Oxidation of Cyclohexane to Adipic Acid

Since 2009, the process has been under evaluation at pilot scale for further commercial application by Daicel in Aboshi (Japan). 

The Ministry of Education, Culture, Sports, Science and Technology of Japan in 2003 awarded The Third Green and Sustainable Chemistry Award to Prof Ishii and the Daicel Chemical Company for their relevant efforts to the development of NHPI-based industrial processes with low environmental impact. 

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Other processes explored, but not commercialized, include the direct nitric acid oxidation of cyclohexane to adipic acid (140—143), carbonylation of 1,4-butanediol [110-63-4] (144), and oxidation of cyclohexane with ozone [10028-15-5] (145—148) or hydrogen peroxide [7722-84-1] (149—150). Production of adipic acid as a by-product of biological reactions has been explored in recent years (151—156). 

A mixture of succinic (15—25 wt %), glutaric (45—55 wt %), and adipic acid (25—35 wt %) is obtained as a by-product in the oxidation of cyclohexane to adipic acid. In 1993, the production of adipic acid by this process was in the range of two million metric tons, which corresponds to a production of about 100,000 metric tons of the mixture of the three acids. 

The liquid-phase oxidation of butane is utilized in the commercial synthesis of acetic acid (see Section 9.5.1). Despite research efforts, however, there is no commercially viable route to the direct one-step oxidation of cyclohexane to adipic acid. 

This reactor is typical of those used in a range of processes involving the direct oxidation of hydrocarbons with air or oxygen. Another example is the oxidation of cyclohexane to adipic acid which... 

Similarly, cyclohexane is readily oxidized by cobalt(III) acetate in acetic acid at moderate temperatures.29Sa d In the absence of oxygen at 80°C the main products were 2-acetoxycyclohexanone and cyclohexyl acetate. Cyclohexane was about half as reactive as toluene under these conditions. Oxidation with Co(III) acetate in the presence of oxygen gave adipic acid as the main product. This reaction has been developed into a process for the single-stage oxidation of cyclohexane to adipic acid.296,297 Selectivities of approximately 75% have been claimed at roughly 80% cyclohexane conversion. 

Liquid-phase oxidation of cyclohexane to adipic acid catalysed hy cobalt containing p-zeolites... 

The aim of the present work is to investigate and compare the cyclohexane oxidation activities of cobalt exchanged zeolites prepared by conventional impregnation or solid-state ion-exchange methods and cobalt substituted zeolites, in order to gain insight into the type of catalysis involved. Herein, the results obtained for oxidation of cyclohexane to adipic acid catalysed by cobalt exchanged zeolites (Co/BEA) and cobalt substituted P-zeolites (Co-BEA) are presented. 

Ishii and Daicel Chemical Company also patented a method for the direct aerobic oxidation of cyclohexane to adipic acid by using NHPI in combination with small amounts of Mn(acac)2 and Co(OAc)2 as cocatalysts (Scheme 16.6) [9]. 

Single-step oxidation of cyclohexane to adipic acid (process 5, Figure 2.12) has been demonstrated [142]. This process involves a liquid-phase air oxidation using acetic acid as a reaction medium and cobalt acetate as an oxidation catalyst. The reaction temperatures are in the range of 70 90°C. At residence times of 6 10 h, conversions to about 80% were obtained with selectivities to adipic acid of 70-75%. Several alternate processes have been described for the oxidation of cyclohexane to form adipic acid [143 148]. 

Various metal ions and complexes have been used to promote the catalytic air oxidation of hydrocarbons. There are some classical reactions that have developed into commercial processes, like the oxidation of n-butane to acetic acid, the oxidation of cyclohexane to adipic acid, or of p-xylene to terephthalic acid, all of which utilize cobalt salts as catalysts. 

The chromic acid oxidation of cyclohexanone to adipic acid via 2-hydroxy-cyclohexanone and cyclohexane-l,2-dione is third order , viz. 

Oxidation of Cyclohexane. The synthesis of cyclohexanol and cyclohexanone is the first step in the transformation of cyclohexane to adipic acid, an important compound in the manufacture of fibers and plastics. Cyclohexane is oxidized industrially by air in the liquid phase to a mixture of cyclohexanol and cyclohexanone.866 872-877 Cobalt salts (naphthenate, oleate, stearate) produce mainly cyclohexanone at about 100°C and 10 atm. The conversion is limited to about 10% to avoid further oxidation by controlling the oxygen content of the reaction mixture. Combined yields of cyclohexanol and cyclohexanone are about 60-70%. 

Air oxidation of /i-butane to maleic anhydride is possible over vanadium phos(4tate and, remaiicably, a 60% selectivity is obtained at 85% conversion. In the gas phase oxidation, in conffast to the situation found in the liquid, n-allcanes are oxidized more rapidly than branched chain alkanes. This is because secondary radicals are more readily able to sustain a chain for branched alkanes the relatively stable tertiary radical is preferentially formed but fails to continue the chain process. Vanadium(V)/ manganese(II)/AcOH has been used as a catalyst for the autoxidation of cyclohexane to adipic acid, giving 25-30% yields after only 4 h. ... 

We have found that the widely used TS-1 oxidation catalyst is distinctly inferior to Mn -framework-substituted microporous AlPOs (AlPO-5) which have been described [10, 11], along with similar M-AlPOs (M = Co ", Mn ", Fe "), in relation to its high performance in the one-step conversion of cyclohexane to adipic acid [9]. 

Cobalt exchanged (3-zeolites obtained by impregnation and solid state ion exchange and cobalt substituted (3-zeolites obtained by incorporation of cobalt in the synthesis gel were studied towards the oxidation of cyclohexane into adipic acid. The Co-substituted P-zeolites were found to be effective catalysts for the oxidation of cyclohexane in acetic acid. In contrast, the use of Co-exchanged p-zeolites always led to inhibition of the oxidation. It was demonstrated that the catalytic activity came as a result of the dissolved cobalt in the reaction medium, while inhibition was ascribed to the accessible uncompensated aluminic sites of the zeolites. 

The Co-exchanged zeolites were not effective catalysts for the oxidation of cyclohexane. The cobalt exchanged ions were not stabilized enough by the zeolite interactions and part of these cations were released in the oxidation medium. Thus, we decided to explore the activity of P-zeolites in which cobalt ions were incorporated into the framework. We hoped that the incorporation would increase the stability of the cation within the solid. We studied the catalytic activities of cobalt substituted P-zeolites containing aluminium (Co-Al-BEA) and boron (Co-B-BEA) towards the oxidation of cyclohexane into adipic acid. 

The nature of the acidity was investigated in order to explain the catalytic activity of the calcined Co-substituted P-zeolite and the role played by the aluminic sites of this solid. A pyridine adsorption followed by IR spectroscopy measurements was performed on the calcined catalyst. It has been shown that adsorption of pyridine emphasized two distinct bands at 1548 cm and 1451 cm corresponding respectively to the adsorption on Brbnsted and Lewis sites [22], In the case of the calcined Co-substituted zeolite, only a weak band at 1548 cm appeared in the IR spectrum. Thus, we deduced that very few Bronsted sites were present in the catalyst. This could explain that the oxidation of cyclohexane into adipic acid in the presence of calcined Co-substituted aluminic P-zeolite was not inhibited. 

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. 

Homogeneous Oxidation Catalysts. Cobalt(II) carboxylates, such as the oleate, acetate, and naphthenate, are used in the Hquid-phase oxidations of -xylene to terephthaUc acid, cyclohexane to adipic acid, acetaldehyde (qv) to acetic acid, and cumene (qv) to cumene hydroperoxide. These reactions each involve a free-radical mechanism that for the cyclohexane oxidation can be written as... 

The molecule has been found to be an efficient electron carrier in electrochemical oxidation, converting secondary alcohols to ketones. Daicel of Tokyo has used NHPI in the development of custom production in proprietary air-oxidation technology , and it can also be used to oxidize cyclohexane to adipic acid and p-xylene to p-toluic acid in the presence of Mn + or Co + salts. The new process produces no nitrogen oxides, is more environmentally friendly and does not require the use of denitration equipment. 

Adipic acid is a most important petrochemical product which is mostly used for the synthesis of nylon 6.6 from its condensation with hexamethylenediamine. Cyclohexane is transformed to adipic acid in two steps (a) oxidation of cyclohexane to a cyclohexanol-cyclohexanone mixture (ol-one) via the formation of cyclohexyl hydroperoxide followed by (b) oxidation of the ol-one mixture to adipic acid by nitric acid (equation 239). 

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],... 

The oxidation of cyclohexane to cyclohexanone and cyclohexanol is an important industrial procedure used in the synthesis of adipic acid. Srinivas and Mukhopadhyay (1994) reported the oxidation of cyclohexane in sc C02, yielding cyclohexanone and cyclohexanol as the major reaction products. At the high temperatures employed in this study (>137°C), cyclohexyl hydroperoxide (c-C6HnOOH), which is produced by the mechanism outlined in Scheme 4.11, decomposes to cyclohexanone and cyclohexanol. 

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