Aminolysis of X-substituted phenyl diphenylphosphinates: Effect of amine nature on reactivity and transition-state structure

Abstract

A kinetic study is reported for aminolysis of X-substituted phenyl diphenylphosphinates (1a-i) in 80 mol % H 2O/20 mol % dimethyl sulfoxide at 25.0 ±0.1 °C. The Brønsted-type plot for the reactions of 2,4-dinitrophenyl diphenylphosphinate (1a) with primary amines is linear withβ nuc = 0.53. The reactions of 1a-i with ethylamine also result in a linear Brønsted-type plot with β lg = -0.81. These β nuc and β lg values are slightly larger than those reported previously for the reactions of 1a with secondary amines (β nuc = 0.38) and for those of 1a-i with piperidine (β lg = -0.66) but typical for reactions that proceed through a concerted mechanism. It has been concluded that aminolysis of 1a-i proceed through a concerted mechanism and the nature of amines does not affect the reaction mechanism. However, the reactions with primary amines have been suggested to proceed through a later transition state (i.e., more bond formation and bond rupture in the transition state) on the basis of the larger β nuc and β lg values. The concerted mechanism has been further supported from the fact that the Yukawa-Tsuno plot for the reactions of 1a-i with ethylamine exhibits an excellent linear correlation with ρ = 2.24 and r = 0.22. Weakly basic primary amines are less reactive than secondary amines of similar basicity. However, strongly basic ethylamine is ca. 2-fold more reactive than piperidine toward 1a, although the former is 0.35 pK a units less basic than the latter. © 2009 American Chemical Society.