GB600629A - Improvements relating to polycarboxylic amino acids - Google Patents

Abstract

Amino polycarboxylic acid salts are prepared by reacting, in aqueous alkaline solution having a pH of at least 9, one mole of an aliphatic or cycloaliphatic amine having at least two replaceable hydrogen atoms attached directly to the same or different amino nitrogen atoms with at least one mole of an alkali metal cyanide and at least one mole of formaldehyde or a substance yielding formaldehyde in alkaline solution, for each of or at least two of the replaceable amino hydrogen atoms, and at a temperature and pressure such that ammonia formed in the reaction is volatilized from the reaction mixture, said cyanide and formaldehyde, or substance yielding the same, being added at such rates that free cyanide is maintained in the reaction mixture but in an amount of not more than about one quarter of the amount necessary to react completely with the original amine and the amount of free formaldehyde present is maintained at less than one mole per mole of free cyanide until substantial completion of the reaction of the amine has occurred, the ammonia being removed as it is formed so that there is substantially no free ammonia present in the reaction mixture. Generally, the process is effected by adding all the amine to the aqueous alkaline solution, which may contain an alkali metal hydroxide if necessary, and then feeding in the cyanide and formaldehyde as described above, the molar amount of free formaldehyde present being about 5 per cent less than the amount of free cyanide present, and when all the cyanide has been added, adding the remaining 5 per cent of formaldehyde and any more required to ensure complete reaction of residual cyanide. By maintaining the reaction mixture at the boil under reduced pressure and a temperature of 60-80 DEG C., the ammonia is boiled-off as it is formed. Paraformaldehyde may be used in place of formaldehyde. The products are salts of aliphatic or cycloaliphatic amino polyacetic acids from which the free acids may be obtained by treatment with a strong acid. A diamine such as ethylene diamine yields the tetra-alkali metal salt of the corresponding amino acetic acid and by reacting an aqueous solution of the salt with an equimolecular amount of the free amino-acetic acid, the dialkali metal salt may be obtained: in a similar manner, this salt may be converted into the mono-alkali metal salt. Examples illustrate the preparation of sodium ethylene diamine tetracetate by reaction of aqueous solutions of formaldehyde and sodium cyanide with a solution of ethylene diamine in aqueous caustic soda. The sodium salts of tetracetic acids of 1 : 2-propylene diamine, dipropylene triamine, 1 : 3-diamino-propanol-2 and diethylene triamine, of N-monohydroxyethyl-ethylene diamine triacetic acid and of N-butylamine-, cyclohexylamine-, and piperazine-diacetic acids may be prepared likewise. Penta- (and higher) alkali metal salts of penta- (or higher) acetic acids may also be prepared from appropriate polyamines generally by reacting at or above atmospheric pressure and at about the boiling point for the pressure used. Specifications 390,166, 482,352 and U.S.A. Specification 2,130,505 are referred to.