Mechanism of alkaline hydrolysis of some HO-pi-COOAr acyl derivatives

To gain knowledge on the role played by the nature of the bridge interposed between hydroxyl and carbonyl groups in esters of the title type, in princ iple able to hydrolyze through dissociative pathways via the conjugate base of the substrate (E1cB mechanism), we have studied the alkaline hydrolyses of 2,4-dinitrophenyl esters in which the pi-system is a biphenyl, azobenze n, benzylideneaniline, or stilbene skeleton. Kinetic data, such as reactivi ty comparisons and Arrhenius parameters, show that these substrates react t hrough the usual, associative, B(Ac)2 mechanism. This outcome is discussed and interpreted from both structural and energetic standpoints. The data su ggest that a value of 0.0 is the most appropriate assignment of the sigma(p ) value for the benzylidenamino substituent (C6H5CH=N-).