title: Diphenyl disulfide
text: # 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.
  
  