Hydrochloric Acid → N-Carbamoylphenylalanine

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Reaction Steps

This Example shows the process in which hydrochloric acid is added first and then the zinc is added. A round bottom flask fitted with a stirrer, thermometer and condenser was charged with 10 grams of 5-benzalhydantoin (0.053 mole), 100 milliliters of methanol and then 21.0 grams of concentrated (37 weight percent) hydrochloric acid (0.213 mole of hydrogen chloride, 400 mole percent based on 5-benzalhydantoin) was added. To this was added very slowly with stirring 6.93 grams of zinc powder (0.106 mole, 200 mole percent based on 5-benzalhydantoin) over a period of 45 minutes. After 30 minutes of additional stirring, some of the zinc powder remained unreacted and so 5 grams more of concentrated hydrochloric acid was added. After about 60 minutes more of stirring, no unreacted zinc powder remained. The reaction was stirred an additional 2 hours. By UV analysis, the reaction mixture showed 98% reduction of the carbon-carbon double bond of the 5-benzalhydantoin. By workup of the reaction mixture N-carbamylphenylalanine was isolated. The melting point was determined to be 186°-188° C. corresponding to the literature melting point of 190° C., reported in Am. Chem. J. 45, 368 (1911) (compound referred to as 4-benzylhydantoic acid).

Provenance & Evidence