Steric Effects in the Hydrolysis Reactions of <i>N</i>-Acylimidazoles. Effect of Aryl Substitution in the Leaving Group
作者:J. P. Lee、Ramesh Bembi、Thomas H. Fife
DOI:10.1021/jo960508d
日期:1997.5.1
The kinetic and mechanistic effects of aryl substitution in the leaving group have been determined in the hydrolysis reactions of N-acylimidazoles. N-Acyl derivatives of 2,4,5-triphenylimidazole hydrolyze rapidly in OH(-) and water reactions. The latter reactions are pH independent from pH 4 to 9. The N-acetyl derivative hydrolyzes with rate constants similar to those of N-acetylimidazole in the OH(-)
在N-酰基咪唑的水解反应中已经确定了在离去基团中芳基取代的动力学和机理作用。2,4,5-三苯基咪唑的N-酰基衍生物在OH(-)和水反应中迅速水解。后面的反应的pH值不受pH值4到9的影响。N-乙酰基衍生物的水解速率常数类似于OH(-)反应中N-乙酰基咪唑的速率常数,但在非pH依赖性反应中的水解速率大40倍。N-(三甲基乙酰基)-2,4,5-三苯基咪唑在15摄氏度下与k(OH)水解,k(OH)反应的二级速率常数比碱性水解的速率常数大26倍。即使在前一反应中对亲核试剂接近的空间位阻是极端的,也可以得到相应的N-乙酰基衍生物。N-三甲基乙酰基化合物的pH依赖性反应比N-乙酰基衍生物的pH依赖性反应快4倍,其特征是D(2)O溶剂同位素效应(k(H)2(O)/ k(D )2(O))的2.0。咪唑环的2-位上的苯基取代基在水解反应中具有较小的缓速作用。在30°C下,N-(三甲基乙酰基)-4,5-二苯基