Manganese dioxide catalysis

Even ia 1960 a catalytic route was considered the answer to the pollution problem and the by-product sulfate, but nearly ten years elapsed before a process was developed that could be used commercially. Some of the eadier attempts iacluded hydrolysis of acrylonitrile on a sulfonic acid ion-exchange resia (69). Manganese dioxide showed some catalytic activity (70), and copper ions present ia two different valence states were described as catalyticaHy active (71), but copper metal by itself was not active. A variety of catalysts, such as Umshibara or I Jllmann copper and nickel, were used for the hydrolysis of aromatic nitriles, but aUphatic nitriles did not react usiag these catalysts (72). Beginning ia 1971 a series of patents were issued to The Dow Chemical Company (73) describiag the use of copper metal catalysis. Full-scale production was achieved the same year. A solution of acrylonitrile ia water was passed over a fixed bed of copper catalyst at 85°C, which produced a solution of acrylamide ia water with very high conversions and selectivities to acrylamide. 

The violent decomposition observed on adding charcoal to cone, hydrogen peroxide is mainly owing to catalysis by metallic impurities present and the active surface of the charcoal, rather than to direct oxidation of the carbon [1], Charcoal mixed with a trace of manganese dioxide ignites immediately on contact with cone, peroxide [2],... 

DEHYDROGENATION Anthraquinone. Chloranil. 2,3-DichIoro-5,6-dicyano-1,4-benzoquinone. Diethyl azodicarboxylate. Manganese dioxide. Palladium catalysis. Potassium hydride. Palladium-on-carbon. N,N,N, N -Tetramethylethylenediamine. Trifluoroacetic acid. 

Catalysis works by making a different pathway available between the reactants and the products. This new pathway has a different mechanism and a different rate law from that of the uncatalyzed reaction. The catalyzed pathway may involve a surface reaction, as in the decomposition of hydrogen peroxide catalyzed by manganese dioxide, and in biological reactions catalyzed by enzymes. Or, the catalytic mechanism may take place in the same phase as the uncatalyzed reaction. 

With the help of metal catalysis amidation takes place at room temperature under apparently neutral conditions. Manganese dioxide in large quantities, or, even better, manganese dioxide on silica gel, is well suited to this conversion. Even compounds with functional groups labile to manganese dioxide, for example benzylic groups, are suited for the hydration. With pentacarlwnylmanganese bromide, nitrile hydration takes place under PTC conditions. ... 

Indolines can be obtained easily from indoles by reduction (see 20.7) and can be cleanly oxidised back to indoles nsing a variety of methods, including oxygen with cobalt catalysis (salcomine), hypochlorite/ dimethyl snlhde, Mn(lll) and An(lll) compounds, DDQ or manganese dioxide. ... 

Magnetic studies have also been made on gel-like manganese dioxide. This substance is perhaps somewhat less important in catalysis than it is in dry-cell technology. 

Without adding a catalyst, the decomposition rate at room temperature is immeasurably small. Fe " ions functimi as a homogeneous catalyst, whereas solid manganese dioxide (Mn02) works as a heterogeneous catalyst. For enzymatic catalysis, we use the enzyme catalase. 

Kobayashi, M., Kobayashi, H., 1972a. Application of transient response method to the study of heterogeneous catalysis I. Nature of catalyticaUy active oxygen on manganese dioxide for the oxidation of carbon monoxide at low temperatures. J. Catal. 27, 100-107. 

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