Thermal decomposition of methylated γ-thiobutyrolactones: A photoelectron spectroscopic study

The thermal decomposition of γ-thiovalerolactone, α-methyl-γ-thiobutyrolactone and β-methyl-γ- thiobutyrolactone has been studied in a gaseous flow system, by monitoring the changes in the photoelectron spectra recorded during the course of the reactions. Three modes of decomposition were observed, two involve loss of carbon monoxide (decarbonylation) and one involves loss of carbonyl sulfide (decarboxylation). The decarbonylation reaction producing an olefin and a thioaldehyde and the decarboxylation producing an olefin are similar to those observed for the unsubstituted thiobutyrolactone. The third reaction, observed only in the methylated compounds, is decarbonylation with the formation of hydrogen sulfide and butadiene. It is proposed that the last reaction can be attributed to the relatively facile elimination reaction of a butenethiol intermediate.