The kinetics of methanolysis of substituted benzamide O-(phenoxycarbonyl)- and O-(alkoxycarbonyl)oximes catalyzed by sodium methanolate was studied at 25 °C. The reaction proceeds in two steps. In the first, faster step, the substituted phenoxy group is exchanged for a methoxy group giving rise to substituted O-(methoxycarbonyl)oximes. In the second step, a benzamide oxime is eliminated and dimethyl carbonate is formed. The slope of the plot of the rate constant in dependence on the sodium methanolate concentration has an increasing tendency in both steps. In the presence of 18-crown-6, the plots are linear and the rate constants are lower than in the absence of the crown ether. The rate constants of the reaction of the substrate with the methanolate ion and with the MeONa ion pair were determined assuming that the sodium cation-catalyzed reactions constitute the rate-determining step of the reaction of the substrate with the MeONa ion pair. For the elimination of the aryloxy group and of the substituted benzamide oxime, the rate constants of the reaction with the ion pair are roughly twelvefold and twentyfold higher, respectively, than in the uncatalyzed reaction. The slope of the dependence of log k on the pKa of the substituted phenols (βlg) has the value of -0.52 for the uncatalyzed reaction of elimination of the substituted phenoxy group, -0.83 for the elimination of the benzamide oxime group, and -0.53 for the reaction with the ion pair. In the first step and probably also in the second step, the reaction proceeds by the concerted mechanism. The relatively high ρ value of methanolysis of substituted benzamide O-(4-nitrophenoxycarbonyl)oximes, 0.63, suggests that the structure of the transition state approaches that of the tetrahedral intermediate.
对苯甲酰胺取代物的甲醇解反应动力学,如在25°C下由甲醇酸钠催化的O-(苯氧羰基)-和O-(烷氧羰基)肟进行了研究。该反应分为两步。在第一步中,取代苯氧基被交换成甲氧基,形成取代的O-(甲氧羰基)肟,这是一个较快的步骤。在第二步中,苯甲酰胺肟被消除,生成二甲基碳酸酯。在两个步骤中,速率常数与甲醇酸钠浓度的关系图的斜率均呈增加趋势。在18-冠-6的存在下,图形是线性的,速率常数比没有冠醚存在时更低。假设钠阳离子催化的反应构成了与MeONa离子对反应的反应速率决定步骤,确定了底物与甲醇酸钠离子对反应的速率常数。对于芳氧基和取代苯甲酰胺肟的消除,与离子对反应的速率常数分别比非催化反应高大约12倍和20倍。对于取代酚的pKa的对数值(βlg)的依赖关系的斜率,未催化消除取代苯氧基反应的值为-0.52,消除苯甲酰胺肟基团的值为-0.83,与离子对反应的值为-0.53。在第一步和可能也在第二步中,反应通过协同机制进行。对于取代苯甲酰胺O-(4-硝基苯氧羰基)肟的甲醇解反应的相对较高的ρ值,0.63,表明过渡态的结构接近四面体中间体的结构。