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|Title:||Homolytic SS bond dissociation of 11 bis(thiocarbonyl)disulfides R-C(=S)-S-S-C(=S)R and prediction of A novel rubber vulcanization accelerator|
|Keywords:||Ab initio calculations|
|Citation:||Mak, A.M., Steudel, R., Wong, M.W. (2008-06-02). Homolytic SS bond dissociation of 11 bis(thiocarbonyl)disulfides R-C(=S)-S-S-C(=S)R and prediction of A novel rubber vulcanization accelerator. Chemistry - An Asian Journal 3 (6) : 1026-1034. ScholarBank@NUS Repository. https://doi.org/10.1002/asia.200800036|
|Abstract:||The structures and energetics of eight substituted bis(thiocarbonyl) disulfides (RCS2)2, their associated radicals RCS 2 •, and their coordination compounds with a lithium cation have been studied at the G3X((MP2) level of theory for R=H, Me, F, Cl, OMe, SMe, NMe2, and PMe2. The effects of substituents on the dissociation of (RCS2)2 to RCS2 • were analyzed using isodesmic stabilization reactions. Electron-donating groups with an unshared pair of electrons have a pronounced stabilization effect on both (RCS2)2 and RCS 2 •. The S-S bond dissociation enthalpy of tetramethylthiuram disulfide (TMTD, R=NMe2) is the lowest in the above series (155 kJ mol-1), attributed to the particular stability of the formed Me2NCS2 • radical. Both (RCS2)2 and the fragmented radicals RCS2 • form stable chelate complexes with a Li+ cation. The S-S homolytic bond cleavage in (RCS2)2 is facilitated by the reaction [Li(RCS2)2]++Li +→2[Li(RCS2)]•+. Three other substituted bis(thiocarbonyl) disulfides with the unconventional substituents R=OSF2, Gu1, and Gu2 have been explored to find suitable alternative rubber vulcanization accelerators. Bis(thiocarbonyl)- disulfide with a guanidine-type substituent, (Gu1CS2) 2, is predicted to be an effective accelerator in sulfur vulcanization of rubber. Compared to TMTD, (Gu1CS2) 2 is calculated to have a lower bond dissociation enthalpy and smaller associated barrier for the S-S homolysis. © 2008 Wiley-VCH Verlag GmbH & Co. KGaA.|
|Source Title:||Chemistry - An Asian Journal|
|Appears in Collections:||Staff Publications|
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