Oxidation cyclohexane product distribution

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],... 

In connection with the research on destructive hydrogenation at the Institute of High Pressures, Maslyanskii (224) passed benzene at 475° under 200 atm. hydrogen over molybdenum oxide (1 mole CeH6 16 moles Ha) to produce 58% methylcyclopentane, 14% cyclohexane, 8% 2-methyl-pentane, 5% n-hexane, and 8% unreacted. Over molybdenum sulfide the product distribution was similar. The preparation of these catalysts was described by him in 1940 (223). Isomerization and other conversions accompanying destructive hydrogenation were also pointed out by Prokopets and by others (257,311,314). 

Catalytic reactions were performed in CH2C12 under an 02 atmosphere Zn was used as an electron source and acetic acid as a proton donor (14). Under these reaction conditions ([2] [substrate] = 1 125), the production of adamantan-l-ol (248%), adamantan-2-ol (50%), and adamantan-2-one (108%) was observed. With cyclohexene as substrate, a mixture of cyclohexanol (54%), cyclohexanone (73%), and cyclohexene oxide (20%) was generated. In a similar experiment with cyclohexane, cyclohexanol (99%), and cyclohexanone (84%) were obtained. The product distribution is inconsistent with a free radical process for ada-mantane, the 3°/2° carbon reactivity ratio is 2.2. Control experiments demonstrated that both Zn dust and acetic acid were necessary, whereas larger quantities of acetic acid quenched the reaction (Table II). This may be due to the acidolysis of the n-oxo bond. Simple monomeric complexes such as FeClTPP (TPP is tetraphenylporphin), Fe(acac)3 (acac is acetylacetonate), and [Fe(HBpz3)2]+, 3, were inactive as catalysts under identical conditions. Furthermore, [Fe3+(Salen)]20, 1, did not show any reactivity. 

The oxidized dimer, [Fe2(TPA)20(0Ac)]3+, 41, was shown to be an efficient catalyst for cyclohexane oxidation using tert-BuOOH as a source of oxygen (69). This catalyst reacts in CH3CN to yield cyclohexanol (9 equiv), cyclohexanone (11 equiv), and (tert-butylperoxy)cyclohexane (16 equiv) in 0.25 h at ambient temperatures and pressures under an inert atmosphere. The catalyst is not degraded during the catalytic reaction as determined by spectroscopic measurements and the fact that it can maintain its turnover efficiency with subsequent additions of oxidant. Solvent effects on product distribution were significant benzo-nitrile favored the hydroxylated products at the expense of (tert-butyl-peroxy)cyclohexane, whereas pyridine had the opposite effect. Addition of the two-electron oxidant trap, dimethyl sulfide, to the catalytic system completely suppressed the formation of cyclohexanol and cyclohexanone, but had no effect on the production of (tert-butylper-oxy)cyclohexane. These and other studies suggested that cyclohexanol and cyclohexanone must arise from an oxidant different from that responsible for the formation of (tert-butylperoxy)cyclohexane. Thus, two modes of tert-BuOOH decomposition were postulated a heterolytic... 

In a base-free medium (dry MeCN), Fe Ch activates HOOH to form a reactive intermediate that oxygenates alkanes, alkenes, and thioethers, and dehydrogenates alcohols and aldehydes. Table 11 summarizes the conversion efficiencies and product distributions for a series of alkene substrates subjected to the Fe Cfi/HOOH/MeCN system. The extent of the Fe Cb-induced monooxygenations is enhanced by higher reaction temperatures and increased concentrations of the reactants (substrate, Fe Cls, and HOOH). For 1-hexene (representative of all of the alkenes), a substantial fraction of the product is the dimer of 1-hexene oxide, a disubstituted dioxane. With other organic substrates (RH), Fe Cb activates HOOH for their monooxygenation the reaction efficiencies and product distributions are summarized in Tables 11(b). In the case of alcohols, ethers, and cyclohexane, a snbstantial fraction of the product is the alkyl chloride, and with aldehydes, for example, PhCHO, the acid chloride represents one-half of the product. In the absence of snbstrate the Fe Cls/MeCN system catalyzes the rapid disproportionation of HOOH to O2 and H2O. 

Photosensitized oxygenation of the enolic forms of cyclohexane-1,2-diones in methanol gives 5-oxoalkanoic acids and methyl 5-carboxy-1-hydroxypentanoates with evolution of CO. The product distribution shows a marked temperature dependence which suggests that endoperoxides (16) and (17), present as unstable intermediates, are trapped by the solvent. a-Oxocarboxylic esters undergo direct photo-oxidation in polar and non-polar... 

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. 

Table 1 shows some representative results for cyclohexane oxidation with t-BHP over calcined Ti-UTD-l(Co) and Ti-UTD-1 (acid treated to remove cobalt [4]). In acetone the cyclohexane is converted to cyclohexanone as the major product with trace amounts of adipic acid as well as the other carboxylic acids and diketones in Scheme 1. Changing the solvent from acetone to t-butanol improves the conversion and the yield of adipic acid, however, the peroxide efficiency decreases. Increasing the amount of peroxide in the system also n proves conversion but the peroxide efficiency is decreased. The product distribution observed with the Ti-UTD-l(Co) sanqjles suggets a homolytic process catalyzed by cobalt. Removal of the cobalt lowers the activity in t-butanol but improves the peroxide efficiency. 

We are advancing in the study of the photocatalytic oxidation of hydrocarbons using the TiOz/metal porphyrin hybrid catalyst and, herein, we report on the importance of surface tayloring of the TIO2 catalyst in order to improve the yields in cyclohexane oxidation. Results of the photo-oxidation of n-heptane and methylcyclohexane are also reported. In this case, the distribution of the photo-oxidation products provides some insight in how the regioselectivity is affected by the surface modification. 

Product distributions resulting from the OH radical induced oxidation of the following hydrocarbons have been determined 2-methyl-propane, 2,3-dimethyl-butane, 2-methyl-butane, n-pentane, cyclohexane, methySubstituted 1-butenes, isoprene, toluene. Whenever possible, branching ratios for the self-reactions of alkylperoxy radicals and decomposition rate coefficients for alkoxyl radicals were derived. 

The catalytic system consisting of PhIO and various iron porphyrins hydroxylates unactivated alkanes under ambient conditions [83,88]. The substrates studied were cyclohexane, cycloheptane, adamantane, cis-decahydronaphthalene and norcarane, and the catalysts - Fe(TPP)Cl, Fe(TTP)Cl, Fe(TNP)Cl and Fe(TMP)Cl. Monohydroxylated products predominated in all cases, with maximum yields of 30-39 % based on PhIO. High selectivity for tertiary centers (adamantane), retention of configuration at carbon (cis-decaline), and a large kinetic isotope effect (12.9) have ben observed. The free radical trap bromotrichloromethane changes the product distribution, pointing to a radical mechanism. The mechanism (Scheme 4) is essentially the same as that proposed previously for alkane oxidation by cytochrome P-450 [89]. 

Mansuy et al. employed alkyl peroxides and iodosylbenzene as oxygen donors and examined the oxidation products of cyclohexane in the presence of a series of M(TPP) complexes (M=Fe, Mn, Co, Rh, and Cr) [284]. As listed in Table 10, cyclohexanol and cyclohexanone are the major products however, the ratio of the alcohol and ketone was dependent on the oxidant employed. For the oxidation by peroxides, involvement of alkoxy radical (RO ) due to the homolytic 0-0 bond cleavage of R-OO-M was proposed. In order to trap possibly formed radical intermediates. He and Bruice examined the oxidation of cw-stilbene and (Z)-l,2-bis(fran5-2,tran5-3-diphenylcyclopropyl)ethane by iron porphyrin/f-BuOOH system [285]. In separate experiments, AIBN was used as a radical chain initiator for the oxidation of the alkenes by t-BuOOH. According to the product distribution, they concluded the products to be derived from initial combination of t-BuOO, rather than 0=Fe (por)", with olefin. 

We have demonstrated recently that epoxidation and hydroxyl-ation can be achieved with simple iron-porphine catalysts with iodosylbenzene as the oxidant (24). Cyclohexene can be oxidized with iodosylbenzene in the presence of catalytic amounts of Fe(III)TPP-Cl to give cyclohexene oxide and cyclohexenol in 55% and 15% yields, respectively. Likewise, cyclohexane is converted to cyclohexanol under these conditions. Significantly, the alcohols were not oxidized rapidly to ketones under these conditions, a selectivity shared with the enzymic hydroxylations. The distribution of products observed here, particularly the preponderance of epoxide and the lack of ketones, is distinctly different from that observed in an autoxidation reaction or in typical reactions of reagents such as chromates or permanganates (15). 

Photochemical reactions of materials enclosed in zeolites can lead to different proportions of products, or in some cases, to different products than those run in solutions.207 The distribution can vary with the zeolite. The enhanced selectivity in the oxidation of hydrocarbons with oxygen208 was mentioned in Chap. 4. The oxidation of cyclohexane in NaY zeolite with oxygen and visible light to yield cyclohexane hydroperoxide with complete selectivity at more than 40% conversion may have considerable industrial potential. Heating the hydroperoxide yields only cyclohexanone which can be oxidized to adipic acid for use in making nylon 6,6.209... 

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