Analysis of Linear Free-Energy Relationships Combined with Activation Parameters Assigns a Concerted Mechanism to Alkaline Hydrolysis of X-Substituted Phenyl Diphenylphosphinates
作者:Ik-Hwan Um、Jeong-Yoon Han、So-Jeong Hwang
DOI:10.1002/chem.200800553
日期:2008.8.18
A kinetic study is reported for alkaline hydrolysis of X-substituted phenyl diphenylphosphinates (1 a-i). The Bronsted-type plot for the reactions of 1 a-i is linear over 4.5 pK(a) units with beta(lg)=-0.49, a typical beta(lg) value for reactions which proceed through a concerted mechanism. The Hammett plots correlated with sigma(o) and sigma(-) constants are linear but exhibit many scattered points
动力学研究报道了X-取代的苯基二苯基次膦酸酯(1 ai)的碱性水解。1 ai反应的布朗斯台德型图在4.5 pK(a)单位上呈线性,其中beta(lg)=-0.49,这是通过协调机制进行的反应的典型beta(lg)值。与sigma(o)和sigma(-)常数相关的Hammett图是线性的,但表现出许多分散的点,而相应的Yukawa-Tsuno图则具有出色的线性相关,rho = 1.42和r = 0.35。r值为0.35表示离开组离开在速率确定步骤(RDS)中部分提前。由于进入的HO(-)离子比离去的芳基氧化物更碱性,并且核收性较差,因此排除了在RDS中发生离去基团与加成中间体的离去的逐步机理。还基于小beta(lg)值排除了解离(D(N)+ A(N))机制。随着离去基团中的取代基X从H变为4-NO(2)和3,4-(NO(2))(2),DeltaH ++从11.3 kcal mol(-1)降至9