Ternary adducts of some P(III) compounds with elemental sulfur and carbon disulfide

Solutions of trialkylphosphites develop a yellow tint (life time: several hours) when reacted with sulfur in the presence of carbon disulfide, Similar phenomena occur with alkyl phosphonites or phosphinites and with trialkylphosphines, although not with triarylphosphines. The curves absorbance/time for (EtO)(3)P at 400 nm indicate a 3rd order kinetic law: dA(400)/dt = k(3) epsilon[(RO)(3)P][S-3][CS2], where epsilon is the(unknown) absorptivity of the adduct and A(400) is taken at 1 cm path length. Formulae X3P+ - S-n - CS2- (A) or X3P--C(S)S-S-a(-) (B) are considered, with more evidence in favour of A. A mechanism is proposed.