Terpin hydrate, turpentine

Terpin hydrate [2451-01-6] (10), one of the most weU-known expectorants, is isolated from cmde pine rosin left after the distillation of volatile terpene hydrocarbons and alcohols. It is also manufactured from turpentine (a-pinene) by acid-cataly2ed hydration. Terpin hydrate may exist as cis and trans isomers, but only the cis isomer forms a stable, crystalline monohydrate. Terpin hydrate is available in the United States only in prescription products. 

Terpine hydrate, CioHig(OH)3 + HjO, is a crystalline alcohol resulting from the action of dilute mineral acids on either pinene or limonene. It can be prepared by several different methods, of W hich the following is typical A mixture of 8 parts of oil or turpentine, 2 parts of alcohol, and 2 parts of nitric acid of specific gravity 1 255 IS allowed to stand for several days in a flat basin. After standing for a few days the mother liquor is poured off from the crystals of terpine hydrate, and neutralised with an alkali, after which a second crop of crystals is obtained. 

A common industrial method of a-terpineol synthesis consists of the hydration of a-pinene or turpentine oil with aqueous mineral acids to give crystalline cis-terpin hydrate mp 117°C), followed by partial dehydration to a-terpineol. Suitable catalysts are weak acids or acid-activated silica gel [83]. 

Turpentine. Turpentine is used directly as a solvent, thinner, or additive for paints, varnishes, enamels, waxes, polishes, disinfectants, soaps, pharmaceuticals, wood stains, sealing wax, inks, and crayons, and as a general solvent. The chemistry of its mono-terpenes offers many possibilities for conversion to other substances, as illustrated in Fig. 28.20. There is increasing use of turpentine to produce fine chemicals for flavors and fragrances. An important use of turpentine is in conversion by mineral acids to synthetic pine oil. It also is a raw material for making terpin hydrate, resins, camphene, insecticides, and other useful commodities. These uses are included in the following summary of its applications. 

Terpin. Terpin Hydrate. Cineol.—In addition to these monohydroxy derivatives there is another important one which is a dihydroxy menthane known as terpan-di-ol or terpin. Terpin boils at 258° and readily forms a crystalline hydrate, terpin hydrate, which melts at 117°. It also loses water yielding an anhydride known as cineol. Terpin and terpin hydrate are obtained from the terpenes in oil of turpentine by the action of acids. Cineol is found in eucalyptus oil. The constitution of these compounds is proven by their relation to geraniol (p. 167). When treated with 5 per cent H2SO4 two molecules of water are added to geraniol and terpin hydrate is formed. This by loss of one molecule of water forms a closed ring yielding terpin and this by loss of another molecule of water yields cineol. These relationships are as follows ... 

Treatment of turpentine with aqueous acid leads to the formation of a-terpineol. The mechanism of this reaction is shown in Scheme 4.20, in which a-pinene is used as an example. Some hydration of a-terpineol to give the diol, terpin hydrate, can also occur, the balance between the products depending on the severity of the reaction conditions. The crude mixture is known as pine oil and is the main ingredient of pine disinfectants. Terpin hydrate can be easily converted into a-terpineol, since the ring hydroxyl group is more readily eliminated than that in the side chain. 

Terpin hydrate—ChiHiii,3H90— formed when oil of turpentine remains for a long time in contact with HjO, the formation being favored by the presence of a mixture of alcohol and dilute HlfO.. It exists in large, colorless, prismatic crystals, odorless, fuses at about 100° (212° F.), sparingly soluble in HiO, soluble in alcohol and in ether. It readily gives up HjO in dry air at 100° (212° P.), and is then converted into terpin. 

Terpin n. Terpinol, 4-hydroxy-a,a,4-tri-methylcyclohexanemethanol. Additional names p-menthane-l,8-diol dipentenegly-col. Molecular formula C10H20O2. Molecular weight 172.26. Percent composition C 69.72%, H 11.70%, O 18.58%. Literature references from Merck Index, 13th edn. 2001 Both cis-and trans-modifications are known. The ds-compound is obtained most readily in the hydrated form, cis-terpin hydrate. Prepn of ds-form from oil of turpentine Hempel, Ann. 180, 71 (1876) Wallach, Ann. 230, 225 (1885) Schmitt, Mfg. Chemist 26, 350 (1955). From d-limonene Sword, /. Chem. Soc. 127y 1632 (1925). Prepn of trans-form from 1,8-cineole, oc-terpineol or ds-terpin hydrate. Matsuura et al. (1958) Bull Chem Soc Japan 31, 990. Lombard, Ambroise, Bull... 

Others. The major use of turpentine oil is as a solvent (e.g., paints) and as a starting material for the synthesis of useful chemicals such as camphor, menthol, terpin hydrate (an expectorant), a-terpineol and other fragrance compounds, and resins (adhesives, chewing gum, etc.), among others. ... 

Terpene hydrate—CioHi<,HaO—formed by distilling terpin with HCl or by allowing French oil of turpentine to remain for some days in contact with alcohol and HjSOt. It is an oily liquid, boils at 210°-214° (410°-117°.2 P.), suffering partial decomposition. 

This turpentine is then distilled at a pressure of around 50 Torr and temperatures of up to 150°C into heads (volatile compounds with almost no commercial value), and a-pinene (bp 156°C) and P-pinene (bp 164°C). Of these, P-pinene is sold as is and a-pinene is further processed to make pine oil. The conversion of a-pinene to pine oil (Figure 3B.5), of which the major component is the tertiary alcohol a-terpineol, involves hydration catalyzed by aqueous sulfuric acid with simultaneous ring-opening and formation of a carbenium carbocation intermediate when the double bond is protonated to give crystalline terpin monohydrate (combustible, efflorescent, lustrous crystals, soluble in alcohol, and ether, mp 117 °C,bp 265 °C), followed by partial dehydration to a-terpineol. Suitable catalysts for this are weak mineral acids or acid-activated silica gel. ° Inversely, terpineol can be synthesized by acid catalysed hydration or enzyme catalysed addition of water to limonene using a wide range of microorganisms as catalyst. The bioconversion of (R.)-(+)-limonene catalyzed by limonene hydratase selectively forms (R)-(+)-a-terpineol. 

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