Alcohols dehydrogenative oxidation

The chemistry of ethyl alcohol is largely that of the hydroxyl group, namely, reactions of dehydration, dehydrogenation, oxidation, and esterification. The hydrogen atom of the hydroxyl group can be replaced by an active metal, such as sodium, potassium, and calcium, to form a metal ethoxide (ethylate) with the evolution of hydrogen gas (see Alkoxides, metal). 

Dehydrogenation of primary alcohols gives aldehydes, but in only moderate yield, but primary allylic alcohols are oxidized in high yield (80-95%). Secondary alcohols are also oxidized in high yield. The method, being neutral, is recommended for oxidation of substrates containing acid- or base-sensitive groups. 

Biological. Dodecane may biodegrade in two ways. The first is the formation of dodecyl hydroperoxide which decomposes to 1-dodecanol. The alcohol is oxidized forming dodecanoic acid. The other pathway involves dehydrogenation to 1-dodecene, which may react with water, giving 1-dodecanol (Dugan, 1972). 

The enzyme isocitrate dehydrogenase is one of the enzymes of the Krebs or citric acid cycle, a major feature in carbohydrate metabolism (see Section 15.3). This enzyme has two functions, the major one being the dehydrogenation (oxidation) of the secondary alcohol group in isocitric acid to a ketone, forming oxalosuccinic acid. This requires the cofactor NAD+ (see Section 11.2). For convenience, we are showing non-ionized acids here, e.g. isocitric acid, rather than anions, e.g. isocitrate. 

Control of pore sizes of known catalysts like zeolites has been known for some time although the use of chemical vapor deposition (CVD) of organosilanes to control pore sizes has been the focus of recent research.7 Other catalysts like silica have been treated with methods like CVD and sol-gel in order to deposit thin films. Monolayer coatings of titanium oxide prepared by sol-gel methods have been recently used to coat silica and such films are active in alcohol dehydrogenation reactions.8... 

Aliphatic alcohols and benzyl alcohol are oxidized by Ph3Bi(OOtBu)2 to the corresponding carbonyl compounds (Equation (141)).233 It has been suggested that the oxidation occurs via dehydrogenation of alcohols by phenyl or tert-butoxy radical. When treated with diethyl ether, Ph3Bi(OOtBu)2 oxidizes the methyl group to afford ethoxyacetic... 

Isobutene is present in refinery streams. Especially C4 fractions from catalytic cracking are used. Such streams consist mainly of n-butenes, isobutene and butadiene, and generally the butadiene is first removed by extraction. For the purpose of MTBE manufacture the amount of C4 (and C3) olefins in catalytic cracking can be enhanced by adding a few percent of the shape-selective, medium-pore zeolite ZSM-5 to the FCC catalyst (see Fig. 2.23), which is based on zeolite Y (large pore). Two routes lead from n-butane to isobutene (see Fig. 2.24) the isomerization/dehydrogenation pathway (upper route) is industrially practised. Finally, isobutene is also industrially obtained by dehydration of f-butyl alcohol, formed in the Halcon process (isobutane/propene to f-butyl alcohol/ propene oxide). The latter process has been mentioned as an alternative for the SMPO process (see Section 2.7). 

Carbon-carbon Imnd oxidation is beyond die scope of this work, but is a consequence of initial hydroxylation followed by further metabolism involving other enzyme systems. Many examples of alcohol dehydrogenation and double bond epoxidation have been published previously, and these will not be considered fordier here. 

Lattice silver also can perform a dehydrogenative oxidation of alcohols with O2. For example, fert-butyl alcohol can be oxidized to isobutylene oxide on an O2 covered Ag(l 10) surface at elevated temperatures (85). However, other oxidation products also were produced. Experiments using 02 labeling revealed that the oxygen in the product is from the original alcohol and they believe the hydrogen atom from the methyl C—H bond is directly transferred to either O2 or another molecule of tcrf-butyl alcohol. Lattice silver is still widely used in industry and further studies hold promise for other industrially suitable methods (Fig. 14). 

This chapter highlights the ruthenium-catalyzed dehydrogenative oxidation and oxygenation reactions. Dehydrogenative oxidation is especially useful for the oxidation of alcohols, and a variety of products such as ketones, aldehydes, and esters can be obtained. Oxygenation with oxo-ruthenium species derived from ruthenium and peroxides or molecular oxygen has resulted in the discovery of new types of biomi-metic catalytic oxidation reactions of amines, amides, y3-lactams, alcohols, phenols, and even nonactivated hydrocarbons tmder extremely mild conditions. These catalytic oxidations are both practical and useful, and ruthenium-catalyzed oxidations will clearly provide a variety of futrue processes. 

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