Alkaline hydrolysis of substituted benzyl substituted benzoates

The kinetics and mechanism of the alkaline hydrolysis of both acyl- and aryl-substituted benzyl benzoates were studied in 80% (v/v) aqueous acetone at 20, 34, and 40 °C. Each of the substituted benzyl alcohols generated an independent σ–ρ plot which was correlated well with the Hammett equation (R = 0·996−0·999). The values of ρ for the acyl moiety showed no tendency either to increase or to decrease with the intrinsic reactivity of the parent benzyl alcohol and were all within ±0·098 of the mean of 2·236. However, the Hammett ρ values for the leaving groups decreased from H to p-NO2 substituents of the acyl part, in which the values were smaller than those of acyl moieties and fairly accurately obeyed the σ0 values rather than the σ values. The rate data for benzyl-substituted benzoates were correlated by the Yukawa–Tsuno equation, log k/k0 = 1·72(σ0 + 0·49Δ) − 0·020, R = 0·996. The results suggested that the alkaline hydrolysis of benzyl benzoates showed a greater sensitivity to acyl than aryl activation, and the rates and activation parameters were largely determined by the addition step. The results are attributed to the preferential partitioning of an unstable tetrahedral intermediate to the products.

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