N-HYDROXY-ALKANE-AMINO-DIPHOSPHONIC ACIDS AND THEIR ALKALI SALTS

The present invention provides a N-hydroxy-alkane-amino-alkane-diphosphonic acid having the general formula wherein R is H, CH3, C2H5, C6H5, CH2CH2OH, CH2COOH, R1 is H, CH3, CnH2nOH, hydroxypropyl or hydroxypropionic acid, R2 is H, CnH2nOH, hydroxypropyl or hydroxypropionic acid provided that R2 is other than hydrogen when R1 is hydrogen and n is 2 or 3 or an alkali salt thereof and a method for the preparation thereof by reacting a corresponding amino-alkane-diphosphonic acid, their hydroxy or carboxy derivatives containing one or two substitutable hydrogen atoms on the nitrogen or their alkali salts with the corresponding cyclic ether in the weight ratio of 1:1 to 1:3 at temperatures of up to 100.degree.C. The phosphonic acids have very good solubility in water for most uses, are good complexing agents for divalent and polyvalent metals and their stability to hydrolysis at high temperatures is particularly good. They can be used in any medium in which the hardness salts of water have a detrimental effect or in which the effects of polyvalent metals are to be eliminated such as the treatment of hard water, baths for treating textiles, paper making and tanning. They are also suitable for stabilizing the hardness of water in amounts below the stoichiometric amount.