Patent ID: 7084298

Claim:
A process for the preparation of N-phosphonomethyliminodiacetic acid, comprising a) reacting an alkali metal salt of iminodiacetic acid with phosphorus trichloride in aqueous solution to obtain the hydrochloride of iminodiacetic acid, phosphorous acid and the corresponding alkali metal chloride, b) halting the reaction mixture at the boil by the exothermic reaction of the phosphorous trichloride with water and removing a sufficient amount of water from the reaction mixture until the concentration of iminodiacetic acid hydrochloride is 44 to 55% by weight, based on the weight of the mixture minus the weight of alkali metal chloride, c) reacting with a formaldehyde source, and d) recovering the N-phosphonomethyliminodiacetic acid thus formed from the reaction mixture.