Hydroxylation of cyclohexane

The hydroxylation of cyclohexane by a strain of Xanthobacterium sp. (Trickett et al. 1990). In cell extracts, a range of other substrates was oxidized including cyclopentane, pinane, and toluene (Warburton et al. 1990). 

In the presence of excess TBHP, the hydroxylation of cyclohexane by (22) becomes catalytic.46... 

Cobalt porphyrins catalyze the hydroxylation of cyclohexane by cumyl or t-butyl hydroperoxide under mild conditions (equation 252).501 This reaction presumably occurs outside the coordination... 

DFT calculations have shown that in C-H hydroxylation of cyclohexane, the nonhaem oxidant (N4Py)FeIV=02+ is more reactive than P450 Cpd I and is predicted to involve multi-state reactivity with a strong solvent effect and a temperature-dependent stereoselectivity reflecting spin crossover effects.58... 

Figure 28. Scheme showing the mechanism of hydroxylation of cyclohexane catalyzed by Mn porphyrins. 

The hydroxylation of cyclohexane, of potential interest for the production of cyclohexanone, is exceedingly slow at near room temperature and has low selectivity at 100 °C [27, 28]. Tertiary C—H bonds yield tertiary alcohols, with little or no oxidation observed at the secondary carbons that may be present in the alkyl chain t-C—H sec-C—H (Table 18.3). The steric constraints introduced by alkyl substitution strongly favor the competition of side reactions, at the expense of hydroxylation. On arylalkanes, oxidation occurs on both the aromatic ring and the alkyl chain, with a general preference for the latter. Consistently, the competitive hydroxylation of benzene and n-hexane or cyclohexane mainly occurs on the alkane. However, benzylic methyls, despite the relative weakness of their C—H... 

Such a side-on approach is reminiscent of a three-center two-electron bond, referred to as an agostic interaction [133-136]. An agostic substrate-catalyst complex has recently been proposed as a key intermediate before the oxygen-transfer step in the hydroxylation of cyclohexane by PhIO with (TPFPP)FeCl, as shown in Scheme 9 [137]. 

D. Mansuy, J. F. Bartoli, J. C. Chottard, M. Lange, Metalloporphyrin-catalyzed hydroxylation of cyclohexane by alkyl hydroperoxides pronounced efficiency of iron-porphyrins, Angew. Chem. Int. Ed. Engl. 19 (1980) 909. 

THE SELECTIVE HYDROXYLATION OF CYCLOHEXANE BY ALKYL HYDROPEROXIDES A CHALLENGE THAT CAN BE SOLVED ... 

Iodosylbenzene has been used as an effective oxidant in hydrocarbon hydroxylation catalyzed by metal-loporphyrins [687-696]. In particular, various iron(III) and manganese(in) porphyrins can be used as catalysts in hydroxylations of cyclohexane, cyclohexene, adamantane and aromatic hydrocarbons [687,688, 692]. Breslow and coworkers have reported regioselective hydroxylations of several steroidal derivatives catalyzed by metalloporphyrins [689-691]. In a specific example androstanediol derivative 644 was... 

The hydroxylation of cyclohexane, adamantane and norcarane with PhIO and ClMnTPP leads mainly to the corresponding cycloalkanols [92]. A hydrogen abstraction mechanism is consistent with the product distribution pattern. A mixture of cyclohexanol and halocyclohexanes is obtained with other MnTPP complexes [93]. 

Iron porphyrin systems containing reducing agents serve as model sytems for cytochrom P-450. The mechanism given in Scheme 5 has been proposed for the biomimetic catalyst system Fe(TPP)Cl/Zn(Hg)/methyl viologen/Ac O in acetonitrile for the hydroxylation of cyclohexane... 

Miscellaneous Cyclohexanes. Various reactions involving hydroxylation of cyclohexane derivatives have been reported. The reaction of cyclohexanol with Fe(C10 )2 and hydrogen peroxide in acidic aqueous MeCN solutions has been shown to be very sensitive to the exact concentrations of Fe", Fe ", and perchloric acid. In MeCN, cis-cyclohexane-l,3-diol forms 72% of the product diol, i.e. hydrogen removal at C-3 occurs with some stereoselectivity cis to the hydroxy-group. In highly aqueous solutions, the dominant oxidation site is at C-4. Evidence is presented for a stepwise process involving an initial directed hydrogen abstraction, oxidation of the radical by Fe" , and stereoselective carbonium ion capture. 

Fe(N4PyXi OOH)f and 495 and 817 cm for Fe(N4PyXiJ -02)j". The former has activity for the hydroxylation of cyclohexane, but the latter looses it, supporting the hypothesis that protonation of the peroxo species activates it for participation in the oxygen activation mechanisms by iron enzymes. Similar results for identification of two peroxo complexesas shown in Fig. 16 were reported by Simaan et al.. ... 

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