Dehydrogenation of alcohol

Oxidative dehydrogenation of alcohols is a new approach in the development of industrial processes for the synthesis of aldehydes and ketones [103-105], In this regard, the technologically most suitable is the method of acetaldehyde synthesis in the presence of melted vanadium oxide, alkaline metals with promoting additives, alkaline metal sulfates or chlorides as catalysts [105], The target product yield equals 65.9% per used alcohol at 69.2% conversion. The disadvantage of the method is the relatively low yield of the target product 

Though precious metal catalysts can be eliminated from the liquid-phase oxidation of sec-butanol [109], nevertheless, the process parameters (23.5% MEK yield and 79.4% selectivity) are lower compared with catalytic processes. Moreover, at 115-130 °C process implementation requires application of 9-20 atm pressure and, to reduce the induction period, the use of initiating additives. 

it may be concluded that dehydrogenation of organic substances in the homogeneous phase by the radical-chain mechanism using chemical induction possesses several essential advantages, for example  

Conjugated Reactions of Oxidation with Hydrogen Peroxide in the Gas Phase 

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Rhenium oxides have been studied as catalyst materials in oxidation reactions of sulfur dioxide to sulfur trioxide, sulfite to sulfate, and nitrite to nitrate. There has been no commercial development in this area. These compounds have also been used as catalysts for reductions, but appear not to have exceptional properties. Rhenium sulfide catalysts have been used for hydrogenations of organic compounds, including benzene and styrene, and for dehydrogenation of alcohols to give aldehydes (qv) and ketones (qv). The significant property of these catalyst systems is that they are not poisoned by sulfur compounds. 

PCSs obtained by dehydrochlorination of poly(2-dilorovinyl methyl ketones) catalyze the processes of oxidation and dehydrogenation of alcohols, and the toluene oxidation207. The products of the thermal transformation of PAN are also catalysts for the decomposition of nitrous oxide, for the dehydrogenation of alcohols and cyclohexene274, and for the cis-tnms isomerization of olefins275. Catalytic activity in the decomposition reactions of hydrazine, formic acid, and hydrogen peroxide is also manifested by the products of FVC dehydrochlorination... 

The above-described reverse reaction (viz. the Fe-catalyzed dehydrogenation of alcohols to ketones/aldehydes) has been reported by Williams in 2009 (Table 9) [58]. In this reaction, the bicyclic complex 16 shows a sluggish activity, whereas the dehydrogenation of l-(4-methoxyphenyl)ethanol catalyzed by the phenylated complex 17 affords the corresponding ketone in 79% yield when 1 equiv. (relative to 17) of D2O as an additive was used. For this oxidation reaction, l-(4-methoxyphenyl) ethanol is more suitable than 1-phenylethanol and the reaction rate and the yield of product are higher. 

The proposed catalytic cycle for the dehydrogenation of alcohols to ketones is shown in Scheme 15. The initial reaction of 17 with H2O affords the hydride complex a and C02- Dehydrogenation of a by acetone gives the active species b and 2-propanol. The subsequent reaction of b with the alcohol yields the corresponding ketone and regenerates a to complete the catalytic cycle. 

Scheme 15 Proposed catalytic cycle for dehydrogenation of alcohols to ketones...

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. 

Johnson and Backvall reported that the bimetallic Shvo catalyst can also catalyze the transfer dehydrogenation of alcohols (Eq. (48)) [83]. 

Dehydrogenation of alcohols.1 Ally lie or secondary alcohols can be oxidized to the ketones by reaction with 1 catalyzed by RuH2[P(C6H5) ,]4 in benzene. The... 

Skeletal catalysts are usually employed in slurry-phase reactors or fixed-bed reactors. Hydrogenation of cottonseed oil, oxidative dehydrogenation of alcohols, and several other reactions are performed in sluny phase, where the catalysts are charged into the liquid and optionally stirred (often by action of the gases involved) to achieve intimate mixing. Fixed-bed designs suit methanol synthesis from syngas and catalysis of the water gas shift reaction, and are usually preferred because they obviate the need to separate product from catalyst and are simple in terms of a continuous process. 

Strength against attrition is particularly important for catalysts in slurry-bed reactors, where physical breakage of the catalyst particles, ultimately to fines, can prevent their use for those reactions. The strength of the high surface area skeletal structures can be contrasted against activated carbon, which readily breaks down due to attrition in these types of environments. For the few environments where attrition is still a problem (e.g., oxidative dehydrogenation of alcohols), the skeletal catalytic material... 

KW Rosenmund, F Heise. Oxidative catalytic dehydrogenation of alcohols. V. Catalytic reduction of esters and aldehydes. Ber 54B 2038, 1921. 

Some information about structure effects on the rate of dehydrogenation of alcohols to aldehydes and ketones on metals is found in the older literature 129-132) from which it follows that secondary alcohols react more easily than the primary alcohols 129) and that the reactivity decreases with the length of the carbon chain 131). Some series can be correlated by the Taft equation using a constants (Ref. 131, series 103, Cu-Cr203 catalyst, 350°C, four points, slope 18 Ref 132, series 104, Cu catalyst, four points, slope 22). Linear relationships have been used in a systematic way by... 

In spite of great effort, the analysis of structure effects on the dehydrogenation of alcohols on metals has not helped much toward an understanding of the mechanism. A broader range of substituents would be necessary in order to distinguish between the electronic and steric influences. 

The dehydrogenation of alcohol, as we have seen, is an acceptor reaction, while the dehydration of alcohol, on the contrary, is a donor reaction. This result is in agreement with Garner s opinion (30). 

It should be observed that in several cases the relation between the electrical conductivity and the activity may break down. This will occur in those intervals of variation of ,+, in which the reaction rate is independent of e,+, e.g., for the reaction of dehydrogenation of alcohols in the region of sufficiently high values, and for dehydration in the region of sufficiently low values of e,+ (Sec. V,B and Fig. 19). It may also occur in the case of a semiconductor with a quasi-isolated surface, when e,+ is independent of e,+ (Sec. VI,B) if the dimensions of the crystal are not too small (Sec. VI,C). 

The selective poisoning of the very active areas may be beneficial in certain cases. Thus Armstrong and Hilditch Proc. Roy. Soc. A, xcvn. 262,1920) noted that small quantities of water vapour in the dehydrogenation of alcohol on a copper surface... 

There are numerous indications in the literature on catalyst deactivation attributed to over-oxidation of the catalyst (3-5). In the oxidative dehydrogenation of alcohols the surface M° sites are active and the rate of oxygen supply from the gas phase to the catalyst surface should be adjusted to that of the surface chemical reaction to avoid "oxygen poisoning". The other important reason for deactivation is the by-products formation and their strong adsorption on active sites. This type of... 

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