Process for the preparation of N-phosphonomethylglycine

A process for the preparation of a phosphono tcompound of the formula I

• in which the radicals R3, which can be identical or different, are C1-C18-alkyl or aryl which is unsubstituted or substituted by C1-C4-alkyl, NO2 or OC1-C4-alkyl, and
• X is CN, COOZ, CONR1R2 or CH2OY,
• Y is H or is a radical which is readily exchangeable for H selected from the group consisting of C1-C6-alkyl, aliphatic acyl having a C1-C6 aliphatic group, and benzoyl;
• Z is H, an alkali metal, alkaline earth metal, C1-C18-alkyl or aryl, which is unsubstituted or substituted by C1-C4-alkyl, NO2 or OC1-C4-alkyl;
• R1 and R2, which can be identical or different, are H or C1-C4-alkyl, in which a hexahydrotriazine derivative of the formula II
• is reacted with a triacyl phosphite of the formulaII
• P(OCOR3)3 (III)
• in which R3 and X are as defined above.