Reactions dehydrogenation, alcohols

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. 

Thaller, L.H., and G. Thodos, "The Dual Nature of a Catalytic-Reaction The Dehydrogenation of sec-Buty Alcohol to Methyl Ethyl Ketone at Elevated Pressures", AIChE Journal, 6(3), 369-373, 1960. 

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

A number of compounds react rapidly with DDQ at room temperature. They include allylic and benzylic alcohols, which can thus be selectively oxidized, and enols and phenols, which undergo coupling reactions or dehydrogenation, depending on their structure. Rapid reaction with DDQ is also often observed in compounds containing activated tertiary hydrogen atoms. The workup described here can be used in all these cases. 

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). 

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. 

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. 

Heterogeneous copper catalysts prepared with the chemisorption-hydrolysis technique are effective systems for hydrogen transfer reactions, namely carbonyl reduction, alcohol dehydrogenation and racemization, and allylic alcohol isomerization. Practical concerns argue for the use of these catalysts for synthetic purposes because of their remarkable performance in terms of selectivity and productivity, which are basic features for the application of heterogeneous catalysts to fine chemicals synthesis. Moreover, in all these reactions the use of these materials allows a simple, safe, and clean protocol. 

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... 

Finally, supported noble metals widely used as hydrogenation catalysts can be used to catalyze the reverse reaction-oxidative dehydrogenation-in the presence of oxygen. This is applied, for example, in the oxidative dehydrogenation of alcohols and carbohydrates (see Sections 9.2 and 9.3). 

Conversion of dihydroxy compounds to diamines requires the repetition of all reaction steps (dehydrogenation, addition, elimination, hydrogenation). Selectivity is much higher when diols are transferred only to amino alcohols or amino alcohols to diamines. This difference is exemplified by the reaction of 1,6-hexanediol with di-methylamine over CU/AI2O3 [25]. Over 90% selectivity for the intermediate N,N-dimethyl-6-amino-l-hexanol was achieved at 180 °C in a continuous fixed-bed reactor. To complete the amination of the second OH group the reactor temperature had to be raised to 230 °C and the highest selectivity for diamine was only 65 %. 

Finally, The dehydrogenation of butanediols to y-butyrolactone is an important commercial reaction that was developed by BASF and named the Reppe process. The most probable reaction mechanism via the y-hydroxybutyraldehyde intermediate clearly shows that the reaction proceeds via two separate alcohol dehydrogenation steps with a rearrangement step taking place in-between (Table 1, Scheme 12) [49]. The reaction is usually performed in the gas phase with hydrogen as carrier gas, to reduce catalyst deactivation, which is a characteristic problem. Thus, extensive research is now being conducted in the liquid phase [50,51]. In addition to a lower catalyst deactivation rate, liquid phase reaction also reduces the number of side-products. The drawbacks are, of course, lower activity but also abrasion problems with the catalyst. The catalyst is preferably stabilized as a powder in a silica matrix (Ludox R) [51]. The catalyst most often encountered in the patent literature is a Cu-Cr with a promoter such as Ba or Mn. The catalyst is also preferably doped with Na or K and pretreated very carefully in a reducing atmosphere [52]. 

The use of copper-based catalysts for the reactions of ester hydrogenolysis and alcohol dehydrogenation is well established [2-26, 30,31]. Raney -type skeletal copper catalysts are widely used in these reactions [5-11,17-26,30,31]. However, significant catalyst deactivation is experienced [5-6,25-29]. Evans et al studied the hydrogenolysis of formates in the gas phase over a variety of copper-based catalysts, including skeletal copper and copper chromite... 

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