KINETICS OF CARBAMATE FORMATION AND BREAKDOWN
KINETICS OF CARBAMATE FORMATION AND BREAKDOWN
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DOI：
10.1021/ja01026a041
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发表时间：
1968-01-01
影响因子：
15
通讯作者：
CAPLOW, M
中科院分区：
文献类型：
--
作者：
CAPLOW, M
胺与二氧化碳反应的速率定律是速率=芳胺（R2 NH）（CO2）+芳胺（R2 NH）（OH）（CO2），其中第一项和第二项用于未催化的和氢氧化物催化的途径。后一种反应，其中涉及质子提取的速率决定步骤中，没有观察到所有的胺。在10处的μ amme值遵循布朗斯台德关系log fcamine（M-1 sec-1）= mpK+ Y，其中对于伯胺和仲胺的反应，m和Y的值等于0.43和-1.50，对于肼和羟胺衍生物的反应，m和Y的值等于0.48和-0.20。氢离子催化的氨基甲酸酯脱羧反应的二级速率常数（pK = 1.05 ~约5）可用Brpnsted关系式log ks*（M ~（-1）sec ~（-1））= 0拟合。10 ℃时11 pK + 3.6。由碱性更强的胺生成氨基甲酸酯的速率几乎与碱度无关，约为108 M~ 1秒~（-1）。氨基甲酸酯的形成和分解与弱碱性胺的限速步骤涉及碳-氮键的形成和裂解。质子转移可能是碱性胺生成氨基甲酸酯的限速反应，氨基甲酸（N-羧基生物素）是几种酶催化的二氧化碳转移反应的中间产物。为了更好地了解这种中间体的化学和动力学性质，我们以前进行了carboxybiotin类似物，N-羧基咪唑烷酮的动力学分析。2我们现在报告了这项工作的扩展，其中研究了具有广泛不同结构和碱性的胺的氨基甲酸酯的形成和分解。
Therate law for reaction of amines with carbon dioxide is rate=^ ami „e (R2NH)(C02)+ Aramine'(R2NH)(0H)(C02), where the first and second terms are for uncatalyzed and hydroxide-catalyzed pathways. The latter reaction, which involves proton abstraction in the rate-determining step, is not observed with all amines. Values for^ amme at 10 follow the Brpnsted relationship log fcamine (M-1 sec-1)= mpK+ Y, with values of m and Y equal to 0.43 and—1.50 for reactions of primary and secondary amines, and 0.48 and—0.20 for the reactions of hydrazine and hydroxylamine derivatives. Second-order rate constants for hydrogen ion catalyzed decarboxylation of car-bamates formedfrom amines of pK— 1.05 to approximately 5 may be fitted to a Brpnsted relationship log ks*(M-1 sec-1)= O. llpK+ 3.6 at 10. Rates for carbamates formedfrom more basic amines are virtually independent of basicity and are approximately 108 M~ l sec-1. The rate-limiting step in carbamate formation and breakdown with weaklybasic amines involves carbon-nitrogen bond formation and cleavage. It is suggested that proton transfer may be rate limiting in the synthesis and breakdown of carbamates formed from basic amines.Acarbamic acid, N-carboxybiotin, is formed as an intermediate in several enzyme-catalyzed carbon dioxide transfer reactions. To better understand the chemical and kinetic properties of this intermediate we have previously carried out a kinetic analysis of a car-boxybiotin analog, N-carboxyimidazolidone. 2 We now report an extension of this work in whichcarbamate for-mation and breakdown have been studied with amines with widely varying structure and basicity.