Diphenyl disulfide
# Diphenyl disulfide

Diphenyl disulfide is the chemical compound with the formula $(C_6H_5S)_2.$ This colorless crystalline material is often abbreviated $Ph_2S_2.$ It is one of the more commonly encountered organic disulfides in organic synthesis. Minor contamination by thiophenol is responsible for the disagreeable odour associated with this compound.

## Preparation and structure

Diphenyl disulfide is usually prepared by the oxidation of thiophenol:

    2 PhSH + $I_2$ → $Ph_2S_2$ + 2 HI

Hydrogen peroxide can also be used as the oxidant. $Ph_2S_2$ is rarely prepared in the laboratory because it is inexpensive, and the precursor has a disagreeable odour.

Like most organic disulfides, the C–S–S–C core of $Ph_2S_2$ is non-planar with a dihedral angle approaching 85°.

## Reactions

$Ph_2S_2$ 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' + $Ph_2S_2$ → RC(O)CH(SPh)R' + LiSPh

### Reduction

$Ph_2S_2$ undergoes reduction, a reaction characteristic of disulfides:

    $Ph_2S_2$ + 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

### Halogenation

$Ph_2S_2$ reacts with chlorine to give phenylsulfenyl chloride PhSCl (Zincke disulfide cleavage). This species is usually generated and used in situ. With xenon difluoride, $Ph_2S_2$ reacts to give phenylsulfur pentafluoride.

### Catalyst for photoisomerization of alkenes

$Ph_2S_2$ catalyzes the cis-trans isomerization of alkenes under UV-irradiation.

### Oxidation

Oxidation of $Ph_2S_2$ with lead(IV) acetate $(Pb(OAc)_4)$ in methanol affords the sulfinite ester PhS(O)OMe.

