Abstract
Absolute rate constants have been measured for the reduction of 1-alkylthiolanium (1a–c), 1-alkylthianium (2a–e), 1-(n-carboxyalkyl)thiolanium (3a,b) and 1–(n-carboxyalkyl)thianium (4a,b) salts, and ω-dimethylsulphonioalkanoic acids (5a,b), including biologically active S-methyl-methionine (6) and dimethyl-β-propiothetin (5b), by hydrated electrons in aqueous solutions using the pulse radiolysis method. This reaction was found to occur very rapidly (k in the range 109–1010 dm3 mol–1 s–1), the individual rate constants being dependent on the electron inductive power of the substituents on the positive sulphur centre. The sulphuranyl radical R3S˙, a possible reaction intermediate, could not be detected within the 0.1 µs time resolution of the applied technique. No reaction was observed between S-methylmethionine and CO2˙– or Me2ĊOH under experimental conditions. The one-electron reduction potential of this sulphonium salt has been estimated to be < –1.8 V. C-centred radicals produced upon the reduction of the cyclic sulphonium salts 1-methyl- and 1-ethylthiolanium and 1-methylthianium salts by e–aq were characterized by using p-benzoquinone as a radical scavenger. It was found that ring opening is the predominant process rather than the cleavage of methyl or ethyl radicals.
Published Version
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