Concurrent nucleophilic and general acid catalysis of the hydrolysis of a phosphate triester
作者:Nabil Asaad、Anthony J. Kirby
DOI:10.1039/b204609a
日期:2002.10.1
The hydrolysis of diethyl 8-dimethylaminonaphthyl-1-phosphate is catalysed by the neighbouring dimethylammonium group, with a rate acceleration, compared with diethyl naphthyl-1-phosphate, of almost 106. The effective pKa of the naphtholate leaving group is reduced from 9.4 to 3.4 by partial protonation in the transition state. The reaction is catalysed by oxyanion nucleophiles, and it is shown that a common nucleophilic mechanism, enhanced by general acid catalysis by the neighbouring dimethylammonium group, accounts for all the observed reactions. The efficiency of general acid catalysis depends on the extent of negative charge development on the leaving group oxygen in the transition state for P–O cleavage, and the strength of the intramolecular hydrogen bond in reactant and transition state.
8 二甲基氨基萘-1-磷酸二乙酯的水解是由邻近的二甲基铵基催化的,与萘-1-磷酸二乙酯相比,水解速度加快了近 106 倍。萘酚离去基团的有效 pKa 因过渡态中的部分质子化而从 9.4 降至 3.4。该反应由氧阴离子亲核物催化,研究表明,邻近的二甲基铵基团的一般酸催化增强了共同的亲核机理,从而解释了所有观察到的反应。一般酸催化的效率取决于 P-O 裂解过渡态中离去基团氧上负电荷的发展程度,以及反应物和过渡态中分子内氢键的强度。