Y-Terpineol

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). 

Principal terpene alcohol components of pine oils are a-terpineol, y-terpineol, p-terpineol, a-fenchol, bomeol, terpinen-l-ol, and terpinen-4-ol. The ethers, 1,4- and 1,8-cineole, are also formed by cydization of the y>-menthane-1,4- and 1,8-diols. The bicydic alcohols, a-fenchol [512-13-0] (61) and bomeol (62), are also formed by the Wagner-Meerwein rearrangement of the pinanyl carbonium ion and subsequent hydration. Bomeol is t / i7< -l,7,7-trimethylbicydo[2.2.1]heptan-2-ol [507-70-0]. Many other components of pine oils are also found, depending on the source of the turpentine used and the method of production. 

Limonene is the major monoterpene in orange oil. This is a colorless and odorless compound at high purity. However, it rapidly oxidizes to carveol and carvone in the presence of air. Under acidic conditions, a-terpineol, P-terpineol, and y-terpineol are also produced. Many of the impurities present in limonene have much higher odor potencies. These odor potent compounds can be perceived as limonene odor . 

Reagents. Analar dichloromethane (B.D.H. Chemicals) was redistilled just prior to use. Pure terpene standards were obtained variously from Aldrich Chemicals Co., Fluka A.G., S.C.M. Organics, Bush Boake Allen Ltd and International Flavours and Fragrances. B-Terpineol and y-terpineol were generous gifts from Firmenich Co. The purity of all standards was greater than 9 % and were used as supplied. 

C10H20O2, Mr 172.27. A monocyclic monoterpene dialcohol with the p-menthane structure occurring in nature in both the trans- and the c/s-forms, "trans-T. , mp. 158-159°C, c -T. ,mp. 104-105°C.The a5-T. exists mostly as the hydrate ( c -terpin hydrate , mp. 118 -119 °C) which is used as an expectorant. The occurrence of T. is probably the result of secondary formation from y-terpineol menth-4(8)-en-l-ol]. T. occurs in Chinese star anise oil (Illicium venim, Illi-ciaceae). For synthesis, see Ut.. ... 

The reaction of pinene to form or-terpineol has been known since the late nineteenth century. Pinene is relatively abundant in nature, with the major source being pine trees, a- and pinene (1) will hydrolyze in aqueous add to form a tertiary carbocation, as shown in Fig. 9.30, followed by a series of carbonium ion rearrangements, which results in a multitude of products. The major product of the reaction is or-terpineol (2) however, as a consequence of carbonium ion rearrangements, terpinen-4-ol (3) and y-terpineol (4,5) are also produced. These monocyclic alcohols are collectively known as terpineol. Smaller amounts of the bicyclic alcohols fenchol (6) and borneol (7) are also formed. Undesirable side reactions... 

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