Process for the preparation of nitrilotriacetonitrile (ntn)

Abstract

Nitrilotriacetonitrile (NTN) is produced in high yeilds from hydrogen cyanide, formaldehyde and ammonia, or its equivalent as an ammonium salt of a strong acid, by utilization of a critical two-stage reaction sequence within a narrow dilution ratio and temperature range. The reaction sequence steps provide for a first mixture to be prepared comprising a mixture of the formaldehyde and ammonia. No external adjustment of the pH of this mixture is permitted. A second mixture is prepared comprised of the HCN in an aqueous solution and a strong mineral acid such as sulfuric acid for adjusting the pH of the mixture to about 1 or less. NTN is produced by combining the mixtures at a temperature of from about 55.degree. C. to about 70.degree. C. either by adding the formaldehyde/ammonia solution to the HCN/acid solution or vice versa. The ratios and dilution of the reactants is critical for good yields. The aqueous solution of formaldehyde and ammonia or ammonium salt (calculated as ammonia) may have a ratio of total solute weight to solution weight within a range of about 25 to 60%, and an optimum mole ratio of formaldehyde to ammonia of no more than 3 to 1. In the combined mixtures a mole ratio of hydrogen cyanide to formaldehyde of 1.1 or greater and a concentration factor of total reactant weight to solution weight of from about 30 to about 40% is required. The nitrilotriacetonitrile produced may be converted by hydrolysis to the carboxylic acid, nitrilotriacetic acid (NTA) or a carboxylic acid salt such as the sodium salt, known as SNTA. NTA and its salt are useful as detergent builders.