Isobomeol

Isobomyl acetate [125-12-2] is also usehil ia produciag isobomeol (42) by saponiftcatioa. Dehydrogeaatioa or oxidatioa of isobomeol... 

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). 

Camphor [126-04-5] (11), menthol [89-78-1] (12), and thymol [89-83-8] (13) ate used in topical over-the-counter cough and cold preparations. Camphor is isolated from the camphor tree, Cinnomomum camphora T. Nees Eherneier, or prepared synthetically from a-pinene or isobomeol. About 75% of the camphor sold in the United States is synthetic. Menthol, commercially the most important terpene alcohol, is obtained by crysta11i2ation from... 

The identification of camphene is best carried out by its conversion into isobomeol under the influence of acetic acid in the presence of sulphuric acid. In order to effect this conversion, 100 grams of the fraction containing the terpene in substantial quantity are mixed with 250 grains of glacial acetic acid and 10 grams of 50 per cent, sulphuric acid. Tne mixture is heated for two to three hours on a water-bath to a temperature of 50° to 60°. At first the liquid separates into two layers, bat soon becomes homogeneous and takes on a pale red colour. Excess of water is added, and the oil which is precipitated, and which contains the isobomeol in the form of its acetate, is well washed with water repeatedly. It is then saponified by heating with alcoholic potash solution on a water-bath. The liquid is then evaporated and extracted with water, and the residue recrystallised from petroleum ether. 

The isobomeol so formed melts at 212°, but the determination must be carried out in a sealed tube, as the melting-point is very dose to the temperature of sublimation. It is, however, very rarely that the isobomeol so prepared is free from impurities, and the melting-point will often be found to be as low as 203° to 205°. It is therefore necessary to pare derivatives of the isobomeol in order to identify it with certainty. Kie compound with bromal melts at 71° to 72°. Other compounds will be found mentioned under isobomeol . By dehydration by means of zinc chloride, isobomeol is easily converted into camphene, melting at about 49° to 50°. 

Pickard and Littlebury have carried out a series of investigations on the separation of the optically active borneols and isobomeols, which is of particular interest, as the method of separation can probably be applied to various other similar bodies. This method depends on the... 

The enantiomerically pure isobomeol allyl sulfoxide derivatives (17 ,2Y,3/ ,4S )-1,7,7-tri-methyl-3-[(S)- or -(/ )-2-propenylsulfmyl]bicyclo[2.2.1]heptan-2-ol are thermally more stable inversion of configuration at sulfur, S -> / , occurs at 135-145 °C. Their lithio derivatives give exclusively y-1,4-adducts with 2-cyclopentenone19. 

Norbomyl cations, besides displaying the 1,2 shifts of a CH2 group previously illustrated for the isobomeol —> camphene conversion, are also prone to rapid hydride shifts from the 3 to the 2 position (known as 3,2 shifts). These 3,2 shifts usually take place from the exo side, that is, the 3-exo hydrogen migrates to the 2-exo position. This stereoselectivity is analogous to the behavior we have previously... 

Reduction of (+ )-camphor with LAH gives a mixture of (—)-isobomeol (90%) and ( + )-bomeol (10%) (129). The complex with bomeol reacts much slower with ketones. 

Geosmin, 2-Methyl isobomeol (MIB) and 2-isopropyl methoxy pyrazine are known to be produced by various types of actinomycete cultures (10-15). Geosmin and MIB are saturated tertiary alcohols and resist oxidation. The steric configuration of the hydroxyl and methyl groups in both compounds are believed to interact with receptors in the nose, imparting their characteristic earthy odour (16). The four compounds itemised as the key osmogenes in this odorous emission have extremely low odour threshold concentrations. Their occasional occurence in drinking water can lead to widespread complaints and are routinely monitored for within this Authority. 

Another aspect of the chemical properties of mixmres of enantiomers has been reported by Wynberg and Feringa in 1976. These authors have smdied some dia-stereoselective reactions on chiral molecules (such as the LiAlH4 reduction of camphor) in the absence of chiral auxiliaries. They found that the product distribution was significantly different if the substrate was enantiopure or racemic. Similarly, it is known that reduction of enantiopure or racemic camphor by K/liquid NH3 gives rise to different isobomeol/bomeol ratios, a detailed mechanistic analysis has been done by Rautenstrauch. °... 

Of synthetic importance is the Wagner-Meerwein rearrangement especially in the chemistry of terpenes and related compounds." For example isobomeol 5 can be dehydrated and rearranged under acidic conditions to yield camphene 6 ... 

Figure 2.5 Reported concentrations of various PPCPs in Wastewater effluents by several research groups. On the x axis are respective PPCPs that are primarily cosmetics (1 = HHCB, 2 = AHTN, 3 = acetophenone, 4 = camphor, 5 = isobomeol, 6 = skatol, 7 = celestolide, i.e., AHMI, 8 = Phantolide, i.e., AHMI), the lotion ingredient (9 = methyl salicylate), two disinfectants (10 = triclosan and 11 = trilocarban), antihypertensive (12 = dehydronifedipine, 13 = diltiazem, 14 = bezafibrate, and 15 = gemfibrozil), analgesics and anti-inflammatories (16 = naproxen, 17 = ibuprofen, 18 = codeine), antimicrobials (19 = chlortetracycline, 20 = erythromycin, 21 = novobiocin, 22 = oxytetracycline, 23 = sulfamethaxazole, 24 = thiabendazole, 25 = trimethoprim), anxiolytic sedative (26 = carbamazepine), antidiabetic (27 = metaformin), reproductive (28 = 17(3 estradiol, 29 = 17a-ethinyl estradiol), GIT (30 = cimetidine, 31 = ranitidine), and respiratory (32 = Albuterol). The concentrations were compiled from Boyd et al. (2003), Gagne et al. (2006), Glassmeyer et al. (2005), Halden and Pauli (2005), Huang and Sedlak (2001), Ricking et al. (2003), and Temes et al. (2003).

It has been shown that the S-amino alcohol (—)-3-exo-(dimethylamino)isobomeol (DAIB) serves as an excellent chiral auxiliary in the enantioselective addition of Ft2Zn to aldehydes. As a model compound for the anticipated intermediate, the structure of MeZn(DAIB) (142) in the solid state was determined by X-ray crystallography. In the... 

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