Studies on the Syntheses of Mercaptans. V.

Abstract

The purification of mercaptans prepared from α-olefins and hydrogen sulfide by urea-adduction was investigated. Because α-olefin contains its isomers, the mercaptans prepared by radical addition of hydrogen sulfide to α-olefins are the mixture of straight-chain n-alkylmercaptans and their branched-chain isomers. As a result, it was found that the best method for separation of n-alkylmercaptans from these mixtures was the urea-adduction by reaction of solid urea with mercaptans dissolved in toluene containing a small amount of methanol.In various experimental conditions, the separations were carried out selectively, and the purified mercaptans contained over 98% of n-C10 or n-C12 mercaptan independently of the yields. The yields of n-alkylmercaptans were markedly dependent on the temperature of adduct-formation and on the solvent for the decomposition of urea-adduct. And it was suggested that the mercaptan itself might be an activator for the adduct-formation.In the case of this experimental condition, urea-adduct seemed to be not formed over 40°C and the urea-adduct of n-C8 mercaptan was hardly formed. And over the temperature range from -10°C to 30°C the rate of adduct-formation was accelerated almost linearly with lowering of temperature.The ratios of urea (moles) to the number of carbon atoms of n-mercaptans in the urea-adducts were not constant and decreased with increase of the number of carbon atoms of n-mercaptans from C8 to C18. This probably reflects the steric and polar effects of SH groups of n-mercaptans.Moreover, it was found that the formation of urea-adduct could be identified by IR spectrum. And it was qualitatively confirmed by NMR and mass spectra that the branched-chain isomers of n-mercaptans were derived from those of α-olefins.