Determination of sulphur functions with iodoso-compounds

Iodoso derivatives, e.g., m- and p-chlorophenyl, m- and p-methylphenyl and p-nitrophenyl-iodosoacetates and o-diacetoxyiodobenzoate, have been thoroughly investigated as oxidants and are proposed as analytical reagents for the determination of thiols, thioureas, isothiocyanates, organic sulphides, disulphides, xanthates, dithiocarbamates, amines and alcohols in aqueous and non-aqueous (acetic acid, acetonitrile, dimethylformamide) media. The error of the determination of thiols is 0.2% thioureas 0.5%, organic sulphides and disulphides 0.4%, isothiocyanates 0.4%, dithiocarbamates 0.4%, and xanthates 0.5%. All the methods are precise to 0.2-0.5%. It is also shown that the properties of the o-derivatives differ markedly from those of the m- and p-derivatives. The o-derivatives contain a 1-substituted 1,2-benzoiodoxilin-3-one ring system. The stability of this system is apparently associated with the size of the five-membered ring; other compounds in which iodine is apparently part of larger rings are less stable. o-Diacetoxyiodobenzoate appears to be the best analytical reagent of the iodoso series. The m- and p-iodosobenzoates are found unsuitable for quantitative oxidation of cysteine.