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

Abstract

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

“…for the four chlorosulfates are in for the sulfonyl chlorides (8). It is probable that the narrow range 1.2-1.25 (Table 3) chlorides (Table 5), hence the charge distribution on the chloride at the transition state is similar.…”

Mechanistic studies of the solvolysis of alkanesulfonyl and arenesulfonyl halides

“…In a third paper [ 30 ], kinetic solvent isotope effects ( k sie values) were reported as k H2O / k D2O for the same group of benzenesulfonyl chlorides as reported on in part II [ 29 ]. Differences are found, as one might predict, in the nucleophilic processes for attack by water on sulfur rather than on carbon, indicating differences in the detailed bimolecular processes.…”

“…Similar behavior was observed for the solvolysis of other electron-rich benzenesulfonyl chlorides [ 44 ] and for 2,4,6-triisopropylbenzenesulfonyl chloride [ 45 ], except that in the latter case the plot was against Y values [ 25 , 33 ]. Such an assignment needs to be treated with caution because the large contributions from solvent nucleophilicity effects to these solvolyses [ 16 – 17 26 – 27 30 ], even with electron-rich substrates, would be expected to lead to perturbations of plots against only solvent-ionizing power.…”

Solvent network at the transition state in the solvolysis of hindered sulfonyl compounds

“…[10,13,15,[17][18][19] Based on the described observations, and others already available in the literature, deviations of the TS structure are expected for a number of hindered substrates. [1,2,4,5,17,18,[20][21][22][23][24][25][26][27] When studying the alcoholysis of deuterated 2,4,6-trimethylbenzenesulfonyl chloride, [28] we obtained kinetic data and activation parameters comparable with those for undeuterated 2,4,6-trimethylbenzenesulfonyl chloride, such evidence lets us neglect σ-π-hyperconjugation as a possible reason of the "positive steric effect" in this particular case. [10,28] The observation of small kinetic solvent isotope effects is an evidence against the catalytic effect of a second nucleophile molecule present in the TS [4,5,11] and supports the participation of a network of alcohol molecules in the TS, even as a cyclic chain.…”