UV-vis and IR spectroscopic characterization of diphenyl disulfide radical cation in acid zeolites and its rearrangement to thianthrenium radical cation

Abstract

Adsorption of diphenyl disulfide (DPDS) from CH₂Cl₂ solutions onto acid zeolites at room temperature generated the “extended” radical cation, DPDS^˙+. At loadings of 3 wt%, oxidation to DPDS^˙+ is essentially complete. Upon heating the loaded zeolite to 200 °C, the adsorbed DPDS^˙+ was converted into thianthrenium radical cation (TH^˙+). Ab initio calculations at the B3LYP and HF levels using the 6-31G* basis set suggest cyclization of a diphenyl disulfide-S,S-dication as a reasonable rate-determining step of the conversion. Non-acidic zeolites devoid of Lewis and Brønsted sites (as determined by the pyridine adsorption–desorption method) failed to generate DPDS^˙+ to an extent detectable spectroscopically; these results support Lewis and/or Brønsted sites as being responsible for the observed oxidation.