Process for manufacturing 1-hydroxyalkylidene-1,1-diphosphonic acid (HADP)

A process for making 1-hydroxyethylidene-1,1-diphosphonic acid (HEDP) consisting essentially of:

• (a) reacting PX.sub.3 and aqueous acetic acid at a temperature of between, about 100.degree. C. and 120.degree. C., and a pressure between about 30 and 80 psig, wherein X is a halogen and the molar ratio of PX.sub.3 :acetic acid:water is 1:1.6-3.3:0.5-1.7, and
• (b) adding water to the product of step (a) to hydrolyze the product and form said HEDP, wherein the molar ratio of water added in step (b) to PX.sub.3 added in step (a) is 1:0.8-2.5.

A process for making 1-hydroxyalkylidene-1,1-diphosphonic acid consisting essentially of:

• (a) reacting PCl.sub.3 and aqueous acetic acid at a temperature of between about 100.degree. C. and 120.degree. C., and a pressure between about 30 and 80 psig, wherein the molar ratio of PCl.sub.3 :acetic acid:water is about 1:1.7-2.3:1-1.7;
• and
• (b) adding to the product of step (a) and hydrolyzing the product at a temperature of between about 100.degree. C. and 140.degree. C., wherein the molar ratio of water added in step (b) to PCl.sub.3 added in step (a) is 1:1-2.