Preparation of N-(phosphonoacetyl)-L-aspartic acid

Claim 1

In a method for the preparation of a sodium salt of N-(phosphonoacetyl)-L-aspartic acid by reacting L-aspartic acid, dibenzyl ester p-toluenesulfonate with triethylamine, followed by the addition of phosphonoacetyl chloride to produce the N-(phosphonoacetyl)-L-aspartic acid moiety in the form of the dibenzyl ester, wherein the carboxyl groups of the N-(phosphonoacetyl)-L-aspartic acid are esterified, adding cyclohexylamine under anhydrous conditions to produce the cyclohexylamine salt of said dibenzyl ester, reacting said cyclohexylamine salt with sodium hydroxide to produce L-aspartic acid, N-(phosphonoacetyl)-, tetrasodium salt, and reacting said tetrasodium salt with acetic acid to produce L-aspartic acid, N-(phosphonoacetyl)-, disodium salt, the improvement which comprises subjecting the obtained disodium salt to a water-ethanol washing procedure, employing 92±1% by volume aqueous ethanol, said washing procedure being carried out at a temperature of from about 26° to about 28° C., thereby reducing impurities, including acetic acid, sodium acetate and ethanol, to an acceptable level.