Diphenyl disulfide

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 comtamination 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  &rarr;  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  &rarr;  RC(O)CH(SPh)R’  +  LiSPh

Reduction
Ph2S2 undergoes reduction, a reaction characteristic of disulfides:
 * Ph2S2 +  2 M  &rarr;  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  &rarr;  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.