Carboxylic acids hydroperoxide oxidation

The direct catalyzed or uncatalyzed oxidation of alkanes with oxygen is an important reaction in the industrial production of carboxylic acids, hydroperoxides (for production of epoxides from alkenes), alcohols, ketones, or aldehydes [60],... 

Common alcohol oxidation methods employ stoichiometric amounts of toxic and reactive oxidants like Cr03, hypervalent iodine reagents (Dess-Martin) and peracids that pose severe safety and environmental hazards in large-scale industrial reactions. Therefore, a variety of catalytic methods for the oxidation of alcohols to aldehydes, ketones or carboxylic acids have been developed employing hydrogen peroxide or alkyl hydroperoxides as stoichiometric oxygen sources in the presence of catalytic amounts of a metal catalyst. The commonly used catalysts for alcohol oxidation are different MoAV(VI), Mn(II), Cr(VI), Re(Vn), Fe(II) and Ru complexes . A selection of published known alcohol oxidations with different catalysts will be presented here. 

The decomposition of carboxyl radical occurs very rapidly, and C02 is formed with a constant rate in the initiated co-oxidation of cumene and acid [104]. Cumylperoxyl radical attacks the a-CH2 group of the carboxylic acid with the formation of a labile hydroperoxide. The concentration of this hydroperoxide increases during oxidation till it reaches a stationary concentration [RCH(OOH)-COOH]st = pi2[RCH2COOH][CuOO ]/A d. This reaction produces C02 with acceleration during some period of time equal to the time of increasing the a-carboxyhydroperoxide concentration. 

No cross ozonide was formed from unsymmetrical alkenes. The authors theorized628 that the carbonyl oxide zwitterionic species formed on wet silica gel immediately adds water followed by rapid decomposition of the intermediate hydroxyalkyl hydroperoxide to carboxylic acid and water. It means that water on silica gel acts as participating solvent. In the absence of adsorbed water, rapid recombination of the adsorbed aldehyde and carbonyl oxide due to a favorable proximity effect gives normal ozonide. The low mobility of adsorbed species on the silica surface accounts for the absence of cross ozonides. 

Heterogeneous palladium catalysts proved to be active in the conversion of simple alkenes to the corresponding allylic acetates, carbonyl compounds, and carboxylic acids.694 704 Allyl acetate or acrylic acid from propylene was selectively produced on a palladium on charcoal catalyst depending on catalyst pretreatment and reaction conditions.694 Allylic oxidation with singlet oxygen to yield allylic hydroperoxides is discussed in Section 9.2.2. 

The ready formation of benzylic hydroperoxides is used in industrial oxidations, as in the synthesis of propylene oxide and phenol (see Sections 9.5.2 and 9.5.4, respectively). In contrast with autoxidation of alkenes, where various secondary processes may follow, autoxidation of arenes is less complicated. Chain termination of 99 may lead to an alcohol and aldehyde [Eq. (9.151)], and the rapid autoxidation of the latter may produce the corresponding carboxylic acid [Eq. (9.152)] ... 

A systematic study to identify solid oxide catalysts for the oxidation of methane to methanol resulted in the development of a Ga203—M0O3 mixed metal oxide catalyst showing an increased methanol yield compared with the homogeneous gas-phase reaction.1080,1081 Fe-ZSM-5 after proper activation (pretreatment under vacuum at 800-900°C and activation with N20 at 250°C) shows high activity in the formation of methanol at 20°C.1082 Density functional theory studies were conducted for the reaction pathway of the methane to methanol conversion by first-row transition-metal monoxide cations (MO+).1083 These are key to the mechanistic aspects in methane hydroxylation, and CuO+ was found to be a likely excellent mediator for the reaction. A mixture of vanadate ions and pyrazine-2-carboxylic acid efficiently catalyzes the oxidation of methane with 02 and H202 to give methyl hydroperoxide and, as consecutive products, methanol and formaldehyde.1084 1085... 

The autoxidation of hydrocarbons catalyzed by cobalt salts of carboxylic acid and bromide ions was kinetically studied. The rate of hydrocarbon oxidation with secondary hydrogen is exactly first order with respect to both hydrocarbon and cobalt concentration. For toluene the rate is second order with respect to cobalt and first order with respect to hydrocarbon concentration, but it is independent of hydrocarbon concentration for a long time during the oxidation. The oxidation rate increases as the carbon number of fatty acid solvent as well as of cobalt anion salt are decreased. It was suggested that the cobalt salt not only initiates the oxidation by decomposing hydroperoxide but also is responsible for the propagation step in the presence of bromide ion. 

Alkyl radicals for such reactions are available from many sources such as acyl peroxides, alkyl hydroperoxides, particularly by the oxidative decarboxylation of carboxylic acids using peroxy-disulfate catalyzed by silver. Pyridine and various substituted pyridines have been alkylated in the 2-position in high yield by these methods. Quinoline similarly reacts in the 2-, isoquinoline in the 1-, and acridine in the 9-position. Pyrazine and quinoxaline also give high yields of 2-substituted alkyl derivatives <74AHC(16)123). 

This work concerns mainly the modification of commercial polymers bearing hydroxy fonctions as alcohol, hydroperoxide or carboxylic acid, by reactive gases or liquid volatil compounds capable to penetrate in the polymer matrix. The modifications of membranes properties as gas permeability or surface tension will also be reported. Few examples will also concern the reaction of double bond with 12 and HBr vapor as well as the oxidation of piperidine group by peracetic acid. 

Potassium nitrosodisulfonate, 258 other methods Bis(tributyltin) oxide, 41 /-Butyl hydroperoxide-Dichlorotris-(triphenylphosphine)rutheni-um(II), 54 Dibutyltin oxide, 95 Hydrogen hexachloroplatinate(IV)-Copper(II) chloride, 145 4-Methoxy-2,2,6,6-tetramethy 1-1 -oxopiperidinium chloride, 183 of alcohols to carboxylic acids Cetyltrimethylammonium permanganate, 69... 

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. 

As indicated, a variety of aldehydes have been demonstrated in oxidized fats. Alcohols have also been identified, but the presence of ketones is not as certain. Keeney (1962) has listed the aldehydes that may be formed from breakdown of hydroperoxides of oxidized oleic, linoleic, Iinolenic, and arachidonic acids (Table 2-23). The aldehydes are powerful flavor compounds and have very low flavor thresholds for example, 2,4-decadie-nal has a flavor threshold of less than one part per billion. The presence of a double bond in an aldehyde generally lowers the flavor threshold considerably. The aldehydes can be further oxidized to carboxylic acids or other tertiary oxidation products. 

Many organic peroxides and hydroperoxides are known.30 Peroxo carboxylic acids (e.g., peroxoacetic acid, CH3CO OOH) can be obtained by the action of H202 on acid anhydrides. Peroxoacetic acid is made as 10 to 55% aqueous solutions containing some acetic acid by interaction of 50% H202 and acetic acid, with H2S04 as catalyst at 45 to 60°C the dilute acid is distilled under reduced pressure. It is also made by air oxidation of acetaldehyde. The peroxo acids are useful oxidants and sources of free radicals [e.g., by treatment with Fe2+(aq)]. Dibenzoyl peroxide, di-r-butyl peroxide, and cumyl hydroperoxide are moderately stable and widely used as polymerization initiators and for other purposes where free-radical initiation is required. 

Oxidation. Oxidations with r-butyl hydroperoxide catalyzed with this Mo complex can be used to effect selective oxidations of secondary alcohols in the presence of primary ones in benzene at 60°. Primary alcohols are oxidized slowly to esters in methanol. Aldehydes are oxidized to carboxylic acids in benzene or to esters in methanol. 

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