Kinetic isotope effect in hydrogen exchange between methanol and diphenylphosphine or dimethylphosphine in liquid and vapour state

The bimolecular rate constants of the homogeneous tritium exchange in the systems: i) (C6H5)(2)PH(1)/CH3OH*(1), ii) (C6H5)(2)PD(I)/MeOD*(I) were determined at 228 K and 250 K. The coefficients of the heterogeneous tritium exchange in the systems: iii) (CH3)(2)PH(v)/CH3OH*(v), iv) CH3)(2)PD(v)/CH3OD*(v) were measured in the range 283-329 K. The HH*/DD* kinetic isotope effects for forward and backward exchange were estimated. The kinetic isotope effect obtained in this study is significantly greater than that for the exchange in CH3CN solution. This difference is explained by the solvation of the four-center transition complex leading to the higher symmetry of this complex.