The kinetics of proton and deuteron transfer from 4-nitrophenylnitromethane and l-(4-nitrophenyl)-l-nitroethane to 2,7-dimethoxy-l,8-bis(dimethylamino)naphthalene in acetonitrile solvent

Author:

Leffek Kenneth T.,Pruszynski Przemyslaw

Abstract

4-Nitrophenylnitromethane reacts with 2,7-dimethoxy-1,8-bis(dimethylamino)naphthalene in acetonitrile in a bimolecular proton transfer, which shows a primary deuterium isotope effect, kH/kD = 12.2 at 25 °C. The large isotope effect on the enthalpy of activation, (ΔHD – ΔHH) = 4.6 ± 0.3 kcal mol−1 is consistent with a significant contribution of proton tunnelling to the reaction rate of the protium substrate.The analogous reaction of 1-(4-nitrophenyl)-1-nitroethane with the same base in acetonitrile gives contrasting kinetics and reaction parameters. The reaction is first order, showing no dependence on base concentration. While the isotope effect kH/kD = 9.3 at 25 °C, the enthalpy of activation difference (ΔHD – ΔHH) is only 0.5 ± 0.1 kcal mol−1. It is concluded that the 1-(4-nitrophenyl)-1-nitroethane undergoes a slow dissociation, with a very small dissociation constant, followed by a fast association with the base to yield the carbanion ion-pair.

Publisher

Canadian Science Publishing

Subject

Organic Chemistry,General Chemistry,Catalysis

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