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Described below is the procedure for the resolution of racemic phenylsuccinic acid. Isolation of the (+)-enantiomer has been successfully completed in our undergraduate organic laboratory for the past four years by more than 1500 students. The success of this resolution is due to the preferential formation and precipitation of the (+)-phenylsuccinic acid-bis proline salt from 2-propanol-that is, two molecules of (-)-proline are associated with one molecule of (+)phenylsuccinic acid. This procedure has been adapted from that published by Shiraiwa et al. (1).
This experiment offers several advantages over other resolution procedures that use toxic alkaloids, such as brucine (2), or unpleasant smelling amines, like a-phenylethylamine (3). It utilizes (-)-proline as the resolving agent and (+/-)-phenylsuccinic acid as the compound to be resolved; both are relatively nontoxic solids that are easy to work with. The procedure for isolating optically pure (+)-phenylsuccinic acid can be completed in about two hours and can also serve to introduce the reflux and recrystallization techniques. The specific rotation of (+)-phenylsuccinic acid is high, [alpha]- = +173.3(deg) (c 1.8235, acetone) (1); therefore, less sample is needed to measure the actual rotation, and pooling of students' products is not necessary to obtain an optical rotation reading.
Although we have never tried this resolution on a microscale, we are confident that this procedure, owing to the high yield and optical rotation value, would...