Cyclohexane cobalt catalysts

A one-step LPO of cyclohexane directly to adipic acid (qv) has received a lot of attention (233—238) but has not been implemented on a large scale. The various versions of this process use a high concentration cobalt catalyst in acetic acid solvent and a promoter (acetaldehyde, methyl ethyl ketone, water). 

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 trianionic cobalt catalyst has been successfully employed in the hydrogenation of 1,3-butadiene in [bmim][BF4] [10], The product from this reaction is 1-butene which is formed with 100% selectivity. Unfortunately the catalyst undergoes a transformation to an inactive species during the course of the reaction and reuse is not possible. The cationic rhodium catalyst together with related derivatives have been used for numerous reductions, including the hydrogenation of 1,3-cyclohexadiene to cyclohexane in [bmim][SbF6] [11],... 

The cobalt-catalyzed oxidation of cyclohexane takes place through cyclohexyl hydroperoxide with the cobalt catalyst acting primarily in the decomposition of the hydroperoxide to yield the products 870 877... 

Cyclohexane, the six-carbon ring hydrocarbon with the molecular formula C6H12, is the most significant of the cyclic alkanes. Under ambient conditions it is a clear, volatile, highly flammable liquid. It is manufactured by the hydrogenation of benzene and is used primarily as a raw material for the synthesis of cyclohexanol and cyclohexanone through a liquid-phase oxidation with air in the presence of a dissolved cobalt catalyst. 

The synthesis of cyclohexanone, which is an intermediate in the manufacture of nylon 6 and nylon 6,6 is an important industrial process [1], One of the major current routes for the synthesis of cyclohexanone is the liquid-phase autoxidation of cyclohexane at 125-160 °C and 10 bar followed by the selective decomposition of the intermediate cyclohexyl hydroperoxide, using a soluble cobalt catalyst, to a mixture of cyclohexanol and cyclohexanone [2]. These severe conditions are necessary due to the low reactivity of cyclohexane towards autoxidation. Due to the high reactivity of the products in the autoxidation step conversions must be kept low (<10%) [3,4]. Heterogeneous catalysts potentially offer several advantages over their homogeneous counterparts, for example, ease of recovery and recycling and enhanced stability. Recently we found that chromium substituted aluminophosphate-5 and chromium substituted silicalite-1 (CrS-1) are active, selective and recyclable catalysts for the decomposition of cyclohexyl hydroperoxide to cyclohexanone [5j. 

Commercially, cyclohexane is oxidized to a mixture of cyclohexyl hydroperoxide, cyclohexanol, and cyclohexanone at 3.5-19 X 10 kP and 400-450 K using a cobalt(II) naphthanate catalyst. The hydroperoxide in this mixture is then decomposed to cyclohexanol and cyclohexanone with a second cobalt catalyst. Adipic acid, the desired end-product of cyclohexane oxidation, is produced by oxidation of the mixture of cyclohexanol and cyclohexanone with 40% HNO3 containing 0.2% of a catalyst consisting of ammonium metavanadate and copper turnings. 

The commercial process for the production of nylon 6 starts with the oxidation of cyclohexane with oxygen at 160°C to a mixture of cyclohexanol and cyclohexanone with a cobalt(II) catalyst. The reaction is taken to only 4% conversion to obtain 85% selectivity. Barton and co-workers have called this the least efficient major industrial chemical process.240 They have oxidized cyclohexane to the same products using tort bu(ylhydroperoxide with an iron(III) catalyst under air (70°C for 24 h) with 89% efficiency based on the hydroperoxide. The oxidation of cyclohexanol to cyclohexanone was carried out in the same way with 99% efficiency. A cobalt catalyst in MCM-41 zeolite gave 38% conversion with 95% selectivity in 4 days at 70 C.241 These produce ferf-butyl alcohol as a coproduct. It can be dehydrated to isobutene, which can be hydro-... 

A new process for synthesis of 3-aminomethyl-3,5,5-trimethylcyclohexylamine (IPDA) has been investigated. The reaction was performed in two steps. In the first step bis (3-cyano-3,5,5 trimethylcyclohexylidene) azine (IPNA) was synthesized from 3-cyano-3,5,5 trimethyl- 1 oxo cyclohexane (IPN) and hydrazine hydrate in solvent. The reaction yield was nearly quantitative. In the second step the azine (IPNA) was hydrogenated under mild conditions on a Raney nickel or cobalt catalyst in the presence of a small amount of ammonia. Isophorone diamine (IPDA) was obtained at high yields (90-95 %). But the main interest of a such process is to minimize the production of byproducts (aminoalcohol, azabicyclic compound, secondary amine) and to use less severe pressure conditions than those generally employed. 

The phenol process based on the oxidation of cyclohexane has been operated for a short time by Monsanto in Australia and is of less importance. In this process, a mixture of cyclohexanone and cyclohexanol is dehydrogenated to phenol at 400 °C, using platinum/activated carbon or nickel/cobalt catalysts. The degree of conversion can reach 90 5%. The crude phenol is refined by distillation. A particular disadvantage of this process lies in the difficulty in refining the crude oxidation mixture from cyclohexane oxidation. 

Functionalization of alkanes under mild conditions catalyzed by coordination complexes is known. For example, much of the cyclohexanol and cyclohexanone used in the synthesis of adipic acid is produced by the oxidation of cyclohexane with a cobalt catalyst. Chapter 18, however, focuses on the t) pes of alkane functionalization that occur by the reactions described... 

One of the routes was the low temperature decomposition of CHHP with the addition of cobalt to the oxidation mixture. The problem of fast deactivation of the cobalt catalyst could partly be solved by introducing a water wash to remove the dibasic acids that were responsible for the fast precipitation of the cobalt catalyst. Nevertheless, even after adding the cohalt catalyst to later stages of the decomposition section, a fraction of the CHHP still remained unconverted. The selectivity losses were caused by radicals obtained from the cobalt-catalysed decomposition of CHHP, which not only reacted with the available cyclohexane, but also with the desired reaction products cyclohexanone and cyclohexanol. Such one-phase decomposition has recently been industrially implemented. 

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