Liquid-phase catalytic oxidations

The Acetaldehyde Oxidation Process. Liquid-phase catalytic oxidation of acetaldehyde (qv) can be directed by appropriate catalysts, such as transition metal salts of cobalt or manganese, to produce anhydride (26). Either ethyl acetate or acetic acid may be used as reaction solvent. The reaction proceeds according to the sequence... 

Liquid-Phase Oxidation. Liquid-phase catalytic oxidation of / -butane is a minor production route for acetic acid manufacture. Formic acid (qv) also is produced commercially by Hquid-phase oxidation of / -butane (18) (see HYDROCARBON OXIDATION). 

Noncatalytic oxidation to produce acetic acid can be carried out in the gas phase (350-400°C, 5-10 atm) or in the liquid phase (150-200°C). Liquid-phase catalytic oxidations are operated under similar mild conditions. Conditions for the oxidation of naphtha are usually more severe than those for n-butane, and the process gives more complex product mixtures.865-869 Cobalt and other transition-metal salts (Mn, Ni, Cr) are used as catalysts, although cobalt acetate is preferred. In the oxidation carried out in acetic acid solution at almost total conversion, carbon oxides, carboxylic acids and esters, and carbonyl compounds are the major byproducts. Acetic acid is produced in moderate yields (40-60%) and the economy of the process depends largely on the sale of the byproducts (propionic acid, 2-butanone). 

The reactivity of the hydrocarbons increases in the order ortho < meta < para in the liquid-phase catalytic oxidation of methyl derivatives of biphenyl into acids by air. The mechanism of the oxidation of hydroxymethylbiphenyls and hydroxymethyl-benzenes involves the formation of an unstable cation radical, which is then stabilized by emitting a proton, giving hydroxybenzyl radical.243... 

Commercial production of acetic acid has been revolutionized in the decade 1978—1988. Butane—naphtha liquid-phase catalytic oxidation has declined precipitously as methanol [67-56-1] or methyl acetate [79-20-9] carbonylation has become the technology of choice in the wodd market. By-product acetic acid recovery in other hydrocarbon oxidations, eg, in xylene oxidation to terephthalic acid and propylene conversion to acrylic acid, has also grown. Production trom synthesis gas is increasing and the development of alternative raw materials is under serious consideration following widespread dislocations in the cost of raw material (see Chemurgy). 

Co saturated hydrocarbons are used extensively in the United States, whereas the acetylene process was used almost exclusively in Europe until recently. These processes were extended by the late 1950 s and early 1960 s by a new approach called the Wacker process or the Wacker-Hoechst process, consisting of the liquid phase catalytic oxidation of ethylene to acetaldehyde, as outlined in Table II. 

Most of these liquid phase catalytic oxidations have been used for the selective oxidation of carbohydrates. In the oxidation of a sugar such as glucose, four basic types of selective oxidation are possible. ... 

Liquid-phase catalytic oxidations can be classified according to the predominant reaction mechanism (i) free-radicals with O2 usually being the oxidizing agent,... 

J.-M. Bregeault, Transition-metal complexes for liquid-phase catalytic oxidation Some aspects of Industrial reactions and of emerging technologies, Dolton Trans. (2003) 3289. 

Liquid phase catalytic oxidation of ethylbenzene with hydrogen peroxide over TS-1 molecular sieves is most appropriate for the production of 1-phenylethanol with high selectivity (up to 93 % of all the oxidation products in methanol) under the reaction conditions studied here. An additional increase of the 1-phenylethanol selectivity could be achieved with smaller amounts of the catalyst. The highest conversion to acetophenone is found over TS-2 zeolites but further oxidation easily takes place in this case. 

Besides the extreme complexity of the mixture resulting from the vapor phase catalytic oxidation of various petroleum fractions, there are numerous other difficulties which act as hindrances to the commercial utilization of the products. This is especially true for the utilization of tlie acids that are formed. The acids are of the aldehydic or aldehydic-hydroxy type and are present in a mixture containing aldehydes of variops molecular weights as well as unsaturated compounds. These compounds give a peculiar, objectionable odor to the acids and a brown or yellow color which is only intensified by polymerization and resinification when the acids are saponified with hot caustic solutions. The same difficulties have been encountered in the rather extensive researches being carried out, particularly in Germany, on the liquid phase, catalytic oxidation of hydrocarbon oils to fonn fatty acids. 

Langhendries et al [5.74] analyzed the liquid phase catalytic oxidation of cyclohexane in a PBMR, using a simple tank-in-series approximate model for the PBMR. In their -reactor the liquid hydrocarbon was fed in the tubeside, where a packed bed of a zeolite supported iron-pthalocyanine catalysts was placed. The oxidant (aqueous butyl-hydroperoxide) was fed in the shellside from were it was extracted continuously to the tubeside by a microporous membrane. The simulation results show that the PBMR is more efficient than a co-feed PBR in terms of conversion but only at low space times (shorter reactors). A significant enhancement of the organic peroxide efficiency, defined as the amount of oxidant used for the conversion of cyclohexane to the total oxidant converted, was also observed for the PBMR. It was explained to be the result of the controlled addition of the peroxide, which gives low and nearly uniform concentration along the reactor length. 

The liquid phase catalytic oxidation of acrolein and methacrolein has been the subject of various investigations [35—38]. Considering the natural tendency of reactants and products to become polymerized as well as the sensitivity of chain oxidations to inhibitors, it is not surprising that the findings of the different investigations are sometimes rather conflicting. Nevertheless, the primary oxidation products are exactly analogous to those of saturated aldehyde oxidation. Only the acid yields are affected, mainly as the result of the lack of acid stability. The overall scheme for the oxidation of acrolein can be written as... 

Benzylic Reactivity. 2,5-Dimethyl-3,4-dinitrothiophen has been condensed with aromatic aldehydes to give 3,4-dinitro-2,5-distyryl-thiophens. " An improved synthesis of 3-nitro-2-styryl-thiophens involves bromination of 3-methyl-2-nitrothiophen with A-bromosuccinimide, followed by a modified Wit-tig reaction. From 2,5-di(chloromethyl)thiophen, the phosphonate was prepared by the Arbusov reaction, which was used for the preparation of 2,5-distyryl-thiophens. Trichloromethyl(thienyl)carbinols have been converted into the corresponding fluoro-derivatives through the reaction with phenyl-tetrafluorophosphorane. The liquid-phase catalytic oxidation of phenyl-(2-thienyl)methane in acetic acid in the presence of cobalt(ll) acetate and sodium bromide has been investigated. ... 

Peroxides of transition metals are themselves active intermediates in heterolytic and homolytic liquid-phase catalytic oxidation reactions of alkenes, aromatic hydrocarbons and alkanes. Heterolytic oxidations are characterized by a requirement for a free coordination volume near the transition metal atom. Homolytic oxidations proceed via M-O bond cleavage in peroxo complexes. 

Homogeneous (liquid phase) catalytic oxidations with dioxygen, hydrogen peroxide and other peroxidic reagents constitute an important area of organic synthesis on both laboratory and industrial scale. When dioxygen is employed as terminal oxidant (i.e. the oxidant which appears in the overall stoichiometric equation of the reaction), of special interest is the way in which 0 enters the catalytic cycle,... 

Liquid-Phase Catalytic Oxidations with Perovskites and Related Mixed Oxides... 

Kishore, D. and Rodrigues, A. (2008). Liquid Phase Catalytic Oxidation of Isophorone with terf.-butylhydroperoxide over Cu/Co/Fe-MgAl Ternary Hydrotalcites, Appl. Catal. A Gen., 345, pp. 104-111. 

Neumaim, R. (2010). Activation of Molecular Oxygen, Polyoxometalates, and Liquid-Phase Catalytic Oxidation, Inorg. Chem., 49, pp. 3594—3601. 

Bregeault, J. (2003). Transition-Metal Complexes for Liquid-Phase Catalytic Oxidation Some Aspects of Industrial Reactions and of Emerging Technologies, Dalton T, 17, pp. 3289-3302. 

Raghavendrachar, R, Ramachandran, S., 1992. Liquid-phase catalytic oxidation of p-xylene. Industrial Engineering Chemistry Research 31. 

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