Addition of compounds containing P-Cl bonds

Addition of phosphorus trichloride to aldehydes or ketones occurs with deoxygenation of the carbonyl compound. It thus provides a simple entry to the phosphonic acid series. After phosphorus trichloride has reacted with 3 moles of a carbonyl compound hydrolytic working up affords ac-hydroxy phosphonic acids, often in good yield. Directions for the preparation of the hydroxymethyl compound from paraformaldehyde have been given by Bannard and his co-workers.104 

The primary formaldehyde adduct, (chloromethyl)phosphonic dichloride, can be isolated by a suitable technique including exclusion of moisture  

Phosphonic chlorides can be prepared analogously from dichlorophosphines, and phosphine oxides from monochlorophosphines.106 

In a different technique for. preparation of a-hydroxy phosphonic acids equimolar amounts of the components are used with glacial acetic acid as solvent. 

General directions for preparation of a-hydroxy phosphonic acids 107 Phosphorus trichloride (10% excess) is added with exclusion of moisture to the carbonyl compound, the temperature not being allowed to rise above 35°, and the mixture is set aside for 2-3 h. Glacial acetic acid (3 moles) is then added, the temperature being kept below 30°. After a further 12 h the mixture is poured into well-stirred ice-water (300 ml), and the whole is evaporated to dryness. 

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