THE E1CB MECHANISM IN THE ALKALINE-HYDROLYSIS OF N,N-DIETHYL-P-(3,5-DIMETHYL-4-HYDROXYPHENYL)PHOSPHONAMIDIC CHLORIDE

The alkaline hydrolysis of the title compound 1 proceeds via an E1cB mechanism. A tricoordinate phosphorus species intermediate 3, or a metaphosphate-like transition state, constitutes the best hypothesis accounting for the observed kinetic results. The apparent bimolecular rate constant for the attack of hydroxide ion on the neutral 4-hydroxy-substituted chloride (k(a)K(a)/K(w)) is more than 5 orders of magnitude larger than the true bimolecular rate constant for the attack of HO- on the corresponding methoxy chloride 2 which possesses the S(N)2(P) mechanism. Support of the E1cB mechanism proposed for 1 comes also from activation entropy studies and by the effect of added nitrogen nucleophiles on reaction rates.