Cyclohexanone, 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 ... 

Rh6(CO)16, the product mixture contains -caprolactone. Analysis of the oxidation products for the uncatalyzed and Rh6(CO)16-catalyzed oxidation of cyclohexanone shows the respective rations of -caprolactone to be 0.43 and 1.00 when measured against an added aliquot of dodecane. Thus there is a decrease in -caprolactone formation in the presence of Rh6(CO)16. This observation is consistent with the premise that the metal carbonyl accelerates the decomposition of peroxides. In the presence of Rh6(CO)16, the increased decomposition rate of peracid leading to a lower steady-state concentration of this species, and hence to its reduced transformation to -caprolactone is expected. These data support a reaction pathway proceeding via hydroperoxide and its sub-... 

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

The amount of cyclohexanone desorbed from the catalyst surface during hydrogenation can be conveniently obtained by applying the equation derived on the basis of the reaction pathways shown in Scheme 11.7, where CA and CB are the concentrations of phenol and cyclohexanone, respectively, when the initial concentration of phenol is taken as unity,/is the fraction of cyclohexanone desorbed from the catalyst... 

On the other hand, the parent, unsubstituted cyclohexanone enters into an apparently much more complex reaction pathway leading to the formation of a tricyclic, cyclohep-tanone-containing product.93 Also, cycloheptanones as starting materials give annu-... 

The reaction pathway of the present photochemical reaction is not clear but presumably proceeds as shown in Scheme 31. The radical ion pair of 73 and DCN is formed on photoirradiation. Electron transfer then occurs between the radical anion of EXTN and cyclohexanone, forming radical ion pair of CR73 and AR14b. The radical cation CR73 cleaves into methoxystannane and aryloxymethyl radical R73, which couples with AR14b to give the enolate (or enol) of 74. 

The numerous reaction pathways found in Figure 32 invariably lead to an elimination of CO giving (CsHe) ion fragments (m/z 66). The PES can be divided into two distinct parts while the first part involves the three cyclohexanone ion isomers 22, 24 and 25, the second consists in the conversion of the cyclic keto-ions into either the various open-chain distonic forms 34 (or its conformers 35 and 36), 37 and 39, or the five-membered cyclic derivatives 29, 30 and 41. There are also some weak hydrogen bond complexes between CO and the CH bond of ionized cyclopentadienes such as 32 and 42. 

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 ammoximation of cyclohexanone to cyclohexanone oxime using TS-1 was invented in 1987 (221). The limited amount ofpubHshed work focuses on the mechanism (222) and the kinetics (223) of this reaction on titanium silicate with dilute hydrogen peroxide as oxidant. There is no agreement thus far regarding the reaction pathway. The following two hypotheses have been formulated (7,90,222b,224) ... 

The oxidation of cyclohexanone is a reaction which has been the subject of considerable study over the years. Continued research in this area has given rise to many recent patents and papers. The product of the oxidation reaction is rather dependent on the metal complex which is used as a catalyst. When manganese(III) complexes are used the major reaction product is adipic acid [280-288]. Selectivity to adipic acid is about 70% in most cases. When copper(II) complexes are used, 5-formylvaleric acid predominates [289, 290] whereas iron complexes catalyze the formation of e-caprolactone [291,292] in up to 56% yield. In fact, liquid phase air oxidation of 2-methyl-cyclohexanone at 100 °C in the presence of copper stearate gave e-methyl- -caprolactone [292a]. Reaction scheme (190) shows the predominant reaction pathways. 

The rhodium cluster compound [Rhg(CO)i6], also catalyzes the oxidation of cyclohexanone to adipic acid at 100°C in homogeneous solution [194]. The reaction pathway was not investigated and in view of the reaction of some group VIII metal dioxygen complexes with ketones, a study of such complexes as catalysts for ketone oxidation could prove interesting. 

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. ... 

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. 

Hasegawa, E., Xu, W., Mariano, P.C., Yoon, U.C., and Kim, J.U., Electron transfer induced photoaddition of the silylamine Et NCHjTMS to a,P-unsaturated cyclohexanones. Dual reaction pathways leading to a ion-pair-selective cation-radical chemistry, J.Am. Chem. Soc., 110, 8099, 1988. 

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