The Mechanism for Hydrolysis of Primary Alkyl Chlorosulfates in Water. The Kinetic Solvent Isotope Effect and the Secondary Deuterium Isotope Effect

Abstract

The temperature coefficients of the enthalpy of activation (AC;) for the hydrolysis of the three chlorosulfates, methyl, ethyl, and 8-chloro, are shown to have values of -50, -55, and -60 cal deg-' mol-'; values in the same range as previously reported for the hydrolysis of the sulfonyl chlorides. The corresponding value for the 8-methoxy isomer was -40 cal deg-' mol-', about the same as found for the p-methoxybenzenesulfonyl chloride. The kinetic solvent isotope effect, however, was significantly lower than reported for the sulfonyl chloride series, being about the same as found for the hydrolysis of the alkyl halides. While some degree of nucleophilic overlap is probably required in the activation process, the requirement here is reduced to about the same level as that for the primary halides, and there is no need to postulate a different mechanism on passing from the methyl to the ethyl member of the series, confirming the earlier conclusion of Buncel and Millington.On montre que les coefficients de temptrature de l'enthalpie d'activation (Ac: ) pour I'hydrolyse des trois chlorosulfates, mtthyle, Cthyle, et /I-chloro, ont les valeurs de -50, -55, et -60 cal deg-' mol-' ; valeurs se situant dans le mime domaine que celle rapporttes prtctdemment pour I'hydrolyse des chlorures de sulfonyl. La valeur correspondante pour I'isomtre /3-mtthoxy ttait de -40 cal deg-' mol-, environ la m&me que celle trouvte pour le chlorure de p-mtthoxybenztnesulfonyl. L'effet cinttique de solvant isotopique ttait toutefois largement plus faible que celui rapport6 pour la strie des chlorures de sulfonyl et ressemblait a celui qu'on avait trouvt pour I'hydrolyse des halogtnures d'alkyles. Alors que le proctdt d'activation demande un certain degrt de recouvrement nuclbophilique, le recouvrement dans le cas qui nous concerne est rtduit environ au mime niveau que dans le cas des halogtnures primaires, sans besoin de postuler un mtcanisme de passage difftrent du mtthyle a I'tthyle dans la strie, confirmant une conclusion prtcedente de Buncel et Millington.

Kinetics of hydrolysis of 1-benzoyl-1,2,4-triazole in aqueous solution as a function of temperature near the temperature of maximum density, and the isochoric controversy

“…In fact, this pattern is shown by published kinetic data for hydrolysis reactions in aqueous solutions as reported by Robertson and co-workers. These data sets also include kinetic data for solvolysis of a range of compounds in water 22-30 and in D 2 O, 22,23,25,31 the TMD of the latter being 284.35 K. The compounds included methyl trifluoroethanoate, succinic and phthalic anhydride, 22 dimethylsulfamoyl chloride, 23 diethyl and methyl(ethyl)sulfamoyl chloride, 24 methanesulfonyl and benzenesulfonyl chloride, 25 methyl chlorosulfate and ethyl chlorosulfate, 27 2-chloroethyl(methyl) sulfide, 28 methyl methanesulfonate 29 and 4-substituted benzenesulfonyl chlorides. 30 Moelwyn-Hughes et al 26 reported rate constants for the solvolysis of 2-chloro-2 methylpropane in aqueous solution at intervals of 1 K from 273.15 to 298.15 K. Novel features in the kinetic data can neither be discerned from isobaric pairs of temperatures nor from around the TMD.…”

Solvent effect correlations and the mechanism of solvolysis of alkyl chlorosulfates

“…which is reflected ill low substrate \ d u e s (n?) and 111 srnall solvatlon nun~bers (11). i n~g h t be lespons~ble for the abnornlally lalge entrop~es of a c t~~a t l o n characteristic of chlorosulfate solvolysis Solvatlon numbel s reflect the degree of reorgan~zation of solkent molecules necessary in the formation of the transition state: the greater the solvent -reorganizat~on, the more negative mrght AS* be expected to be (27,34).…”

“…Related mechanistic studies of chlorosulfates have been reported from this as well as other laboratories (10-12). Solvolytic studies of sulfonyl chlorides (1 [3][4][5][6][7][8][9][10][11][12][13][14][15][16] also have a bearing on this work. In Table 1 are presented the data for the conductimetrically determined rates of hydrolysis of ethyl, n-propyl, isobutyl, and neopentyl chlorosulfate in various dioxane-water media at 25°C.…”