Carboxyl compounds dehydrogenation

Fig. 4.12. "Dehydrogenation" of carbonyl or carboxyl compounds via their a-phenyl-selenyl derivatives.

The design and catalytic activity of dibenzobarrelene-based bifunctional PC(5p )P pincer catalysts for acceptor-less dehydrogenation of primary and secondary alcohols to give carbonylic and carboxylic compounds has been described. The mechanism of the H2 formation involves intra-molecular cooperation between the structurally remote functionality and the metal centre. The feasibility of the complete catalytic cycle was studied using a stoichiometric model. ... 

Dehydrogenation of ethyl 2-methyl-4-hydroxy-5,6,7,8-tetrahydro-4a//-pyrido]l,2-/j]pyridazine-3-carboxylate with mercury(II) acetate in ethanol at 45-50°C or over PtOa in boiling ethanol afforded anhydro 3-ethoxycar-bonyl-2-methyl-4-hydroxy-5,6,7,8-tetrahydropyrido[l,2-h]pyridazinium hydroxide (48) (71CPB159). The last compound could be reduced to the starting tetrahydropyrido[l,2-h]pyridazine over Pt02 in ethanol under hydrogen. 

Fenchone [7787-20-4] containing a small amount of the (-)-isomer [4695-62-9] is prepared by dehydrogenation of (-)-fenchol. (-)-Fenchyl esters are obtained, along with other compounds, by addition of carboxylic acids to a-pinene. Hydrolysis of the esters yields (-)-fenchol. 

Aromatization of alicyclic compounds. Cyclohexane carboxylic acids maybe metabolized by a mitochondrial enzyme system to an aromatic acid such as benzoic acid. This enzyme system requires CoA, ATP, and oxygen and is thought to involve three sequential dehydrogenation steps after the initial formation of the cyclohexanoyl CoA (Fig. 4.36). The aromatase enzyme also requires the cofactor FAD. 

The pyrimidine derivative (177 R = Me) is obtained by dehydrogenation of 2-acetamido-4,5,6,7-tetrahydrobenzo[ ]thiophene-3-carb-oxamide.114 The related compound (177 R = H) is obtained by treatment of ethyl 2-aminobenzo[6]thiophene-3-carboxylate with formamide.114... 

Solid heteropoly compounds are suitable oxidation catalysts for various reactions such as dehydrogenation of O- and N-containing compounds (aldehydes, carboxylic acids, ketones, nitriles, and alcohols) as well as oxidation of aldehydes. Heteropoly catalysts are inferior to Mo-Bi oxide-based catalysts for the allylic oxidation of olefins, but they are much better than these for oxidation of methacrolein (5). Mo-V mixed-oxide catalysts used commercially for the oxidation of acrolein are not good catalysts for methacrolein oxidation. The presence of an a-methyl group in methacrolein makes the oxidation difficult (12). The oxidation of lower paraffins such as propane, butanes, and pentanes has been attempted (324). Typical oxidation reactions are listed in Table XXXI and described in more detail in the following sections. 

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