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

Abstract

The “parent” tertiary alkyl chloroformate, tert-butyl chloroformate, is unstable, but the tert-butyl chlorothioformate (1) is of increased stability and a kinetic investigation of the solvolyses is presented. Analyses in terms of the simple and extended Grunwald-Winstein equations are carried out. The original one-term equation satisfactorily correlates the data with a sensitivity towards changes in solvent ionizing power of 0.73 ±0.03. When the two-term equation is applied, the sensitivity towards changes in solvent nucleophilicity of 0.13 ± 0.09 is associated with a high (0.17) probability that the term that it governs is not statistically significant.

Evaluation of Electronic Effects in the Solvolyses ofp-Methylphenyl andp-Chlorophenyl Chlorothionoformate Esters

“…On the other hand, for PhOCSCl ( 1 ), an l value of 1.88, an m value of 0.56, and an l/m ratio of 3.36 was obtained [26,27] in nucleophilic solvents favoring the stepwise addition-elimination pathway (Scheme 1), and an l value of 0.34, an m value of 0.93 and an l/m ratio of 0.37 was obtained in the highly ionizing solvents suggesting a dissociative S N 1 mechanism (Scheme 2) with moderate rear-side nucleophilic solvation of the developing carbocation. These results and others recently obtained [18,25-43] clearly demonstrate that the introduction of one sulfur in ROCOCl substrates does induce a variety of superimposed mechanisms and the ranges of dominance is dependent on the R group, the presence of one or two sulfurs, and the types of solvent studied (i.e. on the N T and Y Cl values).…”

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

“…It cannot be automatically assumed that 2° and 3° chlorothioformates will follow this pathway, especially because, although tert -butyl chloroformate is low stability [10], the tert -butyl chlorothioformate is sufficiently stable for it to be commercially available [48]. Indeed, the observation by Queen and co-workers of 2-propanethiol as the major product from the hydrolysis in pure water of isopropyl chlorothioformate [40] requires the retention of the isopropyl-sulfur bond throughout the pathway for this solvolysis.…”

“…Expanding the study to the solvolyses of alkyl chlorothioformates, investigations have been carried out on the solvolyses of the methyl [ 44 ], ethyl [ 45 ], isobutyl [ 46 ], isopropyl [ 47 ], and tert -butyl [ 48 ] esters. All of these solvolyses have been carried out in a selection of solvents with widely varying solvent properties and the analyses have been in terms of the Grunwald-Winstein equations (Equations (1) and (2)).…”

“… a Number of solvents; b With accompanying standard error; c Multiple correlation coefficient; d F -test value; e Data from [ 9 ]; f Using all available solvents; g Data from [ 43 ]; h Data from [ 44 ]; i Data from [ 45 ]; j Data from [ 46 ]; k Data from [ 47 ]; l Data from [ 48 ]; m This correlation is using Equation (1). …”

Correlation of the rates of solvolysis of α-bromoisobutyrophenone using both simple and extended forms of the Grunwald-Winstein equation and the application of correlation analysis to related studies

“…The extended Grunwald-Winstein equation [3-6], which has been found to be very useful in its application to the specific rates of solvolysis of a wide variety of substrates, such as phosphorus compounds [34], silicon compounds [35], acid chlorides [36], chloroformate esters [37], chlorothioformate esters [38], and heterocyclic compounds [39], is here applied to the solvolyses of tertiary alpha-substituted ketones, some of which have, contrary to earlier opinions summarized elsewhere [12], been found to be capable of forming carbocations with the charge formally adjacent to the carbonyl group under solvolytic conditions [10-12]. …”