Non-linear effects in the enantiomeric separation of mandelic acid using the mixtures of amphoteric resolving agents

In this study, (S)-phenylalanine, aspartame and (S)-pregabalin, which contain α-, β- and γ-amino acidic moieties were successfully applied as resolving agents for the enantiomeric separation of mandelic acid via the formation of diastereomeric salts. The resolution of mandelic acid was also attempted with mixtures of the corresponding resolving agents and a more efficient enantiomeric separation of the mandelic acid was observed compared with the given sole resolving agents in a few instances. The best results were obtained with a mixture of (S)-phenylalanine and (S)-alanine; the latter resolving agent was insufficient when it was applied alone. The resolution efficiency of mandelic acid could also be improved by applying structurally related amphoteric achiral additives along with the corresponding resolving agents.

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(+)-(S)-Mandelic acidC8H8O3ee = 76%[α]D25 = +115.5 (c 1, water)Source of chirality: resolutionAbsolute configuration: (S)