Isoborneol, oxidation

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. 

The structure of the bicychc monoterpene borneol is shown in Figure 26 7 Isoborneol a stereoisomer of borneol can be prepared in the labora tory by a two step sequence In the first step borneol is oxidized to camphor by treatment with chromic acid In the second step camphor is reduced with sodium borohydride to a mixture of 85% isoborneol and 15% borneol On the basis of these transformations deduce structural formulas for isoborneol and camphor... 

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. 

Camphor, Cj HjgO, occurs in the wood of the camphor tree Laurus camphora) as dextro-camphor. This is the ordinary camphor of commerce, known as Japan camphor, whilst the less common laevo-camphor is found in the oil of Matricaria parthenium. Camphor can also be obtained by the oxidation of borneol or isoborneol with nitric acid. Camphor may be prepared from turpentine in numerous ways, and there are many patents existing for its artificial preparation. Artificial camphor, however, does not appear to be able to compete commercially with the natural product. Amongst the methods may be enumerated the following —... 

Camphor is then obtained from isoborneol by oxidation of the secondary alcohol to a ketone. 

Steric effects are evident in the oxidation of sterically hindered alcohols exo-isoborneol is oxidized 2 times faster than endo-homeo], and endo-norborneol is oxidized 2.5 times faster than exo-norborneol (equation 248) [1145]. 

Bicyclic cyclopropyl compounds are anodically dimethoxylated to give stereoisomeric cis and trans) cyclopropane ring-opened products, as in Eq. (48) [322]. Shono and coworkers [323] reported a different type of ring-opening reaction of a cyclobutyl compound through anodic methoxylation. They also found that anodic oxidation of borneol and isoborneol in methanol resulted in a rearrangement to provide methoxylated stereoisomeric products with the same endo-exo ratio, as in Eq. (49) [324] ... 

A vast array of chiral auxiliaries have been derived from naturally occurring compounds containing the bicyclo[2.2.1]heptane unit (for review articles, see refs 1 -3). In all cases, the ultimate sources of these auxiliaries are the ketones camphor and fenchone, and the alcohols borneol and fenchol, as at least one enantiomer of each compound is provided in enantiomericaUy pure form by nature. Thus. ( + )-camphor [( + )-2], (-)-borneol [(-)- ], and (+)-fenchonc [( + )-5] are enan-tiomerically pure, convenient and inexpensive starting materials for organic synthesis and deriva-tization to give chiral auxiliaries. Most other compounds of this series are also commercially available, but can be prepared by oxidation or reduction of inexpensive precursors by standard methods. The evo-alcohols, such as the enantiomeric isoborneols, are accessible by standard complex hydride reductions of the ketones. The interconnection between these compounds is shown diagrammatically. 

Isoborneol can be formed via simple acid hydrolysis of the ester linkage. Oxidation of the alcohol forms the ketone (camphor) ... 

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. 

Steric Effects.—The consequences upon chemical reaction of non-bonded interactions between enantiomeric pairs of molecules have been discussed an antipodal interaction effect was observed in a reductive camphor dimerization and in a camphor reduction. The full paper on the correlation of the rates of chromic acid oxidation of secondary alcohols to ketones with the strain change in going from the alcohol to the carbonyl product has now appeared. It is concluded that the properties of the product are reflected in the transition state for the oxidation. High yields of hindered carbonyls are available from the corresponding alcohols by reaction with DMSO and trifluoroacetic anhydride (TFAA) indeed, the more hindered the alcohol, the higher the yield of carbonyl compound reported Since the DMSO-TFAA reaction occurs instantaneously at low temperatures (<—50°C), it is possible to oxidize alcohols that form stable sulphonium salts only at low temperature. Thus, ( )-isoborneol reacts at room temperature to give camphene, the product of solvolysis of the sulphonium salt the oxidation product, ( + )-camphor, was obtained by the addition of base at low temperature. 

This experiment will illustrate the use of an oxidizing agent (pyridinium chiorochromate) for converting a secondary alcohol (borneoi) to a ketone (camphor). The camphor is then reduced by sodium borohydride to give the isomeric alcohol isohomeol. The spectra of bomeol, camphor, and isoborneol will be compared to detect stmctural differences and to determine the extent to which the final step produces a pure alcohol isomeric with the starting material. 

Determine the infrared spectium of fhe sublimed camphor and compare it to the spectrum provided in the experiment (use the dry film method in Technique 25, Section 25.4 or other method recommended by your instructor). The spectrum should demonstrate complete oxidation to camphor (absence of OH peak and presence of C=0 peak). There should be sufficienf material for the reduction of camphor to isoborneol. Part B. At the option of fhe instructor, determine the H and NMR spectra of your camphor. Also, at the option of the instructor, determine the melting point (literature mp about 177°C, but it is often lower than this value). Store the camphor in a tightly sealed vial. 

The catalytic efficiencies of ions of the first series of transition metals in the controlled Ce(IV) oxidation of borneol, isoborneol, and menthol do not follow the theoretically expected sequence. The rate order in absence of metal ions is borneol > isoborneol > menthol. The relative rates have been explained on the basis of structures, steric factors, and isomeric characteristics of the alcohols studied. ... 

CiaH2a02S2f 2-O,3 Dithian-2-yl)isoborneol 1 -oxide, 44B, 325 Cl5H10OS2, 3,5-Diphenyl-1,2-dithiolylium-4-olate, 44B, 325 C15H11CIO5S2, 4-Hydroxy-3,5-diphenyl-1,2-dithiolium perchlorate,... 

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