Nucleofugality of Aliphatic Carboxylates in Mixtures of Aprotic Solvents and Water
作者:Mirela Matić、Bernard Denegri、Olga Kronja
DOI:10.5562/cca2495
日期:——
The leaving group ability (nucleofugality) of fluoroacetate, chloroacetate, bromoacetate, dichloroacetate, trifluoroacetate, trichloroacetate, heptafluorobutyrate, formate, isobutyrate, and pivalate have been derived from the solvolysis rate constants of the corresponding X,Y-substituted benzhydryl carboxylates in 60 % and 80 % aqueous acetonitrile and 60 % aqueous acetone, applying the LFER equation: log k = sf (Ef + Nf). The experimental barriers (iota G(double dagger,exp)) for solvolyses of 11 reference dianisylmethyl carboxylates in these solvents correlate very well (r = 0.994 in all solvents) with iota G(double dagger,model) of the model sigma-assisted heterolytic displacement reaction of cis-2,3-dihydroxycyclopropyl trans-carboxylates calculated earlier. Linear correlation observed between the log k for the reference dianisylmethyl carboxylates and the sf values enables estimation of the reaction constant (sf(estim)). Using the iota Gt(double dagger,exp) vs. iota G(double dagger,model) correlation, and taking the estimated sf(estim), the nucleofugality parameters for other 34 aliphatic carbovlates have been determined in 60 % and 80 % aqueous acetonitrile and 60 % aqueous acetone. The most important variable that determines the reactivity of aliphatic carboxylates in aprotic solvent/water mixtures is the inductive effect of the group(s) attached onto the carboxylate moiety.