N.C([O-])(=O)/C=C\C([O-])=O.[NH4+].[NH4+].[NH2:12][CH:13]([C:18]([O-:20])=[O:19])[CH2:14][C:15]([O-:17])=[O:16].[NH4+].[NH4+].N[C@H](C(O)=O)CC(O)=O.Cl>>[NH2:12][CH:13]([C:18]([OH:20])=[O:19])[CH2:14][C:15]([OH:17])=[O:16]Reaction vessel was a 0.33 liter autoclave which was charged with a saturated aqueous solution of ammonia (150 g) and diammonium maleate (30 g) at a temperature of about 25-40 degrees C. The autoclave was sealed and then pressurized through a gas inlet valve with ammonia gas to a constant pressure of about 114 psig for a period of 30 minutes. The gas inlet valve was then closed and the autoclave maintained at 40 degrees C. for 30 minutes. The autoclave was thereafter heated to about 140-150 degrees C. over a period of 40 minutes and maintained in this temperature range for an additional 50 minutes. The pressure within the reaction vessel rose from about 114 psig to about 700 psig during this heating period. After the temperature of about 140-150 degrees C. and the autogenous pressure had been maintained for 50 minutes, the contents of the reactor were expelled into a second vessel at ambient pressure. The resulting solution of diammonium D,L-aspartate was then neutralized while in the second vessel to a pH of 2.8 (isoelectric point of aspartic acid) with concentrated hydrochloric acid (about 12 molar). A white precipitate of D,L-aspartic acid formed within a few minutes of neutralization with the acid. The precipitated D,L-aspartic acid was isolated by filtration and dried to afford a 71% yield of white crystalline powder. The product was identical to an authentic sample of D,L-aspartic acid obtained by both NMR (Nuclear Magnetic Resonance) and IR (InfraRed) techniques.
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