A phosphate-catalysed acyl transfer reaction. Hydrolysis of 4-nitrophenyl acetate in phosphate buffers

Abstract

The pseudo-first-order rate constants for the phosphate-catalysed hydrolysis of 4-nitrophenyl acetate have been determined in water at 310.5 K. The reaction has been followed spectrophotometrically by the disappearance of the ester and with n.m.r, spectroscopy by the appearance of both acetyl phosphate and the acetate ion and by the disappearance of ester. A phosphate-catalysed acyl transfer mechanism has been identified, in which the aryl ester is attacked by phosphate to give acetyl phosphate which is subsequently hydrolysed by water to acetate ion and regenerated catalyst. At concentrations of total phosphate exceeding 1.0 mol dm-3 the presence of dimeric phosphate species causes the appearance of a non-linear rate-concentration profile. Catalysis has been also been observed in 2,2'-(propane-1,3-diyldiimino)bis(propane-1,3-diol) buffer solutions.