Cyclohexanol, reaction pathway

The recombination of the cyclohexyl peroxy radicals produced in one of these two reaction pathways gives rise to cyclohexanol, cyclohexanone and oxygen ( disproportionation ) ... 

The reaction pathway and product distribution observed in the Re2(CO)io- and Rh6(CO)16-catalyzed autoxidation of cyclohexanol and cyclohexanone are shown in Scheme II. An important intermediate is the peracid. In this sequence the peracid is the final intermediate ... 

Scheme II. Reaction pathway in the Re2(CO)10- and Rh6(CO)16-catalyzed autoxidation of cyclohexanol and cyclohexanone...

Reaction Pathway and Products. In the presence of a catalytic amount of a tetraphenylporphyrin (TPP) Mn(III) complex (34) and sodium borohydride, treatment of cyclohexene with excess oxygen (air) in benzene-ethanol leads effectively to cyclohexanol and cy-clohexenol. The reaction is quite different from the known autoxidation catalyzed by TPP Mn(III) in the absence of NaBH4 (Figure 7). The most significant characteristics of the present TPPMn-NaBH4-02 reaction compared with the autoxidation are ... 

The easy hydrogenolysis of 1,3-cyclohexanedione over palladium catalyst has been applied to the preparation of 3,3-dimethylcyclohexanone from 5,5-dimethyl-1,3-cyclohexanedione (eq. 5.40).129 The reaction pathway outlined in Scheme 5.7 has been suggested for this transformation. 1,3-Cyclohexanedione was also hydro-genolyzed to give cyclohexanol in a 95% yield over copper-chromium oxide at 200°C and 17.7 MPa H2.130... 

In a study related to the conformational properties of the cyclohexane-fused six-membered heterocycles, new bicyclic dithiolanes, 285-/ra r (Scheme 52) and 285-crr (not shown), were prepared along the reaction pathway, as precursors used further for the syntheses of 2-methyl substituted and unsubstituted /ra r-fused 4a,5,6,7,8,8a-hexahydro-2//,4//-1,3-benzodithiines, exemplified by structure 288-/ra ir (R=R = H) <2002JOC1910>. Thus, ditosylation of cis-Z-hydroxymethyl cyclohexanol 284, and subsequent reaction with sodium sulfide and sulfur, provided a mixture of new bicyclic products 285 and 286, albeit in very low yields, with configurational inversion at C-1. These were reduced by LiAlH4 to provide /ra r-2-mercaptomethyl cyclohexanethiol 2 l-trans. Upon acetalization or transacetalization, the desired 2SS-trans derivative was obtained. The same methodology with the precursor 2E4-trans was extended to the preparation of the r-fused bicyclic compounds 285-288. 

Nitrosation may potentially also occur on cyclohexanol in fact, cyclohexanol can be oxidized at much lower temperatures than cyclohexanone. The active reactant is H NO2 therefore, in this case, the first product of cyclohexanol oxidation is cyclohexyl nitrite. The latter is then rearranged into 2-nitrosocyclohexanone, which is also the key intermediate in the main reaction pathway involving cyclohexanone. 

The well-known oxidations of primary and secondary alcohols with Cr species proceed through chromate esters. The definitive mechanistic expeii-ments " demonstrating that previously observed chromate esters were indeed on the reaction pathway showed that either formation or decomposition of the ester could be rate-determining. The rates of oxidation of cyclohexanol and the secondary hydroxyl group of a very steiically hindered steroid in aqueous acetic acid were measured as a function of the solvent composition. The former increased radically as the acetic add concentration increased whereas the latter remained invariant. The former exhibited a primary deuterium kinetic isotope effect of 5, whereas there was no KIE on the oxidation of the crowded steroid. Therefore, the rate-determining step in the oxidation of the cyclohexanol was decomposition of the chromate ester and in the oxidation of the steroid it was its formation, with the ester an obligate intermediate in both reactions. 

A unified reaction pathway invoking a protonated cyclopropane 49 was formulated to rationalize formation of the reaction products 46 to 48. Thus, for substrate 43, addition of water to 49 at the a-carbon generates the cyclohexanol 46. For the substrates 44 and 45, which both contain an electron-donating methyl group, products 47 and 48 are formed by either addition of water to the 3-carbon of intermediate 49, or loss of a proton from 49. The observed product distribution and asymmetry can thus be ascribed to the direct control of the central car-bo cation intermediate 49 by the antibody catalyst. 

Scheme 8.59. A representation of a possible reaction pathway for the addition of cyclohexanol to phenyhsocyanate to prodnce the corresponding cyclohexyl phenylcarbamate (a urethane).

Reports have appeared on the rates of decomposition of cyclohexyl hydroperoxide (an intermediate in the industrial oxidation of cyclohexaneto cyclohexanol and cyclohexanone catalyzed by Ru(porp)CO and Ru(porp)(0)i systems (porp = rCPP, mCrPP, TDCPP, TMCPP, TMP, TPP) either in solution or anchored to polystyrene or silica . The systems were studied in 20 1 cyclohexane/CH2Cl2 at 25°C, when decompositions in the 28-66% range were observed after 2 h, and close to 100% after 48 Several, plausible reaction pathways were... 

The main feature of the Meerwein-Ponndorf-Verley reaction pathway involves the coordination of both reactants to the Lewis-acid metal eentre and hydride transfer from the alcohol to the earbonyl group. Aluminium or titanium alkoxides are usually effective homogeneous catalysts. With tin-Beta catalyst, cyclohexanone reduction with 2-butanol led selectively to cyclohexanol at 100 °C. Ketone conversion was >95%, whereas silicon-Beta, Sn02/Si02 and SnCl4 -5H20 were inaetive under the same experimental conditions. Therefore, the activity is likely due to tetrahedral tin in the zeolite framework, and not to extra-framework tin or to leached tin. ... 

Cyclohexanol conversion over H-ZSM-5 and H-boralite was also studied by Brabec et al. [188], who addressed the effects of concentration and strength of acid sites on catalytic activity. They found the number of acid sites needed increases in the order of dehydrogenation (formation of cyclohexene) < isomerization (formation of methylcyclopentene) < intermolecular reactions (formation of cyclohexane and methylcyclopentane). Even at reaction temperatures around 180 °C all products were observed. The intermolecular reaction pathway decreased in importance with TOS and practically vanished after 30 min. Deactivation, which is in general only slight on these catalysts. 

Despite the relatively simple stoichiometry, which can be represented theoretically by Eqs. 13.1 and 13.2 below, the reaction mechanism is much more complex. In fact, Eqs. 13.1 and 13.2 imply, but do not reveal, two different reaction pathways for the formation of adipic acid, one from cyclohexanol and the other from cyclohexanone, each consuming a different quantity of nitric acid, which is reduced to nitrous oxide. 

Radical hydroxylation of hydrocarbons by autooxidation yields alcohols (major products), ketones, and acids (minor products). Cyclohexanol, for example, is formed in 90% yield from cyclohexane and peroxyacetic acid (275). The high -ol/-one ratio at low conversions can sometimes be used as a partial diagnostic tool to distinguish between the radical and electrophilic pathways. The predominant reaction of electrophilic radicals, such as HO, ROO, and CH 3 is H-atom abstraction from reactants (S-H) or peracids, as exemplified by the following ... 

Two mechanistic pathways may be considered by which methylcyclopentenes could be produced from cyclohexanol. In the first, (II) and (III) are formed from (I) in parallel reaction with or without consecutive interconversion of the cycloalkenes ... 

In the absence of ultrasound, the results show a substantial amount (49 %) of the dimer bicyclohexyl from the one-electron pathway, together with cyclohexylmethyl-ether, cyclohexanol and other products from the two-electron pathway (approx. 30%). The methyl cyclohexanoate ester (17%) can be thought to arise from the acid catalysed chemical esterification of the starting material with the solvent methanol. (As a result of the high current densities needed, (parasitic) discharge of the solvent methanol produces a large quantity of protons around the anode as a competitive reaction [54].)... 

Tabushi and Koga reported the use of manganese porphyrins to catalyze the 02-oxidation of cyclohexene to cyclohexanol and cyclohexene-ol in the presence of borohydride these workers suggest that an equilibrium such as depicted in Reaction 32 is involved in non free-radical pathways (112). 

Although Curran s rate data for the reduction of radicals to organosamar-iums allow for an element of predictablity,2 problems can arise when multifunctional substrates are involved. For example, in the attempted intramolecular Barbier reaction of alkyl iodide 13, treatment with Sml2 results in the formation of side product 15 in addition to the expected product cyclohexanol 14 (Scheme 3.7).8 In this case, the p-keto amide motif in 13 is reduced at a rate competitive with alkyl iodide reduction, indicating that there are likely two mechanistic pathways through which the reaction proceeds a thermodynamic pathway initiated by reduction of the R I bond providing the... 

The volume of activation of AnI (and iil)-like reactions is around -10 to -20mLmoN as the separation of charges polarises solvent molecules and pulls them in to solvate the new ions, a process known as electrostriction. Therefore, increasing pressure disfavours homolytic and favours heterolytic pathways. The plots of rate of decomposition of cyclohexanol nitrate or propane-1,2-diol dinitrate versus applied pressure at 170 °C are U-shaped, with a minimum between 0.4 and 0.8 GPa, in accord with a change in mechanism... 

Studies continue into systems involving Ag(II) as an oxidant. The reactions with cyclohexanol, pentan-2-ol, and benzyl alcohol proceed via two pathways ... 

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