Hydrolysis of Monothio-β-diketones. II. Hydrolysis of three fluorinated Monothio-β-diketones

Abstract

The rapid decomposition of the fluorinated monothio-β-diketones RC(SH)=CHCOCF₃, 4-(3?-bromophenyl)-1,1,1-trifluoro-4-mercaptobut-3-en-2- one (R = m-BrC₆H₄), 4-(4?-bromophenyl)-1,1,1-trifluoro-4-mercaptobut-3- en-2-one (R = p-BrC₆H₄) and 1,1,1-trifluoro-4-mercaptopent-3-en-2-one(R = Me), in acid solution has been shown to occur by hydrolytic cleavage to yield the ketone RCOCH₃, hydrogen sulphide and probably trifluoroacetic acid. The pseudo first-order rate constants for these compounds are (8.0±0.3)x 10^-3, min^-1, (6.0 ± 0.6) x 10^-3 min^-1 and 0.12±0.01 min^-1, respectively. The greater vulnerability of 1,1,1- trifluoro-4-mercaptopent-3-en-2-one, compared to the other two monothio-β-diketones, towards hydrolytic cleavage is related to the nature of the R substituent in that conjugation involving the terminal aromatic ring stabilizes the monothio-β-diketone.