Kinetic evaluation of the solvolysis of isobutyl chloro- and chlorothioformate esters

Abstract

SummaryThe specific rates of solvolysis of isobutyl chloroformate (1) are reported at 40.0 °C and those for isobutyl chlorothioformate (2) are reported at 25.0 °C, in a variety of pure and binary aqueous organic mixtures with wide ranging nucleophilicity and ionizing power. For 1, we also report the first-order rate constants determined at different temperatures in pure ethanol (EtOH), methanol (MeOH), 80% EtOH, and in both 97% and 70% 2,2,2-trifluoroethanol (TFE). The enthalpy (ΔH≠) and entropy (ΔS≠) of activation values obtained from Arrhenius plots for 1 in these five solvents are reported. The specific rates of solvolysis were analyzed using the extended Grunwald–Winstein equation. Results obtained from correlation analysis using this linear free energy relationship (LFER) reinforce our previous suggestion that side-by-side addition–elimination and ionization mechanisms operate, and the relative importance is dependent on the type of chloro- or chlorothioformate substrate and the solvent.

Influence of Sulfur for Oxygen Substitution in the Solvolytic Reactions of Chloroformate Esters and Related Compounds

“…Similarly, the primary isobutyl chlorothioformate also reacts primarily by the ionization pathway [46], with evidence for a dominant A-E pathway only in 100% and 90% ethanol, 100% and 90% methanol, and 20% TFE-80% ethanol.…”

Correlation of the rates of solvolysis of tert-butyl chlorothioformate and observations concerning the reaction mechanism

“…In the present study we consider the solvolyses of a tertiary alkyl chlorothioformate ( t -BuSCOCl, 1 ). It has previously been shown [5–9] for chloroformates that the replacement of the alkoxy oxygen by sulfur leads to a move away from an addition-elimination mechanism (Scheme 1) towards one of several possible ionization mechanisms (Scheme 2). …”

The Grunwald-Winstein Relationship in the Solvolysis of β-Substituted Chloroformate Ester Derivatives: The Solvolysis of 2-Phenylethyl and 2,2-Diphenylethyl Chloroformates

“…The solvent systems divided into 100%TFE, 97%TFE, 97, 90, 70, 50%HFIP (n = 6) and the remainder (n = 22), from ref. [13]. h From ref.…”

“…(1) and (2), we previously reported that the results of primary, secondary and tertiary alkyl chloroformates (ROCOCl) in a wide range of solvent mixtures can follow bimolecular and/or unimolecular pathways. [10][11][12][13][14][15][16][17] Kevill and D'Souza 10 showed that, particularly in ethyl chloroformate (4,EtOCOCl) solvolysis, an addition-elimination mechanism dominates [l = 1.56, m = 0.55] in all except the highly ionizing solvents, and the major reaction channel in the least nucleophilic solvents involves ionization mechanism [l = 0.69, m = 0.82]. Bentley et al also carried out a series studies of the solvolyses of acyl chloride and their derivatives using the G-W equation.…”