KINETIC ISOTOPE EFFECT IN HYDROGEN-EXCHANGE BETWEEN METHANOL AND DIPHENYLPHOSPHINE OR DIMETHYLPHOSPHINE IN LIQUID AND VAPOR 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 heterogene ous 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 est imated. The kinetic isotope effect obtained in this study is significa ntly greater than that for the exchange in CH3CN solution. This differ ence is explained by the solvation of the four-center transition compl ex leading to the higher symmetry of this complex.