A study of cobalt catalysis and copper modification in the coupled decompositions of hydrogen peroxide and peroxomonosulfate ion

Abstract

The decompositions of HOOH and HOOSO 3 − in a mixture are mechanistivally linked when cobalt(II) near pH 0 is the catalyst. This linkage, here termed coupling, is seen in the facts that HOOH is an inhibitor of the free radical decomposition of HOOSO 3 − and the two peroxides are lost in close to a one-to-one ratio. The kinetics of the coupled decompositions have been investigated, and the rate law is − d[ HOOSO 3 −] dt k H [ Co 2+][ HOOSO 3 −] [H + ] which holds when [ HOOH]≧2×10 −2 M . The constant k H is about one-sixth of the value that has been found for the identical rate law for cabalt catalysis of HOOSO 3 − decomposition in the absence of HOOH. Inhibition is attributed to the trapping of the intermediate Co(III) and possibly also of SO 4 .− and .OOSO 3 − by HOOH with consequent formation of HOO . which then reacts by termination only. The presence of the peroxoradical HOO . has been proven through its being trapped by Cu 2+, which thereby starts a new and more complicated free radical chain decomposition. The stoichiometry and kinetics of the cobalt-catalyzed, coupled decompositions have been investigated and a tentative set of steps proposed. Some data on copper promotion are reported.