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

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) ion 1 and other cobalt(III) complexes 2 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 process 3 . Dwyer and Sargeson 4 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 Co 2+ . 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.