Diphenyl disulfide is the chemical compound with the formula [C₆H₅S]₂. This colorless crystalline material is often abbreviated Ph₂S₂. It is one of the most popular organic disulfides used in organic synthesis. Minor contamination by thiophenol is responsible for the disagreeable odour associated with this compound.

Preparation and structure

Ph₂S₂ is usually prepared by the oxidation of thiophenol:

2 PhSH + I₂ → Ph₂S₂ + 2 HI

Hydrogen peroxide can also be used as the oxidant. Ph₂S₂ is rarely prepared in the laboratory because it is inexpensive, and the precursor has a disagreeable odour.

Like most organic disulfides, the C₂S₂ core of Ph₂S₂ is non-planar with a dihedral angle approaching 85°.

Reactions

Ph₂S₂ is mainly used in organic synthesis as a source of the PhS substituent. A typical reaction entails the formation of PhS-substituted carbonyl compounds via the enolate:

RC(O)CHLiR’ + Ph₂S₂ → RC(O)CH(SPh)R’ + LiSPh

Reduction

Ph₂S₂ undergoes reduction, a reaction characteristic of disulfides:

Ph₂S₂ + 2 M → 2 MSPh (M = Li, Na, K)

Hydride reagents such as sodium borohydride and super hydride can also be used as reductants. The salts PhSM are sources of the potent nucleophile PhS^-. Most alkyl halides, RX (X = halide) convert it to the thioethers with the general formula RSPh. Analogously, protonation of MSPh gives thiophenol:

PhSM + HCl → HSPh + MCl

Chlorination

Ph₂S₂ reacts with chlorine to give phenylsulfenyl chloride PhSCl (Zincke disulfide cleavage). This species is difficult to isolate, so it is usually generated in situ.

Catalyst for photoisomerisation of alkenes

Ph₂S₂catalyzes the cis-trans isomerization of alkenes under UV-irradiation.

Oxidation

Oxidation of Ph₂S₂ with lead(IV) acetate (Pb(OAc)₄) in methanol affords the sulfinite ester PhS(O)OMe.

References