Abstract
Sulfur vulcanisation, of alkenes is a widely employed industrial chemical process delivering a range of organic polysulfanes as principal products. Notwithstanding their practical importance, the fundamen-tal understanding of thermally activated vulcanisation without the use of accelerants is available only in restricted sense: it is highly unselective process and there is little knowledge whether the accompa-nying reactions occur through ionic or free-radical mechanisms. Here, the work details the mechanism of the sulfur vulcanisation under non-accelerated conditions using density functional computations at B3PW91/6-311+G(3d,f) level of theory in a simulated reaction system at the temperature of sulfur polymerisation (432.15 K). The study starts from the investigation of the homolytic and heterolytic S–S bond dissociation of the octasulfur ring and its transformations into other reactive forms. It predicts that the heterolysis is a principal reaction leading to the octasulfur zwitterions, relative to the homoly-sis into diradicals, as well as that the formation of macrocyclic sulfur derivatives is more likely to take place as opposed to linear analogous products; however, it also demonstrates that disulfur diradicals might favourably form via pseudoreversible decomposition of macrocyclic sulfur into the initial eight-membered ring form. This work also analyses model reactions between sulfur and cis-2-butene via addition to double bonds or through the substitution of allyl hydrogens identifying preferred reaction pathways. Possibly, the addition products are generated from the reaction of the alkene and the oc-tasulfur through the formation of zwitterions. Alternatively, disulfur diradicals may substitute allyl hydrogens forming hydrodisulfanes that further convert into polysulfanes by the addition to double bonds or by the oxidation with molecular oxygen.
References
Chung W.J., Griebel J.J., Kim E.T., Yoon H., Simmonds A.G., Ji H.J., Dirlam P.T., Glass R.S., Wie J.J., Nguyen N.A., Guralnick B.W., Park J., Somogyi Á., Theato P., Mackay M.E., Sung Y.-E., Char K., Pyun J. The use of elemental sulfur as an alternative feedstock for polymeric materials. Nat. Chem. 2013. 5. 518-524.https://doi.org/10.1038/nchem.1624
Bodachivskyi I.S., Pop G.S. Synthesis of organosulfanes - multi-grade lubricant additives. Kataliz i neftehimiâ. 2017. 26. 12-25. [In Ukrainian]
Bodachivskyi Yu.S., Pop G.S. Synthesis and structure of sulfur-containing antifriction additives for lubricants. Kataliz i neftehimiâ. 2014. 23. С. 15-20.
Bodachivskyi I.S., Pop G.S. Designing and characterization of aqueous microemulsions for metalworking operations. Kataliz i neftehimiâ. 2016. 25. 1-4.
Bodachivskyi I., Pop G., Zheleznyi L., Zubenko S., Okhrimenko M. Oleochemical synthesis of sulfanes, their structure and properties. Chem. Chem. Technol. 2017. 11. 365-371. https://doi.org/10.23939/chcht11.03.365
Lim J., Cho Y., Kang E.H., Yang S., Pyun J., Choi T.L., Char K. A one-pot synthesis of polysulfane-bearing block copolymer nanoparti-cles with tunable size and refractive index. Chem. Commun. 2016. 52. 2485-2488. https://doi.org/10.1039/C5CC08490C
Zhou D., Chen Y., Li B., Fan H., Cheng F., Shanmukaraj D., Ro-jo T., Armand M., Wang G. A stable quasi‐solid‐state sodium-sulfur battery. Angew. Chem. Int. Ed. 2018. 57. 10168-10172. https://doi.org/10.1002/anie.201805008
Steudel R. Liquid sulfur. Elemental sulfur and sulfur-rich com-pounds I. Berlin, Heidelberg: Springer, 2003. 81-116. https://doi.org/10.1007/b12115
Bodachivskyi Yu.S., Pop G.S., Rogalskyi S.P. Effect of accelera-tors on oil higher fatty acid esters sulfurization. Kataliz i neftehimiâ. 2015. 24. 41-46. [In Ukrainian]
Bodachivskyi I.S., Pop G.S., Golovchenko O.V. Synthesis of sul-fur-containing lubricant additives on the basis of fatty acid ethyl esters. Journal of Chemistry and Technologies. 2016. 24. 62-72. [In Ukrainian]
Farmer, E.H., Shipley, F.W. 298. The reaction of sulphur and sulphur compounds with olefinic substances. Part I. The reaction of sulphur with mono-olefins and with Δ 1: 5-diolefins. J. Chem. Soc. 1947. 1519-1532. https://doi.org/10.1039/JR9470001519
Ross G.W. 580. The reaction of sulphur and sulphur com-pounds with olefinic substances. Part X. The kinetics of the reaction of sulfur with cyclohexene and other olefins. J. Chem. Soc. 1958. 2856-2866. https://doi.org/10.1039/jr9580002856
Bateman L., Moore C.G., Porter M. 581. The reaction of sul-phur and sulphur compounds with olefinic substances. Part XI. The mechanism of interaction of sulphur with mono-olefins and 1 : 5-dienes. J. Chem. Soc. 1958. 2866-2879. https://doi.org/10.1039/jr9580002866
Akiba M., Hashim A.S. Vulcanization and crosslinking in elas-tomers. Prog. Polym. Sci. 1997. 22. 475-521. https://doi.org/10.1016/S0079-6700(96)00015-9
Nieuwenhuizen P.J., Ehlers A.W., Haasnoot J.G., Janse S.R., Reedijk J., Baerends E.J. The mechanism of zinc(II)-dithiocarbamate-accelerated vulcanization uncovered; theoretical and experimental evidence. J. Am. Chem. Soc. 1999. 121. 163-168. https://doi.org/10.1021/ja982217n
Frisch M.J., et al. Gaussian 09 (Revision D.01). Wallingford CT: Gaussian Inc., 2009.
Peter L. Density functional calculations on homonuclear poly-sulfur ring molecules S5-S16. Phosphorus, Sulfur Silicon Relat. Elem. 2001. 168. 287-290. https://doi.org/10.1080/10426500108546569
Jones R.O., Ballone P. Density functional and Monte Carlo studies of sulfur. I. Structure and bonding in Sn rings and chains (n = 2-18). J. Chem. Phys. 2003. 118. 9257-9265. https://doi.org/10.1063/1.1568081
Bodachivskyi I.S. Synthesis, properties, and application of ole-ochemical polysulfanes: dissertation to receive a scientific degree of Candidate of Chemical Sciences. V.P. Kukhar Institute of Bioorganic Chemistry and Petrochemistry of the National Academy of Sciences of Ukraine. Kyiv, 2018. [In Ukrainian]