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Sulfurization of P(III) Compounds with 1,2,4-Dithiazoles - Investigation of the Reaction Mechanism
Authors: Ponomarov Oleksandr | Hanusek Jiří
Year: 2012
Type of publication: ostatní - přednáška nebo poster
Page from-to: nestránkováno
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Language Name Abstract Keywords
eng Sulfurization of P(III) Compounds with 1,2,4-Dithiazoles - Investigation of the Reaction Mechanism In the case of 1,2,4-dithiazoles the influence of solvent polarity or proton donor ability on the rate of sulfurization is only negligible. Also the Hammett ρ-values for the reaction of m- and p-substituted triphenyl phosphites with 3a or 7a and 4a or 5a in acetonitrile are from −1.3 to –0.7, respectively, which together with high and negative entropy of activation is consistent with a bimolecular association step leading to the transition state. To get better insight into the reaction mechanism, especially onto S–S bond cleavage in the transition state, we also studied the transmission of the polar effects in four substituted series of 1,2,4-dithiazoles 3a-e, 4a-f, 5a,c,d,g,h and 7a-e. In all series the second-order rate constants for reaction with triphenyl phosphite were measured in acetonitrile at 25 °C and then plotted against pKa of thiobenzamides (which best resemble leaving group) or σ-values to generate Brønsted-type relationship and Hammett plot, respectively, whose slopes give after normalization βlg(3a-e) = –0.34 and βlg(7a-e) = –0.40 reflecting little progress of S–S bond cleavage in the transition state and ρ-values (+1.38 and +1.11 for related series 3a-e and 7a-e or +0.75 and +0.57 for 4a-f and 5a,c,d,g,h) reflecting the moderate negative charge developing on the leaving sulfur in the transition state. From all these observations it can be suggested an early transition state with little build up of charge on phosphorus as well as on sulfur. Sulfurization; P(III) Compounds; 1,2,4-Dithiazoles; Reaction mechanism

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