Oxidation of camphene

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 oxidation of camphene is somewhat more difficult. Using deuterated chloroform as the solvent and H2O2 as the oxidant, a low conversion is obtained after 3 h (27%), and only cleavage and rearrangement products are formed. When switching to UHP as the oxidant, a very good conversion of 92% is obtained after 30 h with complete selectivity toward the epoxide [37]. 

Chlorohydroboration-oxidation of camphene yields a 3 1 endo exo mixture of (185 X = CH20H), and bornylene is converted into a mixture of borneols and epiborneols, the -isomers predominating in each case. ... 

Oxidation of camphene. When camphene (1) is allowed to react in acetonitrile at 80° with /-butyl perbenzoate and catalytic amounts of cuprous chloride and cupric benzoate, mainly alcohols are obtained after saponification (237o yield) rather than ethers (87o yield). The two principal alcohols are (2) and (3) the former is identical to nojigiku, isolated originally from a Japanese chrysanthemum. 

Nambudiry, M. E. N., and G. S. Krishna Rao Studies in Terpenoids Part XXXVI. Manganic Acetate Oxidation of Camphene, Longifolene and 3-Pinene. Indian J. Chem. 13,633(1975). 

The amount of the coupling product was found to be dependent upon the concentration of the dihalide in the metal-ammonia reductions, perhaps because of local high concentration effects. The oxidation of camphene by t-butyl perbenzoate in the presence of Cu salts affords, after saponification of the reaction mixture, nojigiku alcohol (458), among other products. ... 

Camphenilone is formed by the tropospheric oxidation of camphene, initiated by reaction with O3. Since reaction with O3 is a minor loss mechanism for camphene, the yields of camphenoline are low (Atkinson and Aschmann, 2003). 

The Prins reaction with formaldehyde, acetic acid, acetic anhydride, and camphene gives the useful alcohol, 8-acetoxymethyl camphene, which has a patchouli-like odor (83). Oxidation of the alcohol to the corresponding aldehyde also gives a useful iatermediate compound, which is used to synthesize the sandalwood compound dihydo- P-santalol. 

Most synthetic camphor (43) is produced from camphene (13) made from a-piuene. The conversion to isobomyl acetate followed by saponification produces isobomeol (42) ia good yield. Although chemical oxidations of isobomeol with sulfuric/nitric acid mixtures, chromic acid, and others have been developed, catalytic dehydrogenation methods are more suitable on an iadustrial scale. A copper chromite catalyst is usually used to dehydrogenate isobomeol to camphor (171). Dehydrogenation has also been performed over catalysts such as ziac, iadium, gallium, and thallium (172). 

The oxidation products of camphene are of considerable interest, but as they vary very considerably according to the exact method of oxidation employed, they are not of very great use in the characterisation of the terpene. 

Isoborneol yields camphor on oxidation, but it yields camphene on dehydration much more readily than borneol does. If a solution of isoborneol in benzene be heated with chloride of zinc for an hour, an almost quantitative yield of camphene is obtained. Pure borneol under the same conditions is practically unchanged. 

Manganese(m) acetate oxidation (cf. Vol. 3, p. 34) of camphene gives (186) as a 95 5 mixture by carboxymethyl radical insertion no rearranged products were obtained, in contrast to /3-pinene which gave Wagner-Meerwein products only, and no free-radical insertion.279 The E- and Z-isomers of (187) probably result from a non-concerted biradical intermediate formed by benzyne addition to camphene.280 Benzyl-lithium adds to the aminocamphor (188) exclusively from the exo-side whereas only the competing enolization reaction occurs with more sterically hindered organometallics.281... 

Reaction of the hydrocarbons in this series with phenols or phenol ethers in the presence of suitable catalysts is well known, a-fenchene and phenol yielding a mixture of o- and p-isofenchylphenols in the presence of aluminium phen-oxide practically the same reaction was described seven years ago. Reaction of camphene with a phenol ester in the presence of stannic chloride is reported to give a bornyl compound, but terpenoid rearrangements are notorious under such conditions, and it is doubtful whether this is the only product. 3,3-Dibromocamphor (261) has been converted into substituted cyclo-hexanecarboxylic acids by the route shown in Scheme 13. ... 

The oldest process of organic electrochemistry is the indirect oxidation of hydrocarbons with chromic acid. It has been employed industrially for more than 90 years by Hoechst— now Clariant—in Gersthofen, Germany [102]. Other sites are or were located in Great Britain. The oxdiations of naphthalene, anthracene, and camphene are examples. Companies like Emery Industries, L. B. Holliday, and Boots have also used chromic acid regeneration commercially [103]. It has been employed for the bleaching of montan waxes for more than 70 years. 

Metabolism, Biological Activity, Miscellaneous.—Camphene was converted into its 1,2-diol in rabbit,953 and the pathways from a- and p-pinenes and car-3-ene to hydroxylated, ring-opened, and decarboxylated compounds have been determined.954 The 9,10-oxide of THC was initially hydroxylated at C-8(p), and in the side-chain by rat 955 AU-THC was hydroxylated at C-8, C-10, and in the side-chain and subsequently epoxidized.956 The metabolism and degradation of various... 

A new synthesis of nojigiku alcohol (773) (Vol. 4, p. 554) starts from tricyclene (774) and we should perhaps recall the preparation of the latter from camphor (40) tosylhydrazone and sodium methoxide in decalin. [Tricyclene is also produced in other reactions leading to camphene (775), such as the reaction of 3-bromocamphor with methylaniline. ] TTie new synthesis consists in anodic oxidation with triethylamine in acetic acid, and yields 76% of 773, with 8% of the endo-isomer and 11% of diols. Oxidation of tricyclene (774) with lead tetraacetate also gives nojigiku alcohol (773), but as a minor (16%) product, the main product being camphor (40). Tricyclene having a plane of symmetry, these methods all lead to racemic 773. 

Lhomme and Ourisson,11 in working on the oxidation of camphanols with lead tetraacetate in benzene found that there was considerable risk that very volatile products would be entrained during removal of the benzene by distillation. Since sulfolane has been used in the industry for the extraction of aromatics from hydrocarbon mixtures, they tried adding pentane and then extracting the solution several times with the nonmiscible sulfolane. The residual pentane solution could then be washed with water for the removal of sulfolane and recovery of the volatile cyclic ethers formed in the oxidation. The procedure was verified by showing that more than 70% of camphene could be recovered in this way. 

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... 

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. 

The production of camphene is usually carried out by isomerization of a-pinene over titanium oxide catalysts [3]. These are prepared by treating titanium oxide with an acid in order to obtain a layer of titanic acid on the surface of the oxide [4]. The reaction was reported as showing zero order [4] or a transition from first order at low conversion to zero order above ca. 30% conversion [5]. 

In view of optimizing the production of camphene it is of interest to have comprehensive kinetic data and models for the isomerization of a-pinene over titanium oxide. The catalyst is previously treated with sulfuric acid. It is of interest to know the effect on catalyst activity and selectivity of varying (i) the amount of sulfuric acid in relation to the amount of oxide (ii) the amount of catalyst in relation to the amount of pinene (iii) the time of catalyst activation (iv) the temperature of catalyst activation. 

Longifolene on hydroboration followed by oxidation with alkaline hydrogen peroxide furnishes, in 74% yield, essentially pure longifolol (57) as a result of endo attack (46). On the other hand, camphene, under the same treatment, is known (47) to give almost exclusively endo-iso-camphanol (58) by way of exo approach of the reagent. Oxidation of longifolyl-borane with air or silver oxide results in transannular products which are discussed in a later section. 

Reaction with iodine monochloride or phenylsulphenyl chloride also results in co-substituted products (120, 121) (74). Longifolene reacts with oxides of nitrogen to furnish, like camphene, the co-nitrolongifolene... 

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. 

As a matter of convenience, the results of oxidation of longifolene with lead tetraacetate, and ruthenium tetraoxide will also be summarized here steric diversion may have little role in forming the products of these reactions. One of the important reactions of lead tetraacetate with olefins is allylic substitution/rearrangement (J02). Since, this pathway is blocked for longifolene, the major product of this reaction is the ring-expanded enol acetate (154) (Chart 17), exactly parallel to what happens with camphene (8J, 99). 

Mehta, G., and U. R. Nayak Selenium Dioxide Oxidation of Ectocyclic Olefins Formation and Structures of Selenides from Longifolene and Camphene. Indian J. Chem. 158,419(1977). 

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