Liquid-phase oxidation of secondary

Promotion and Deactivation of Platinum Catalysts in Liquid-Phase Oxidation of Secondary Alcohols... 

CrAPO-5-CATALYZED LIQUID PHASE OXIDATION OF SECONDARY ALCOHOLS WITH O2... 

As part of an ongoing programme on redox molecular sieves we are investigating the use of metal substituted alumino-phosphates (MeAPOs) in liquid phase oxidations. We have found that CrAPO-5 is an active and selective catalyst for the liquid phase oxidation of secondary alcohols with TBHP or O2. 

Autooxidation. Liquid-phase oxidation of hydrocarbons, alcohols, and aldehydes by oxygen produces chemiluminescence in quantum yields of 10 to 10 ° ein/mol (128—130). Although the efficiency is low, the chemiluminescent reaction is important because it provides an easy tool for study of the kinetics and properties of autooxidation reactions including industrially important processes (128,131). The light is derived from combination of peroxyl radicals (132), which are primarily responsible for the propagation and termination of the autooxidation chain reaction. The chemiluminescent termination step for secondary peroxy radicals is as follows ... 

It is generally agreed that alkenyl hydroperoxides are primary products in the liquid-phase oxidation of olefins. Kamneva and Panfilova (8) believe the dimeric and trimeric dialkyl peroxides they obtained from the oxidation of cyclohexene at 35° to 40° to be secondary products resulting from cyclohexene hydroperoxide. But Van Sickle and co-workers (20) report that, The abstraction/addition ratio is nearly independent of temperature in oxidation of isobutylene and cycloheptene and of solvent changes in oxidations of cyclopentene, tetramethylethylene, and cyclooctene. They interpret these results to support a branching mechanism which gives rise to alkenyl hydroperoxide and polymeric dialkyl peroxide, both as primary oxidation products. This interpretation has been well accepted (7, 13). Brill s (4) and our results show that acyclic alkenyl hydroperoxides decompose extensively at temperatures above 100°C. to complicate the reaction kinetics and mechanistic interpretations. A simplified reaction scheme is outlined below. 

The Bashkirov oxidation (liquid-phase oxidation of n-alkanes or cycloalkanes in the presence of boric acid and hydrolysis) yields the corresponding secondary alcohols [16, 17]. The reaction is used industrially for oxidation of C10 to C18 n-alkanes, providing raw materials for detergents and for oxidation of cyclododecane to cyclo-dodecanol as an intermediate for the production of Nylon 12 (Table 1, entry 8). The process is not of much commercial importance in the western world, however. Oxidation in the absence of boric acids usually leads to mixtures of alcohols, ketones, and carboxylic acids (Table 1, entry 9). 

The liquid phase oxidation of alcohols on platinum metal catalysts can be carried out under mild conditions and with air as oxidant. Heptane, ethyl acetate or 2-butanone have been suggested as solvents for water-insoluble alcohols [1]. However, only the aqueous phase oxidation is of practical importance, due to safety reasons [2]. The possibility of applying a "water-detergent" system for water-insoluble substrates will be shown here using the example of the selective oxidation of secondary alcohols to ketones. 

Characterizing the mechanism of the action of amines, the overwhelming majority of tiie authors believe that their basic role reduces to the termination of kinetic oxidation chains on account of reaction (3). Actually, stable radicals (CjH5)2NO have been detected by the method of electron paramagnetic resonance as a result of the interaction with peroxide radicals, formed in the liquid-phase oxidation of a hydrocarbon inhibited with diphenylamine [30]. The interaction of certain secondary amines (Ar2NH) with peroxide radicals, prepared by oxidative radiolysis. 

Demirel et al studied the liquid-phase oxidation of polyalcohols with both primary and secondary alcohol groups they compared the reactivity of n-propanol and glycerol at 60°C, pH = 12, />o2 = 1 on ceria-supported gold catalysts. It was difficult to correlate oxidation activity with the specific surface area the most active catalyst was... 

Liquid-phase oxidation of organic compounds is accompanied by weak chemiluminescence, which was found in 1959 by R.F. Vasil ev, V.Ya. Shlyapintokh, and O.N. Karpukhin. Chemiluminescence is due to the fact that the disproportionation of secondary peroxide radicals affords triplet-excited ketone. The yield of excited molecules of ketone is 10 -10 per disproportionation act. The most part of excited molecules is quenched the emission yield is 10 -10 quanta per excited molecule. The low quantum luminescence yield results in the low luminescence intensity. 

Liquid-phase oxidation when secondary peroxyl radicals lead chains is characterized by chemiluminescence when the disproportionation of two secondary peroxyl radicals affords triplet-excited ketone, which is the emitter of luminescence... 

Vardanyan [65,66] discovered the phenomenon of CL in the reaction of peroxyl radicals with the aminyl radical. In the process of liquid-phase oxidation, CL results from the disproportionation reactions of primary and secondary peroxyl radicals, giving rise to trip-let-excited carbonyl compounds (see Chapter 2). The addition of an inhibitor reduces the concentration of peroxyl radicals and, hence, the rate of R02 disproportionation and the intensity of CL. As the inhibitor is consumed in the oxidized hydrocarbon the initial level of CL is recovered. On the other hand, the addition of primary and secondary aromatic amines to chlorobenzene containing some amounts of alcohols, esters, ethers, or water enhances the CL by 1.5 to 7 times [66]. This effect is probably due to the reaction of peroxyl radicals with the aminyl radical, since the addition of phenol to the reaction mixture under these conditions must extinguish CL. Indeed, the fast exchange reaction... 

Catalysis by transition metals in liquid-phase oxidation has been thor- oughly investigated. The roles of other ions have not been sufficiently studied. This paper is concerned with catalysis by hydrogen ions and some anions, in the chain oxidation of secondary alcohols such as cyclohexanol and 2-propanol. Secondary alcohols, because of their polarity, are convenient for studying ionic homolytic reactions and their role in chain oxidation. 

Dehydrogenases also represent a class of interesting enzymes since enantiose-lective reduction of ketones can lead to the production of enantiomerically pure secondary alcohols for the fine chemicals industry. Compared to liquid systems, in which the cofactor is often eliminated by the circulating phase in continuous systems, solid/gas catalysis can be highly suitable since it has been demonstrated that the cofactor is stable and its regeneration effective by addition of a second substrate. Also, stereoselective oxidation of secondary alcohols by these systems can help in the resolution of racemic mixtures. 

Clearly the above scheme of liquid-phase oxidation by oxygen shows H202 and ROOH formed as intermediate products. However, they cannot be related to active sites of another, secondary reaction as is customary in, for example, conjugated processes. The reasons for making such comparisons are as follows firstly, H202 and ROOH are final products of a complex reaction and initial reagents for other thermodynamically probable reactions secondly, their formation and consumption (by the scheme selected) do not correspond to the notion of active site of conjugated reactions. 

Oxidation of secondary ammine (liquid phase) porous, dense polymeric... 

Xia et al. reported the oxidation of secondary alcohols with PhI(OAc)2/Mn(salen) reagent system in a mixture of CH Clj and [bmim][PFg] (Scheme 14.18) [18]. Under the reaction conditions, ketones were produced in relatively good yields. Ionic liquid phase containing Mn(salen) catalyst could be recovered and employed in five consecutive reactions. 

Phase transfer catalysis can be effective in triphase solid/solid/liquid mixtures. Solid potassium phenoxide and solid sodium iodide react with alkyl halides in the presence of (64). The solid/solid/liquid method also succeeds for hypochlorite oxidation of secondary alcohols and periodate oxidation of glycols catalyzed by commercial AERs (3). 

Nickel, cobalt, copper catalysts supported on oxides or activated carbon are prepared following this procedure and are used for the liquid phase hydrogenation of long chain nitriles. Their activities and selec-tlvities towards the formation of amines (primary, secondary, tertiary) are compared with the one obtained with conventional catalysts. 

Finally, atmospheric chemical transformations are classified in terms of whether they occur as a gas (homogeneous), on a surface, or in a liquid droplet (heterogeneous). An example of the last is the oxidation of dissolved sulfur dioxide in a liquid droplet. Thus, chemical transformations can occur in the gas phase, forming secondary products such as NO2 and O3 in the liquid phase, such as SO2 oxidation in liquid droplets or water films and as gas-to-particle conversion, in which the oxidized product condenses to form an aerosol. 

One of the exciting results to come out of heterogeneous catalysis research since the early 1980s is the discovery and development of catalysts that employ hydrogen peroxide to selectively oxidize organic compounds at low temperatures in the liquid phase. These catalysts are based on titanium, and the important discovery was a way to isolate titanium in framework locations of the inner cavities of zeolites (molecular sieves). Thus, mild oxidations may be run in water or water-soluble solvents. Practicing organic chemists now have a way to catalytically oxidize benzene to phenols alkanes to alcohols and ketones primary alcohols to aldehydes, acids, esters, and acetals secondary alcohols to ketones primary amines to oximes secondary amines to hydroxyl-amines and tertiary amines to amine oxides. 

Chemiluminescence in the liquid-phase hydrocarbon oxidation was discovered. It was proved to be the result of secondary peroxyl radicals disproportionation R. F. Vasi ev, O. N. Karpukhin, and V. Ya Shlyapintokh [69]... 

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