Reaction of alcohol with phosphorus halides and SOCl2

Reaction with phosphorus halides and SOCl₂
Alcohols react with phosphorus tri or penta halides or thionyl chloride in pyridine to form the corresponding alkyl halides.

3R - OH + PX₃ --------------> 3R - X + H₃PO₃
R - OH + PX₅ --------------> R - X + POX₃ + HX
R - OH + SOCl₂ -------(pyridine)---------> R - Cl + SO₂ + HCl

Alcohols are converted to alkyl bromides by reaction with phosphorus tribromide

3ROH + PBr₃ ---------------> 2RBr + H₃PO₃

Alkyl iodides are obtained by reacting and alcohol with PI₃

3ROH + PI₃ -------(red p + I₂)-------> 3RI + H₃PO₃

3C₂H₅OH + PI₃ -------(red p + I₂)-------> 3C₂H₅OH + H₃PO₃

PBr and PI₃ are obtained in the reaction mixture by the action of red phosphorous and bromine or iodine.

Alkyl chlorides are prepared by reacting an alcohol with phosphorus trichloride, phosphorus penta chloride or thionyl chloride.

3R - OH + PCl₃ ----------------> 3R - Cl + H₃PO₃

3C₂H₅OH + PCl₃ ----------------> 3C₂H₅Cl + H₃PO₃

R - OH + PCl₅ ----------------> R - Cl + POCl₃ + HCl

C₂H₅OH + PCl₅ ----------------> C₂H₅OH + POCl₃ + HCl

C₂H₅OH + SOCl₂ --------(pyridine)--------> C₂H₅Cl + SO₂ + HCl

The reaction with thionyl chloride is preferred as the by products (SO₂ and HCl) formed are gases and are easily removed from the reaction mixture.

 Related post Chemical properties of Alcohols and Phenols