Reactions of thiols and organic disulfides with iron and its oxides

Abstract

The influence of O 2 and H 2 O on the formation of iron dithiolates (IDTs) by the reactions of thiols and organic disulfides with the iron powder was studied under the static (without mechanical activation of the reaction) and dynamic (with mechanical activation of the reac tion) conditions. Under the static conditions in the absence of O 2 or H 2 O, only BnSH and PhSH give IDTs, whereas DdSH (Dd is dodecyl) produces IDTs in the presence of O 2 or H 2 O. For the mechanical activation of the reactions of organic disulfides with the iron powder, the formation of IDTs is possible if the reaction mixture contains H 2 O. On the interaction with iron oxides excess thiols are oxidized to organic disulfides and also afford IDTs.Organic disulfides are widely used as additives de creasing friction and frictional wear of steel surfaces. In this case, disulfides partially decompose to thiols under boundary friction conditions. 1 Mechanochemical reac tions occurring via the reactions of organic disulfides and thiols with iron favor continuous service of steel mecha nisms. However, chemical methods for analysis of prod ucts of mechanochemical reactions have not been devel oped up to recently. We have previously 2 proposed the method for studying mechanochemical reactions with the help of a mechanochemical vibrational mill. It has been shown 2 that, contrary to the popular opinion, 3,4 IDTs appear from thiols rather than from organic disul fides.The purpose of the present work is to study the influ ence of O 2 and H 2 O on the formation of IDTs by the reactions of thiols and organic disulfides with the iron powder under the static and dynamic conditions. Results and DiscussionThe following reactions were studied:where R = Pr (a), Bu (b), Dd (dodecyl, c), Bn (d), and Ph (e).The influence of O 2 in the reaction medium was stud ied in the processes involving thiols 1b-e, and the effect of an H 2 O admixture was examined in the reactions of thiol 1c and disulfide 3a. The results are presented in Table 1.Static conditions. Some IDTs are formed without mechanochemical activation of the reactions of thiols with the iron powder. For instance, the formation of IDTs 2b,d,e was visually observed by the appearance of the color several minutes or hours after mixing the reactants. When IDTs 2d,e were formed, hydrogen bubbles evolved for several weeks. In the first case, in several months a black product with metallic luster formed instead of brown IDT 2d, whereas red brown IDT 2e did not change its color. If the reaction mixture is sealed in an air atmo sphere, thiols 1b-e initially turned to green. The brown color characteristic of IDTs appears in several days.In the absence of O 2 , thiol 1c with the iron powder forms no IDT 2c. No changes on the iron surface were visually observed even after many year contact of the re actants in an evacuated ampule. However, if the ampule containing thiol 1c and the iron powder was sealed off under atmospheric pressure without degassing, then the brown color characteristic of IDTs appears already in 30-6...

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

“…In the previous work, 3 we have shown that in the reaction with the powder of reduced iron thiols 1d,e form iron dithiolates (IDT) at room temperature, and thiol 1e exceeds thiol 1d in reactivity, which is undoubtedly re lated to a higher acidity of thiol 1e compared to thiol 1d. It is found in the present work that these thiols, when reduced with hydrogen, form mostly H 2 S (cf.…”

Formation of Ferrous Didodecanethiolate in the Mechanochemical Reaction between Dodecanethiol and Metallic Iron and Iron Sulfides: Investigating the Effect of Different Additives and Solvents

“…(3) The formation of ferrous dithiolates was not observed upon mechanochemical activation of the reaction between organic disulfides and metallic iron [4,5].…”

“…The formation of Fe(SDd) 2 was identified by the color reaction for ferrous dithiolates containing n-alkyl or benzyl radicals. In this reaction, the brown color due to Fe(SDd) 2 changes into green upon contact with dioxygen [4,5].…”

“…The aim of this work was to investigate the effect radical reaction inhibitors and solvents (both polar and nonpolar) have on the formation of ferrous didodecanethiolate [Fe(SDd) 2 ] in the mechanochemically activated reaction of dodecanethiol (DdSH) and metallic iron. It was shown in [5] that this reaction does not occur without mechanical activation.…”

“…A color reaction specific to ferrous dithiolates containing n-alkyl and benzyl moieties was described for the first time, conclusive evidence against the thiolate (mercaptide) mediated mechanism of antiwear-anti-scoring action of organic disulfides. The interaction between thiolates and iron and iron oxides was studied in [5], along with the effect oxygen and water have on the formation of ferrous dithiolates under static and dynamic conditions. X-ray photoelectron spectroscopy (XPS) also showed that organic disulfides do not produce ferrous dithiolates on steel surfaces under typical conditions of boundary friction.…”