So you hear all the time these days that green chemistry is important. Green this, environmentally friendly that. There’s even a new term for workers at environmentally friendly companies–“green-collar.” That made me wonder what collar color (heh) chemists would get. Not exactly blue collar, but certainly not white collar…”burnt-collar workers” perhaps? Horrible brown-black nasty mess collar?
Anyway, I’m continuing my recent march through group 15 with a JOC paper from the University of Ottawa, which explores Pd-catalyzed thiocarbonylation reactions in phosphonium salt ionic liquids, or PSILs. The group had achieved thiocarbonylation in the past using certain Pd-based catalyst systems in conjunction with carbon monoxide, thiols, and aryl iodides, but they turned their attention to the reaction solvent in this paper. Using trihexyl(tetradecyl)phosphonium-PF6 as the solvent and a catalyst system of 1:4 Pd(OAc)2:PPh3, they achieved 91% coupling of PhI and PhSH. Typical yields of aryl thioesters from aryl iodides and aryl or arene-containing thiols were in the 60-70% range.
A notable feature of their reaction system was recyclability of the solvent–the product thioester could be easily separated from the ionic liquid by extraction, leaving only wet ionic liquid. After a drying step and readdition of reactants they achieved the same yield of product as they did in the first run. Hooray for green chemistry!
The paper is here.