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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 these key intermediates is readily achieved by standard functional group manipulation. Materials in this family serve as starting points for the synthesis of a wide range of perfumery materials including esters of the rose alcohols. The ionones are prepared from citral by aldol condensation followed by cyclization of the intermediate y-ionones.

The sources of the above key substances fall into three main categories: natural extracts, turpentine, and petrochemicals. The balance depends on economics and also on the product in question. For example, while about 10% of geraniol is sourced from natural extracts, it is only about 1% in the case of linalool. Natural grades of geraniol are obtained from the oils of citronella, geranium, and palmarosa (including the variants jamrosa and dhanrosa). Citronella is also used as a source of citronellal. Ho, rosewood, and linaloe were used as sources of linalool but conservation and economic factors have reduced these sources of supply very considerably. Similarly, citral was once extracted from Litsea cubeba but over-harvesting has resulted in loss of that source.

Various other natural extracts are used as feedstocks for the production of terpenoids as shown in Figure 5.35. Two of the most significant ones are clary sage and the citrus oils (obtained as by-products of the fruit juice industry). After distillation of the oil from clary sage, sclareol (203) is extracted from the residue and this serves as a starting material for naphthofuran (204), known

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