Ethane anodic oxidation

Anodic acetoxylation is an illustrative example of these principles. Anodic oxidation of sodium acetate in acetic acid at a platinum anode under constant current conditions yields ethane in almost quantitative yield. The mechanism was supposed to be discharge of acetate ion at the anode with formation of an acetoxy radical, which subsequently would undergo decarboxylation with formation of methyl radicals as shown in Eqs. (14) and (15). 

Kolbe synthesis — The definition and use of the terms - Kolbe synthesis, K. reaction, K. electrolysis, and K. process are not very clearly distinguished and often bear different nuances of meaning. Kolbe electrolysis or synthesis mainly accounts for the anodic oxidation of carboxylic acids or carboxylates, followed by a decarboxylation step, when concentrated aqueous solutions of the respective carboxylates are electrolyzed. Kolbe picked up earlier results from -> Faraday on the electrolysis of acetic acid or acetate solutions to CO2 and ethane [i] and continued these experiments during 1843-1845 with further homologs as, e.g., valerianic acid [ii]. The carboxy-late R-COO- is anodically oxidized to form an unstable radical R-COO, which is stabilizing via a decarboxylation reaction, leaving radical rest R ... 

Imidazole carboxylic acids are readily converted into hydrazides,436 acid halides,437 amides,437-439 and esters,439-440 and they may be reduced to alcohols with lithium aluminum hydride,441 and to aldehydes by controlled potential reduction.442 Anodic oxidation of l-methylimidazole-5-acetic acid (94) using cooled platinum electrodes yields l,2-bis(l-methylimidazol-5-yl)ethane (95).443... 

A point of view which brings together some of the essential features of both the foregoing theories, d at the same time accounts for many of the facts which these theories fail to explain, is similar to that previously described in connection with the anodic oxidation of thiosulfate. It is suggested that hydroxyl radicals, or hydrogen peroxide formed by their combination in pairs, react with the acetate ions to form acetate radicals, which then combine, possibly with the intermediate formation of acetyl peroxide, to yield ethane and carbon dioxide thus,... 

The oxidation of acetate by peroxodisulphate is much slower than that of formate. Glasstone and Hickling showed that the products, which include carbon dioxide, methane, ethane, and ethylene, are similar to those produced by the anodic oxidation of acetate ions (Kolbe electrolysis), and they inferred that the same organic radicals are formed as intermediates. Similar results are reported by Eberson et al. for the oxidations of ethyl terf.-butyl-malonate, tert.-butyl-cyanoacetate, and ferl.-butyl-malonamate ions. The oxidations of these ions and of acetate by peroxodisulphate are first order with respect to peroxodisulphate and zero order with respect to the substrate. Mechanisms involving hydroxyl radicals are excluded because the replacement of peroxodisulphate by Fenton s reagent leads to different products, so Eberson et al. infer that the initial attack on the substrate is by sulphate radical-ions. Sengar and Pandey report that the rate of the silver ion-catalysed oxidation of acetate is independent of the peroxodisulphate concentration. 

Variation in the rate of anodic oxidation of normal saturated hydrocarbons with the number of carbon atoms parallels the variation in the rate of diffusion of the hydrocarbon through the electrolyte. This holds for different electrolytes (CsF/HF, H3PO4, HF, H2SO4) and electrodes (Pt-black, Raney-Pt). The rates are low for methane, highest for ethane and propane and then gradually decrease . ... 

The use of low molecular weight Refs. 33-37 hydrocarbons such as methane, ethane, and propane was considered to be an economic alternative to the anodic oxidation of hydrogen in the fuel cell. Extensive research and development was undertaken in this area in the 1960s. 

In 1859, Friedel electrolytically oxidized acetone and found a mixture of formic, acetic, and carbonic acids with evolution of carbon dioxide and oxygen at the anode in an acetone-sulfuric acid mixture. Further studies on ketones were not reported until 1931, when a similar study was carried out resulting in the formation of methane, ethane, and unsaturated hydrocarbons, in addition to carbon dioxide and oxygen at platinum anodes. The first anodic oxidation of benzene was reported in 1880, with the observation that the electrolytic oxidation of benzene in an ethanolic-sulfuric acid medium yielded unidentifiable substances. A few years later Gotterman and Friedrichs reported that hydrocarbons were obtained from the anodic oxidation of benzene in alcoholic-sulfuric acid solution at platinum anodes. 

Fleischmann, M., Mansfield, J.R. and Wynne-Jones, W.K.F. (1965) The anodic oxidation of acetate ions at smooth Pt electrodes. Part 2. The non-steady state of the Kolbe synthesis of ethane. Journal of Electroanalytical Chemistry. 10, 522. 

Evidence for the presence of more than one type of chemisorbed species was found in studies [7—9, 61, 62] of the species formed during the anodic oxidation or the reactions at open circuit of hydrocarbons on platinum in acid solutions. It was observed that a part of the chemisorbed species desorbs from the surface at potentials below 0.2 V. The results [21] on ethane in Fig. 52 are an example. A programmed... 

An anodic oxidation with a long history is the Kolbe synthesis of hydrocarbons, exemplified by the electrolysis of an alkali-metal acetate solution to give ethane ... 

Binder and others [230] found that Raney platinum was the best single catalyst for electrochemical oxidation of hydrocarbons. Data obtained by Bianchi [231], Grubb [232], and Cairns and Mclnemey [203], who compared the catalytic activities of various platinum blacks in the anodic oxidation of propane, are consistent with this conclusion. As found by Petrii and Marvet [100], the oxidation rate of methane decreases sharply on changing from platinum to other platinum catalysts. Bockris and Dahms [192] showed that the oxidation rate of ethylene decreases in the series Pt > Rh > Ir and Pd > Au, where platinum is considerably more active than palladium. It was found in [233] that the oxidation rate of propane in alkali decreases in the order Pd > Pt > Ag, and those of ethane ethylene, propylene, and n-butane decrease in the order Pt > Pd... 

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-... 

They find that the anode potential determines the effect. The first reaction which occurs predominatingly at iron and palladium electrodes, requires the lowest potential. With platinized platinum electrodes the potential lies higher the oxidation action can exceed the evolution of oxygon and with a particularly high potential, which is obtained by prepolarizing the platinized anode,1 ethane is produced. With polished platinum and iridium anodes the potential is still higher than with prepolarized platinized platinum anodes. Thus the production of ethane predominates over the oxidation of acetic ester. 

The presence of free alkali is always injurious to the production of ethane. The evolution of oxygen at platinized platinum increases with increasing alkalinity and decreases at polished anodes, while the oxidation of acetic ester increases. 

If neutral salts are added to the electrolyte, especially if this consists of acetic acid only, with no acetate, the extent of the Kolbe reaction is diminished under these conditions also, methyl alcohol is formed by the so-called Hofer-Moest reaction (1902). When the conditions are such that the acetate is oxidized to ethane the anode potential is about 2.2... 

It is possible that some acetate radicals are formed by the direct discharge of the ions as, it will be seen shortly, is the case in non-aqueous solutions but an additional mechanism must be introduced, such as the one proposed above, to account for the influence of electrode material, catalysts for hydrogen peroxide decomposition, etc. It is significant that the anodes at which there is no Kolbe reaction consist of substances that are either themselves catalysts, or which become oxidized to compounds that are catalysts, for hydrogen peroxide decomposition. By diverting the hydroxyl radicals or the peroxide into an alternative path, viz., oxygen evolution, the efficiency of ethane formation is diminished. Under these conditions, as well as when access of acetate ions to the anode is prevented by the presence of foreign anions, the reactions mentioned above presumably do not occur, but instead peracetic acid is probably formed, thus,... 

Methane can be catalytically oxidized in the fuel cell mode to simultaneously generate electricity and C2 hydrocarbons by dimerization of methane using a yttria-stabilized zirconia membrane. A catalyst, used as the anode, is deposited on the side of the membrane that is exposed to methane and the cathode is coated on the other side of the membrane. When the catalyst Ag>Bi2C>3 is used as the anode for the reaction at 750> 900X and atmospheric total pressure, the selectivity to ethane and ethylene exceeds 90%. But this high selectivity is at the expense of low power output and low overall methane conversion (less than about 2%). 

---