Geraniol

Geraniol is a, highly valuable aroma chemical and having extensive use in perfumery and flavour compounds. There are three sources to isolate this aroma chemical. Palmarosa oil Cymbopogon martini commonly known 'Rosha' or russa is the main source of geraniol (80-95%) and Jamrosa oil contains 80-89%. Another source of geraniol is Cymbopogon winterianus (Java citronella oil), which contains 40-45% including citronellol. This paper reports the processing of these essential oils to the recovery of geraniol content and find out the comparative study in respect of yield and cost economics.

Geraniol is a monoterpenoid C-10 (branched) alcohol found widely as a chief constituent in essential oils including ilang-ilang oil, palmarosa oil, geranium oil, orange flower oil, lemongrass oil, hops oil, and lavender oil. It is a clear to pale-yellow liquid; boiling point 230 C; insoluble in water; soluble in alcohol, ether and most common organic solvents. It is the major constituent of rose-like odor. It is used in perfumery and flavoring. Nerol is the cis-isomer of geraniol. Geranial and neral are the corresponding aldehydes. Citronellol is the dihydrogeraniol and citronellal is the corresponding aldehyde. Citral is the mixture of geranial (trans-citral, called citral A) and neral (cis--citral, called citral A). Citral is the major constituent of emongrass oil, verbena oil, lemon oil, nikkel oil, lime oil, ginger oil, and other plant essential oils. It is the main source of lemon odor. Neral has a less intense, but sweeter. Citral is also used as a flavor. Citral is used as a raw material in the synthesis ionone which is a perfumery and flavoring component itself and used in the production of retinol. Geraniol is a pheromone of certain species of bees, being secreted by the scent glands of worker bees to signal the location of nectar-bearing flowers and the entrances to their hives. Geraniol also find an application as an insect repellants or deterrants.

Isomeric with linalool is geraniol C₁₀H₁₈O which is distinguished from the former by its optical inactivity, higher boiling point and higher specific gravity. It is the "lemonol" of Barbier and Bouveault, the "rhodinol" of Erdmann and Huth and of Poleck. Both as such and as ester it is found rather frequently in volatile oils. It constitutes the bulk of palmarosa oil, of German and Turkish rose oils, and is found in appreciable quantities in the oils of geranium, citronella and lemongrass. It has further been found in the oils of gingergrass, Canada snakeroot, ylang-ylang, champaca flowers, nutmeg, sassafras leaves, laurel leaves, kuro-moji, tetranthera (?), cassie flowers (from Acacia Cavenia and A. Fames/ana), neroli, petitgrain, coriander, Mexican and Cayenne lignaloe, of Darwinia fascicularis (?), Eucalyptus Macarthuri, E. Staigeriana, Leptospermum Liversidgei, verbena, spike (?) and lavender. As acetate it occurs in the needle oil of Callitris glauca, the oils of palmarosa, lemongrass, sassafras leaves, kuro-moji, lemon, petitgrain, Eucalyptus Macarthuri, E. Staigeriana, Leptospermum Liversidgei, Darwinia fascicularis and lavender; as Isovalerianate in sassafras leaf oil; as /7-capronate in pal-marosa and lavender oils; and as tiglinate in geranium oil.

As a primary alcohol, geraniol forms a crystalline addition product with calcium chloride,1) which is insoluble in ether, ligroin, benzene and chloroform, and which is resolved into its components by water. By this extremely simple method, geraniol can be obtained chemically pure (see below). With magnesium chloride, calcium nitrate and magnesium nitrate, crystalline derivatives are likewise formed.

For the isolation of geraniol from mixtures with hydrocarbons and other substances a number of other methods have been suggested. All of them have this in common that they aim at the preparation of an acid phthalate of geraniol. This ester can be prepared either by the action of phthalic acid anhydride on the sodium compound of crude geraniol,3) or by heating geraniol with phthalic acid anhydride without solvent in the water bath4) or in benzene solution.5) The ester can be purified through the crystalline silver salt. The geraniol is regenerated by saponifying either the acid ester, or its sodium salt, the latter being prepared from the silver salt. These methods, however, do not possess any advantages over the calcium chloride method. Indeed, they are more complicated and yield no purer product.

Geraniol, or rather its acetate, results together with terpineol and nerol, when linalool is heated for a long time with acetic acid anhydride.1) The reverse reaction takes place when geraniol is heated with water to 200° in an autoclave. At higher temperatures hydrocarbons and their polymerization products are formed.2) When hydrogen chloride is allowed to act on a mixture of geraniol and toluene, linalyl chloride results which, with silver nitrate, yields linalool.3) Hence it can be explained how Tiemann3) could obtain linalool when treating geraniol with hydrogen chloride and saponifying the reaction product with alcoholic potassa.

In general, geraniol is not as readily acted upon by acids as is linalool. However, the action of acid reagents may cause ring formation, cyclogeraniol being produced. When boiled with acetic acid anhydride it is quantitatively converted into the acetate, but not isomerized. When shaken with dilute sulphuric acid it is converted into terpinhydrate, as is linalool, but not as readily.4) Concentrated formic acid, like potassium acid sulphate or phosphoric acid, acts as dehydrating agent. Whereas the action of potassium acid sulphate is said to produce an open chain hydrocarbon,5) the other reagents produce terpenes. Thus formic acid produces a-terpineol, dipentene and terpinene.6). Upon reduction of geraniol with platinum sponge and hydrogen, Willstatter and Mayer7) obtained a mixture of 2,6-dimethyl octane and 2,6-di-methyloctanol-8. The same products were obtained by Enklaar8) with Sabatier's method. In addition, however, there resulted a cyclic alcohol C₁₀H₂₀O not further characterized.