The synthesis of α-hydroxy-and α-chlorophosphonic acid derivatives starting from benzaldehydes and phosphorous acid or dimethyl phosphite

The addition of phosphorous acid on the C=O group of substituted benzaldehydes in the presence of hydrochloric acid in water affords a mixture of the corresponding α - chlorophosphonic acid and α-hydroxyphosphonic acid. The selectivity towards the α-chloro derivatives may be increased to 92% by the excess of HCl applying forcing conditions. α- Hydroxyphosphonic acids may be synthesized better in yields of 83-92% by the hydrolysis of the corresponding dimethyl α-hydroxyphosphonates. α-Chlorophosphonic acids may also be obtained in yields of 66-79% from α -hydroxyphosphonic esters by reaction with thionyl chloride followed by hydrolysis. The α -chlorophosphonic acids and esters are useful intermediates for other phosphonic derivatives.