Geraniol (frans-3,7-Dimethyl-2,6-octadien-1-ol) is a colourless—to pale yellow liquid oil with pleasant geranium-like odour, specific gravity 0.8894 (at 20 °C), refractive index 1.4766 (at 20 °C), soluble in alcohol as well as in ethers but insoluble in water. It is the major constituent of rose oil and palmarosa (Indian grass) oil; it is also found in appreciable amounts in citronella oil (used as insect repellent).
Citronellol (mixture of the less abundant 3,7-dimethyl-6-octen-1-ol form and 3,7-dimethyl-7-octen-1-ol form), normally found in oils of citronella, geranium, rose, savin and other essential oils is a colourless liquid with somewhat rosy odour. It is soluble in two or more volumes of 70 %-alcohol and in the most part of oils.
Borneol (2-hydroxyl camphene), also called 2-camphanol or bornyl alcohol, is found in several essential oils such as thyme oil. It is commercially derived from wood of Dryobalanops camphora, a tree in Sumatra and Borneo. It has camphor-like odour and burning taste, specific gravity 1.011, melting point 208 and
210.5 °C for enantiomers and the racemic mixture, respectively, (Surburg and Panten 2016). It is soluble in alcohol and ethers, and very slightly soluble in water.
As a mixture of a- and P-isomers, citral (3,7 dimethyl-2,6 octadienal) is the principal constituent of lemon grass oil, having strong lemon odour. It is soluble in 5 volumes of 60 %-alcohol.
Safrole (4-allyl-1,2-methylene dioxybenzene, Fig. 2.5), is a colourless or pale yellow-liquid oil with sassafras odour. It is found in sassafras and camphorwood and other essential oils. It has specific gravity 1.096 (at 20 °C), melting point 11 °C, boiling point range 232-234 °C and refractive index 1.5383 at 20 °C (Kar 2003). It is soluble in alcohol and ethers but insoluble in water. Safrole is considered as the most harmful allergen and FSSR, 2011 specifies maximum limit for its presence in food articles up to 10 ppm.