Reactions of thiols and organic sulfides with hydrogen in the presence of iron powder

Abstract

Previously unknown reduction of thiols to hydrocarbons and H 2 S with hydrogen formed by the interaction of powdered iron with dilute HCl was found.Organic disulfides in a mixture of chlorohydrocarbons are efficient additives to mineral oils that decrease friction and attrition wear of steel surfaces. As a result of the boundary friction they decompose to evolve H 2 S and HCl, respectively, and the mobile hydrogen atom in hydrocar bons reacts with air oxygen to form H 2 O. Therefore, it was of interest to reveal whether thiols and organic sul fides, disulfides, and trisulfides can be reduced to H 2 S with hydrogen formed by the reaction of HCl with iron.In the present work, we studied the reduction of thiols (RSH) 1a-e, sulfides (R 2 S) 2d,e, disulfides (R 2 S 2 ) 3a-e, trisulfides (R 2 S 3 ) 4a,b (R = Bu (a), Bu t (b), Dd (do decyl, c), Bn (d), and Ph (e)), and O containing iron thiolates C 10 H 24 Fe 2 O 6 S (5) and C 14 H 16 Fe 3 O 7 S 2 (6) with hydrogen. Results and DiscussionThe results of quantitative determination of H 2 S are presented in Table 1. It is seen that monosulfides 2d,e and sterically hindered disulfide 3b are not reduced with hydro gen to H 2 S. For the reduction of sterically hindered trisul fide 4b, the yield of H 2 S is by 15 times lower than that for the reduction of trisulfide 4a (cf. entries 5 and 10) con taining unbranched butyl radicals. Upon the addition of pentane, the yield of H 2 S during the reduction of thiols 1a,b decreases, which is caused, most likely, by the re moval of thiols with volatile pentane from the reaction mixture. The improvement of conditions for contact of powdered iron with reduced compounds in a pentane solution exerts virtually no effect on the yield of H 2 S during the reduction of thiols 1c-e and disulfide 3a (cf. entries 12 and 13, 17 and 18, 24 and 25, 3 and 4). For the reduction of disulfide 3d and trisulfides 4a and 4b, the yield of H 2 S increases by 5.8, 2.1, and 3 times, respec tively (cf. entries 21 and 22, 5 and 6, 10 and 11). When thiol 1c is reduced, the increase in the Fe : 1c ratio by 3 times increased the yield of H 2 S by 2.8 times (cf. en tries 12 and 14). When thiol 1d is reduced with the iron powder preliminarily wetted with water, the yield of H 2 S decreases by 3.5 times (cf. entries 18 and 19).Unlike disulfide 3a containing n butyl radicals, steri cally hindered disulfide 3b is not reduced with hydrogen, and wetting Fe with water decreases the yield of H 2 S in the case of reduction of thiol 1d. Therefore, it can be assumed that only the molecules adsorbed on the Fe sur face are reduced. In this case, organic disulfides are re duced with hydrogen to thiols, which then interact with the Fe surface purified from oxides using the chemical method. In fact, the formation of so called "self assembled monolayers" of Fe thiolates already at 100-150 K was found in numerous works (see, e.g., Refs 1 and 2) on the interaction of thiols with the surface of Fe single crystals under ultrahigh vacuum conditions. At 256-298 K iron thiolates decompose t...