Methylcyclohexanols, oxidation

Scheme 6.31. A representation of the pathway for hydroboration of 1-methylcyclohexene with the dimer of 9-borabicyclo[3.3.1]nonane (9-BBN) (i.e., [9-BBN]2), which yields (a)(E)-or (frani)-2-methylcyclohexanol oxidatively (hydrogen peroxide anion, HO2 ), or (b) meth-ylcyclohexane, reductively (acetic acid, CH3CO2H). The kinetics of hydroboration are in accord with rapid, reversible formation of 9-BBN monomer from the dimer prior to the ratedetermining step. (See Brown, H.C. Chandrasekharan, X Wang, K. K. Pure Appl. Chem., 1983,55,1387.)...

Does hydroboration/oxidation of methylenecyclohexane yield cyclohexyl-methanol or 1-methylcyclohexanol ... 

Figure 13.21 (a) The 1H NMR spectrum of cyclohexylmethanol, the product from hydroboration/oxidation of methylenecyclohexane, and (b) the 1H NMR spectrum of 1-methylcyclohexanol, the possible alternative reaction product. 

The oxidation of tertiary alcohols by chromic acid is comparatively slow and shows a zero-order dependence of the rate upon oxidant concentration For 1-methylcyclohexanol the kinetics are... 

Asymmetric ring-opening of saturated epoxides by organocuprates has been studied, but only low enantioselectivities (< 15% ee) have so far been obtained [49, 50]. Muller et al., for example, have reported that the reaction between cyclohexene oxide and MeMgBr, catalyzed by 10% of a chiral Schiff base copper complex, gave trans-2-methylcyclohexanol in 50% yield and with 10% ee [50]. 

Biological. May be oxidized by microbes to 4-methylcyclohexanol, which may oxidize to give 4-methylcycloheptanone (Dugan, 1972). 

Hydrogenolysis of epoxides to alcohols by catalytic hydrogenation over platinum requires acid catalysis. 1-Methylcyclohexene oxide was reduced to a mixture of cis- and /ranj-2-methylcyclohexanol [652]. Steroidal epoxides usually gave axial alcohols stereospecifically 4,5-epoxycoprostan-3a-ol afforded cholestan-3a,4/J-diol [652 ]. 

The mechanism of oxidation of alkanes with dimethyldioxirane has been examined by measurement of the primary kinetic isotope effect for the oxidation of cyclohexane and methylcyclohexane in solution and in the gas phase. These experiments indicated that the major products (cyclohexanol and methylcyclohexanol) are probably formed via an electrophilic oxygen-insertion reaction while minor by-products may arise from radical reactions.90... 

Several biochemical oxidations can be applied to the conversions of secondary alcohols into ketones. In a complex system containing horse liver alcohol dehydrogenase, ( )-trans-3-methylcyclohexanol and ( )-cis-2-methylcyclopentanol are dehydrogenated to (-)-(5)-3-methylcyclohex-anone (yield 50% ee 100%) and to (+ )-(5)-2-methylcyclopentanone (yield 55% ee 96%), respectively [1036]. 

In acid medium the epoxide is hydrogenolyzed in such a way as to break that carbon-oxygen bond that gives the more stable carbocation. 1-Methyl-cyclohexene oxide was opened, under these conditions, to give a mixture of cis and Irons 2-methylcyclohexanol. No 1-methylcyclohexanol was formed (Eqn. 20.32).75... 

Although infrequently used, sodium cyanotrihydroborate in the presence of BF3 has been shown to reduce epoxides with interesting regio- and stereo-chemical results. For example, 1-methylcyclohexene oxide is converted in high yield to c/s-2-methylcyclohexanol contaminated with only small amounts of the n ans and 1-methylcyclohexanol isomers. 

Johnson and co-workers oxidized 2-methylcyclohexanol by a similar process but without use of a huge excess of oxidant. An aqueous solution of the reagents in-H OH... 

From an industrial point of view, gas-phase reactions are often preferred due to their ease of operations. The reduction of 4-methylcyclohexanone and the oxidation of cis- and trans-4-methylcyclohexanol over Ti-beta and Al-beta in the gas phase were studied at 100°C. As can be seen from Fig. 3, both Ti-beta and Al-beta are active, but Ti-beta has a considerably lower rate of deactivation. The deactivation of Al-beta is probably caused by the higher acidic strength of the protonic aluminium site compared to the non-protic titanium site. Another difference between the two catalysts is the pronounced dehydration of the alcohols formed over Al-beta. Two important differences between the gas-phase and liquid-phase reaction were observed. The most striking is the selectivity towards the cis-alcohol. Under liquid phase conditions (Table 1.) a selectivity of 99 % towards the cis-alcohol was observed, while in the gas-phase over Ti-beta only 53 - 62 % cis-alcohol was obtained. 

Fig. 5 The gas-phase Oppenauer oxidation of the 4-methylcyclohexanols with acetone over Ti-beta at 100°C. a) cis-4-Me-OL and b) trans-4-Me-OL. = conversion = ds4-Me-OL x = trans4-Me-OL a = 4-Me-ONE. n = 4-Me-ENK...

As was already shown in Fig. 3 and 5a, Ti-beta exhibits a low deactivation rate in the reduction of 4-methylcyclohexanone and a significantly higher deactivation rate in the oxidation of cis-4-methylcyclohexanol. In both cases, frequent regeneration of the catalyst will be necessary. Catalyst stability was tested by regeneration at 480°C in air after each run. No significant loss in activity, selectivity or product distribution was observed, even after 35 consecutive runs. Similar results were also obtained for the Ti-beta used in liquid-phase reductions after regenerating the Ti-beta catalyst 5 times, the same initial catalytic activity per gram of catalyst was observed. 

METHYLCYCLOHEXANOL or 2-METHYLCYCLOHEXANOL (25639-42-3) CtH,40 Combustible liquid (flash point 149°F/65°C Fire Rating 2). Strong oxidizers may cause fire and explosions. Reacts with boranes, alkalis, aliphatic amines, amides, nitric acid, sulfuric acid. Attacks some plastics, rubber, and coatings. On small fires, use dry chemical powder (such as Purple-K-Powder), alcohol-resistant foam, or CO2 extinguishers. 2-METHYLCYCLOHEXANONE or 0-METHYLCYCLOHEXANONE or 1-... 

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