Liquid phase oxidation reactions

Typical examples of liquid-phase oxidation with molecular oxygen catalyzed by heteropoly compounds are listed in Table XXVI. Introduction of Vs + or 

PV2M010O40 has usually been used in the acid form. H5PV2M010O40 catalyzes aerobic oxidative cleavage of cycloalkanes, 1-phenylalkanes, and ketones. For example, the oxidation of 2,4-dimethyl cyclopentanone and 2-methylcyclo-hexanone gives 5-oxo-3-methylhexanoic acid and 6-oxoheptanoic acid, respectively, in yields higher than 90% [285, 286). Bromination of arenes with HBr [287), oxidative dehydrogenation of cyclohexadiene [288, 289) and a-terpinene [290), oxidation of 2,4-dimethylphenol [291) and sulfides [292) are other examples. 

Co2 +-Substitution at the addenda atoms gives catalysts for the epoxidation of olefins in the presence of aldehyde [293). PWM-Co is the most active among the mono-transition-metal-substituted polyanions the order of activity is PWn-Co -Mn 2= -Fe 2= -Cu -Ni. Here, PWll(M + )0(379 , ) (M = Co2 +, Cu2+, Fe3 +, Ni2 +, Mn2 + ) is denoted by PWn M. The same order was observed for the oxidation of isobutyraldehyde, suggesting that the oxidation of aldehyde to give peracid is an important step in the reaction. It has been reported that substitution of V5+ for Mo6+ in PMo O3 gives a good catalyst for epoxidation and the Baeyer-Villiger reaction [294). 

Styrene and 1-decene are selectively epoxidized, as shown in Table XXVII (293). The rates observed for PWM-Co are greater than those observed for Ni(dmp)2 and Fe(dmp)3, and the selectivities are comparable or higher for the former (295). It is also remarkable that PWn—Co polyanion exhibits a steric effect comparable to that of a moderately hindered TTMPP ligand in the 

TOSHIO OKUHARA, NORITAKA MIZUNO, AND MAKOTO MISONO 

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Liquid phase oxidation reaction of acetaldehyde with Mn acetate catalyst can be considered as pseudo first order irreversible reaction with respect to oxygen, and the reaction occurred in liquid film. The value of kinetic constant as follow k/ = 6.64.10 exp(-12709/RT), k2 = 244.17 exp(-1.8/RT) and Lj = 3.11.10 exp(-13639/RT) m. kmor. s. The conversion can be increased by increasing gas flow rate and temperature, however the effect of impeller rotation on the conversion is not significant. The highest conversion 32.5% was obtained at the rotation speed of 900 rpm, temperature 55 C, and gas flow rate 10" m. s. The selectivity of acetic acid was affected by impeller rotation speed, gas flow rate and temperature. The highest selectivity of acetic acid was 70.5% at 500 rpm rotation speed, temperature of 55 C... 

CoSalen Y carries oxygen as a cargo.72 The catalytic properties of the zeolite-encapsulated metal complexes depend mainly on the complexed metal atoms, which are used usually as oxidation catalysts but other applications are also beginning to emerge. The zeolite-encapsulated catalysts can be regarded as biomimetic oxidation catalysts.73 In liquid-phase oxidation reactions catalyzed... 

Including mixed systems among the research on the mechanism of liquid-phase oxidation reactions aids subsequent development of the chain theory and undoubtedly contributes to practical chemistry. 

The effect of the medium on the rates and routes of liquid-phase oxidation reactions was investigated. The rate constants for chain propagation and termination upon dilution of methyl ethyl ketone with a nonpolar solvent—benzene— were shown to be consistent with the Kirkwood equation relating the constants for bimolecular reactions with the dielectric constant of the medium. The effect of solvents capable of forming hydrogen bonds with peroxy radicals appears to be more complicated. The rate constants for chain propagation and termination in aqueous methyl ethyl ketone solutions appear to be lower because of the lower reactivity of solvated R02. .. HOH radicals than of free RO radicals. The routes of oxidation reactions are a function of the competition between two R02 reaction routes. In the presence of water the reaction selectivity markedly increases, and acetic acid becomes the only oxidation product. 

One of these catalysts prepared starting from N,N -ethylene-diaminoacetic acid proved particularly successful in typical liquid-phase oxidation reactions. 

Liquid-Phase Oxidation Reactions with Molecular Oxygen Catalyzed by Heteropoly Compounds Reaction Catalyst Temp. (K) Ref. 

Liquid-Phase Oxidation Reactions with tert-Butylhydroperoxide or Other Oxidants Catalyzed bv... 

The recent development of inorganic crystalline-supported metal catalysts for various liquid-phase oxidation reactions such as alcohol oxidation, epoxidation, Baeyer-Villiger oxidation and oxidation via C—H activation using molecular oxygen (02) or hydrogen peroxide (H202) as an oxidant are reviewed in this chapter. 

As shown for liquid-phase oxidation reactions of various organics with hydrogen peroxide and homogeneous and heterogeneous catalysts, they are conjugated with H202 dissociation, in the absence of which they either cannot or can hardly be implemented. 

The most straightforward immobilization method for catalytically active redox elements for liquid phase oxidation reactions consists of isomorphic substitution. Well-known systems with very peculiar properties that will not be treated in further detail are ... 

Since the application of POMs is so widespread across areas such as homogeneous and heterogeneous catalysis, as well as acid and redox catalysis, it is not possible to exhaustively review all the applications. Thus the rest of this chapter focuses only on the catalytic properties of the polyoxometallates in heterogeneous gas- or liquid-phase oxidation reactions, and reviews the most recent progress in the knowledge of their properties and working process, underlining both their potential and their limitations. 

Copper-containing molecular sieve materials are very important catalysts in many liquid-phase oxidation reactions. The analysis of metal content is usually obtained using atomic absorption spectroscopy (AAS) but this provides no information on the distribution of the metal within the material. In this paper, we report on the characterisation of a siliceous MCM 41 material postmodified with a Schiff base copper complex by x-ray photoelectron spectroscopy (XPS), AAS and other standard techniques. Quantitative estimations of the copper concentrations and chemical states and its distribution within the material have been made using XPS. The effect of modification by the Schiflf base copper complex on the surface characteristics of the MCM 41 was investigated by nitrogen sorption at 77 K. 

Ti, V and Sn-modified mesoporous silicates were reported to be active in a number of liquid phase oxidation reactions. Ti-containing samples were used for the selective oxidation of large organic molecules in the presence of te/t-butyl hydroperoxide (TBHP) or dilute H2O2 [71,136,137,139-141,147,186,237]. Typical data shown in Table 5 indicate that both Ti-MCM-41 and Ti-HMS are efficient cat ysts for the epoxidation of bulky olefins such as a-terpineol and norbomene in the presence of TBHP or H2O2. Comparison with H-B indicates that the accessibility of active sites plays a critical role in the liquid phase oxidation of organic molecules. Mesoporous titanosilicates also exhibited remarkable activity in the hydroxylation of 2,6-di-rerr-butyl phenol (2,6 DTBP) [142,147] and the oxidation of cyclododecanol [147], naphthol [147] aniline [237] and chloroaniline [186]. However, they were disappointingly poor catalysts for the liquid phase oxidation of n-hexane and aliphatic primary amines, as well as the ammoximation of cyclohexanone [147,238]. 

M. J. Haanepen, J. H. C. Van Hooff, VAPO as catalyst for liquid phase oxidation reactions. Part I preparation, characterization and catalytic performance, Appl. Catal. A 152 (1997) 183. 

In recent years, the unexpected observation of highly active Au as a low temperature CO oxidation catalyst59,60 has initiated extensive research activity into the use of supported gold for liquid phase oxidation reactions. In general, the adsorption characteristics and catalytic properties of Au depend crucially on particle size, which can be controlled by the preparation method and the support.61-66 The crucial question involving gold catalysis, which as yet has not been fully answered, is the concept of why Au nanoparticles exhibit such radically different behaviour than bulk Au.67-70... 

Since 1980, the applications zeolites and molecular sieves in the speciality and fine chemicals increased enormously. Zeolites are being used in the various types of reactions like cyclization, amination, rearrangement, alkylation, acylations, ammoxidation, vapour and liquid phase oxidation reactions. Zeolites and molecular sieves have also been used to encapsulate catalytically active co-ordination complexes like ship-in-bottle and as a support for photocatalytic materials and chiral ligands. Redox molecular sieves have been developed as an important class of liquid and vapour phase oxidation and ammoxidation reactions. We have discussed few typical recent examples of various types of reactions. 

Most liquid-phase oxidation reactions were performed in water, sometimes on highly concentrated solutions, e. g. for glucose up to 1.7 mol L [61]. For water-insoluble alcohols, organic solvent could, in principle, be used, but most should be strictly avoided for safety reasons. Acetic acid was, however, used as solvent for the oxidation of retinol (3,7 dimethyl-9-(2,6,6-trimethyl-l-cyclohexe-nyl)-2,4,6,8-nonatetraen-l-ol) to retinal [84], Oxidation of water-insoluble molecules can be performed in the presence of surfactants [50]. 

In optimal conditions, Pd-Te-C catalyst shows 27.0 mol/h/g-atom Pd and 89% l,4-diacetoxy-2-butene selectivity [15]. This method was the first practical application of a liquid phase oxidation reaction with a heterogeneous catalyst. 

The phenomenon of selective inhibition of chain reactions was for the first time explained by N.M. Emanuel, E.A. Bliunberg, L.A. Tavadyan and S.A. Maslov [11]. It was experimentally observed in a mnnber of liquid-phase oxidation reactions. Thus, introducing small amoimts of an additive stable nitroxyl radical (4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl, TEMPOL) and a heterogeneous inhibitor (WSc2) makes it possible to increase the selectivity of formation of imsaturated acids and epoxides in chain oxidation reactions of a-methylacrolein, 2-ethylhexenal, as well as co-oxidation of aldehydes and olefins (Table 5.1). 

Zhabotinsky, A. M. 1964b. Periodic Liquid-Phase Oxidation Reactions, Dokl. Akad. Nauk SSSR 157, 392-395. 

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