An ab initio study of the mechanisms of the di- and tri-merization of thiocarbonyl compounds resulting in cyclic oligomers

The dimerization and trimerization of thioformaldehyde as well as the dimerization of thioketene has been studied using G3(MP2) calculations. The investigations have elucidated the reaction mechanisms. The activation Gibbs energy of the trimerization of thioformaldehyde has been determined as 118.1 kJ/mol and that of the dimerization of thioketene as 139.2 kJ/mol. The trimerization of thioformaldehyde is shown to proceed through an open chain dimer with the activation Gibbs energy 74.0 kJ/mol. The results explain that the direct dimerization of thioformaldehyde to 1,3-dithietane is not experimentally observed.