Alcohols alcohol dehydrogenation

Until World War 1 acetone was manufactured commercially by the dry distillation of calcium acetate from lime and pyroligneous acid (wood distillate) (9). During the war processes for acetic acid from acetylene and by fermentation supplanted the pyroligneous acid (10). In turn these methods were displaced by the process developed for the bacterial fermentation of carbohydrates (cornstarch and molasses) to acetone and alcohols (11). At one time Pubhcker Industries, Commercial Solvents, and National Distillers had combined biofermentation capacity of 22,700 metric tons of acetone per year. Biofermentation became noncompetitive around 1960 because of the economics of scale of the isopropyl alcohol dehydrogenation and cumene hydroperoxide processes. 

Dehydrogenation of Isopropyl Alcohol. In the United States about 4% of the acetone is made by this process, and in Western Europe about 19% (22). Isopropyl alcohol is dehydrogenated in an endothermic reaction. 

Recently it has been shown that certain unsaturated ketones and alcohols are dehydrogenated extremely easily by DDQ. While the rapid dehydrogenation of the A ° -dien-3-one (73) is predictable (c/. A -3-ketones), the equally facile reaction of the 3-alcohol (75) is surprising. Presumably (73) is an intermediate in the conversion of (75), although oxidation of nonallylic alcohols normally requires higher temperatures. A -3-Ketones, A ° -3-ketones and A ( o) 3(x aicohols do not react at room temperature. ... 

These pentahydrides have attracted attention as catalysts for hydrogenation of the double bond in alkenes. IrH5(PPr3)2 catalyses vinylic H-D exchange between terminal alkenes and benzene, the isomerization of a,f3-ynones, isomerization of unsaturated alcohols and dehydrogenation of molecules such as secondary alcohols [176],... 

Catalytic dehydrogenation of alcohol is an important process for the production of aldehyde and ketone (1). The majority of these dehydrogenation processes occur at the hquid-metal interface. The liquid phase catalytic reaction presents a challenge for identifying reaction intermediates and reaction pathways due to the strong overlapping infrared absorption of the solvent molecules. The objective of this study is to explore the feasibility of photocatalytic alcohol dehydrogenation. 

A third possibility is represented by a two-step mechanism where the donor alcohol is dehydrogenated and the ketone reduced by the H2 produced. In this case, the easier the donor alcohol is dehydrogenated, the higher is the hydrogen availability on the catalyst surface and the faster is the reaction. If the donor is slowly dehydrogenated, the hydrogen availability is lower. 

Dehydration of alcohols, however, can occur on metal catalysts, too. This reaction takes place mainly in the case of tertiary alcohols, where dehydrogenation to ketones cannot occur. 

Fig. 2. Initial reaction rate versus total pressure for alcohol dehydrogenation, 250 and 285°C. 

Fig. 3. Linearized initial rate plots for alcohol dehydrogenation, 285°C.

The residuals discussed thus far have been associated with some dependent variable, such as the reaction rate r. It is particularly advantageous in pinpointing the type of defect present in an inadequate model to expand this definition to include parametric residuals. The parametric residual, then, is simply the difference between a value of a given parameter estimated from the data and that predicted from a model. For example, the dots in Fig. 17 represent the logarithm of the alcohol adsorption constants measured in alcohol dehydrogenation experiments from isothermal data at each of several temperature levels (FI). The solid line represents the expectation that these... 

Fig. 17. Dependence of ethanol adsorption constant on temperature—alcohol dehydrogenation.

Fig. 18. Dependence of residuals of ethanol adsorption constant on temperature— alcohol dehydrogenation.

Fig. 15.12 (a) Acid-base mechanism of alcohol dehydrogenation. Reprinted with permission from [70], Copyright (1993) Pergamon (Elsevier), (b) Redox mechanism of cyclohexanol ODH. Reprinted with permission from [74]. Copyright (1998) Elsevier. 

AcetaJdehyde is old. It is not ancient like ethyl alcohol, the essential ingredient in wine, but it owes its discovery to this closely related compound. Scheele first prepared acetaldehyde in 1774 by dehydrogenation of ethyl alcohol. Just as many nicknames get attached to people at infancy, this process generated the name aldehyde. It is a contraction for compounds that are alcohol dehydrogenates. 

Processes that enable direct catalytic C-C functionalization of carbinol C-H bonds are highly uncommon. Rh-catalyzed alcohol-vinylarene C-C coupling has been described. The requirement of BF3 and trends in substrate scope suggest these processes involve alcohol dehydrogenation-reductive Prins addition [26-29]. 

Desaturation of alkyl groups. This novel reaction, which converts a saturated alkyl compound into a substituted alkene and is catalyzed by cytochromes P-450, has been described for the antiepileptic drug, valproic acid (VPA) (2-n-propyl-4-pentanoic acid) (Fig. 4.29). The mechanism proposed involves formation of a carbon-centered free radical, which may form either a hydroxy la ted product (alcohol) or dehydrogenate to the unsaturated compound. The cytochrome P-450-mediated metabolism yields 4-ene-VPA (2-n-propyl-4pentenoic acid), which is oxidized by the mitochondrial p-oxidation enzymes to 2,4-diene-VPA (2-n-propyl-2, 4-pentadienoic acid). This metabolite or its Co A ester irreversibly inhibits enzymes of the p-oxidation system, destroys cytochrome P-450, and may be involved in the hepatotoxicity of the drug. Further metabolism may occur to give 3-keto-4-ene-VPA (2-n-propyl-3-oxo-4-pentenoic acid), which inhibits the enzyme 3-ketoacyl-CoA thiolase, the terminal enzyme of the fatty acid oxidation system. 

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