Cyclohexanol. oxidation reactions

Hydrocarbon Oxidation. The oxidation of hydrocarbons (qv) and hydrocarbon derivatives can be significantly altered by boron compounds. Several large-scale commercial processes, such as the oxidation of cyclohexane to a cyclohexanol—cyclohexanone mixture in nylon manufacture, are based on boron compounds (see Cylcohexanoland cyclohexanone Eibers, polyamide). A number of patents have been issued on the use of borate esters and boroxines in hydrocarbon oxidation reactions, but commercial processes apparently use boric acid as the preferred boron source. The Hterature in this field has been covered through 1967 (47). Since that time the Hterature consists of foreign patents, but no significant appHcations have been reported for borate esters. 

When nitric acid was added to cyclohexanol when preparing cyclohexane-1,2-dione, the reactor detonated, probably because of the exothermicity of the oxidation reaction, which was complete instead of partial (reaction (2)). 

Cyclohexanol oxidation, 41 299-300 reactions over reduced nickel oxide catalyst, 35 355-357 Cyclohexanone... 

An aqueous solution of soditun ruthenate is able to oxidize cyclohexanol. These reaction conditions are hardly appropriate for routine employment in the laboratory because of the high price of Na2Ru04 that is used stoichiometrically and of the need to perform the reaction in aqueous 1M NaOH in order to avoid the dismutation of sodium ruthenate. Some mechanistic studies suggest that the real oxidant could be perruthenate,9 present in very small amounts and in equilibrium with ruthenate regardless of... 

The majority of studies on oxidation reactions in scC02 have involved catalyzed processes promoted by molecular oxygen, in which the role of the catalyst is to generate free radicals that will react with the chemical oxidant, leading to a product distribution that is typical of an unselechve chain process. Among these can be mentioned the oxidation of cyclohexane to cyclohexanol and cyclohexanone (Scheme 2.2) as an intermediate step in the production of the adipic acid that is a key component in the production of Nylon 6,6 polyamide [52-54],... 

Olefins undergo a two-step oxidative process, with the first step leading to an epoxide that, in the presence of excess oxidant, subsequently is cleaved to afford aldehydes or ketones, dependent on the position of the olefinic bond. Oxidative reactions by peroxovanadates tend to be retarded by protic solvents such as water or methanol. For instance, oxidation of norbomene by picolinatooxomonoperoxo-vanadate in acetonitrile affords 22% of the product epoxide in 9 min. After 120 min in methanol solvent, only 1.8% yield was obtained. In dichloromethane, even cyclohexane is oxidized faster than this, giving 4% cyclohexanol and 9% cyclohexanone in 120 min, whereas benzene in acetonitrile yields 56% of phenol [23],... 

The oxidation of a secondary alcohol to a ketone is usually accomplished with a solution of the alcohol and aqueous acidic chromic acid in either acetone or acetic acid, with a solution of sodium dichromate in acetic acid, or by reaction of the alcohol with aqueous acidic chromic acid as a heterogeneous system. An example is the oxidation of the substituted cyclohexanol below (Reaction XXXV) with sodium dichromate in sulfuric acid (55). 

First the amino group was converted to a hydroxy group via a diazonium ion (Section 17.10). The benzene ring was reduced with hydrogen and a catalyst to produce cyclohexanol. Oxidation with potassium dichromate (Section 10.14) gave cyclohexanone. The bonds between the carbonyl carbon and both a-carbons were then cleaved by a series of reactions not covered in this book. The carbon of the carbonyl group was converted to carbon dioxide in this process. One-half of the original radioactivity was found in the carbon dioxide, and the other one-half was found in the other product, 1,5-pentanediamine. Additional experiments showed that the 14C in the diamine product was located at C-l or C-5. 

Experiment was also conducted for 02 and C6Hi2 in place of C2H4. In the case of 2 , main products were CH3CHO and ethanol, which were the same in the previous oxidation reaction in the C2H6/02 mixtures [1], In the case of C6H12, the main products were cyclohexanone and cyclohexanol. These products are considered to be produced via certain radical reactions which are derived by the excited oxygen molecules and/or oxygen atoms. 

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. 

In the direct oxidation of cyclohexanol a significantly higher conversion is obtained with HPTP / Fe complexes, contrasting with that of monouclear iron complexes [12] or the blanc reaction. Thus cyclohexanone is not only formed through CHHP decomposition, but also by direct cyclohexanol oxidation (table 6). 

Iron-phthalocyanine (Fe-Pc) encapsulated in Y and VPI-5 zeolites were used for the oxidation of alkanes or olefins in presence of t-butylhydroperoxide or H2O2 (Fig. 9). Fe-Pc-Y also catalyzed the oxidation of cyclohexane to cyclohexanol and cyclohexanone with t-butylhydroperoxide ( TBHP ). Ruthenium perfluorophthalocyanine complexes encapsulated in NaX ( Ru-Fi6 Pc-X ) were active for the oxidation of cyclohexane with TBHP at room temperature.Manganese(II) bipyridyl complexes in faujasite ( Y ) zeolite are active for the oxidation of cyclohexene to adipic acid in the presence of H2O2 at room temperature. Similarly oxidation reactions have been reported using copper complexes encapsulated in X,Y, and VPI-5 molecular sieves. 

Mo-containing MCM-41 has been prepared by direct hydrothermal synthesis and characterized by XRD, IR, TGA and N2 adsorption measurements, Though the state of Mo in MCM-41 is not clear, they are found to be stable and active for cyclohexanol and cyclohexane oxidation reactions. Activity has been compared with that of Ti-MCM-41 and impregnated Mo on pure siliceous MCM-41. 

The catalytic activity of the samples prepared were analyzed for cyclohexanol oxidation and cyclohexane oxidation reactions using 30 wt.% H2O2. Table 2 gives the TON for cyclohexanol oxidation for various catalysts. 

The mechanism of cyclohexanol oxidation has been studied in detail and is rather complex [23,26,32,48—50,57,58]. Various reactions involving H202 decomposition and cyclohexanone oxidation play the main part in the later stages of the process. 

Hydrogen peroxide decay in cyclohexanol oxidation occurs by several routes, (a) By reaction with hydroxycyclohexyl radicals [57]... 

The most popular cationic catalysts are soluble Co " and Cr " salts and mixtures thereof Examples of such salts that are added to catalyze the oxidation are cobalt stearate and cobalt naphthenates. Applied concentrations of these transition metals range from more than 10 ppm down to sub-ppm levels. These catalysts also catalyze the decomposition of CHHP, reducing the residual concentrations of CHHP. Nevertheless, both for economic and safety reasons, the residual CHHP is decomposed to mainly cyclohexanone and cyclohexanol. This reaction is carried out in an after-reactor either in a monophasic system in cyclohexane or in a biphasic system with an aqueous caustic solution as second phase. 

We tried to accumulate oxidation reactions using copper chloride under these conditions (Fig. 6) but observed that the system had already started to deactivate after the first reaction. Furthermore, the system began to produce cyclohexanol in the accumulation reactions, which was not observed before. After 4 accumulations we obtained a 0.120 M solution of one + ol (8.3 1) with 100% selectivity but only 18% efficiency with respect to hydrogen peroxide. Using copper perchlorate in the absence of acetic acid, we were also able to accumulate one + ol to a concentration of 0.120 M (one ol = 5.9 1), but observed that the reaction was less efficient at the beginning (Fig. 7). Interestingly, the... 

The encapsulation of metalloporphyrins in the cavities of an indium imidazoledicarboxylate-based rho-zeolite-like metal-organic framework (rho-ZMOF) has been reported by Eddaoudi and coworkers [71]. The catalytic activity of this material was assessed by cyclohexane oxidation with TBHP as the oxidant, with cyclohexane conversion reaching 91.5% after 24 h at 65 °C. Cyclohexanol and cyclohexanone were the only observed products, suggesting that the investigated oxidation reaction is selective toward the desired products. Furthermore, upon reuse of the catalyst, no loss of crystaUinity, reactivity, and selectivity in up to 11 cycles was observed, while no leaching of the encapsulated metalloporphyrin into the product solution was detected by the UV-vis spectra. 

Microflow systems serve as effective environments to perform various oxidation reactions using chemical reagents. The oxidation using dimethyl sulfoxide (DMSO), which is known as Moffatt-Swern type oxidation, is one of the most versatile and reliable methods for the oxidation of alcohols into carbonyl compounds in laboratory synthesis [1, 2]. However, it is well known that activation of DMSO leads to an inevitable side-reaction, Pummerer rearrangement, at temperatures above — 30°C (Scheme 7.1). Therefore, the reaction is usually carried out at low temperatures (—50 °C or below), where such a side-reaction is very slow [3, 4]. However, the requirement for such low temperatures causes severe limitations in the industrial use of this highly useful reaction. The use of microflow systems solves the problem. For example, the oxidation of cyclohexanol can be accomplished using a microflow... 

---