Process for the manufacture of aminomethanephosphonic acid

A process for the manufacture of aminomethanephosphonic acid which comprises

• 1) reacting a compound of formula R--CH.sub.2 --NH--CO--NH--CH.sub.2 --R' wherein R and R', which may be the same or different, represent a phosphonation leaving group with a phosphonating agent which is selected from the group consisting of phosphorous trichloride, a dialkyl chlorophosphinate of formula ClP(OR.sup.1).sub.2 wherein R.sup.1 is C.sub.1-7 alkyl, and a mixture of phosphorous trichloride and an alcohol of formula R.sup.1 OH in the presence of a water-miscible solvent to form a compound of formula (II) when the phosphonating agent is phosphorous trichloride and a compound of formula (II') when the phosphonating agent is a dialkyl chlorophosphinate or a mixture of phosphorous trichloride and the alcohol R.sup.1 OH;
• ##STR2## 2) hydrolysing the compound of formula (II) or (II') with water under mild conditions to form a compound of formula (IV):
• ##STR3## 3) separating the water-miscible solvent by distillation and replacing it by a water-immiscible solvent.
• 4) adding water and extracting the compound of formula (IV) into the aqueous phase thus formed and
• 5) hydrolysing the aqueous phase from stage (4) at a temperature of from 100.degree. C. to 200.degree. C., the pressure being adjusted accordingly thereby forming aminomethanephosphonic acid.