Heat capacity of activation for the hydrolysis of methanesulfonyl chloride and benzenesulfonyl chloride in light and heavy water

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The temperature dependence of the rate of solvolysis of t-butyl chloride in mixtures of tetrahydrofuran and of acetonitrile in water have been determined. In the high-water range both minor co-solvents lead t o a reduction in the value ofAHf similar to that found previously where alcohol was the co-solvent. However, a remarkable difference in the values of A C~ across the same concentration range reflected a difference in the effect of these two co-solvents on the structural properties of the several solvent media. Where tetrahydrofuran or alcohols are the mirior co-solvent, AC,f becomes much more negative until that concentration is reached where the quasi-aqueous structure collapses. Where acetonitrile is the minor co-solvent A C~ becomes more positive relative to the value found for hydrolysis in water until a value of about -40 cal deg-' mol-' is reached. The implication of these findings concerning the nature of solvation of weakly polar solutes in such mixtures is discussed.On a determine I'influence de la temperature sur la solvolyse du chlorure de r-butyl dans des melanges de tetrahydrofuranne et d'acetonitrile dans l'eau. Dans le domaine de haute concentration en eau, les deux co-solvants mineurs menent a une rtduction de la valeur de AH+ semblable a celle qu'on a trouve precedemment, ou I'alcool Ctait le co-solvant. Toutefois, une difference remarquable dans les valeurs de A C ,~ dans le meme domaine de concentration reflete une difference de I'effet de ces deux co-solvants sur les proprittes structurales des differents milieux de solvants. Lorsque la tttrahydrofuranne ou les alcools sont le co-solvant mineur, A C~ devient beaucoup plus negatifjusqu'a ce qu'on atteigne la concentration ou la structure quasi-aqueuse s'effondre. Lorsque l'acetonitrile est le co-solvant mineur, A C~ devient plus positif comparativement a la valeur qu'on trouve pour I'hydrolyse dans I'eau, jusqu'a ce qu'on atteigne une valeur d'environ -40 cal deg-' mol-I. On discute de I'implication de ces rtsultats relativement a la nature de la solvatation des solutes faiblement polaires dans de tels melanges.

Section: Solvolysis In Acetonitrile-water Mixturesmentioning

confidence: 64%

The Hydrolysis of t-Butyl Chloride in Aquo-Organic Mixtures: Heat Capacity of Activation and Solvent Structure

Robertson¹,

Sugamori²

1972

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“…were dependent on changes in the para-substituent of the benzene ring. In our initial investigation (5) we noted the claim by Vizgert (6) that the solvolytic rate constant for mesitylenesulfonyl chloride was not increased by base addition. This is in contrast to a "normal" acceleration of lo5-lo7 (7,8).…”

Section: Introductionmentioning

confidence: 90%

Sulfonyl Chloride Kinetics. Part III. Nucleophilic Interaction on the Transition State for 4-X-Benzenesulfonyl Chloride Solvolyses

Rossall¹,

Robertson²

1971

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The kinetic solvent isotope effect (k.s.i.e.) = kH20/kD20, was measured for 4-X-benzenesulfonyl chlorides (where X = MeO, Me, H, Br, and NO2) and shown to vary systematically, giving linear correlations with Hammett o values and with koH-/kHz, ratios. These results contrast with the lack of sensitivity in k.s.i.e. to structural changes for displacement from a saturated carbon atom. This behavior is attributed to a greater degree of bond making required to achieve a critical charge on the chloride of the sulfonyl chloride at the transition state.On a mesure I'effet isotopique cinktique du solvant (e.i.c.s.) = k~~o / k~~~, pour des chlorures de benzenesulfonyles substitues en position 4 et on a dCmontrC qu'il varie d'une f a~o n systematique donnant une correlation lineaire entre les valeurs o de Hammet et les rapports koH-/kH20. Ces resultats sont en opposition avec ceux obtenus pour des reactions de substitutions sur des carbones satures alors que e.i.c.s. est peu sensible aux changements structuraux. Ce comportement serait dii a ce que 1'Ctat de transition ressemble au produit final et nkcessite un haut degre de formation de lieu pour atteindre une charge critique sur le chlorure du chlorure de sulfonyle.Canadian Journal of Chemistry, 49, 1451 (1971) IntroductionRobertson and Laughton (I) showed that the kinetic solvent isotope effect ((k.s.i.e.) = kH2,/ k,,,) for benzenesulfonyl chloride and methane sulfonyl chloride were similar (1.58 at 10 and 20°, respectively) and larger than the values which characterize the hydrolysis of alkyl halides (1.2 to 1.3 over widely differing temperature ranges) (2, 3). These results are interesting since it seemed unlikely that a phenyl and a methyl group could have identical electronic effects. ~s~& i a l l~ so, since Rogne (4) measured k.s.i.e. for dimethylsulfamoyl chloride at 25" = 1.33. Hence our studies were extended to discover whether k.s.i.e. were dependent on changes in the para-substituent of the benzene ring. In our initial investigation (5) we noted the claim by Vizgert (6) that the solvolytic rate constant for mesitylenesulfonyl chloride was not increased by base addition. This is in contrast to a "normal" acceleration of lo5-lo7 (7,8). We expected this compound to have a k.s.i.e. distinct from that arising from nucleophilic interaction. Unfortunately, this substrate proved quite insoluble in

“…The purification of solvents and the procedures of kinetic measurements were as reported in the previous paper (17).…”

Section: Methodsmentioning

confidence: 99%

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

Ko¹,

Robertson²

1972

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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.