Dehydrogenations alcohols

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. 

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. 

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]. 

Aldehydes and ketones both may be reduced to alcohols by hydrogenation (see the alcohol dehydrogenation reaction, equation 5). Aldehydes may react with either water or alcohol to form aldehyde hydrates or hemiacetals, respectively (also see figure 7 for intramolecular hemiacetals formed by sugars). Reaction of an aldehyde with two molecules of alcohol leads to acetal formation. 

Alcohol dehydrogenation in liquid phase (8-11, 51). H2 evolution from aqueous methanol solutions with Pt/TiC>2 (or Pt and TiC ) had been reported (52). Moreover, it was claimed that H2 also resulted from water decomposition (52). From a set of experiments we have established that in that case the dehydrogenation of methanol accounts for the H2 produced (8). 

Copper on a synthetic polypeptide demonstrated a remarkable selectivity in alcohol dehydrogenation by virtually excluding alcohols of complex structure such as diisopropyl and diisobutyl carbinol, while admitting simple alcohols such as n-butyl, isobutyl and sec-butyl 129). 

A deep study of the 4-tert-butylcyclohexanone reduction aimed at understanding the effect of the donor alcohol structure revealed the existence of a two-step mechanism based on donor alcohol dehydrogenation and ketone hydrogenation. In particular, when the reaction was carried out in the presence of Cu/Si02, in order to exclude a contribution from the support, all the alcohols used as donors were capable of transferring H2, and in the case of (iPr)2CHOH and 3-octanol, not only was the formation of the corresponding ketone observed but it continued after complete conversion of the substrate. 

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