RATES OF IONIZATION OF 1,1-DINITROETHANE IN 50-PERCENT DIMETHYL SULFOXIDE-50-PERCENT WATER - SOLVENT EFFECT ON PROTON-TRANSFER

The rates of ionization of 1, 1-dinitroethane have been measured in 50% Me2SO-50% water (v/v) in the presence of various buffers. For a given pK difference between 1, 1-dinitroethane and the buffer, the rates are up to ten times higher than those in pure water. This increase is consistent with the notion that solvational reorganization is at least partly responsible for the slow rates of proton transfer involving nitroalkanes, but it also shows that the rate enhancing effect of Me2SO is relatively small as long as there is a significant protic component in the solvent. The data refute the hypothesis that the recently reported high rate of protonation of 1 on carbon by the hydronium ion is due to a solvent effect and support the notion of an intramolecular proton transfer 5 → 2. © 1979, American Chemical Society. All rights reserved.