Mercaptans, detection identification

From 1966 through 1974 several notable studies were conducted on 5-containing compounds in tobacco smoke. In 1966, Philippe (2940) reported on the identification of thiocyanogen, thiocyanic acid, hydrogen sulfide, carbonyl sulfide, methylthionitrite, dimethyl sulfide, carbon disulfide, and thiophene in MSS. In that same year, ethyl mercaptan was qualitatively detected by Grob (1419). 

These compounds are characterized by a very unpleasant odor if they have a sufficiently high vapor pressure. Among color reactions used for their detection, those with sodium nitroprusside, phosphotungstic acid, and nitrous acid are most commonly used. The preparation of heavy-metal salts is important both for detection and identification also used for identification are the reactions with 2,4-dinitrochlorobenzene, m-nitrobenz-amide, or (for chromatography) 3,5-dinitrobenzoyl chloride and 2,4-di-nitrophenylsulfenyl chloride (see (1)]. On mild oxidation mercaptans give disulfides —for example, with iodine,... 

Photolysis of 1,2,3-thiadiazole (15a) in argon or nitrogen matrices gave thioketene (16a) and ethynyl mercaptan (17a) as the main products (Scheme 4). When the singly labeled deuterium isotopomers 15b and 15c were similarly photolyzed, the two isotopomers of ethynyl mercaptan, 17b and 17c, were formed in the same ratio from each precursor. Since the isomeric deuterium labeled mercaptans were not interconverted under the matrix photolysis conditions, it was concluded that an intermediate was involved in their formation — probably thiirene (18b,c) — in which the deuterium label became scrambled. The same conclusion was reached when labeled isotopomers of 15a were also photolyzed in matrices. In this second study, a new species was detected that arose on initial photolysis of the thiadiazole at 300 nm and decomposed on further photolysis, with concomitant production of ethynyl mercaptan. It seemed likely that this species was thiirene (18a), but an unequivocal identification could not be made on the basis of the few IR bands observed. 

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