Oxidation of organic compounds

The oxidation of organic compounds by water-soluble inorganic oxidants is often made difficult not only by the insolubility of the organic substrate in water, but also by the susceptibility of many of the miscible non-aqueous solvents to oxidation. Solubilization of the ionic oxidant into solvents such as benzene, chloroform, dichloromethane or 1,2-dichlorobenzene, by phase-transfer catalysts obviates these problems, although it has been suggested that dichloromethane should not be used, as it is also susceptible to oxidation [1]. 

This field of enzyme application can be of the greatest interest, because, on the one hand, electroorganic reactions require high overvoltages and, on the other, the use of enzymes is bound to open the way for carrying out reactions which do not proceed on conventional electrocatalysts. 

The reaction of D-glucose oxidation to 5-glucolactone is accelerated by glucose oxidase. The transport of electrons to the electrode was realized with the aid of mediators such studies are historically the first examples of the successful use of the mediator approach in bioelectrocatalysis. 

Glucose oxidase is immobilized in a polyacrylamide matrix. Oxygen and quinone which serve as mediators are reduced to hydrogen peroxide and hydroquinone, respectively. Since their oxidation starts at E, 0.7-0.9 V, it is possible to displace the initial potential for the oxidation of glucose by 0.6-0.8 V towards positive values compared to its stationary electrochemical oxidation to gluconic acid on platinum.  

The mediatorless electrooxidation of glucose has been realized in the presence of glucose oxidase adsorbed on an electrode made of organic metal. Oxidation occurs at E, 0.5 V and the electrode preserved its activity for more than 100 days. 

To accelerate the electrooxidation of lactic acid, NAD -dependent lactate dehydrogenase has been used with FMN as a mediator. For the same purpose (as well as for the oxidation of alcohols) NAD-dependent dehydrogenases with two conjugated pairs of mediators have been proposed  

As described in Section 4.1.2, nucleophilic organic compounds are oxidized at the electrode. Some oxidizable organic compounds are listed in Table 8.7 with the potentials of the first oxidation step in non-aqueous solvents. By using a solvent of weak basicity and a supporting electrolyte that is difficult to oxidize, we can expand the potential window on the positive side and can measure oxidations of dif- 

Compounds Solvent Supporting electrolyte Potential Reference Potential 

A reversible one-electron oxidation CV peak for C60 has been obtained at room temperature and at lOOmVs-1 in 1,1,2,2-tetrachloroethane (TCE) containing Bu4NPF6 as supporting electrolyte. In other solvents such as AN and DCE, the oxidation was irreversible and contained multi-electrons. The HOMO-LUMO energy gap for C60 in TCE was 2.32 V [52 a]. 

In solvents of weak basicity (e.g. AN), aromatic hydrocarbons (AH) are oxidized, at least in principle, in two steps. In the first step, the compound gives an electron in its highest occupied molecular orbital (HOMO) to the electrode to form a radical cation (AH +), whereas, in the second step, it gives another electron to the electrode to form dication AH2+  

The two-step oxidation really occurs, for example, with 9,10-diphenylanthracene. As shown by the CV curve in Fig. 8.19, the two waves are reversible or nearly reversible. The radical cation of 9,10-diphenylanthracene is fairly stable and, as in the case of radical anions, its ESR signals can be measured. 

All water sources may contain natural organic matter, but concentrations (usually measured as dissolved organic carbon, DOC) differ from 0.2 to more than 10 mg L l. NOM is a direct quality problem due to its color and odor, but more important are indirect problems, such as the formation of organic disinfection by-products (DBPs, e. g. M -halomethanes (THMs) due to chlorination), support of bacterial regrowth in the distribution system, disturbances of treatment efficiency in particle separation, elevated requirements for coagulants and oxidants or reductions in the removal of trace organics during adsorption and oxidation, etc. 

Removal of NOM or its alteration to products less reactive to chlorine is a priority task in modem water treatment, comprising chemical oxidation by ozone, biodegradation, adsorption, enhanced coagulation or even membrane technologies. A DOC-level of approximately 1 mg L 1 appears to be the lower limit of ozone applications, but a few cases exist, where waters with lower concentrations of NOM (ground water) have been treated. 

The first three tasks are much more relevant and applicable to full-scale plants, compared to the last topic. The reason is the high ozone demand for direct chemical mineralization, with typically more than 3 g 03 g l DOC initially present needed to achieve a removal efficiency of 20 % or more. 

The removal of color and UV-absorbance is one of the easier tasks due to quick reactions and comparatively low required specific ozone consumptions in the range below 

1 g 03 g 1 DOC. Thus, this effect is observed in preozonation steps for improved particle separation. Color can be removed by 90 % or more, while UV-absorbance at 254 nm is commonly reduced to 20-50 % of the initial value. The reaction mechanism here is primarily the direct ozone attack on C-double bonds in aromatic and chromophoric molecules leading to the formation of bleached products, like aliphatic acids, ketones and aldehydes. 

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R. A. Sheldon and J. K. Kochi, Metal-Catalj d Oxidations of Organic Compounds, Academic Press, Inc., New York, 1981. 

Additionally, the enthalpies of activation (142) for the permanganate oxidation of organic compounds is characteristically low in the range of... 

The most common oxidation states and the corresponding electronic configuration of mthenium are +2 and +3 (t5 ). Compounds are usually octahedral. Compounds in oxidations states from —2 and 0 (t5 ) to +8 have various coordination geometries. Important appHcations of mthenium compounds include oxidation of organic compounds and use in dimensionally stable anodes (DSA). 

The oxidation of organic compounds by manganese dioxide has recently been reviewed. It is of limited application for the introduction of double bonds, but the advantages of mildness and simple workup make it attractive for some laboratory-scale transformations. Manganese dioxide is similar to chloranil in that it will oxidize A -3-ketones to A -dienones in refluxing benzene. Unfortunately, this reaction does not normally go to completion, and the separation of product from starting material is difficult. However, Sondheimer found that A -3-alcohols are converted into A -3-ketones, and in this instance separation is easier, but conversions are only 30%. (cf. Harrison s report that manganese dioxide in DMF or pyridine at room temperature very slowly converts A -3-alcohols to A -3-ketones.)... 

Cytochrome P-450 — an effective catalyst of the oxidation of organic compounds by peroxides. D. I. Metelitsa, Russ. Chem. Rev. (Engl. Transl), 1981, 50,1058-1073 (147). 

In such a synthesis the lengths of the pulses are variable as well as the potentials of the square wave. Recently a potential-time profile has been used to maintain the activity of an electrode during the oxidation of organic compounds (Clark et al., 1972) at a steady potential the current for the oxidation process was observed to fall, but a periodic short pulse to cathodic potentials was sufficient to prevent this decrease in electrode activity. 

Conversely, the use of elevated temperatures will be most advantageous when the current is determined by the rate of a preceding chemical reaction or when the electron transfer occurs via an indirect route involving a rate-determining chemical process. An example of the latter is the oxidation of amines at a nickel anode where the limiting current shows marked temperature dependence (Fleischmann et al., 1972a). The complete anodic oxidation of organic compounds to carbon dioxide is favoured by an increase in temperature and much fuel cell research has been carried out at temperatures up to 700°C. 

Oxidation of Organic Compounds at the Nickel Hydroxide Electrode H.-J. Schafer... 

Dissimilatory sulfate reducers such as Desul-fovibrio derive their energy from the anaerobic oxidation of organic compounds such as lactic acid and acetic acid. Sulfate is reduced and large amounts of hydrogen sulfide are generated in this process. The black sediments of aquatic habitats that smell of sulfide are due to the activities of these bacteria. The black coloration is caused by the formation of metal sulfides, primarily iron sulfide. These bacteria are especially important in marine habitats because of the high concentrations of sulfate that exists there. 

For a review of reactions of H2O2 and metal ions with all kinds of organic compounds, including aromatic rings, see Sosnovsky, G. Rawlinson, D.J. in Swem Organic Peroxides, vol. 2 Wiley NY, 1970, p. 269. See also Sheldon, R.A. Kochi, J.K. Metal-Catalyzed Oxidations of Organic Compounds, Academic Press NY, 1981. 

Hazards arising from the oxidation of organic compounds are greater when the reactants are volatile, or present as a dust or an aerosol. Liquid oxygen and various concentrated acids, e.g. nitric, sulphuric or perchloric acid, and chromic acid are strong oxidizing agents. The use of perchloric acid or perchlorates has resulted in numerous explosions their use should be avoided when possible (refer to Table 6.5). 

The slow step of this reaction corresponds to removal of hydride from an anion and finds several counterparts in oxidations of organic compounds by MnO. The anion may have the structure... 

W. A. Waters, Mechanisms of Oxidation of Organic Compounds, Methuen, London, 1964. 

As has already been mentioned, during the iron(II)-hydrogen peroxide reaction a number of organic compounds which do not react, or react only slowly with hydrogen peroxide, are readily oxidizable. In the induced oxidation of organic compounds, hydrogen peroxide plays the role of the actor and iron(II) is the inductor. 

Lenoir, D. (2006) Selective Oxidation of Organic Compounds - Sustainable Catalytic Reactions with Oxygen and without Transition Metals Angewandte Chemie International Edition, 45, 3206-3210. 

Sheldon, R.A. and Kochi, J.K., 1981, Metal Catalysed Oxidations of Organic Compounds , Academic Press, New York. 

Sandorfy, C. Vibrational Spectra of Hydrogen Bonded Systems in the Gas Phase. 120, 41-84 (1984). Schafer, H.-J. Oxidation of Organic Compounds at the Nickel Hydroxide Electrode. 142, 101-129 (1987). 

Dispersing a number of water-floatable particles on an oil film, the particles of a material that, under illumination and in the presence of air, accelerates the oxidation of organic compounds in the oil film... 

The particles consist of a bead with an exterior surface that is at least partially coated with a material capable of accelerating the oxidation of organic compounds floating on water, under illumination, and in the presence of air. The coated bead is water-floatable and has a diameter of less than 2 mm. The bead consists of a plastic material coated with an intermediate layer of a material that will not accelerate the oxidation of the plastic material by air or by itself, oxidized under illumination and in the presence of air by the outer coating material. 

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