Rose alcohols

Nerol, geraniol, and linalool, known as the rose alcohols, are found widely in nature. Nerol and geraniol have mild, sweet odors reminiscent of rose flowers. They are manufactured by the hydrochlorination of mycene at the conjugated double bonds when a copper catalyst is used (88,89). 

Pyrolysis of -pinene results in the triene myrcene, which leads to menthol and its derivatives, on one hand, and the rose alcohols and citral-related chemicals, on the other hand. 

Guterman, L, Masci, T., Chen, X., Negre, R, Pichersky, E., Dudareva, N., Weiss, D. and Vainstein, A. (2006) Generation of phenylpropanoid pathway-derived volatiles in transgenic plants rose alcohol acetyltransferase produces phenylethyl acetate and benzyl acetate in petunia flowers. Plant Mol. Biol, 60, 555-63. 

A. H. Rose, Alcoholic Beverage Production, Bath University, 1977. 

Total rose alcohol and citral related materials 22500... 

The major producers of the rose alcohols and citral have become so for a variety of reasons. Companies which manufacture wood and paper products produce sulfate turpentine or similar by-products rich in pinenes. They, or their subsidiaries, may then produce terpenoid fragrance materials from pinenes as a way of generating income from their by-product. Pharmaceutical companies which manufacture vitamins use terpenoid intermediates and so will often diversify into the manufacture of aroma chemicals. Their basic feedstocks are likely to be of petrochemical origin. Similarly, manufacturers of synthetic rubber possess technology for the use of isoprene as a feedstock and so are also likely to diversify into terpene aroma chemical manufacture. Fragrance companies will develop a position in terpenoid chemistry because of the importance of terpenoids as ingredients. 

Among the vast number of applications, an important example is the production of the so-called rose alcohols from p-pinene, viz. nerol, geraniol and linalool, key intermediates in the synthesis of many major fragrances. This process involves the thermal isomerization to myrcene, followed by addition of HCI, substitution by acetate and alkaline hydrolysis, as shown in Fig. 2.5 [3]. 

In volume terms, the terpenoids represent the largest group of natural and nature identical fragrance ingredients (Daniker, 1987 Sell, 2007). The key materials are the rose alcohols [geraniol (63)/nerol (90), linalool (23), and citronellol (91)], citronellal (103), and citral (71). Interconversion of... 

The so-called rose alcohols (geraniol, nerol, citronellol, and linalool) together with the corresponding aldehydes citral and citronellal, lie at the heart of the major production routes in terpenoid chemistry as shown in Fig. 8.7. In this figure, the basic feedstocks are contained in ellipses and it can be seen that there is a balance between natural (hence, renewable) and petrochemical feedstocks. 

The major petrochemical routes to the rose alcohols and the corresponding aldehydes are directed toward linalool and citral. This is partly for historic reasons as the earliest syntheses involved 6-methylhept-5-en-2-one (19) [110-93-0] as a key intermediate and the early industrial syntheses were developed from these academic routes. The other reason is that the major companies manufacturing terpenoids from petrochemical feedstocks are all producers of vitamins A, E, and K, and citral is key to the synthesis of these. 

By far, the most important use of a-pinene is as a feedstock for production of other terpenoids and a wide variety of fragrance ingredients. Some of the more important conversions are shown in Fig. 8.8. a-Pinene undergoes thermal isomerization to ocimene and alloocimene, acid-catalyzed isomerization to camphene, hydration to pine oil/terpineol, and polymerization to terpene resins. Its epoxide is a useful intermediate and hydrogenation with subsequent oxidation leads on to the rose alcohols linalool, nerol, and geraniol. 

Citronellol (85) is sold under various trade names, such as Cephrol and Corel, but more usually simply as citronellol. Similarly, the laevorotatory isomer is usually called ( )-citronellol or ( -citronellol, but the trade name Levocitrol is also used. Some confusion arises from the use of the name Rhodinol, which has been used for the laevo-isomer, but also for various grades of mixtures of rose alcohols. 

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