A method for synthesis of N-phosphonoalkyliminodiacetic acid or derivatives thereof by forming a reaction mixture having an acid catalyst, a compound of the following general formula R1—CH2—NX—CH2—R2 and a compound having one or more P—O—P anhydride moieties to form a compound having a formula R1—CH2—N(—CH2PO3R32)(—CH2—R2) wherein in R1—CH2—NX—CH2—R2: X is —CH2—OH or —CH2—COOH; R1 and R2 are independently selected from the group consisting of nitrile, C1-C4 alkyl carboxylate, and carboxylic acid for when X is —CH2—OH, or R1 and R2 are both carbonyl groups linked by a hydrogen substituted nitrogen atom or a C1-C4-alkyl substituted nitrogen atom; and R3 is H, an alkyl group, or an aryl group; the anhydride moieties in the P—O—P anhydride compound have one P atom at the oxidation state (+III) and one P atom at the oxidation state (+III) or (+V); and 2) hydrolyzing the mixture to form N-phosphonomethyliminodiacetic acid or one of its derivatives.