Method for the synthesis of aminoalkylenephosphonic acid

A method for the synthesis of an aminoalkylenephosphonic acid or its phosphonate esters including the following steps: a) forming, in the presence of an aldehyde or ketone and an acid catalyst, a reaction mixture by mixing a compound having at least one HNR1R2 moiety or a salt thereof, with a compound having one or more P-O-P anhydride moieties, the moieties having one P atom at the oxidation state (+III) and one P atom at the oxidation state (+III) or (+V), wherein the ratio of moles of aldehyde or ketone to N-H moieties is 1 or more and wherein the ratio of N-H moieties to P-O-P anhydride moieties is 0.3 or more, and b) recovering the resulting aminoalkylenephosphonic acid having compound or its phosphonate esters.