54 JOURNAJ, OF CHROMATOGRAPHY THE SEPARATION AND IDENTIFICATION OF THE COMPONENTS OF THE AROMATIC ETHER FRACTION OF ESSENTIAL OILS BY GAS-LIQUID CHROMATOGRAPHY

In recent years the study of the volatile components of natural products has been enormously extended by the development of the techniques of gas-liquid chromatography. The detection, isolation, and identification of unsuspected minor components, either in the lower boiling (terpenaceous) or higher boiling (aromatic) fractions of essential oils, has provided both taxonomic assignment and insight into plausible biogenetic pathways. This latter fraction, that which is made up to a large extent of phenols and their ethers, has always proved difficult to analyze for numerous reasons. Most of the known components are oils at ordinary temperature, thus distillation cuts rarely crystallize. If there is any complexity in the natural mixture, a continuous temperature increase is observed during distillation even with the use of efficient fractionation equipment. Secondly, there is a consistent similarity in the substitution groups present; the ether groups are invariably methoxys or methylenedioxys, and the aliphatic chain is usually found to be allyl, cis-propenyl, or tralss-propenyl. Attempts at differential extraction or partition within these distillation cuts have been generally unsuccessful