Trialkyl trithioarsenites, (RS) 3 As, bearing terminal carboxy ( COOH) or carboxylate ( COO − Na + ) or zwitterionic ( CH(NH 3 + )COO − ) groups were studied for their ability to be oxidized by octasulfur, S 8 , and by dioxygen. The carboxy-bearing trithioarsenites are not oxidized by S 8 to the corresponding As(V) esters, (RS) 3 As=S, probably because they cannot open the octasulfur ring, but they react with S 8 in the presence of triethylamine, which acts as an activator of S 8 . The carboxylatebearing trithioarsenites, however, do react under drastic conditions with S 8 . In both cases colored insoluble solids were obtained which could not be characterized. The carboxy-bearing trithioarsenites are oxidized by air in a hydrocarbon chain-length depended manner, while the carboxylate-bearing trithioarsenites are not, if at all, oxidized by air to arsenic(III) oxide, As 2 O 3 , and disulfide, RSSR. The zwitterionbearing tris(penicillamine), tris(cysteine), and tris(glutathione) trithioarsenites are air oxidized slower than their corresponding parent thiols and this may be of biochemical significance.