Investigation into thiol-(meth)acrylate Michael addition reactions using amine and phosphine catalysts

This work describes a study into thiol-ene based Michael addition reactions. Different catalysts, primary and tertiary amines and phosphines, were investigated for the reaction of a range of thiols with dimers and oligomers of some (meth)acrylates. Primary and tertiary amines are efficient catalysts for the thiol-ene reaction, although these catalysts require several hours to reach high conversion. Moreover, the phosphine catalysts, dimethylphenylphosphine (DMPP) and tris-(2-carboxyethyl)phosphine (TCEP), were investigated in detail. DMPP is an efficacious catalyst yielding complete conversion in few minutes under optimized conditions. Importantly, the concentration of DMPP should be kept at catalytic levels to avoid the formation of by-products, originating from the addition of DMPP to the vinyl group. Furthermore, TCEP is an efficient catalyst for thiol-ene reactions in aqueous media when the pH of the medium is higher than 8.0 since at acidic pH the formation of by-products is observed.