GB703180A - Improvements in alkylene polyamino phosphonic acids and method of producing same - Google Patents

Abstract

The invention comprises as new compounds those having the structure <FORM:0703180/IV(b)/1> wherein Alk represents an alkylene radical CnH2n containing two to six carbon atoms, and the alkali metal salts thereof. The compounds are sequestering agents for metal ions in aqueous solutions being capable of chelating and complexing mono- and polyvalent metal ions to form non-ionic compounds. The compounds may be prepared by reacting a chloromethyl phosphonic acid with an alkylene diamine diacetic acid in heated alkaline aqueous solution, preferably at a pH of 10 to 11. In this process, the acetic acid groups of the amino acid may be immobilised by chelating the same with a divalent heavy metal such as copper which may be subsequently removed by precipitation with hydrogen sulphide, the substitution reaction with the chloromethyl phosphonic acid being thus facilitated. In an example of this procedure one mol. of ethylene diamine diacetic acid and one mol. of freshly precipitated copper hydroxide are dissolved in water to give a 40 per cent. to 50 per cent. solution of the resulting copper complex of the amino acid and the solution heated to from 60 DEG C. to the refluxing temperature and caustic soda is added to give a pH of 10-11. Two mols. of chloromethyl phosphonic acid are then added and the heating continued to complete the substitution reaction, a strong base being also added so as to maintain alkaline conditions. The reaction mixture is then diluted with water, cooled, neutralized with hydrochloric acid to a pH of 6.5 to 7 and hydrogen sulphide passed through to precipitate the copper ions as insoluble copper sulphide. The methylene phosphonic acid may be recovered from the copper-free solution, after boiling to expel the hydrogen sulphide, by precipitation by the addition of hydrochloric acid to a pH of about 2, or by adding free caustic alkali to give a pH of 10-11 and then crystallizing the sodium salt from the solution. Another method of forming the products is to treat ethylene diamine di-methylene phosphonic acid, which may be prepared in the manner described in Specification 703,181, with sodium cyanide and formaldehyde in alkaline solution of pH about 9, the product being obtained as the solid hexa sodium salt by addition of ethanol. The calcium chelate of ethylene diamine di(methylene phosphonic) diacetic acid sodium salt is referred to and this chelate may be formed in aqueous solution from insoluble calcium compounds, e.g. the oxalate, carbonate, and phosphate. The iron chelate of the same compound is also referred to and is formed by treating with ferric chloride and sodium hydroxide in solution. When the ratio of metal ion to chelating agent is greater that 1:1 the metal may still be completely complexed, thus two mols. of the calcium chelate is found to chelate one mol. of Fe+++ ion. The propylene diamine and trimethylene diamine derivatives are also referred to.