Effects of solvents on the cobalt phthalocyanine-catalyzed oxidation of hydrophobic thiols

The use of organic solvents in the oxidation of 1-dodecanethiol, catalyzed by cobalt (II) phthalocyanine-tetrasodiumsulfonate (CoPc(NaSO3)4)/2,4-ionene, drastically influences the reaction mechanism. Without an organic solvent the reaction proceeds at the thiol-water phase boundary, where the ionene interacts with the negatively charged 1-dodecanethiol 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 apolar solvent used over the whole range of solvent compositions. It is proposed that the reaction proceeds at the phase boundary, but the degree of complexation between the quaternary ammonium groups of the ionene 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 stabilizing the active dimeric form of the catalyst. When water-insoluble more polar solvents such as 1-octanol are used, the opposite phenomenon is observed: the optimal 2,4-ionene concentration rises. In the latter situation the 2,4-ionene is still able of interacting strongly with the thiolate anions present at the interface of the droplets.