Study of retention behaviour of primary, secondary and tertiary anilines in normal- and reversed-phase liquid chromatography

Abstract

A series of alkyl-substituted primary, secondary and tertiary anilines were chromatographed on three liquid chromatographic systems: one normal-phase system on a nitrile stationary phase and two reversed-phase systems on octadecyl- and octylsilane. On the nitrile stationary phase the elution order is tertiary, secondary and primary anilines and within each group the retention is mainly determined by the base strength, the number and size of ortho-alkyl groups and the size of the alkyl groups substituted at the nitrogen atom. On the reversed phases the anilines within each group are mainly eluted in order of increasing alkyl carbon number. The relationship between the p K b values of the anilines and log k′ on the nitrile stationary phase is discussed and a comparison is made between k′ for primary anilines and the corresponding phenols on the same stationary phase. Identification of different kinds of anilines by means of a two-phase plot is discussed and a method is described for the systematic separation of alkylanilines into structural types and individual compounds.