Free‐radical reactions involving sulphur compounds. I. The interaction of 2‐cyano‐2‐propyl radicals and thiols

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Abstract
The reaction of thiols (R'SH) with 2‐cyano‐2‐propyl radicals (R), generated by thermal decomposition of 2,2′‐azoisobutyronitrile (RN = NR), was investigated.The radicals (R) readily abstract a hydrogen atom from the thiol (R'SH), producing isobutyronitrile (RH) and thiyl radicals (R'S), whilst their dimerisation product, tetramethylsuccinonitrile (RR), is also formed in appreciable quantities. Using primary, secondary and tertiary thiols respectively, decreasing yields of isobutyronitrile (RH) and increasing yields of tetramethylsuccinonitrile (RR) were obtained. This indicates that the reactivity of thiols towards R decreases in the same order. There appeared to be little difference between toluene‐α‐thiol and n‐octane‐1‐thiol.The thiyl radicals (R'S) combine to form disulphide (R'SSR') and with 2‐cyano‐2‐propyl radicals (R), to form mixed sulphides (R'SR). The latter are formed in far lower yields than both the disulphides and tetramethylsuccinonitrile. This phenomenon may be related to the fact that the CS bond is weaker than could be expected from the energies of the CC and SS bonds.