Method For The Synthesis Of Alkane-1-Hydroxy-1,1-Diphosphonic Acid

A method for the synthesis of alkane-1-hydroxy-1,1-diphosphonic acid or its salts, under controlled thermal conditions, by substantially avoiding the formation of phosphines and low oxides of phosphorus and the accumulation of phosphite intermediates, comprising the steps of:

• a) forming a reaction mixture by gradually adding tetraphosphorus hexaoxide, under optimal mixing conditions, to the liquid phase comprising a carboxylic acid, while controlling the temperature of the reaction mixture in the range of from 80° C. to 200° C. wherein said reaction mixture comprises a molar ratio of carboxylic acid to tetraphosphorus hexaoxide comprised between 3 and 15, selected in such a way that the viscosity of the reaction mixture enables said optimal mixing conditions, the gradual addition leading to the formation of alkane-1-hydroxy-1,1-diphosphonic acid condensates;
• b) hydrolyzing the alkane-1-hydroxy-1,1-diphosphonic acid condensates of the reaction mixture of step a) by adding water, wherein the molar ratio of water to tetraphosphorus hexaoxide, added in step a) is 1 or more, and maintaining the reaction mixture at a temperature of at least 100° C. to obtain a solution comprising the alkane-1-hydroxy-1,1-diphosphonic acid.