Purification of the Optical Antipodes of α-Arylalkylamines by the Formation of Clathrates

Abstract

THE classical methods for resolving amines such as α-phenylethylamine^1,2, α-(p-tolyl) ethylamine^2,3, or α-phenylpropylamine⁴ into their optical antipodes involve salt formation with a naturally occurring acid such as d-tartaric or d-camphoric acid. By these methods, one of the antipodes can usually be isolated in a pure state by successive crystallizations of the less soluble diastereoisomeric salt. The antipode remaining in the mother liquor, however, is always contaminated by the other and another resolving agent is necessary for further purification. Theilacker¹ has purified d-α-phenylethylamine by sulphate formation; we did not, however, obtain the same result with other α-arylalkylamines. In most cases, the isolation of d-amines by these methods requires the use of expensive reagents such as l-malic acid.