Occurrence and consequences of differences in the cation/anion ratios during classical resolution: D‐/L‐serine benzyl ester 2,3‐toluyl‐D‐tartrate

Differences in physical‐chemical properties of diaste‐reomeric salts allow the separation into the respective salts and subsequently into enantiomers by crystallization. Within this study unusual deviations in the cation‐/anion‐ratio of a diastereomeric salt pair were observed and characterized. While the n‐salt (L‐serine benzyl ester 2,3‐toluyl‐D‐tartrate) crystallizes in a ratio of two cations and one anion, the p‐salt (D‐serine benzyl ester 2,3‐toluyl‐D‐tartrate) consists of only one cation and one anion. Consequently the classical definition of a diastereomeric salt pair does not apply. In this contribution all differences in relevant thermodynamic properties of the unusual resulting diastereomeric salt pair are presented and discussed.