Limonene hydration

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... 

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. 

Heteropoly acids such as H3PW12O40 (PW) are good catalysts for the hydration of limonene and other monoterpenes. PWs can be used as homogeneous catalysts in solution or supported on, for example, silica or MCM-41 materials. In aqueous acetic acid limonene gives, in the presence of PW, mainly a-terpineol (7) and a-terpinyl acetate (8) [17]. 

Limonene (10.128) is an analogue of 4-vinylcyclohexene, and, like the latter, it undergoes epoxidation of both the C(1)=C(2) and C(8)=C(9) bonds. Like in the dioxide 10.127, the two epoxide groups are hydrated at different rates by EH. Indeed, incubations in rat liver microsomes showed that hydrolysis of limonene 1,2-epoxide was 70 times slower than that of the 8,9-epoxide, a much larger difference than that observed for the dioxide 10.127 [192], Comparison of EH-catalyzed hydration of the four epoxy groups in 4-vinyl-cyclohexene and limonene confirmed that the relative rates decreased with increasing steric hindrance at these groups. 

DIPA See diisopropanolamine. dip-o or de T pe a dipentene org chem A racemate of limonene. dT pen,ten dipentene glycol See terpin hydrate. dT pen.ten glT,k6l dipentene hydrochloride See terpene hydrochloride. dT pen,ten,hT-dr3 kl6r,Td ) diphacinone orgchem C23H16O3 A yellow powder with a melting point of 145-147°C used to control rats, mice, and other rodents acts as an anticoagulant. do fas-3,non ... 

Selective conversion of pinene, 3-carene, and limonene or dipentene to terpineol, without terpin hydrate formation, is also used. Addition of organic acids (weak acids require catalytic amounts of mineral acids) produces terpinyl esters, which are subsequently hydrolyzed to terpineol, sometimes in situ. 

Rearrangement of limonene with a cationic exchange resin, rather than with soluble acids,218 substantially reduces polymer formation. Limonene is hydrated using chloroacetic acids to furnish (-t-)-a-terpineol selectively in high yield, depending upon the conditions.219... 

The results above suggested that selective monooxymercuration of dienes is possible, and indeed this has been realized. In the ease of symmetrical dienes such as 1,5-pentadiene, the yield of enol is lower than predicted for a statistical reaction (50 % enol) the statistical value is approached in longer chain dienes. Yields can be raised by using mercuric trifluoroacctate(2,195). In the case ofunsymmelricaldienesselective hydration can be achieved. Thus limonene (1) can be converted to the enol (2) in 70% yield. 

Three percent of o-limonene was found to cause skin damage. However, instead of roughening, the damage caused smoothing as shown by a decrease of fractal dimension and was suggested to be a result of hydration and/or edema formation in the shallow part of the skin.f Hence fractal analysis can be used to elucidate the damage mechanism and provides quantitative measurement of skin damage. ... 

Various chemical processes of limonene, which lead to the obtainment of useful chemicals and some analytical methods, are based on these reactions. Many flavor chemicals are synthesized from limonene by reaction with water, sulfur and halogens, or hydrolysis, hydrogenation, boration, oxidation and epoxide formation (Thomas and Bessiere, 1989). Hydroperoxides have also been studied and isolated because of their effect on off-flavor development in products containing citrus oil flavoring agents (Clark et al., 1981 Schieberle et al., 1987). Hydration of d-limonene produces alpha-terpineol, a compound that gives off an undesirable aroma in citrus-flavored products. It is also possible to produce alpha-terpineol and other useful value-added compounds... 

Composition 30-55% (-)-menthol, 14-32% (-)-menthone, 1.5-10% (-i-)-iso menthone, 2.8-10% menthyl acetate, 3.5-14% 1,8-cineole, 1-9% menthofuran, up to 4% pule-gone [220], as well as 3-octanol, trans-sabinene hydrate, piperitone, viridrflorol, mono- and sesquiterpene hydrocarbons. For further constituents see [221, 222, 223[. On the differentiation between peppermint oils and the detection of dementholised commint oil as a major adulterant see the results of Lawrence et al. [224], The ratio of 1,8-cineole limonene (min. 2) was even implemented in the European Pharmacopoeia. The latter also limits the isopulegol content for Mentha piperita oil to 0.2%. 

Composition (-)-Carvone, which is present in a concentration of 60-70%, functions as main aroma carrier. Dihydro cumic alcohol and carvyl acetate are also assumed to contribute to the overall aroma profile. Furthermore, limonene, 3-octanol, trans-sab-inene hydrate, cis-dihydrocarvone and P-bourbonene occur in marked amounts. Virid-iflorol (0.1-0.5%) is only detectable in the native oil type. In its monographs ISO distinguishes between Native , Chinese (80%, 60%) , Indian and Scotch Type [228]. For further literature on the composition of native spearmint and Scotch spearmint see also [229]. 

Scheme 1 - Acid catalysed isomerization and hydration of a-pinene. 1 a-pinene 2 camphene 3 bomeol 4 isobomeol 5 limonene 6 a-terpinene 7 y-terpinene 8 terpinolene 9 a-terpineol 10 1,8-terpine.

Figure 1.26 shows the release time-courses of four flavors included in RM-Jl-CD at 50°C and 31%-75% RH (Furuta et al., 2008). D-limonene and L-menthol were more stable than AITC and EB under various RH conditions. At 75% RH, except for L-menthol, the flavors initially released markedly, nonetheless the release slackened off noticeably after 24 h. This might be caused by the occurrence of collapse of the powders, in which case the powder surface was covered with a hydrated layer, resulting in a decrease in the flavor evaporation flux, as mentioned in Section I.4.2.2. 

Terebintliinae aetheroleum T. rectifiaitum aeth. Turpentine oil Pinus palustris MILLER Pinus pinaster AITON et al. OAB 90, Helv VII, BP 88, MD (resin), Japan Distillate of turpentine (oleoresin) from various Pinus ssp. S0% 90% TllC (a-, p pinene, limonene, phellandrene) auloxidation produces a-pinene peroxides and subsequently verbenol and pinol hydrate (=sorbenol)... 

The GCxGC resolution advantage is known to improve the efficiency of enantioselective essential oil analysis (in contrast to one-dimensional analysis). In a single temperature-programmed analysis, the individual antipodes of optically active components can be separated and are effectively free from matrix interferences. The enantiomeric compositions of a number of monoterpene hydrocarbons and oxygenated monoterpenes in Australian tea tree Melaleuca alternifolia), including sabinene, a-pinene, (3-phellandrene, limonene, trans-sabinene hydrate, ds-sabinene hydrate, linalool, terpinen-4-ol, and a-terpineol shown in Figure 7,... 

Figure 7 2D contour plot for the enantio-GCxGC analysis of flush growth Melaleuca alternifolia. Individual isomers are differentiated by a (+) or (—) sign. Component identity 1, a-thujene 2, a-pinene 3, sabinene 4, p-pinene 5, myrcene 6, a-phellandrene 7, a-terpinene 8, p-cymeme 9, limonene 10,1,8-cineole 11, y-terpinene 12, trons-sabinene hydrate ... 

Figure 12.2 Small-angle x-ray scattetgtams obtained from (A) untreated 20 to 40% hydrated stratum corneum and stratum comeum treated with (B) propyiene giycoi, (C) d-limonene saturated in propylene glycol, (D) nerolido 190% w/w in propyiene glycol, and (E) 1-8-cineole saturated in propylene glycol. (Reprinted from Corn-well, RA., Barry, B.W. Bouwstra, J.A., and Gooris, G.S., Int. J. Pharm., 127 9-26, 1996, with permission from Elsevier.)...

The intermediacy of strained cycloalkenes in such reactions is further supported by the reaction of limonene. As shown in Figure 12.35, photohydration of limonene (16) produces an 89% yield of the alcohol 17 (plus a small amoimt of 18) as a result of hydration of the endocyclic double bond only. In contrast, acid-catalyzed hydration of 16 produces only the diol 19, in which both double bonds have been hydrated. ° ... 

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... 

---