Primary Phosphinic Acids and Esters

7 PHOSPHONIC AND PHOSPHINIC ACIDS [1-18] 6.7.1 Primary Phosphinic Acids and Esters 

Primary phosphinic esters (6.248) are of importance as intermediates because of their reactive P-H bonds. They are obtained when phosphonous dichlorides are reacted with alcohols at ice-cold temperatures (6.249). The low temperature is necessary to prevent cleavage of the second ester group (6.164). They can also be obtained by the hydrolysis of phosphonous diesters (6.224), from phos-phonamidous esters (7.190), or from treatment of hypophosphorous acid with diazoalkanes (6.250). Some ketones will react with hypophosphorous esters to give primary phosphinic esters (6.251). 

Primary phosphinic esters react with sodium in dry ether to give sodio derivatives which are soluble in organic solvents. With chlorine at 0°C, phosphonochloridates are produced. Phosphonochloridates are also produced by reaction with carbon tetrachloride in the presence of a tertiary amine (Atherton-Todd reaction), and phosphonamidic esters are obtained with aqueous chloramine at -5°C to -30°C. 

Methylphosphinic esters react with paraformaldehyde and with doubly bonded compounds to give various secondary methylphosphinic esters. 

---