EFFECTS OF SOLVENTS ON THE COBALT PHTHALOCYANINE-CATALYZED OXIDATION OF HYDROPHOBIC THIOLS

The use of organic solvents in the oxidation of 1-dodecanethiol, catal yzed by cobalt(II) phthalocyanine-tetrasodiumsulfonate (CoPc(NaSO3)(4) )/2,4-ionene, drastically influences the reaction mechanism. Without a n organic solvent the reaction proceeds at the thiol-water phase bound ary, where the ionene interacts with the negatively char ed 1-dodecane thiol droplets. The degree of complexation between the 2,4-ionene and the thiolate anions diminishes when apolar solvents, like toluene, are added. This leads to a tremendous shift of the N+/Co ratio, which is a measure of the optimal ionene/CoPc(NaSO3)(4) ratio, from 1250 to 15. Only the maximal catalytic activity is dependent on the amount of apo lar solvent used over the whole range of solvent compositions. It is p roposed that the reaction proceeds at the phase boundary, but the degr ee of complexation between the quaternary ammonium groups of the ionen e and the thiolate anions decreases with addition of an apolar solvent . The low optimal N+/Co ratio of about 15 is apparently sufficient for both binding the ionene to the droplet surface as well as for stabili zing the active dimeric form of the catalyst. When water-insoluble mor e polar solvents such as 1-octanol are used, the opposite phenomenon i s observed: the optimal 2,4-ionene concentration rises. In the latter situation the 2,4-ionene is still able of interacting strongly with th e thiolate anions present at the interface of the droplets.