Kinetic and product analytical study of the effect of substituents upon the solvolysis of benzyl azoxytosylate in aqueous trifluoroethanol

Abstract

Six variously substituted benzyl azoxytosylates, ((1) a: X=4-OCH3, 4-CH3, S-CH3, H, 4-CI, S-CI; Y=4-CH3) three 4-methylbenzyl 4-substituted-azoxyarenesulphonates, ((1) b: X=4-CH3; Y=CW, Br, OCH3), three 3-chlorobenzyl 4-substituted-azoxyarenesulphonates, ((1) c: X=3-CI; Y=CW. Br, OCH3) and three 3-chlorobenzyl 4-substituted-arenesulphonates, ((2): X=3-C1; Z=CW, Br, OCH3) have been prepared, and the rates and activation parameters of their solvolysis in 1:1 v/v aqueous 2,2,2-trifluoroethanol studied. For each series of compounds k28°c ¬has been correlated with v or v¬- in a Hammett-type study and the following p-values were obtained1- (1)a: p(r+) = -S.27, r > 0.999; (1)b: p(σ) = +1.37, r > 0.999. Using these p-values, it has been established, that, in the transition state of the solvolysis of (1), the cleavage of bonds (a) and (b) is concerted. In addition, from the relative magnitude of the p-values, the position of the transition state on the reaction map has been deduced. The unusual correlation of compounds (1)c with v- (p is positive) is discussed in terms of resonance stabalisation of the ground state by electron withdrawing substituents. Product analyses (some of a preliminary nature) have been carried out of the solvolysis of (1)a: X= 4-CH3, 4-OCH3, 3-CI and the arenesulphonates, (2).