Benzaldehyde, cobalt-catalyzed oxidation

Photochemical oxidation, induced by benzoyl peroxide or catalyzed by a cobalt salt oxidation of benzaldehyde in liquid phase. 

The cobalt(II) catalyzed oxidation of benzaldehyde in acetic acid by 0 at room temperature has been studied in detail [5-10]. 

Similarly, the oxidation in liquid phase at about 25°C. of ethanal and of benzaldehyde catalyzed by a cobalt salt, seems to involve the... 

The tedious preparation of the monopyrrolic precursor 2.147 necessary for the tris-(phenyl)cobalt(III) corrole 2.153 led Paolesse, et al. to consider a third approach to preparing tris-(phenyl)cobalt(III) corroles. It centers around an initial acid-catalyzed condensation between the diacid dipyrrylmethane 2.144 with benzaldehyde (2.154) that is followed by a subsequent cyclization step carried out in the presence of Co(OAc)2 and PPh3. In this case, it was found that 2,3-dichloro-5,6-dicyano-I,4-benzoquinone (DDQ) helped mediate the requisite final oxidation step. While this approach did give a slightly lower yield of corrole (18%), it had the advantage of being quite streamlined. 

Transition metal complexes, zeolites, biomimetic catelysts have been widely used for various oxidation reactions of industrial and environmental importance [1-3]. However, few heterogenized polymeric catalysts have also been applied for such purpose. Mild condition oxidation catalyzed by polymer anchored complexes is attractive because of reusability and selectivity of such catalysts. Earlier we have reported synthesis of cobalt and ruthenium-glycine complex catalysts and their application in olefin hydrogenation [4-5]. In present study, we report synthesis of the palladium-glycine complex on the surface of the styrene-divinylbenzene copolymer by sequential attachment of glycine and metal ions and investigation of oxidation of toluene to benzaldehyde which has been widely used as fine chemicals as well as an intermidiate in dyes and drugs. 

The oxidation of benzaldehyde catalyzed by manganese(II) and (III) acetate, cobalt(II) naphthenate, and cerium(IV) naphthenate has been studied by Kresge [46] with acetic acid as the solvent at a temperature of 50°C and an oxygen pressure of about 1 atm. In the case of oxidation in the presence of manganese with an aldehyde concentration of less them 0.5 mole 1 1 and a manganese concentration of less than 10 5moler1, the kinetics of the initial oxidation follow the empirical equation... 

The rate constant of the reaction of cobalt(III) acetate with benzaldehyde in the absence of dioxygen was determined in independent experiments. It turned out to be virtually the same as the rate constant of the chain initiation in the oxidation reaction in the presence of O2- However, the contribution of chain initiation to the radical formation is insignificant in the developed oxidation process. The radicals are mainly formed in the reactions of the intermediates in the process of degenerate chain branching. These reactions are also catalyzed by transition metal ions. Especially well studied is the acceleration of radical decomposition of intermediately formed hydroperoxides (see, e.g., [10]). 

During the oxygen or air oxidation of benzaldehyde catalyzed by cobalt and bromide several measureable parameters oscillate including redox potential, absorbance at 620 nm, oxygen concentration, rate of benzaldehyde disappearance and free radical concentration. At 55-100°C in a 90/10 acetic acid/water mixture the oscillations will last for many hours[l]. A typical cycle is shown in Figure 1. 

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