Ptr, Ttr) (2) Vevap(t) = [1 – R(Y) – T(Y)]I(t)Vm DHeff (P, T) (3) dY dt T(Y)I(t) DH(liq.; Ptr, Ttr) [1 – R(Y) – T(Y)]I(t) DHeff (P, T) = – (4)Mendeleev Communications Electronic Version, Issue 1, 1998 (pp. 1–42) function X(Y) = X0exp(–2aY) (where a is the absorbance coefficient and the term X0 is determined by the refraction n and attenuation k indices of the contacting phases). The main physical processes and regimes of destruction of a carbon target through evaporation at high temperatures can be found from an analysis of equation (4) if it is written in the following form The steady-state regime for the evaporation destruction of the melt film is described by the expression Vmelt(t) = Vevap(t) [F(T) = 0].The influence of the melting and evaporation processes result in a steady-state film thickness over a radiation pulse of the Gaussian shape with duration being established, equation (6), where B = 2 atI0VmDHeff(P, T)–1 The rate at which the steady-state regime is established is determined by the parameter B; the main terms in this parameter are a, I0 and DHeff(P, T).For the steady-state regime to exist, optical (n, k) and thermodynamic [DHeff(P, T)] properties of the melt should be invariable. When the sign of F(Y) is positive [Vmelt(t) > Ve vap(t)], this corresponds to a non-steady-state growth of the film during the radiation pulse at high transmittance for a moderately absorbing melt film or at large DHeff(P, T).This effect can be realised in the case of a ‘metal–dielectric’ phase transition at high melt temperatures when a ‘transparency’ wave propagates in the melt of a metal.1 If we take into account the weak absorbance in this non-ideal dielectric, we obtain, with slow evaporation, a limited growth of the film thickness owing to the radiation absorbance in the film In turn, the negative sign of F(Y) means destruction of the melt film during the radiation pulse owing to the high velocity of movement of the destruction front; the latter can be accounted for by the low heat of the process or by the low transmittance and reflectance of the film. One of the most probable reasons for the appearance of this regime is the sharp decrease in DHeff(P, T) near the spinodal curve to DH(liq.; Ptr, Ttr ® P, T).10 The authors are grateful to the Russian Foundation for Basic Research (grant no. 96-03-33324) for financial support. References 1 V. A. Batanov, F. V. Bunkin, A. M. Prokhorov and V.B. Fedorov, Zh. Eksp. Teor. Fiz., 1972, 63, 586 (in Russian). 2 O. V. Kolyasnikov and S. I. Kudryashov, Tezisy vserossiiskoi konferentsii molodykh uchenykh ‘Sovremennye problemy teoreticheskoi i eksperimental’noi khimii’ (Abstracts of the All-Russian Conference of Young Scientists ‘Contemporary Problems of Theoretical and Experimental Chemistry’), Saratov, 1997, p. 74 (in Russian). 3 S. I. Anisimov, Ya. A. Imas, G. S. Romanov and Yu. V. Khodyko, Deistvie izlucheniya bol’shoi moshchnosti na metally (Influence of High-Intensity Radiation on Metals), Nauka, Moscow, 1970, ch. 3–4 (in Russian). 4 A. A. Uglov, I. Yu. Smurov, A. M. Lapshin and A. G. Gus’kov, Modelirovanie teplofizicheskikh protsessov impul’snogo lazernogo vozdeistviya na metally (Simulation of Thermal Processes in Metals Induced by Pulse Laser Radiation), Nauka, Moscow, 1991, ch. 3 (in Russian). 5 A. M. Prokhorov, V. I. Konov, I. Ursu and I. N. Mikhailesku, Vzaimodeistvie lazernogo izlucheniya s metallami (Interaction of Laser Radiation with Metals), Nauka, Moscow, 1988 (in Russian). 6 A. M. Malvezzi, N. Bloembergen and C. Y. Huang, Phys. Rev. Lett., 1986, 57, 146. 7 M. A. Sheindlin, Teplofizika Vysokikh Temperatur, 1981, 19, 630 (in Russian). 8 A. V. Kirillin, M. D. Kovalenko and M. A. Sheindlin, Teplofizika Vysokikh Temperatur, 1985, 23, 699 (in Russian). 9 M. Born and E. Wolf, Principles of Optics, Pergamon Press, Oxford, 1968, ch. 13. 10 A. H. Matveev, Molekulyarnaya fizika (Molecular Physics), Vysshaya Shkola, Moscow, 1981, ch. 4 (in Russian). T(Y) DH(liq., Ptr, Ttr) [1 – R(Y) – T(Y)] DHeff (P, T) = – (5) F(Y) 2pt 2 DHeff(P, T) DH(liq., Ptr, Ttr) Y(t) = ln[(T0(1 + ) + R0)(1 – exp{–Berfc(t/ t)})] 2 2a = = Yst + (2a)–1 ln(1 – exp{–Berfc(t/ t)}) 2 (6) Y(t) = (2a)–1ln[2 atT0I0VDH(liq., Ptr, Ttr)–1erfc(t/ t)] 2 2 (7) Received: Moscow, 25th July 1997 Cambridge, 25th October 1997; Com. 7/05901I

ISSN:0959-9436     

出版商:RSC    

年代:1998

数据来源: RSC

摘要:

Mendeleev Communications Electronic Version, Issue 1, 1998 (pp. 1–42) Laser-induced phase transitions of carbon Sergei I. Kudryashov,* Alexander A. Karabutov, Mariya A. Kudryashova, Vladimir I. Beketov and Nikita B. Zorov Department of Chemistry, M. V. Lomonosov Moscow State University, 119899 Moscow, Russian Federation. Fax: +7 095 431 3063; e-mail: serg@laser.chem.msu.su The rate of laser-induced phase transitions (melting and evaporation) of carbon in the subcritical region of the phase diagram is determined by optical characteristics of the air–melt–graphite layered system.During laser-induced phase transitions (LIPT) of carbon, the optical feedback channel apparently exerts a greater influence on the LIPT dynamics than the heat-conduction mechanism, for which thermal resistance of the melt is the key factor in the feedback mechanism.1 In this case, the reflectance, transmittance and absorbance of a film of the carbon melt vary as functions of the film thickness due to interference, and thus control the dynamics of melting and evaporation.However, up to now only a few studies dealing with laser-induced melting and evaporation of carbon have been carried out.The separate results of these studies do not permit an elucidation of the roles of both feedback channels in the LITP dynamics. It is known that when the surface of graphite is heated by laser radiation to the graphite–liquid–vapour triple point Ttr, ca. 5000 K, a heat wave and phase transition fronts of melting and evaporation begin to propagate deep into the material.The movement of the melting front into the target in the case of the moderately absorbing graphite melt [a(532 nm) = 8±2×105 cm–1)] with low heat conductivity is maintained as a result of heating and melting of graphite at the interface by the radiation that has passed through the melt. The depth of penetration of the melting front (the thickness of the melt film Y) during a 25 ns laser pulse reaches a value of the order 2a–1(532 nm) = 2.4×10–5 cm, which is in better agreement with the experimental result2 Y(532 nm) = = 1.8×10–5 cm than the depth of penetration of the heat wave: cm (at a temperature conductivity of graphite3 c(4000 K) = 2.5×10–3 cm2 s–1).The thickness Y of the molten film existing due to dissimilar velocities of propagation of the melting and evaporation fronts which differ in the heats of transition [DH(liq.; Ptr, Ttr) = = 200 kJ mol–1 and DevapH(Ptr, Ttr) = 265 kJ mol–1],3,4 determines the reflectance (R), transmittance (T) and absorbance (A) of the air–melt–graphite layered medium [Figure 1, for n(532 nm) = = 0.84±0.01, k(532 nm) = 0.45±0.15]1 owing to the interference of radiation in the molten film.5 These values determine the following velocities of propagation of phase transition fronts induced by radiation with instantaneous intensity I(t), equations (2) and (3), [Vm is the molar volume of graphite, DHeff(P, T) is equal to the sum of DevapH(P, T) and DH(liq.; Ptr, Ttr ® P, T)] and thus complete the feedback mechanism.In a study carried out by laser reflectometry,1 we discovered interference of the laser radiation in the air–melt–polycrystalline graphite (PCG) layered medium formed at a power density of 0.017–0.7 GW cm–2.The interference extrema are manifested by the angular dependence of the intensity of the reflected radiation at an optical thickness of the film Y specified by relationships for the minima and maxima of reflectance: where j12 = –1.2±0.1 rad and j23 = 0.2±0.1 rad are phase shifts of the light wave at the vapour–melt (12) and melt–graphite (23) interfaces.1 The presence of characteristic interference maxima in the range of effective (with allowance for the incidence angle) power density of 0.06–0.3 GW cm–2 made it possible to elucidate the dependence of the film thickness in the middle of the radiation pulse Y(I0, t/2) (Figure 1); this dependence reproduces the profile of the Y(I0, t) curve found by TEM measurements of the re-crystallised layer thickness of highly oriented pyrolytic graphite melted by laser radiation with similar characteristics.2 In both cases, the thresholds for the beginning of melting (0.015 and 0.020 GW cm–2) and for flattening of the curves (0.054 and 0.062 GW cm–2) are virtually identical; in addition, a clear-cut plateau is observed, i.e.there is a steady-state regime when a film with Yst = 0.18 mm is maintained during a laser pulse. According to equation (1), this plateau can be attributed to the beginning of intensive 2c 4000 K ( )t 10 5 – » liquid film depth/mm 1.0 0.8 0.6 0.4 0.2 0.0 0.0 0.2 0.4 0.6 0.8 1.0 liquid film depth/mm 0.4 0.3 0.2 0.1 0.0 0.01 0.1 0.5 effective power density/ GW cm–2 (a) (b) Figure 1 (a) Dependences of the reflectance (R), transmittance (T) and absorbance (A) of the air–liquid carbon–graphite medium on Y.(b) Dependences of the thickness of the liquid carbon film Y(I0, t/2) and Y(I0, t): dark and light squares. A T R dY dt = Vmelt(t) – Vevap(t) (1) thermoacoustic and recoil pressure (a.u.) normalised thermoacoustic and recoil pressure (a.u.) 100 10 0.1 1 80 70 60 50 40 30 power density/GW cm–2 0.1 1 power density/GW cm–2 (a) (b) Figure 2 (a) Dependences of Pta(I0) and Prec(I0) (light and dark squares) for PCG.(b) Dependences of the normalised Pta /I0 and Prec /I0 values (light and dark squares). Vmelt(t) = T(Y)I(t)Vm DH(liq., Ptr, Ttr) (2) Vevap(t) @ [1 – R(Y) – T(Y)]I(t)Vm DHeff (P, T) (3) (2m + 1 – )0.25l = Y(I0)n 2(j23 – j12) p n2 q1 sin – ( ) 1 – 2 (4) (m– )0.5l = Y(I0)n (j23 – j12) p n2 q1 sin – ( ) 1 – 2 (5)Mendeleev Communications Electronic Version, Issue 1, 1998 (pp. 1–42) evaporation at a power density I0 higher than the threshold value equal to 0.05 GW cm–2. In fact, when the film of the melt occurs under steady-state conditions in the power density range 0.06–0.3 GW cm–2, R(Y) and T(Y) reach their minimum values (0.06 and 0.2), whereas the absorbance, conversely, reaches its maximum (0.74) (Figure 1).Consequently, starting from 0.06 GW cm–2, a fast linear increase is observed in the plot for the integrated thermoacoustic pressure Pta(I0) (Figure 2) characterising the energy absorbed per unit liquid phase6 (Vf is the vibrational velocity, b, Cp and a are temperature expansion and isobaric heat capacity coefficients and the absorbance coefficient of liquid carbon, respectively, r0 is the density of graphite and c0 is the speed of sound in the direction perpendicular to the basis plane).Since the b value depends only slightly on the temperature in the 5000–6100 K range of the subcritical region in the curve of evaporation of carbon,7 according to equation (6), the constancy of the specific value in the corresponding range of I0 confirms the invariance of the absorbance capacity of the carbon melt film.The intensive evaporation of carbon in the range of I0, higher than the threshold equal to 0.05 GW cm–2 and correlating with the establishment of the steady-state thickness of the film, is stimulated by the high absorbance ability of the latter.The average deepening of the crater X(I0) and average recoil pressure of the evaporation products Prec(I0) per pulse directly describe the integrated velocity of the evaporation front per pulse (Figures 2,3). The linearity of these dependences in the range 0.06–0.3 GW cm–2 implies that the A(Y) value is constant, since DHeff(P, T) scarcely changes in the subcritical range of the evaporation curve.4,8 The expression for determining Prec(t) in terms of Vevap(t): (where Vvap and rvap are the velocity and the vapour density) not only describe qualitatively the steady-state character of the Prec /I0 and Prec(I0) dependences in the range 0.1–0.3 GW cm–2 (Figure 2), but also make it possible to calculate Psat(T) for a steady-state regime for destruction and to normalise Prec(I0). In fact, when carbon is vaporised under the action of nanosecond laser pulses on the surface, only thermal equilibrium is established, because the flux of radiation energy falling on the surface from the environment is counterbalanced by the reverse flux of energy carried away by the vaporised substance.Conversely, neither mass-exchange nor mechanical equilibrium is established on the surface, because the substance is transferred in virtually one direction. As a result, the instantaneous gas-dynamic recoil pressure Prec on the target surface becomes half the saturated vapour pressure under steady-state evaporation conditions at the same instantaneous temperature of the surface.The average Vevap per radiation pulse t = 25 ns needed for calculations was found from the X value. The velocity of vapour in the free path distance from the target surface corresponds to the velocity of the products of decomposition of an activated complex on the surface at temperature T and mass of the removed fragment M; for the species C3, which predominates in the vapour in the temperature range 5000– 6100 K,3 it is equal to (1.1–1.2)×103 m s–1.The values Psat(T) = 120–230 atm for the region of steady-state destruction of PCG, 0.15–0.3 GW cm–2, calculated from the formula lie within the subcritical branch (Figure 4) according to the published data.4 This confirms the adequacy of the model proposed in our study for the appearance of recoil pressure and also attributes the steady-state regime of LIPT to the subcritical region of variation of the thermodynamic variables characterising the state of carbon.Since the average Prec over the radiation pulse in the case of steady-state destruction of PCG does not depend on its duration t, the calculated and experimental values of Prec should coincide; this makes it possible to normalise the Prec(I0) dependence in bar outside the subcritical region (Figure 4).The authors are grateful to the Russian Foundation for Basic Research (grant no. 96-03-33324) for financial support. References 1 S. I. Kudryasov, A. A. Karabutov, V. I. Emel’yanov, M. A. Kudryashova, R. D. Voronina and N. B. Zorov, Mendeleev Commun., 1998, 27. 2 T. Venkatesan, D. C. Jacobson and J. M. Gibson, Phys. Rev. Lett., 1984, 53, 360. 3 M. A. Sheindlin, Teplofizika Vysokikh Temperatur, 1981, 19, 630 (in Russian). 4 A. V. Kirillin, M. D. Kovalenko and M. A. Sheindlin, Teplofizika Vysokikh Temperatur, 1985, 23, 699 (in Russian). 5 M. Born and E. Wolf, Principles of Optics, Pergamon Press, Oxford, 1968, ch. 13. 6 V. E. Gusev and A. A. Karabutov, Lazernaya optoakustika (Laser Optoacoustics), Nauka, Moscow, 1991 (in Russian). 7 H.R. Leider, O. H. Krikorian and D. A. Young, Carbon, 1973, 11, 555. 8 Termodinamicheskie svoistva individual’nykh veshchestv (Thermodynamic Properties of Individual Substances), ed. V. P. Glushko, Nauka, Moscow, 1979, vol. 2, book 1, p. 9 (in Russian). òPta(t)dt = r0c0òVf(t)dt = I0 [1 – R(Y) – T(Y)]b aCp 0 t 0 t (6) [1 – R(Y) – T(Y)]b aCp Pta I0 = crater depth/mm power density/GW cm–2 1.0 0.8 0.6 0.4 0.2 0.0 0.0 0.5 1.0 1.5 1.2 1.0 0.8 0.6 0.4 0.2 normalised crater depth/mm 0.0 0.5 1.0 1.5 power density/GW cm–2 (a) (b) Figure 3 Dependences of the average crater depth for polycrystalline graphite: (a) X(I0) and (b) normalised X/I0. Prec(t) = rvapVvap[T(t)]2 = r0Vevap(t)Vvap[T(t)] = 0.5Psat[T(t)] (7) saturated vapour pressure (kbar) vapour recoil pressure (kbar) 2.0 1.0 0.1 4.0 1.0 0.1 0.50 0.55 0.60 0.65 0.70 0.1 1 3 (a) (b) T/104 K power density/GW cm–2 Figure 4 (a) Temperature dependence Psat(T) according to published data4 and (b) dependence of the normalised (in bar) recoil pressure Prec(I0). kTM –1 Psat T ( ) 2r0 X t --- kT M ----- = (8) Received: Moscow, 25th July 1997 Cambridge, 25th October 1997; Com. 7/05902G

ISSN:0959-9436     

出版商:RSC    

年代:1998

数据来源: RSC

摘要:

Mendeleev Communications Electronic Version, Issue 1, 1998 (pp. 1–42) Electroluminescence of anthracene-containing polyimides Eugene I. Mal’tsev,*a Maria A. Brusentseva,a Vladimir I. Berendyaev,b Vladislav A. Kolesnikov,a Elena V. Lunina,b Boris V. Kotovb and Anatolii V. Vannikova a A. N. Frumkin Institute of Electrochemistry, Russian Academy of Sciences, 117071 Moscow, Russian Federation. Fax: +7 095 952 0846; e-mail: vanlab@glasnet.ru b L.Ya. Karpov Institute of Physical Chemistry, 103064 Moscow, Russian Federation. Fax: +7 095 975 2450 Electroluminescence has been revealed in a new class of electroactive polymers, the anthracene-containing aromatic polyimide derivatives; high thermal stability, ability to cast layers from solution and excellent film-forming properties make these materials of potential interest for technological applications. Since the first report of efficient electroluminescence from conjugated polymers1 this phenomenon has attracted attention due to its potential for use in wide-screen flat display technology.Conjugated polymers as emitting layers have become a subject of great interest. Currently, poly(p-phenylene vinylene) and its derivatives are the most studied electroactive polymers as conducting and light-emitting materials in electroluminescent light-emitting devices (ELEDs). However, certain nonconjugated polymers, e.g.polyimides, combined with electron transporting layers in the ELEDs, also rank as efficient electroluminophores.2 Commonly used unilayer ELEDs consist of an electroactive polymer layer sandwiched between a transparent In–SnO2 anode and a low work-function metal cathode. The basic electronic processes occurring in the operating ELEDs include electron–hole injection, transport of charges and their recombination in the bulk.The recombination leads to the formation of excitons which transfer their energy to the luminophore moieties (luminescent centres) of the polymer chains. The luminophore sites emit electroluminescent quanta.Previously,3–4 the synthesis of some new aromatic polyimides (API) based on 9,10-bis(p-aminophenyl)anthracene which exhibit photoluminescence was reported.4 It should be stressed that the APIs are known as a class of polymers with high thermal stability and tolerance towards oxidation. In this communication we present results on the electroluminescence of one of the APIs whose structure is shown in Figure 1.This API is soluble and forms excellent films from solutions. Soluble anthracene-containing APIs with sulfur atoms in the back-bone have been shown previously to be efficient electron–hole conductors.2 Bright electroluminescence (Figure 2, curve 2) was observed in bilayer ELEDs based on the APIs in combination with tris(8-quinolinolato)aluminium complex (Alq3) as an electron conducting layer.The photoluminescence of the anthracene-containing APIs has a strong pronounced exciplex character due to interchain electron donor–acceptor interaction of electron-excited anthracene groups with diimide fragments.3–5 The studied unilayer ELEDs with maximum brightness over 600 cd m–2 at 15 V consisted of an emitting API layer sandwiched in between transparent indium–tin oxide (ITO) and Mg:Ag electrodes.Polymer films 400–600 nm thick were formed on the ITO/glass by spin coating from a chloroform solution containing API under ambient conditions. The Mg:Ag electrodes were prepared by conventional vacuum vapour deposition at pressures below 5×10–6 Torr.All measurements were carried out at room temperature in ambient air. The experimental details are described elsewhere.6 The presence of diimide groups in the backbone makes APIs electronically conductive, while 9,10-diphenylanthracene (DPA) moieties play the role of hole-transporting sites in these polymers. At room temperature, the electron and hole drift mobilities directly measured by conventional time-of-flight (TOF) techniques7 indicated effective bipolar transport in the APIs.Taking into account the comparatively high photoluminescent efficiency in these materials,4 one would expect to observe electroluminescence in the API layers. We found experimentally that these polymers are excellent electroluminophores, being used in unilayer ELEDs.The high brightness is achieved due to efficient hole and electron conductivity. For the API the electron and hole mobilities are of the same value mh @ me = 2×10–5 cm2 V–1 s–1 for an electric field 3.3×105 V cm–1.7 On the other hand, the brightness is aided by the favourable relative positions of the energy levels providing an electron–hole injection balance in these polymers.Figure 2 shows the absorption and photoluminescence spectra of the API films and electroluminescence spectra of typical ITO/API/Mg:Ag devices measured at 10 V. When illuminated at 350 nm, the API exhibited a photoluminescence spectrum at 540 nm while the electroluminescence band had a peak at 565 nm. Note that the electroluminescent peak position did not coincide with the lmax of the photo-luminescence band.The essential difference in lmax position between the photoluminescence and electroluminescence spectra observed for the API should presumably be accounted for by the difference in the mechanism of the two emission processes. In the case of photoluminescence, light is randomly absorbed by occasional luminescent centres in the polymer, whereas the mechanism of electroluminescence involves electron–hole recombination which gives rise to the formation of excitons.In API structures, in contrast to polyconjugated macromolecular systems, exciton states should be less moveable. If so, N C C O O C C C N O O n C O O Figure 1 Chemical structure of aromatic polyimide anthracene derivatives. 3.0 2.5 2.0 1.5 1.0 0.5 0.0 290 390 490 590 690 790 Optical density l/nm 1.2 1.0 0.8 0.6 0.4 0.2 0.0 Intensity (arbitrary units) Figure 2 (1) Absorption spectrum of a polymer layer formed by spincasting from a chloroform solution of API; (2) electroluminescence of bilayer ELED (ITO/API/Alq3/Mg:Ag); (3) photoluminescence of API; (4) electroluminescence of unilayer ELED (ITO/API/Mg:Ag).(1) (2) (3) (4)Mendeleev Communications Electronic Version, Issue 1, 1998 (pp. 1–42) immediately after the formation they will transfer their energy to the nearest luminescent centre. Because charge carrier jumping through shallow traps is the most probable conduction mechanism for both types of carriers in these polymers,7 it is reasonable to assume that trapped charges participate in the recombination. Trapped charge formation implies the initiation of electronic and dipole polarization of the medium.Polymer structure defects, polarized luminophore moieties or electron donor–acceptor inter- and/or intramolecular polymer complexes may be candidates for these traps. The latter are transport sites of reduced energy. Since the interchain electron donor–acceptor complex formed by the two transporting centres (diimide and DPA) may be a luminescent centre in the API, one may expect that the energy of emitting quanta should be reduced.The electroluminescence spectrum will have to shift towards the long-wave region when compared with the photoluminescence band. At the present time, efforts are underway on APIs of various chemical structure to elucidate the role of donor–acceptor interactions on the electroluminescence band location in the visible range in order to handle the problem of electroluminescence colour tuning for the API based ELEDs.In summary, we have revealed electroluminescence in a new class of electroactive polymers, anthracene-containing aromatic polyimide derivatives. The high thermal stability, the ability to cast API layers directly from solution, excellent film-forming properties and efficient electroluminescence make APIs of potential interest for technological applications.This work was supported in part by the Russian Foundation for Basic Research (grant no. 97-03-32739a) and the International Science and Technology Center (grant no. 872). References 1 J. H. Burroughes, D. D. C. Bradley, A. R. Brown, R.N. Marks, K. Mackay, R. H. Friend, P. L. Burn and A. B. Holmes, Nature, 1990, 347, 539. 2 E. I. Mal’tsev, V. I. Berendyaev, M. A. Brusentseva, A. R. Tameev, V. A. Kolesnikov, A. A. Kozlov, B. V. Kotov and A. V. Vannikov, Polym. Int., 1997, 42, 404. 3 B. V. Kotov, G. V. Kapustin, S. N. Chvalun, N. A. Vasilenko, V. I. Berendyaev and T. A. Maslennikova, Polym. Sci., Ser. A, 1994, 36, 1666. 4 G. V. Kapustin, B. M. Rumyantsev, D. V. Pebalk and B. V. Kotov, Polym. Sci., Ser. A, 1996, 38, 875. 5 B. V. Kotov, Zh. Fiz. Khim., 1988, 62, 2709 (Russ. J. Phys. Chem., 1988, 62, 1408). 6 E. I. Mal’tsev, M. A. Brusentseva, V. A. Kolesnikov, A. V. Vannikov, A. V. Anikeev and L. I. Kostenko, Polym. Sci., Ser. A, 1995, 37, 959. 7 A. R. Tameev, A. A. Kozlov, V. I. Berendyaev, E. V. Lunina, B. V. Kotov and A. V. Vannikov, Zh. Nauch. Prikl. Fotogr. Kinematogr., 1997, 42, 38 (in Russian). Received: Moscow, 27th August 1997 Cambridge, 6th November 1997; Com. 7/06557D

ISSN:0959-9436     

出版商:RSC    

年代:1998

数据来源: RSC

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Mendeleev Communications Electronic Version, Issue 1, 1998 (pp. 1–42) Radiolysis of 2,6-di-tert-butyl-4-methylphenol (ionol) in a lipid membrane in the presence of oxygen Dmitry V. Paramonov,*a Elena A. Antonova,b Lenar T. Bugaenko,b Vladislav I. Trofimova and Vsevolod M. Byakovc a Scientific and Technological Centre ‘Lekbiotech’, 117246 Moscow, Russian Federation. Fax: +7 095 331 0101 b Department of Chemistry, M.V. Lomonosov Moscow State University, 119899 Moscow, Russian Federation. Fax: +7 095 932 8846 c Institute of Theoretical and Experimental Physics, 117259 Moscow, Russian Federation. Fax: +7 095 123 6584 Radiation-induced destruction of the ionol molecules in liposomes built of L-a-lecithin depends on the ionol concentration in the lipids and on the concentration of the lipid in the dispersion.Ionol (2,6-di-tert-butyl-4-methylphenol) has been used to study the action of a flux of active particles on the liposomes built of egg yolk lecithin (L-a-phosphatidylcholine). Decomposition of ionol, which is a radical acceptor, incorporated in the lipid membrane of liposomes, has been investigated. The ionol present in a lipid membrane (ionol is readily soluble in hydrocarbons and lipids but is insoluble in water; according to direct experimental measurements, its concentration in water does not exceed 2×10–5 mol dm–3) competes with the membrane lecithin for trapping the active species resulting from radiolysis.From the amount of ionol consumed, one can estimate the flux of active particles falling on the membrane.In our experiments, the concentration of ionol in the lipid membrane varied, while the lipid concentration in the aqueous phase remained constant. The following lipid concentrations were used: 2.4 and 4.8 mg ml–1. The radiation yield of the destruction of ionol was calculated using a standard procedure from the experimental dependences of the consumption of ionol on the absorbed dose of radiation at low radiation doses.The general approach to the preparation of aqueous dispersions of liposomes is described in a monograph.1 A 10.0±0.5% ethanolic solution of the ‘lecithin standard’ (egg yolk lecithin2) was used. To remove the alcohol, the lecithin was kept in a flask of a known weight on a rotary evaporator at 25–30 °C until a constant weight was attained.The quantity of lecithin obtained was determined as the difference between the weights of the filled and empty flasks. An ethanolic solution of ionol was then introduced by an analytical syringe into the flask containing lecithin, so that the final concentration of ionol in the lecithin varied from 0.2×10–4 to 2.5×10–4 mol dm–3. The resulting mixture was thoroughly stirred and dried on a rotary evaporator at 26–30 °C to a constant weight.After that, distilled water was added to the dried mixture of lecithin with ionol in such a way that the lipid concentration in water was either 24 or 48 mg ml–1. The resulting suspension was sonicated (the absorbed ultrasound power varied from 1.8 to 2.4 W cm–3), centrifuged for 15 min at 625 g and diluted to the required concentration with distilled water in a measuring flask.The average size of liposomes in the suspension was determined from the modified Rayleigh equation3,4 using turbidity spectra5 recorded on a Specord M40 spectrophotometer at wavelengths ranging from 440 to 900 nm. Using the Angstrom relation D = const·l–n, where D is the optical density of the liposome dispersion at the wavelength l and n is the exponent, and experimental D(l) values, the n and const values were calculated.The resulting values were used to calculate the average radius of liposomes from the Rayleigh equation. The consumption of ionol and the formation of radiolysis products were monitored by HPLC (Millichrom chromatograph, 64×4 mm column with Silasorb C18, acetonitrile–ethanol mixture as eluent).The chromatograph permitted recording the UV spectra of the products during the separation. The concentration of ionol in the samples of the liposome suspension was determined by comparing the heights of the chromatographic peaks for the solution under analysis and for the standard solution. The liposome suspensions were irradiated using an RC-100M cobalt setup.Aqueous suspensions of liposomes were irradiated under aerated conditions (air was bubbled through the cell) at a dose rate of 110 Gy min–1. Dispersions of L-a-lecithin liposomes with a concentration of 2.4 or 4.8 mg ml–1 containing 2.1×10–5 to 2.5×10–4 mol g–1 of ionol per gram of the lipid were exposed to radiation. The average radius of the liposome vesicles was 47±9 nm (Table 1).During irradiation, air was permanently bubbled through the suspensions. The g-irradiation resulted in a diminution of the concentration of ionol, which followed a linear dependence on the absorbed dose, at least until the concentration halved. The radiation yields for the decomposition of ionol were calculated from the linear sections of the ionol consumption plots; they are given in Table 1.It is noteworthy that our study is the first in which the radiation yields of the transformation of a radical acceptor implanted in a liposome membrane were directly determined. It can be seen from Table 1 that the radiation yield of the ionol decomposition G(–PhOH) increases with an increase in its concentration. The largest G value attained was 1.7 molecules of ionol per 100 eV.Since the flux of radicals from the solution bulk depends only slightly on the concentration of liposomes,6 both series of experimental results can be regarded, within experimental accuracy, as a unified set of data, because both series of experimental points fall satisfactorily on a common dependence. The resulting non-linear dependence implies the occurrence of a competition between ionol and lecithin for the radicals resulting from the radiolysis of the disperse system.Transformations of ionol caused by the direct action of radiation can be neglected, because its concentration was small (the electron fraction of ionol in the whole system was less than 0.0003, that of lecithin was less than 0.005). To describe the experimental dependence of the radiation yield of ionol destruction on its initial concentration in the Table 1 Dependence of the radiation yield of the destruction of ionol on the initial concentration of ionol in a lipid membrane for two concentrations of lecithin in an aqueous suspension.Clecithin / mg ml–1 Cionol /mol per g of lipid G/molec per 100 eV Rav/nm 4.8 2.5×10–4 1.3±0.02 56 4.8 2.4×10–4 1.4±0.01 48 4.8 2.0×10–4 1.7±0.03 42 4.8 1.2×10–4 1.1±0.03 40 4.8 8.3×10–5 1.0±0.04 45 4.8 3.4×10–5 0.4±0.06 49 4.8 2.1×10–5 0.5±0.01 43 2.4 2.3×10–4 1.5±0.09 38 2.4 2.0×10–4 1.5±0.02 39 2.4 1.9×10–4 1.1±0.02 50 2.4 1.0×10–4 0.8±0.02 49 2.4 3.6×10–5 0.5±0.03 52Mendeleev Communications Electronic Version, Issue 1, 1998 (pp. 1–42) lecithin membrane, two simplifying assumptions were made.Firstly, we assumed that ionol was uniformly distributed in the liposome membrane and that it reacted with only one sort of radical present in the system. Then we may consider two competing reactions: where PhOH is ionol, Lec is lecithin and K1 and K2 are the rate constants for the corresponding reactions. Using the method of steady-state concentrations, we obtain and where GR 0 is the overall yield of radicals participating in reactions (1) and (2), P is the dose rate and [PhOH] and [Lec] are the concentrations of ionol and lecithin, respectively.A simple expression for the dependence of GR on the lecithin and ionol concentrations follows, which is in good agreement with experimental data. Solution of this equation for each series of lecithin concentrations gives the following average values of GR 0 and K2 /K1 for the two series: Having found the parameters of equation (5), we can reconstruct the exact form of the dependence of the destruction of ionol with the assumption that the method of steady-state concentrations is valid.This curve is described by the following differential equation By substituting expression (5) into (6), we obtain the differential equation Under the boundary condition [PhOH] = [PhOH]0 and at t = 0, the solution of this equation is Within the parameters found from equation (5), equation (8) holds within the accuracy of determination of the ionol concentration and is described satisfactorily by a straight line up to a 50–60% degree of destruction of ionol; after that, the destruction of ionol is retarded.It follows from the above K2 /K1 value that under the assumptions made, ionol is almost 20 times more efficient as a radical acceptor than lecithin. This fact makes it possible to tentatively identify the radical R. Radiolysis of the disperse system under study yields OH and H2O/O2 – radicals, H atoms and hydrated electrons. The concentration of H atoms is very small; hydrated electrons do not react with lecithin;7 besides, both of these species are efficiently trapped by oxygen.The rate constant for the reaction of OH with lecithin was reported7 to be 5×108 dm3 mol–1 s–1. Thus, it can be expected that the rate constant for the reaction of OH with ionol would be ca. 1010 dm3 mol–1 s–1, which is quite permissible in view of the fact that the rate of reaction of lecithin with OH radicals is limited by the hydration shell of lecithin.The HO2/O2 – radicals exhibit a low reactivity towards organic substances except for some radicals and compounds containing charged groups; for example, the rate constants for the reaction of HO2/O2 with molecules containing polar quaternary alkylammonium groups, similar to the choline group of lecithin, are ca. 107–108 dm3 mol–1 s–1.8 It could hardly be expected that the rate constant for the reaction of HO2/O2 – with ionol would be an order of magnitude larger than that for the reaction with lecithin. Therefore, as a first approximation, we consider that the radicals R in our model are OH radicals. This study was supported by the Russian Foundation for Basic Research (grant no. 95-03-09162). References 1 L. B. Margolis and L. D. Bergel’son, Liposomy i ikh vzaimodeistvie s kletkami. Ser. Biologicheskie i Tekhnicheskie Membrany (Liposomes and Their Interaction with Cells, Ser. Biological and Tehnological Membranes), Nauka, Moscow, 1986, p. 240 (in Russian). 2 L-a-Lecithin from Egg Yolk. Technical Requirements 6-09-10-28990 (in Russian). 3 M.V. Genkin, B. P. Ulanov, O. E. Dotsenko and R. V. Davydov, Zh. Fiz. Khim., 1987, 61, 220 (Russ. J. Phys. Chem., 1987, 61, 114). 4 Yu. N. Levchuk and Z. N. Volovik, Biofizika, 1983, 28, 266 (in Russian). 5 V. T. Klenin, Kharakteristicheskie Funktsii Svetorasseyaniya Dispersnykh Sistem (Characteristic Functions of Light Scattering by Disperse Systems), Izdatel’stvo Saratovskogo Universiteta, Saratov, 1977 (in Russian). 6 V. N. Byakov, L. T. Bugaenko and I. G. Bachtadze, Khim. Vys. Energ., 1993, 27, 19 [High Energy Chem. (Engl. Transl.), 1993, 27, 420]. 7 D. J. W. Barber and J. K. Thomas, Rad. Res., 1978, 74, 51. 8 B. H. J. Bielski, D. E. Cabelli, R. L. Arudi and A. B. Ross, Phys. Chem. Ref. Data, 1985, 14, 1041. R + PhOH products, R + Lec products, K1 K2 (1) (2) [R] = GR 0 P/(K1[PhOH] + K2[Lec]) (3) G(–PhOH)P = GR 0 PK1[PhOH]/(K1[PhOH] + K2[Lec]) (4) 1/G(–PhOH) = (1/GR 0 ) (1 + K2[Lec]/K1[PhOH]) (5) GR 0 = 1.7±0.8 molecule/100 eV; K2/K1 = 0.05±0.02 –d[PhOH]/dt = K1[PhOH][R] (6) (1 + K2[Lec]/K1[PhOH])d[PhOH] = GR 0 Pdt (7) GR 0 Pt = ([PhOH]0 – [PhOH]) + (K2[Lec]/K1) ln([PhOH]0/[PhOH]) (8) Received: Moscow, 20th February 1997 Cambridge, 21st October 1997; Com. 7/01442B

ISSN:0959-9436     

出版商:RSC    

年代:1998

数据来源: RSC