Cleavage of CS bond in thiourea by electron transfer process with Cu+ ion as a model study of sulphur removal and recovery

This communication reports a novel process of the formation of elemental sulphur (S0) that involves a specific electron transfer process (ETP) from a model organic sulphur compound thiourea. Solubility of CuCl in different systems were studied at 30 °C. Treatment of Cu+ as CuCl with naphthalene, an electron transfer agent taken in a protic solvent ethanol produces ion-radical i.e., naphthalenide anion. Formation of this ion-radical was proved by the solubility of copper in the absence and presence of naphthalene as well as by the absorption study at 30 °C. Increased solubility of copper in a system containing CuCl, naphthalene and thiourea in ethanol further proved the generation of ion-radical. Production of (S0) in the temperature range of 30-40 °C suggested the cleavage of CS bond present in the organic sulphur compound. The effect of reaction time revealed that the formation of S0 was not continuous. Temperature had a profound influence on the formation of S0 as substantial increase in the formation of S0 was observed for every 5 °C rise in temperature. The method succeeded in removing 66.4 mol% sulphur from thiourea as S0 at 6 h and 40 °C. Discontinuity in the formation of S0 inferred trapping of minor amount of it by the dissolved S2− ion leading to the formation of probably S22−, the formation of which proceeded at a slow rate. Pseudo-first-order kinetic model was used to unfold the rates of formation of S0. In the temperature range of 30-40 °C, intrinsic rate constant of S0 generation was found in the range of (8.3-40.6) × 10−6 s−1. The S0 formation process possessed an activation energy of 114.9 kJ mol−1 and a preexponential factor of 5.8 × 1014s−1. The way by which S0 was formed has a considerable relevance in the desulphurization of organic sulphur compound and the recovery of S0 from fossil fuels.