Electrochemical synthesis of amino acids by reductive amination of keto acids. I. Reduction at mercury electrodes

Racemic 2-amino-2-phenylacetic acid, monoammonium glutamate, 2-aminobutyric acid, α-alanine and ammonium 5-amino-5-phenylvalerate have been prepared by electrochemical reductive amination of the corresponding keto acids in aqueous ammonia/ammonium chloride solution at a mercury electrode. The yields ranged from 24% for ammonium 5-amino-5-phenylvalerate to 88% for 2-amino-2-phenylacetic acid. The current efficiency and yield of 2-amino-2-phenylacetic acid from reductive amination of 2-oxo-2-phenylacetic acid increased with increase in ammonia concentration. Also, decreasing the reduction potential from -1.10 to -1.30 V (with respect to a saturated calomel electrode) in 2 M ammonia raised the initial current density from c. 2 mA/cm2 to c. 7 mA/cm2 but halved the yield of 2-amino-2-phenylacetic acid.