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6. From Gattefossé’s Aromatherapy René-Maurice Gattefossé 1937 (revision & introduction by Tisserand 1993) pub C.W. Daniel.

Gattefossé frequently alluded to the use of terpeneless essential oils. Thus on page 14: “Terpeneless mint essences contain menthol & no menthone (a potentially dangerous ketone)”. On p47 of the same book: “Terpenes should always be removed from the essence of mint, which in its raw state, contains menthone, as menthone is eliminated during fractionation along with the terpenes, which have a similar boiling-point”.

It may seem a little unfair to criticise such an old text with modern scientific insight, but this appears wrong even by the former standards of the day. The boiling point of menthone under reduced pressure is considerably higher than the monoterpene hydrocarbons, and therefore if the fractionating column in the still was properly designed, effective separation of the last eluting fractions of the latter (rich in p-cymene & terpinolene) should be easily effected. A rise in vapour temperature then heralds the emergence of 3-octanol and other eight carbon derivatives, can be reckoned to herald the start of the elution of the terpeneless oil. This gives way to the considerably larger menthone and isomenthone fractions, and later the menthol and neo-menthol containing fractions emerge. It is usual to bulk the acceptable smelling fractions together afterwards – some of the more unpleasant smelling sulphide fractions are likely to be left behind in the monoterpene hydrocarbons, and of the terpeneless fractions, perhaps only some of the later (burnt smelling) tail fractions might be excluded from bulking.

Some of Tisserand’s notes at the end of the book are of dubious accuracy.

p142: “I know of no evidence that carvone is toxic”. Tisserand seems to miss the fact that there is a difference in oral and dermal toxicity between the d- and l- forms of carvone (and in Essential Oil Safety). The d-form found in Caraway oil is more toxic (LD₅₀ orl-rat : 3710 micrograms /Kg).

p143: "Ylang ylang has 25% terpenes". I think there is a mix-up between monoterpene hydrocarbons (which are only present in minute amounts in Ylang ylang oil) and sesquiterpene hydrocarbons such as Germacrene D, which do occur in substantial amounts in the oil. Note also that poorer grades of Ylang ylang oil (such as Ylang ylang III) , commonly sold by essential oil traders, contain higher amounts of sesquiterpenes.

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