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991.
以二甲酰亚胺钾3a~3g与2-氯-5-氯甲基吡啶的N原子氧化后得到的2-氯-1-氧-5-氯甲基吡啶发生亲核取代反应, 用传统和微波两种方法合成了7种未见文献报到的化合物N-(2-氯-1-氧-5-吡啶甲基)二甲酰亚胺类化合物4a~4g. 对比两种合成方法, 在常压下, 微波辐射作为反应热源具有用时少、环境友好、易纯化和产率高的特点. 这些目标化合物4a~4g的结构经元素分析结果, IR, GC-MS, 1H NMR, 13C NMR确证. 初步的生物活性测定结果表明, N-(2-氯-1-氧-5-吡啶甲基)二甲酰亚胺类部分化合物具有良好的杀虫活性. 相似文献
992.
以2-溴丙酸甲酯、α,α-二氯甲基甲醚和胍唑为原料, 经缩合以及环化反应制得2-氨基-6-甲基-5-氧代-4,5-二氢-1,2,4-三氮唑并[1,5-a]嘧啶. 为了提高其在有机溶剂中的溶解性, 该化合物再同1-溴丁烷发生亲核取代反应得到了2-氨基-6-甲基-5-氧代-4-正丁基-4,5-二氢-1,2,4-三氮唑并[1,5-a]嘧啶, 然后与芳基醛和叔丁基异氰发生Ugi多组分反应, 合成了一系列具有潜在催吐活性的2-取代氨基-6-甲基-5-氧代-4-正丁基-4,5-二氢-1,2,4-三氮唑并[1,5-a]嘧啶类衍生物, 产品结构经质谱、核磁共振谱及元素分析确认. 相似文献
993.
Evgenij V. Zarudnitskii Anatolij S. Merkulov Andrej A. Tolmachev 《Tetrahedron》2008,64(45):10431-10442
The reactivity of 2-aryl-5-trimethylsilyl-1,3,4-oxadiazoles toward different types of electrophiles was investigated. These silanes readily react with chlorine, bromine, aliphatic acyl chlorides, 2-nitrobenzenesulfenyl chloride, and some reactive isocyanates affording the corresponding substituted 1,3,4-oxadiazoles. The reactions with carbonyl compounds proceed only in the presence of F− anions. 相似文献
994.
L. N. Vakhitova K. V. Bogutskaya N. A. Taran N. G. Razumova V. A. Savelova A. F. Popov 《Theoretical and Experimental Chemistry》2008,44(2):84-92
The acid-base equilibrium of hydrogen peroxide in aqueous solutions of CTAB and the reactivity of the peroxide anion toward
4-nitrophenyl diethylphosphate and 4-toluenesulfonate were studied. It was shown that the acid ionization rate constant of
hydrogen peroxide is increased by three times with increase in the CTAB concentration from 0 to 0.03 M. This makes it possible
to realize the decomposition of the substrates by their reaction with the peroxide anion at lower pH values in micellar cationic
systems than in aqueous solutions.
__________
Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 44, No. 2, pp. 83–89, March–April, 2008. 相似文献
995.
Jacobsson M Oxgaard J Abrahamsson CO Norrby PO Goddard WA Ellervik U 《Chemistry (Weinheim an der Bergstrasse, Germany)》2008,14(13):3954-3960
The mechanism for the acid-mediated substitution of a phenolic hydroxyl group with a sulfur nucleophile has been investigated by a combination of experimental and theoretical methods. We conclude that the mechanism is distinctively different in nonpolar solvents (i.e., toluene) compared with polar solvents. The cationic mechanism, proposed for the reaction in polar solvents, is not feasible and the reaction instead proceeds through a multistep mechanism in which the acid (pTsOH) mediates the proton shuffling. From DFT calculations, we found a rate-determining transition state with protonation of the hydroxyl group to generate free water and a tight ion pair between a cationic protonated naphthalene species and a tosylate anion. Kinetic experiments support this mechanism and show that, at moderate concentrations, the reaction is first order with respect to 2-naphthol, n-propanethiol, and p-toluenesulfonic acid (pTsOH). Experimentally determined activation parameters are similar to the calculated values (Delta H exp not equal =105+/-9, Delta H calcd not equal =118 kJ mol(-1); Delta G exp not equal =112+/-18, Delta G calcd not equal =142 kJ mol(-1)). 相似文献
996.
We have designed a new library of readily available, highly modular phosphite-phosphoramidite ligands for asymmetric allylic substitution reactions. They are easily prepared in one step from commercially available chiral 1,2-amino alcohols. The introduction of a phosphoramidite moiety into the ligand design is highly advantageous for the product outcome. This ligand library affords high reaction rates (TOFs of up to 800 mol (mol h)(-1)) and enantioselectivities (ees of up to 99%) and, at the same time, contains a broad range of disubstituted hindered and unhindered substrate types. NMR study of the Pd-pi-allyl intermediates provide a deeper understanding of the effect of the ligand parameters on the origin of enantioselectivity. 相似文献
997.
Carboxymethyl potato starch (CMPS) was synthesized under heterogeneous reaction conditions. The influences of etherification temperature, alkalization and etherification time, sodium hydroxide to monochloroacetic acid (MCA) molar ratio (nNaOH/nMCA), theoretical degree of substitution (DSt), the ratio of isopropyl alcohol (IPA) volume to starch mass (vIPA/mst) on degree of substitution (DS) and reaction efficiency (RE) of CMPS were investigated. Compared with the previous literature data, the results had significant difference for the optimal carboxymethylation conditions of potato starch from different sources. CMPS prepared under optimal conditions showed the highest DS and RE, which were 1.36 and 0.88, respectively. Furthermore, the RE value in this work is considerably higher than that reported in the literature. The time of alkalization and etherification were also discussed independently. In addition, CMPS was characterized by Fourier transform infrared spectrophotometry and scanning electron microscopy (SEM). Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
998.
We have theoretically studied the gas‐phase nucleophilic substitution at group‐14 atoms (SN2@A) in the model reactions of Cl?+AH3Cl (A=C, Si, Ge, Sn, and Pb) using relativistic density functional theory (DFT) at ZORA‐OLYP/TZ2P. Firstly, we wish to explore and understand how the reaction coordinate ζ, and potential energy surfaces (PES) along ζ, vary as the center of nucleophilic attack changes from carbon to the heavier group‐14 atoms. Secondly, a comparison between the more common backside reaction (SN2‐b) and the frontside pathway (SN2‐f) is performed. The SN2‐b reaction is found to have a central barrier for A=C, but none for the other group‐14 atoms, A=Si–Pb. Relativistic effects destabilize reactant complexes and transition species by up to 10 kcal mol?1 (for SN2‐f@Pb), but they do not change relative heights of barriers. We also address the nature of the transformation in the frontside SN2‐f reactions in terms of turnstile rotation versus Berry‐pseudorotation mechanism. 相似文献
999.
Debaprasad Mandal Dr. Markus Jurisch Dipl.‐Chem. Crestina S. Consorti Dr. John A. Gladysz Prof. Dr. 《化学:亚洲杂志》2008,3(10):1772-1782
Solutions of the fluorous alkyl halides Rf8(CH2)mX (Rfn=(CF2)n?1CF3; m=2, 3; X=Cl, Br, I) in perfluoromethylcyclohexane or perfluoromethyldecalin are inert towards solid or aqueous NaCl, NaBr, KI, KCN, and NaOAc. However, halide substitution occurs in the presence of fluorous phosphonium salts (Rf8(CH2)2)(Rf6(CH2)2)3P+X? (X=I ( 1 ), Br ( 3 )) and (Rf8(CH2)2)4P+I? (10 mol %), which are soluble in the fluorous solvents under the reaction conditions (76–100 °C). Stoichiometric reactions of a) 1 with Rf8(CH2)2Br and b) 3 with Rf8(CH2)2I were conducted under homogenous conditions in perfluoromethyldecalin at 100 °C and yielded the same Rf8(CH2)2I/Rf8(CH2)2Br equilibrium ratio (≈60:40). This shows that ionic displacements can take place in extremely nonpolar fluorous phases and suggests a classical phase‐transfer mechanism for the catalyzed reactions. Interestingly, the nonfluorous salt (CH3(CH2)11)(CH3(CH2)7)3P+I? ( 4 ) also catalyzes halide substitutions, but under triphasic conditions with 4 suspended between the lower fluorous and upper aqueous layers. NMR experiments established very low solubilities in both phases, which suggests interfacial catalysis. Catalyst 1 is easily recycled, optimally by simple precipitation onto teflon tape. 相似文献
1000.