Oxides, Epoxides and Peroxides

Terpene oxides, epoxides or peroxides are encountered more often than is usually believed during TLC of essential oils [248]. Eucalyptol (1,8-cineole) and ascaridole, which is easily accessible by photochemical treatment of a-terpinene, are the best known. These compound types play a special part in the determination of the value of individual oils. 

Gyanchandani [85] has thus chromatographed caraway seed oil and dill oil under standard conditions and determined the position of the limonene epoxide (1,2) which had been formed by autoxidation of limonene. Nigam, Sahasrabudhe and Levi [185] have detected piperitone oxide in peppermint oils in a similar way. Attention has been drawn repeatedly to the bisabolene oxides I, II and III along with chamazulene in the assessment of camomile oils [78, 224, 305, 306]. 

The position of these substances in the chromatogram is determined by the polarity of the parent compound. Menthofuran migrates just behind guaiazulene [182 a, 247]. The terpene and sesquiterpene epoxides follow, lying in the upper part of the ester zone on silica gel G layers (Table 23) (cf. also [155]). in agreement with El-Deeb [55]. The carbonyl and alcohol oxides follow with lower hRf-values. This sequence holds even at — 9° C using Freon (Frigen 21) as solvent [255]. 

Solvent Colour reactions with various reagents 

85 light brown 35 brown-grey 24 brown-grey 63 red-blue 

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Table 23. hjtf-values and colour reactions of some terpene- and sesquiterpene oxides, epoxides and peroxides cm silica gel layers ... 

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