Adipic oxidative decarboxylation

In the autoxidation of neat hydrocarbons, catalyst deactivation is often due to the formation of insoluble salts of the catalyst with certain carboxylic acids that are formed as secondary products. For example, in the cobalt stearate-catalyzed oxidation of cyclohexane, an insoluble precipitate of cobalt adipate is formed. 18fl c Separation of the rates of oxidation into macroscopic stages is not usually observed in acetic acid, which is a better solvent for metal complexes. Furthermore, carboxylate ligands may be destroyed by oxidative decarboxylation or by reaction with alkyl hydroperoxides. The result is often a precipitation of the catalyst as insoluble hydroxides or oxides. The latter are neutralized by acetic acid and the reactions remain homogeneous. 

The photo-Kolbe reaction is the decarboxylation of carboxylic acids at tow voltage under irradiation at semiconductor anodes (TiO ), that are partially doped with metals, e.g. platinum [343, 344]. On semiconductor powders the dominant product is a hydrocarbon by substitution of the carboxylate group for hydrogen (Eq. 41), whereas on an n-TiOj single crystal in the oxidation of acetic acid the formation of ethane besides methane could be observed [345, 346]. Dependent on the kind of semiconductor, the adsorbed metal, and the pH of the solution the extent of alkyl coupling versus reduction to the hydrocarbon can be controlled to some extent [346]. The intermediacy of alkyl radicals has been demonstrated by ESR-spectroscopy [347], that of the alkyl anion by deuterium incorporation [344]. With vicinal diacids the mono- or bisdecarboxylation can be controlled by the light flux [348]. Adipic acid yielded butane [349] with levulinic acid the products of decarboxylation, methyl ethyl-... 

After two minor dust explosions in an industrial adipic acid dryer, evidence was obtained that adipic acid forms an iron complex capable of both decarboxylation/ dehydration of adipic acid to cyclopentanone and of catalysing air oxidation, giving exotherms from as low as 135°C. 

The thermal decarboxylation of a mixture of barium salts has been used to prepare unsymmetrical ketones the yields are not stated. The earlier procedure has been modified by carrying out the reaction in vacuo in an iron flask. Glass reaction vessels are inferior. In this manner, a large number of the high-molecular-weight methyl ketone s, C9, C,o, C,j-C , and C, are prepared in 54-67% yields. Cyclopentanone has been synthesized in 80% yield by distillation of adipic acid from barium hydroxide at 295°. In a study of metallic oxides and carbonates, magnesium oxide is preferred for the liquid-phase ketonization of stearic acid at 330-360° (95%). A convenient method for the preparation of dibenzyl ketone is the reaction of phenylacetic acid, acetic anhydride. 

Dicarboxylic acids decarboxylate by attack of peroxy radicals on a-C— H bonds. The evidence for such a mechanism was obtained from data on the decarboxylation of adipic acid, with COOH and COOD groups, in oxidizing cumene, when the velocities of C02 production were found to be the same [299]. Carbon dioxide is produced from the acid in the initiated oxidation of cumene (Table 14) and cyclohexanol [215] after the induction period associated with the formation of an intermediate, probably a-hydroperoxide, after attack of peroxy radicals on a-C—H... 

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