Role of solvent in the solvolysis of tert-alkyl halides

Abstract

In the Winstein-Grunwald relationship for solvolysis reactions, log k¡k0 = mY, Fis a parameter taken to represent "solvent ionizing power" and not the nucleophilicity of the solvent or its ability to promote rate-determining elimination. Using r-butyl chloride, the reference compound chosen by Winstein and Grunwald to evaluate F, it is impossible to rule out these other mechanistic contributions. In order to assess the role of solvent, rate constants for solvolysis of 1-adamantyl bromide in fourteen solvents were determined; data for eight additional solvents were obtained from the literature. In such a bridgehead substrate, backside nucleophilic solvent attack and elimination are both impossible. In general, an excellent correlation between data for r-butyl chloride and 1-adamantyl bromide is found indicating that r-butyl chloride, in most instances, solvolyzes by a limiting mechanism, free from nucleophilic solvent participation and from rate-determining elimination. Significant dispersion is found for aqueous trifluoroethanol solvent systems; this deviation is discussed in terms of specific substrate and leaving group effects. The Winstein-Grunwald relationship for solvolysis reactions, log k/ko = mY, affords a useful although not entirely precise tool for the calculation of solvolysis rates.3 The parameter m is taken to be a measure

Concentrated salt effects on the rates of solvolyses involving carbocations as reaction intermediates in acetone–water mixed solvents

“…8 Fig. 1 shows that the log (k/s Ϫ1 ) values for the solvolysis rates of tert-butyl chloride in 90 vol% acetone-10 vol% H 2 O at 50 ЊC were almost linear with respect to the concentrations of metal perchlorates.…”

The kinetics and mechanisms of organic reactions in liquid ammonia

“…Schleyer later showed that the solvolysis of t-butyl and 1-or 2-adamantyl chlorides and adamantyl tosylates occur without nucleophilic assistance from the solvent and can be best regarded as "true" S N 1 process, although protic solvents can facilitate the expulsion of the leaving anion by strong Introduction 23 hydrogen bonding. 35 However, studies also found that the solvolysis rates for t-butyl chloride and adamantyl chloride are very different in some nucleophilic solvents, which suggests partial nucleophilic assistance from some solvents. 36 In order to account for possible nucleophilic solvent assistance, the Grunwald-Winstein equation was later modified to a multiple parameter one (Equation 3).…”

Revisiting the Reactions of t‐BuX (X = Br, I) with Monoalcohols: A Mechanistic Analysis through Numerical Integration and Nonlinear Regression Methods

“…Since the pioneering work by Hughes and Ingold in 1935 , the reactions of tertiary alkyl halides, and in particular of tertiary butyl halides, (CH 3 ) 3 CX (or t– BuX, where X stands for Cl, Br, or I) with hydroxylic solvents have been thoroughly investigated and commonly considered to follow first‐order kinetics . However, most of the published studies were limited to the only generally acknowledged meaningful reaction step, viz .…”