Abstract
In previous syntheses of aspartic acid the following reactions have been used: The decomposition of acid ammonium malate by heat, 1 the racemization of active aspartic acid 2 and active asparagine, 3 the reaction of maleic or fumaric acid with ammonia, 4 the reduction of oxalacetic ester oxime, 5 the reaction of silver fumarate or potassium acid fumarate with hydroxylamine hydrochloride, 6 the reduction of nitrosuccinic ester, 7 the catalytic reduction and ammonation of oxalacetic acid, 8 and the hydrolysis of the addition compound formed from sodium malonic ester and chloroacetic ester. 9
The present synthesis is believed to be more satisfactory than those previously reported for aspartic acid.
Phthalimido malonic ester, prepared from potassium phthalimide and bromodiethylmalonate, was converted to sodium phthalimido malonic ester by allowing it to react with molten metallic sodium suspended in toluene. A stable addition product was then formed as a dark colored oil by the reaction of chloroacetic ester with sodium phthalimido malonic ester. This product was readily hydrolyzed by hydrochloric acid with the formation of dl aspartic acid, phthalic acid, carbon dioxide, and ethyl alcohol. Side reaction products are not probable.
The acid hydrolysate was evaporated to precipitate the phthalic acid which was removed by filtration. Hydrochloric acid was removed by the addition of the calculated quantity of silver oxide to the boiling diluted diltrate. After removing the precipitate of silver chloride and evaporating the filtrate to a small volume d,1 aspartic acid crystals separated after standing for 3 days. Upon recrystallization from hot, 50% ethyl alcohol these crystals darkened and decomposed over the range, 311-325°C. Within the limits of experimental error they were shown to contain the theoretical quantity of amino nitrogen.
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