Camphene hydrate

It is possible, however, that camphene hydrochloride is not a uniform body, but that some of the terpene suffers some rearrangement in the molecule by the action of hydrochloric acid, and that the hydrochloride consists of a mixture of a-camphene hydrochloride and /8-camphene hydrochloride there is, however, no evidence to suggest that camphene itwlf is a mixture of two terpenes, so that the two camphenes are not known to exist. Aschan obtained an alcohol, camphene hydrate, by acting on camphene hydrochloride with milk of lime, a reagent which does not produce molecular rearrangement in the terpene nucleus. 

Camphene hydrate is a tertiary alcohol, and a study of its characters and method of preparation caused Aschan to consider that it is improbable that borneol and isoborneol are stereoisomeric, but that they probably have different constitutional formulae. 

Figure 2 - Concentration profiles of a-pinene, and camphene, Hydration reaction over USY in aqueous acetone at 55 °C. The lines represent the fit to a first order kinetics.

Selectivity to a-terpineol in a-pinene hydration and to isobomeol in camphene hydration, increases with NEPAL (Figure 4). This is also contrasting with what is observed in the isomerization of pure a-pinene, where the curve selectivity vs. NEPAL shows a minimum [18]. 

The main products of the hydration reactions of a-pinene and of camphene over USY zeolites are a-terpineol and isobomeol, respectively. In the hydration of a-pinene simultaneous isomerization takes place whereas with camphene, hydration is observed nearly exclusively. 

Monoterpenes are widely used in the pharmaceutical, cosmetic and food industry as active components of drugs and ingredients of artificial flavours and fragrances [1]. Camphene is converted to isobomeol and bomeol that are used in formulation of soaps, cosmetic perfumes and medicines, as well as in the industrial production of camphor [2], which is used as an odorant/flavorant in pharmaceutical, household and industrial products [7]. Traditionally, homogeneous catalysts, e.g sulphuric acid, are used, but the effluent disposal leads to environmental problems and economical inconveniences. These problems can be overcome by the use of solid acid catalysts. USY zeolite [3], heteropolyacids [4,5] and sulfonic acid surface-functionalised silica [6] have also been used for the camphene hydration. 

Figure 2 shows the initial activity of the catalytic composites for camphene hydration (A), expressed as the initial reaction rate calculated finm the slope of the camphene kinetic curve and the initial activity for isobomeol oxidation (B), expressed as the initial reaction rate calculated from the slope of the isobomeol kinetic curve. It was observed that the initial activity regarding camphene hydration, decreases when the crosslinking degree increases, for the catalysts Co(acac)2/PVAx (fig. 2 bar Cl > bar C2), in spite of the increase in the number of acid sites. This result, which is also in contradiction with those observed for the oxidation of isobomeol, is likely to be due to the expectable decrease in the sorption coefficient of camphene caused by the increase of the number of sulfonic groups. The same explanation may be given for the decrease in activity observed when the load of Co(acac)2trien NaY in the polymeric matrix... 

By far, the most important use of a-pinene is as a feedstock for production of other terpenoids and a wide variety of fragrance ingredients. Some of the more important conversions are shown in Fig. 8.8. a-Pinene undergoes thermal isomerization to ocimene and alloocimene, acid-catalyzed isomerization to camphene, hydration to pine oil/terpineol, and polymerization to terpene resins. Its epoxide is a useful intermediate and hydrogenation with subsequent oxidation leads on to the rose alcohols linalool, nerol, and geraniol. 

Borneol and isoboineol are respectively the endo and exo forms of the alcohol. Borneol can be prepared by reduction of camphor inactive borneol is also obtained by the acid hydration of pinene or camphene. Borneol has a smell like camphor. The m.p. of the optically active forms is 208-5 C but the racemic form has m.p. 210-5 C. Oxidized to camphor, dehydrated to camphene. 

Ordinary commercial camphor is (-i-)-cam phor, from the wood of the camphor tree. Cinnamonum camphora. Camphor is of great technical importance, being used in the manufacture of celluloid and explosives, and for medical purposes, /t is manufactured from pinene through bornyl chloride to camphene, which is either directly oxidized to camphor or is hydrated to isoborneol, which is then oxidized to camphor. A large number of camphor derivatives have been prepared, including halogen, nitro and hydroxy derivatives and sulphonic acids. 

It is well known that Rh(I) complexes can catalyze the carbonylation of methanol. A heterogenized catalyst was prepared by ion exchange of zeolite X or Y with Rh cations.126 The same catalytic cycle takes place in zeolites and in solution because the activation energy is nearly the same. The specific activity in zeolites, however, is less by an order of magnitude, suggesting that the Rh sites in the zeolite are not uniformly accessible. The oxidation of camphene was performed over zeolites exchanged with different metals (Mn, Co, Cu, Ni, and Zn).127 Cu-loaded zeolites have attracted considerable attention because of their unique properties applied in catalytic redox reactions.128-130 Four different Cu sites with defined coordinations have been found.131 It was found that the zeolitic media affects strongly the catalytic activity of the Cd2+ ion sites in Cd zeolites used to catalyze the hydration of acetylene.132... 

The presence of water was subsequently identified as being essential for the performance of the above set-up and for maintaining high enantiose-lectivity (Lindstrom et al., 1990). The preparative-scale enantiomeric separation of racemic camphene with a separation factor as high as a — 3.7 (measured at 30°C on an analytical column) was subsequently achieved at 45°C on a 2.1 m x 4 mm (i.d.) column containing a-cyclodextrin hydrate in formamide (1 5, w/w) coated on Chromosorb W (AW, 45-60 mesh) by saturating the carrier gas (helium) with water vapour (Lindstrom et al., 1990). 

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. 

Use Solvent for protective coatings, polishes, and waxes synthesis of camphene, camphor, geraniol, terpin hydrate, terpineol, synthetic pine oil, terpene esters and ethers, lubricating oil additives, flavoring odorant. 

Neither the anhydrous bulk zirconium sulfate nor the silica-supported, sul ted zirconia were active in the addition of acetic acid (4) to camphene (5). The lack of activity is due to the fact that addition of acetic anhydride removes water completely from the reactants. Also the liquid-phase reaction thus demonstrates that Lewis acid sites are not active in our catalysts. Addition of water leads to a well measurable activity with both catafysts. Fig. 5 represents the activity of the silica-supported sulfated catalyst after pre-hydration. The... 

The acid catalysed hydration reactions of a-pinene and camphene, respectively, using USY catalysts in aqueous acetone at 55 C, are studied. The catalyst samples were prepared from zeolite Y by hydrothermal treatments at temperatures ranging from 450 to 850 C. The so generated extra-framework aluminium species were kept in the samples. 

The main products of both hydration reactions are a-terpineol, in the case of a-pinene hydration and isobomeol, when camphene is used as the starting reagent. Although zeolite H-Y is not active as catalyst for these hydration reactions, USY catalysts show a reasonable activity and are very selective to the above mentioned terpenic alcohols. Selectivity increases with the relative concentration of Lewis sites. 

The hydration of a-pinene (1) with aqueous mineral acids leads to a complex mixture of monoterpenes known as s)mthetic pine oil [2], The main products are monocyclic terpenes, namely a-terpineol (9). The reaction mechanism has been extensively studied [3-7]. It is generally accepted that it proceeds through cation I (Scheme 1). Subsequent carbonium ion rearrangements leads to two parallel pathways. One yields bi- and tricyclic products such as camphene (2), bomeol (3) and isobomeol (4). The other )delds monocyclic products such as li-monene (5), a- (6) and y-terpinenes (7) terpinolene (8), a-terpineol (9)and 1,8-terpine (10) Products from the cyclization of terpineol, like 1,8-cineol, can also be formed. By controlling the many reaction variables the process can be directed to produce a maximum of terpene alcohol s. 

The direct hydration of a-pinene and camphene to bomeol and/or isobomeol is of great interest since presently a two step procedure is used in industrial practice acetolysis of camphene and subsequent hydrolysis of bomyl acetate [8]. 

The hydration of camphene leads mainly to isobomeol and bomeol [9], being the reaction product dominated by isobomeol (Scheme 2). 

Heteropoly acids [9] and natural mordenite [13] have been previously used in the hydration of camphene with high selectivities to isobomeol. 

In this work we study the effect of EFAL species in steam dealuminated USY zeolites with different framework compositions, on the hydration reactions of a-pinene and camphene, at 328 K. Scheme 2... 

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.

On the other hand, the hydration of camphene leads mainly to isobomeol. The study of catalytic activity towards the hydration of a-pinene or cam-... 

In both cases a pseudo first order kinetics was observed, being a-pinene more reactive than camphene, due to the angle strain of the cyclobutane ring (Figure 2). This kinetic behaviour is in agreement with what was observed for the hydration of a-pinene over zeolite H-beta... 

For both substrates, a-pinene and camphene, initial activity (taken as the initial reaction rate, to) shows a strong dependence on Nai (figure 3). In both hydration reactions, ro achieves a maximum value at values of Nai around 22. 

Although Lewis sites exhibit a very low activity in the hydration reactions of a-pinene and camphene, they are very selective to a-terpineol and isobomeol respectively (Figure 5). The highest selectivities — 70 % to a-terpineol, in the hydration of a-pinene and 90 % to isobor-neol, in the hydration of camphene — are reached at the highest relative concentration of Lewis sites. This concentration, however, corresponds to the lowest catalytic activity. 

Selectivities to a-terpineol, in the hydration of a-pinene and to isobomeol, in the hydration of camphene, can be as high as 70% and 90%, respectively. Selectivities to both terpene alcohols grow continuously with NEFAL. Apparently they are not affected by the changes in the acid strength. 

Bifimctional catalytic composites consisting in poly(vinyl alcohol) crosslinked with sulfosuccinic acid and Co(acac)2 complex or Co(acac)2trien encaged in NaY zeolite dispersed in the polymeric matrix, are active catalysts for the hydration of camphene and oxidation of isobomeol, making possible the one pot synthesis of camphor from camphene. The way as the Co complex is immobilised in the polymer matrix, directly or entrapped in zeolite Y, leads to opposite effects in the catalytic activity, probably due to the competition between transport and sorption phenomena. 

By way of comparison it may be pointed out that camphene (4) with chromic acid in aqueous acid gives, as the chief product, camphor (135) and not camphenilanic acid (136), apparently due to fast prior hydration of camphene to isoborneol (83, R = H) (85). This reaction has not been observed with longifolene. Low conversions of camphene to the acid (136) can be, however, achieved by carrying out this oxidation in acetic anhydride-carbon tetrachloride (87), and under these conditions camphene epoxide has been demonstrated (88) as the primary oxidation product. 

Figure 6.36 shows some of the major products manufactured from a-pinene (65) (Sell, 2003, 2007). Acid-catalyzed hydration of a-pinene gives a-terpineol (74), which is the highest tonnage material of all those described here. Acid-catalyzed rearrangement of a-pinene gives camphene (89)... 

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