Thermochemistry of Sulfones Relevant to Oxidative Desulfurization

Abstract

Oxygen can react with thioethers and thiophenes to produce sulfones, which is the first reaction step in an oxidative desulfurization process. Thermal decomposition of the sulfone-containing compounds to remove sulfur as SO2 could be part of the final recovery step in such a process. The thermochemistry of selected acyclic aliphatic (dimethyl sulfone and di-n-butyl sulfone), cyclic aliphatic (tetrahydrothiophene 1,1-dioxide and 2,5-dihydrothiophene 1,1-dioxide), acyclic aromatic (diphenyl sulfone), and aromatic (thianaphthene 1,1-dioxide and dibenzothiophene 5,5-dioxide) sulfones was studied. The melting point temperature, enthalpy of fusion, and vapor pressure data are reported. The onset of thermal decomposition of acyclic aliphalic sulfones and sulfones attached to two aromatic groups took place at >350 °C and was inconsistent with the low values for the homolytic bond dissociation energy of these sulfones. The onset of thermal decomposition of five-membered cyclic sulfones in a terminal ring, irrespective of whether it was aliphatic or aromatic, took place at <300 °C. The more facile elimination of SO2 from cyclic sulfones present in a terminal ring structure appeared to proceed by an addition reaction, followed by elimination of SO2. This reaction pathway was consistent with the decomposition products that were identified.