Esters that have an acidic proton α to the carboxyl group (or in a vinylogous situation) and a good leaving group may undergo hydrolysis by elimination to an intermediate ketene, which rapidly hydrates. Examples are found in p-hydroxybenzoate, malonate, and acetoacetate esters of nitrophenols. The evidence for this mechanism (E1cb type) includes the independence of rate with pH in the region of dissociation of the acidic proton and, in ...
