Effect of Electrolytes on the Catalytic Racemization of Tris(Ethylenediamine)-Cobalt(III) Ion

Abstract

ACTIVATED carbon has been used as a catalyst in a number of methods for the preparation of cobalt-(III) complexes. It has been shown that the racemization of tris(ethylenediamine)cobalt(III) ion¹ and other cobalt(III) complexes² is accelerated in the presence of activated carbon. Since the rate of exchange in the system [Co(en)₃]^3+−*en in the presence of charcoal is slower than the rate of racemization of d-[Co(en)₃]³⁺, the racemization cannot be attributed solely to a ligand exchange process³. Dwyer and Sargeson⁴ have observed that on boiling a solution of d-tris(ethylenediamine)cobalt(III) chloride with activated carbon for 3 min., the optical activity was lost completely and about 4 per cent of the total cobalt was reduced to Co²⁺. In the presence of sulphuric acid (0.1 N) and carbon, the complex was reduced to about the same extent, but the optical rotation decreased only slightly (by 6 per cent). They interpreted these results to mean that the racemization occurs through an electron exchange process involving [Co(en)₃]²⁺. Sulphuric acid would destroy the labile cobalt(II) complex and inhibit the racemization by this mechanism.