Terpineols

Rerfision Problem 2 a-Terpineol also occurs widely in plants and was one of the first natural products to be isolated pure. There was originally some doubt as to whether its structure was TM 394A or TM 394B. Suggest syntheses of both these compounds so that they can be compared with the natural product. 

In the eyent, TM 394A proyed to be a-terpineol and the shortest synthesis is by Alder and Vogt (Annalen. 1940, 564, 109) using the Diels-Alder reaction ... 

Dehydration. Dehydration of hydroxy fatty acids is quite common. Other compounds undergo the same reaction, eg, elymoclavine [548-43-6] to agroclavine [548-42-5] chanoclavine [2390-99-0] and other compounds and <7j -terpin hydrate [2541-01-63] to a-terpineol [98-55-5] (19). 

Terpenes are characterized as being made up of units of isoprene in a head-to-tail orientation. This isoprene concept, invented to aid in the stmcture deterrnination of terpenes found in natural products, was especially useful for elucidation of stmctures of more complex sesquiterpenes, diterpenes, and polyterpenes. The hydrocarbon, myrcene, and the terpene alcohol, a-terpineol, can be considered as being made up of two isoprene units in such a head-to-tail orientation (1). 

Synthetic pine oil is produced by the acid-catalyzed hydration of a-pinene (Fig. 1). Mineral acids, usually phosphoric acid, are used in concentrations of 20—40 wt % and at temperatures varying from 30—100°C. Depending on the conditions used, alcohols, chiefly a-terpineol (9), are produced along with /)-menthadienes and cineoles, mainly limonene, terpinolene, and 1,4- and 1,8-cineole (46—48). Various grades of pine oil can be produced by fractionation of the cmde products. Formation of terpin hydrate (10) from a-terpineol gives P-terpineol (11) and y-terpineol (12) as a consequence of the reversible... 

Pine oils can be fractionally distilled to produce a higher a-terpineol product, but usually contain bomeol and y-terpineol, along with small amounts of other components. High grade perfumery a-terpineol can be made by the partial dehydration ofyvmenthane-l,8-diol (terpin hydrate) under mildly acidic conditions (117,118). 

Hydrogenation of a-terpineol gives dihydroterpineol [498-81-7] a mixture of cis- and trans-compounds (120). Dihydroterpinyl acetate [80-25-1] produced from the mixture is also a useful fragrance compound. 

Linalool has been used to prepare a mixture of terpenes useful for enhancing the aroma or taste of foodstuffs, chewing gums, and perfume compositions. Aqueous citric acid reaction at 100°C converts the linalool (3) to a complex mixture. A few of the components include a-terpineol (34%) (9), Bois de Rose oxide (5.1%) (64), ocimene quintoxide (0.5%) (65), linalool oxide (0.3%) (66), tij -ocimenol (3.28%) (67), and many other alcohols and hydrocarbons (131). 

This cieam also contains zinc naphthenate, terpineol, chloiciesol, and methyl salicylate [119-36-8J.S The latter has a deeply penetrative effect. It combines... 

The glucosides of menthol, citronellol, nerol, geraniol, cw-myrtenol, L-borneol, linalool and a-terpineol yielded yellow-green fluorescent chromatogram zones in long-wavelength UV light (2 = 365 nm). The same applied to arbutin (hRf 45 — 50). 

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