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运用密度泛函理论(DFT)的B3LYP方法,在6-311~(++)G(d,p)基组水平上,采用CPCM模型对水溶剂条件下4种卤代羧酸和4种羰基(氰基)羧酸在无催化剂及水催化条件下的脱羧反应机理进行了研究。结果表明,在卤代羧酸的脱羧反应中,水催化时反应比无催化剂参与时容易,其中CCl_3COOH(A)和CF_3COOH(C)脱羧(H_2O催化)所需克服的能垒分别为192.60、210.33 kJ/mol,与Belsky等的实验结果基本一致。而对于4种羰基(氰基)羧酸,无水参与时脱羧主要经六元环过渡态进行,反应的活化能分别为300.01(CH_3COCOOH)、160.02(CNCH_2COOH)、94.01(CHOCH_2COOH)、105.26(NH_2COCH_2COOH)kJ/mol,比H_2O催化时反应的活化能低。
Based on the B3LYP method of density functional theory (DFT), CPCM model was used to determine the content of 4 kinds of halocarboxylic acids and 4 kinds of carbonyl groups in aqueous solution under 6-311 ~ (++) G (d, p) (Cyano) carboxylic acid in the absence of catalyst and water decarboxylation reaction under the catalytic conditions were studied. The results showed that in the decarboxylation reaction of halocarboxylic acids, the reaction when water catalyzed was easier than that without catalyst. The energy barriers to be overcome by decarboxylation (H_2O catalysis) of CCl_3COOH (A) and CF_3COOH (C) were 192.60 and 210.33 kJ / mol, and Belsky other experimental results are basically the same. For the four kinds of carbonyl (cyano) carboxylic acids, the decarboxylation was mainly carried out via the six-membered ring transition state under anhydrous conditions. The activation energies of the reaction were 300.01 (CH_3COCOOH), 160.02 (CNCH_2COOH), 94.01 (CHOCH_2COOH), 105.26 (NH_2COCH_2COOH ) kJ / mol, the activation energy is lower than the reaction of H_2O.