Autoxidation process

The first commercial-scale anthrahydroquinone autoxidation process in the United States was put into operation by E. I. du Pont de Nemours Co., Inc. (Memphis, Tennessee) in 1953, followed by EMC Corporation (West Virginia), LaPorte Chemicals, Ltd. (U.K.), Degussa (Germany), Mitsubishi-Gas Chemical Co. (Japan), and others. 

WorkingS olution Regeneration and Purification. Economic operation of an anthraquinone autoxidation process mandates fmgal use of the expensive anthraquinones. During each reduction and oxidation cycle some finite amount of anthraquinone and solvent is affected by the physical and chemical exposure. At some point, control of tetrahydroanthraquinones, tetrahydroanthraquinone epoxides, hydroxyanthrones, and acids is required to maintain the active anthraquinone concentration, catalytic activity, and favorable density and viscosity. This control can be by removal or regeneration. 

Nitrogen Compound Autoxidation. CycHc processes based on the oxidation of hydrazobenzene and dihydrophenazine to give hydrogen peroxide and the corresponding azobenzene—phenazine were developed in the United States and Germany during World War II. However, these processes could not compete economically with the anthrahydroquinone autoxidation process. 

This electrolytic process technology is no longer used because of the extensive and continuous electrolyte purification needs, the high capital and power requirements, and economic inabiHty to compete with large-scale anthrahydroquinone autoxidation processes. 

All pioduceis use the alkylanthiaquinone autoxidation process except where noted. 

Because of the importance of hydroperoxy radicals in autoxidation processes, their reactions with hydrocarbons arc well known. However, reactions with monomers have not been widely studied. Absolute rate constants for addition to common monomers are in the range 0.09-3 M"1 s"1 at 40 °C. These are substantially lower than kL for other oxygen-centered radicals (Table 3.7). 454... 

Consequently, as a result of increasing environmental pressure many chlorine and nitric acid based processes for the manufacture of substituted aromatic acids are currently being replaced by cleaner, catalytic autoxidation processes. Benzoic acid is traditionally manufactured (ref. 14) via cobalt-catalyzed autoxidation of toluene in the absence of solvent (Fig. 2). The selectivity is ca. 90% at 30% toluene conversion. As noted earlier, oxidation of p-xylene under these conditions gives p-toluic acid in high yield. For further oxidation to terephthalic acid the stronger bromide/cobalt/manganese cocktail is needed. 

The situation is different when I [Pg.515]

Because of the foregoing we will not attempt in this article to compile every observation recorded so far in the field of induced reactions only the results where the mechanism is sufficiently clear will be referred to. Also, the wide and technically important field of autoxidation processes will be omitted, because they can be considered more properly later in the series. 

In conclusion, oxidation of carotenoids by molecular oxygen, the so-called autoxidation process, is a complex phenomenon that is probably initiated by an external factor (radical, metal, etc.) and for which different mechanisms have been proposed. The autoxidation of a carotenoid is important to take into account when studying antioxidant activity because it can lower the apparent antioxidant activity of a carotenoid. ... 

The type I mechanism is a radical process, and involves the excited state of the photosensitizer in electron-transfer processes, as indicated in Scheme 1. The reactions there are essentially photochemically stimulated autoxidation processes. 

It should be emphasized that clear-cut situations described in Schemes 1-3 are uncommon and typically the combination of these models needs to be considered for kinetic and mechanistic description of a real system. However, even when one of the limiting cases prevails, each of these models may predict very different formal kinetic patterns depending on where the rate determining step is located. For the same reason, different schemes may be consistent with the same experimental rate law, i.e. thorough formal kinetic description of a reaction and the analysis of the rate law may not be conclusive with respect to the mechanism of the autoxidation process. 

The general features discussed so far can explain the complexity of these reactions alone. However, thermodynamic and kinetic couplings between the redox steps, the complex equilibria of the metal ion and/or the proton transfer reactions of the substrate(s) lead to further complications and composite concentration dependencies of the reaction rate. The speciation in these systems is determined by the absolute concentrations and the concentration ratios of the reactants as well as by the pH which is often controlled separately using appropriately selected buffers. Perhaps, the most intriguing task is to identify the active form of the catalyst which can be a minor, undetectable species. When the protolytic and complex-formation reactions are relatively fast, they can be handled as rapidly established pre-equilibria (thermodynamic coupling), but in any other case kinetic coupling between the redox reactions and other steps needs to be considered in the interpretation of the kinetics and mechanism of the autoxidation process. This may require the use of comprehensive evaluation techniques. 

A prolific author, Professor van Eldik has been responsible for some 580 papers in refereed journals, and four books as editor or co-editor. His current research intrests are the application of high pressure techniques in mechanistic studies metal-catalyzed autoxidation processes and bioinorganic studies. As such he is eminently qualified to edit the prestigious Advances in Inorganic Chemistry. We are confident that he is a worthy successor to Professor Geoff Sykes and that he will maintain the high standards for which the series is known. 

We have used the reaction of m-chloroperbenzoic acid with Co/Mn/Br as a model system to attempt to understand the nature of this important autoxidation catalyst. Using stopped-flow and UV-VIS kinetic techniques, we have determined the step-wise order in which the catalyst components react with each other. The cobalt(II) is initially oxidized to Co(III) by the peracid, the cobalt(III) then oxidizes the manganese to Mn(III), which then oxidizes the bromide. The order of these redox reactions is the opposite to that expected from thermodynamics. Suggestions will be made of the relationship of this model to the known characteristics of autoxidation processes. 

These two reactions compete. Reaction 16 requires a significant activation energy and will therefore be favored at elevated temperatures and in polymers containing labile (tertiary) hydrogens. It will also occur at low doses when the concentration of RO/ is too small to make mutual combination likely. This reaction is actually responsible for the well-known autoxidation process, which can be initiated in certain polymers by fairly low doses of radiation. 

Autoxidation without Discharge. To compare our results with normal autoxidation, the reaction was carried out using a reaction mixture similar to Run 4 without silent discharge. Low conversion of cyclohexene (0.051% ) was observed at 60°C., indicating that the discharge oxidation was hardly affected by the normal autoxidation process under the present reaction conditions. The major product was 3-cyclohexenylhydroperoxide, and minor products were 3-cyclohexenol, 3-cyclohexenone, cyclohexene oxide, and trace amounts of residue saturated materials such as cyclo-hexanol and cyclohexanone were not detected. The conversion of cyclohexene was raised to 0.15% when the reaction temperature was elevated to 140°C. however, the kinds of product were not changed. 

Various methods have been employed to measure the extent of autoxi-dation in lipids and lipid-containing food products. For obvious reasons, such methods should be capable of detecting the autoxidation process before the onset of off-flavor. Milk and its products, which develop characteristic off-flavors at low levels of oxidation, require procedures that are extremely sensitive to oxidation. Thus methods of measuring the decrease in unsaturation (iodine number) or the increase in diene conjugation as a result of the reaction do not lend themselves to quality control procedures, although they have been used successfully in determining the extent of autoxidation in model systems (Haase and Dunkley 1969A Pont and Holloway 1967). 

Badings, H. T. 1960. Principles of autoxidation processes in lipids with special regard to the development of autoxidation off-flavors. Neth. Milk Dairy J. 14, 215-242. 

Each of the standard TAG chromatograms exhibits one main peak, which grows during the autoxidation process of the samples. These main peaks do not characterize one pure compound, because shoulders can be seen in them. Present knowledge about the oxidation of TAGs and the... 

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