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

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