Лако-красочные материалы — производство

Introduction

The terpenes form the largest group of natural odorants, so it is only to be expected that they also form the largest group of modern fragrance ingredients.

Thousands of different terpene structures occur in perfume ingredi­ents, both natural and synthetic. The chemistry of terpenes is rich and varied and attempts to understand it have, on many occasions, contributed fundamentally to our total understanding of chemistry. One example is the work of Wagner and Meerwein, whose studies in terpene chemistry led, amongst many discoveries, to elucidation of the rearrangement that bears their names. This work made a very signifi­cant contribution to our fundamental understanding of the properties and reactions of carbocations. Chemistry of Fragrance Substances by Paul Teisseire (1993) serves as an excellent general introduction to the exciting field of terpene chemistry.

As far as perfume materials are concerned, the most important members of the terpene family are the oxygenated monoterpenes. The terpene hydrocarbons generally have weaker odours and are used mainly as feedstocks. The higher molecular weights of the sesqui­terpenes result in their having lower vapour pressures than their monoterpene counterparts. Thus, sesquiterpenes are present at lower concentrations in the air above a perfume than are monoterpenes, with the result that to be detected they must have a greater effect on the receptors in the nose. Hence, a lower percentage of sesquiterpenes have useful odours than monoterpenes. For the same reason, very few di — or higher terpenes have odours. However, those sesqui — and higher terpenes that do have odours are very tenacious because their lower volatility means that they are lost more slowly from perfumes. Such materials form the base of perfumes and serve also to fix the more volatile components.

People in the fragrance industry tend to misuse two terms in terpene nomenclature. The word terpenes means materials whose carbon skeletons are made up from isoprene units. However, in the industry ‘terpenes’, is often used to mean specifically monoterpene hydrocar­bons (compare the note on deterpenation of essential oils in Chapter 3). Similarly, to the chemist, geraniol is £’-3,7-dimethylocta-2,6-dien-l-ol and nerol is Z-3,7-dimethylocta-2,6-dien-l-ol; whereas, in the fragrance industry, the word geraniol usually implies a mixture of the two isomers. In this chapter the terms are used in the correct chemical sense, but the reader should be aware of possible ambiguity elsewhere.

Table 4.1 shows the odour type and approximate annual consump­tion of some of the highest-tonnage terpene fragrance ingredients. Volumes range from these figures down to expensive specialities, which are produced in kilogramme rather than tonne quantities. The major terpene producers fall into three categories. Companies that manufacture wood and paper products produce sulfate turpentine or similar by-products rich in pinenes. Many of these companies, such as Union Camp, then produce terpenoid fragrance materials from pinenes to gain income from their by-product. One such company, Gildco, has actually split off from its parent, SCM, and become an independent aroma chemical producer. Companies (such as Hoffmann-La Roche, Bayer and BASF) that manufacture vitamins use terpene intermediates and so usually also manufacture aroma chemicals. In fact, two of these own fragrance companies; Hoffmann-La Roche own Givaudan-Roure

and Bayer own Haarmann & Reimer. The Japanese company Kuraray manufactures synthetic rubber from isoprene and so has diversified into terpene aroma chemical manufacture from this basic feedstock.

The remainder of this section is divided into 20 sub-sections. The first nine describe the main approaches to the production of the large — volume terpenes and the subsequent 11 describe individual groups of terpenes, sometimes classified biogenetically and otherwise, when more appropriate, by odour type. The multitude of terpene-derived fragrance ingredients makes it impossible to mention them all in the context of this book. Therefore, only a selection of the more important and interesting ones are included in this chapter.