Alcohols dehydrogenation catalyzed

Scheme 6 Proposed mechanism for alcohol dehydrogenation catalyzed by 2/L5 mixtures...

Zhang D-D, Chen X-K, Liu H-L, Huang X-R. A computational mechanistic study of pH-dependent alcohol dehydrogenation catalyzed by a novel [C, N] or [C, C] cyclometalated Cp Ir complex in aqueous solution. New J Chem. 2014 38 3862—3873. 

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]. 

When allylic alcohols were used as substrates for dehydrogenation catalyzed by rhodium(I) complexes, isomerization to carbonyl compounds occurred instead. The product yields were excellent (Table IV) and the remarkably mild reaction could be effected in the absence of the phase-transfer catalyst with nearly as good results (55). Hydroxy-ir-allylrhodium complexes are probable reaction intermediates. 

This type of reactor has been used in the past to study solid-catalyzed gaseous reactions. Tajbl, Simons, and Carberry (3) used a CSTCR to study the highly exothermic oxidation of carbon monoxide on a commercial palladium catalyst. Ford and Perlmutter (2) used a CSTCR with a catalytic wall to study sec-butyl alcohol dehydrogenation. In both studies, the authors found that data were obtained more easily and accurately with a CSTCR. 

Several non-noble metal-catalyzed iV-alkylation reactions have also been reported in recent years. In 2010, Ramon, Yus and co-workers reported Cu(OAc)2-catalyzed A-alkylation of poor nucleophilic amine derivatives and alcohols (Eq. 30) [125]. Control experiments indicated that a base was indispensable in the reaction to force the alcohol dehydrogenation step, which was later confirmed by DFT calculations reported by Liu, Huang and co-workers [63]. In 2011, Ramon and co-workers reported the results of their own mechanistic studies and proposed two possible catalytic cycles [126]. The main aldehyde-free cycle, depicted with plain arrows, requires the presence of a base. The minor cycle, depicted in dashed arrows, may proceed when an aldehyde exists in the reaction media (Scheme 23). In the same year, Li and co-workers also disclosed a CuCl-catalyzed A-alkylation of heteroarylamines [127]. 

It has been noted that dehydration prevails over metal oxide catalysts which are acidic (e.g., AI2O3) and dehydrogenation becomes dominant over basic oxides. Thus, dehydrogenation of alcohols is catalyzed by ZnO, MgO, Cr203 and CuO. Similar variations of dehydrogenation vs. dehydration can be found for the reaction of formic acid. Increase of dehydrogenation activity with increasing basicity has been reported for... 

A detailed discussion of the mechanism of the pH-dependent alcohol dehydrogenation in aqueous solution catalyzed by related [C,N] or [C,C] cyclometalated Cp Ir complexes was recently reported, generally supporting the mechanistic su estions and demonstrating a significant dependence of the studied reaction system on pH. 

Zhang G, Hanson SK. Cobalt-catalyzed acceptorless alcohol dehydrogenation synthesis of imines from alcohob and amines. Org Lett. 2013 15 650-653. 

Acetone can also he coproduced with allyl alcohol in the reaction of acrolein with isopropanol. The reaction is catalyzed with an MgO and ZnO catalyst comhination at approximately 400°C and one atmosphere. It appears that the hydrogen produced from the dehydrogenation of isopropanol and adsorbed on the catalyst surface selectively hydrogenates the carhonyl group of acrolein ... 

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. 

Table 9 Fe-catalyzed dehydrogen conversion of alcohol to ketone ...

The oxidation by strains of Pseudomonas putida of the methyl group in arenes containing a hydroxyl group in the para position is, however, carried out by a different mechanism. The initial step is dehydrogenation to a quinone methide followed by hydration (hydroxylation) to the benzyl alcohol (Hopper 1976) (Figure 3.7). The reaction with 4-ethylphenol is partially stereospecific (Mclntire et al. 1984), and the enzymes that catalyze the first two steps are flavocytochromes (Mclntire et al. 1985). The role of formal hydroxylation in the degradation of azaarenes is discussed in the section on oxidoreductases (hydroxylases). 

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