Homogeneous catalysis of deuterium transfer by potassium hydroxide and potassium methoxide D2-H2O and D2-CH3OH exchange

The kinetics and mechanism of exchange of deuterium between D2 and water and between D2 and methanol, catalyzed respectively by concentrated potassium hydroxide and potassium methoxide, has been studied between 348 and 398 K. In the D2-KOH-H2O case, the transfer of deuterium was found to be controlled by the rate of activation of the D2 molecule by OH-. Rapid exchange of D+ with the aqueous solution followed. From the D2-KOCH3-CH3OH studies, it was concluded that deuterium exchange depended upon the rates of both D2 activation by methoxide and interaction of the solvent with the transition, or encounter, complex. The dependence of second-order rate constants on solvent activity for both systems was determined by normalization of the exchange reaction rates to unit reagent activity. Analysis of the kinetic isotope effects for each system suggested that their increase with base concentration or temperature was due to solvation effects. (author)