Journal of the American Chemical Society p. 1805 - 1809 (1987)
Update date:2022-08-24
Topics:
Young, Paul R.
Huang, H. C.
The iodide reduction of N-(substituted ethyl or phenyl)-S,S-dimethylsulfilimmonium salts (aqueous solution, 25 deg C, μ = 1.0 with KCl) is first order in proton activity and iodide concentration in the pH range 0.5-5.The solvent deuterium isotope effects for the reduction reaction vary in the range kH/kD = 0.26-0.48 as the nitrogen substituent is changed from ethyl- to trifluoroethylamine.Electron-withdrawing groups in the leaving group decrease the rate of the reaction and give βl.g. values of ca. 0.7 for cyanoethyl- and trifluoroethylamine leaving groups and ca. 0.1 for the more basic ethylamine derivatives; a βl.g. of 0.58 is observed for aniline derivatives.General acid catalysis is observed in the reduction of the acidic ethylamine and aniline derivatives with Broensted α values of 0.59 and 0.39 for cyanoethyl- and trifluoroethylamine leaving groups, respectively; for anilines, the Broensted α values decreased from 0.67 to 0.50 as the leaving group is changed from 4-methyl- to 3-nitroaniline.The value of βl.g. decreases with decreasing strength of the catalyzing acid and the term pxy = (δβl.g./δpKaHA) = (δα/δKal.g.) ca. -0.06 to -0.1.The solvent deuterium isotope effect on the general catalyzed reduction reaction increases with increasing acid strength; for the cyanoethylamine derivative, kBH/kBD = 1.47-2.32 for acetic and chloroacetic acids, respectively.A mechanism is suggested involving concurrent stepwise and concerted mechanisms for the reduction reaction; the mechanism observed seems to depend on the nature of the catalyzing acid.
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