Cyclohexanone/cyclohexanol oxidation

Reactions. The most important commercial reaction of cyclohexane is its oxidation (ia Hquid phase) with air ia the presence of soluble cobalt catalyst or boric acid to produce cyclohexanol and cyclohexanone (see Hydrocarbon oxidation Cyclohexanoland cyclohexanone). Cyclohexanol is dehydrogenated with 2iac or copper catalysts to cyclohexanone which is used to manufacture caprolactam (qv). 

The oxidation of cyclohexane to a mixture of cyclohexanol and cyclohexanone, known as KA-od (ketone—alcohol, cyclohexanone—cyclohexanol cmde mixture), is used for most production (1). The earlier technology that used an oxidation catalyst such as cobalt naphthenate at 180—250°C at low conversions (2) has been improved. Cyclohexanol can be obtained through a boric acid-catalyzed cyclohexane oxidation at 140—180°C with up to 10% conversion (3). Unreacted cyclohexane is recycled and the product mixture is separated by vacuum distillation. The hydrogenation of phenol to a mixture of cyclohexanol and cyclohexanone is usually carried out at elevated temperatures and pressure ia either the Hquid (4) or ia the vapor phase (5) catalyzed by nickel. 

Essentially, all cyclohexane is oxidized either to a cyclohexanone-cyclohexanol mixture used for making caprolactam or to adipic acid. These are monomers for making nylon 6 and nylon 6/6. 

Oxidation of Cyclohexane (Cyclohexanone-Cyclohexanol and Adipic Acid)... 

Results of the cyclohexane oxidation tests are shown in Table 41.4. Mono-oxygenated products are cyclohexanone, cyclohexanol and cyclohexyl hydroperoxide. Cu and Cr were very active, but subsequent tests showed considerable leaching for both metals, whereas Co-Si-TUD-1 did not show ai r leaching. Tests with different Co loadings indicate that the lowest Co concentration has the best conversion and ketone selectivity. Isolated cobalt species are most efficient for the conversion of cyclohexane, as agglomeration of Co reduces... 

Fire and explosion hazards of processes involving the oxidation of hydrocarbons are reviewed, including oxidation of cyclohexane to cyclohexanone/cyclohexanol, ethylene to ethylene oxide, of cumene to its hydroperoxide, and of p-xylene to terephthalic acid. 

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

Figure 11.2 The large tower on the right is the cyclohexane oxidation chamber and purification unit to convert cyclohexane to the hydroperoxide and then to cyclohexanone/cyclohexanol. An elevator leads to the top platform of this narrow tower, where an impressive view of this and other surrounding plants can be obtained. (Courtesy of Du Pont)...

Caprolactam is discussed more completely in Chapter 11, Section 5. It is made from cyclohexane by oxidation to cyclohexanone-cyclohexanol mixture, formation of cyclohexanone oxime, and acid-catalyzed rearrangement. 

Adipic acid (1,4-butanedicarboxylic acid) is used for the production of nylon-6,6 and may be produced from the oxidation of cyclohexane as shown in structure 17.1. Cyclohexane is obtained by the Raney nickel catalytic hydrogenation of benzene. Both the cyclohexanol and cyclohexanone are oxidized to adipic acid by heating with nitric acid. 

Most of the work reported with these complexes has been concerned with kinetic measurements and suggestions of possible mechanisms. The [Ru(HjO)(EDTA)] / aq. HjOj/ascorbate/dioxane system was used for the oxidation of cyclohexanol to cw-l,3-cyclohexanediol and regarded as a model for peroxidase systems kinetic data and rate laws were derived [773], Kinetic data were recorded for the following systems [Ru(Hj0)(EDTA)]702/aq. ascorbate/dioxane/30°C (an analogue of the Udenfriend system cyclohexanol oxidation) [731] [Ru(H20)(EDTA)]70j/water (alkanes and epoxidation of cyclic alkenes - [Ru (0)(EDTA)] may be involved) [774] [Ru(HjO)(EDTA)]702/water-dioxane (epoxidation of styrenes - a metallo-oxetane intermediate was postulated) [775] [Ru(HjO)(EDTA)]7aq. H O /dioxane (ascorbic acid to dehydroascorbic acid and of cyclohexanol to cyclohexanone)... 

Several oxidative routes are available to change cyclohexane to cyclohexanone, cyclohexanol, and ultimately to adipic acid or caprolactam. If phenol is hydrogenated, cyclohexanone can be obtained directly this will react with hydroxylamine to give cyclohexanone oxime that converts to caprolactam on acid rearrangement. Cyclohexane can also be converted to adipic acid, then adiponitrile, which can be converted to hexamethylenedi-amine. Adipic acid and hexamethylenediamine are used to form nylon 6,6. This route to hexamethylenediamine is competitive with alternative routes through butene. 

Adipic Acid Nitric Acid oxidizes cyclohexanone-cyclohexanol mixtures (so-called KA oil) to adipic acid, nylon-6,6, other resins and plasticizers. 

Today the main route for cyclohexanone manufacturing is liquid-phase oxidation of cyclohexane. The synthesis involves the formation of cyclohexyl-hydroperoxide, further converted to cyclohexanone, cyclohexanol and byproducts, as illustrated by the following scheme ... 

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. 

All that remains is to make cyclohexanone by oxidation of cyclohexanol. 

As mentioned earlier, soluble salts of cobalt and manganese catalyze oxidation of cyclohexane by oxygen to cyclohexanol and cyclohexanone. Cyclohexanol and cyclohexanone are oxidized by nitric acid to give adipic acid. The oxidation by nitric acid is carried out in the presence of V5+ and Cu2+ ions. These reactions are shown by Eq. 8.8. Adipic acid is used in the manufacture of nylon 6,6. 

A type c catalytic membrane was developed and tested by Jacobs et al. [91]. It consisted of a polydimethylsiloxane polymer matrix loaded with 30 wt% of iron phthalocyanine-containing zeolite Y crystals (see Figure 33). The membrane (thickness 62 pm) is m between two liquid streams cyclohexane and 7 wt% t-butyl hydroperoxide in the membrane and the iron sites inside the zeolite catalyze the oxidation of cyclohexane towards cyclohexanol and cyclohexanone. The oxidation products are distributed over the two phases. 

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. 

Nylon 6, commonly known as Perlon, in which the repeating units always contain six carbon atoms, is obtained by the polymerization of caprolactam. The first stage, as with the manufacture of nylon 66, is the reduction of phenol to cyclohexanol, which is converted into cyclohexanone by oxidation. The latter reacts with hydroxylamine to form an oxime. 

Adipic acid is an important intermediate extensively used for the manufacture of nylon 66. It is currently produced from cyclohexane oxidation by a two steps process [1]. During the first step, oxidation of cyclohexane by air in the liquid phase forms cyclohexanol and cyclohexanone. Further oxidation of this mixture by nitric acid gives adipic acid. In addition to its cost, the use of nitric acid generates corrosion risks and requires recovery of the nitrogen oxides effluents. 

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). 

Oxidation of cyclohexane with cobalt(III) acetate in acetic acid under nitrogen at 343 K gives mainly cyclohexyl acetate, 2-acetoxycyclohexanone and cyclohexylidene diacetate and traces of cyclohexanone, cyclohexanol, and bicyclohexyl. In the presence of O2, adipic acid is the main product. Reactivities of cyclohexane and cyclohexane-tfi2 are equal within experimental error, and loss of a proton does not occur in the ratecontrolling step. The mechanism for this oxidation has been rationalized in terms of an initial electron transfer, in which the species are in equilibrium, followed by loss of a proton from the radical cation ... 

The activity of the catalysts for cyclohexane oxidation are shown in Table 3. Similar trends analogous to cyclohexanol oxidation is observed in this case also. It can be observed that the conversion for cyclohexane oxidation of Mo-MCM-41 is higher than that reported for TS-1 [16]. This is apparently because of the larger pore size of Mo-MCM-41 permitting a bulky molecule like cyclohexane into the pores in comparison to TS-1. Ulf Schuchardt et al. [16] have reported that the turn over numbers are in the range of 1-100 for cyclohexane oxidation on TS-1 under comparable experimental conditions. The selectivity ratio of cyclohexanol to cyclohexanone is around 1 for TS-1 [14] whereas it is of the order of 0.15 for Mo-MCM-41 and is of the order of 0.40 for the impregnated samples. It is seen that Mo-MCM-41 is more selective to the production of cyclohexanone. 

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. 

Inhibition of initiated cyclohexanol oxidation by Br" is peculiar. It starts a certain time after the addition of Br" and the rate of the inhibited oxidation does not depend on the Br" concentration. Cyclohexanone has no effect. Obviously, the inhibiting action is not due to Br" ions but to bromine oxides and bromoxygen acids. 

The oxidation mixture with about 5% cyclohexanone, cyclohexanol, and CHHP that is discharged from the last oxidation reactor is fed as such to the neutralization and decomposition section. In addition, an aqueous caustic solution and optionally a catalyst are fed to this section. In the resulting biphasic system, the CHHP is almost completely decomposed and the acids are neutralized. Subsequently, the biphasic system is separated into an aqueous slightly caustic waste stream and a cyclohexanol and cyclohexanone containing cyclohexane stream. The molar ratio between cyclohexanone and cyclohexanol, also called KA ratio, ranges from 0.3 to 0.8. 

Although air oxidation of the cyclohexanone-cyclohexanol mixtures on a Cu-Mn catalyst in acetic acid [140] is possible, the principal commercial operations entail oxidation with nitric acid. The reaction is usually carried out at 60 80°C and pressures of 0.1 to 0.4 MPa, employing 50-60% nitric acid and a copper-vanadium catalyst containing between 0.1 and 0.5% Cu and 0.1 and 0.2% V [141]. The yields of adipic acid are in the range of 90-96%. The main by-products are succinic acid and glutaric acid. Their concentration generally increases as the purity of the feed mixture decreases. The adipic acid is isolated by crystallization and purified by recrystallization from water. 

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