Oxidation of ethanol

Acetobacter 3nd Gluconobacter C3.n be separated based on their relative abilities to oxidize ethanol. Over-oxidizers Acetobacter) convert ethanol to acetic acid and then to CO2 and H2O. Conversely, acetic acid is an end product for Gluconobacter. Two methods commonly used to differentiate these bacteria on this basis involve either the Carr medium or Frateur s 

Using Frateur s or CCF media, acid produced by bacteria neutralizes the insoluble CaCOs resulting in a clear zone or halo around the colony. These media differ only in the concentrations of yeast extract (1% w/v for Frateur s and 0.5% w/v for calcium carbonate—ethanol) and ethanol (2% v/v for Frateur s and 3% v/v for CCF). 

Both Gluconobacter and Acetobacter will oxidize ethanol to acetic acid, thereby bringing about a clearing in the media (more transparent) due to neutralization of the CaCOj by acid production. Redevelopment of an opaque background in previously cleared halos is indicative of overoxidation due to acid oxidation Acetobacter), whereas failure of the medium to re-cloud suggests Gluconobacter. 

Detection of over-oxidation of ethanol may require an incubation of 3 or more weeks. Under extended incubations, desiccation (loss of water) from media must be limited by maintaining a high humidity around the 

Once dissolved, dilute to volume (1000mL) with distilled water. Adjust pH to 5.5 with 50% v/v H3PO4 or 6M KOH prior to autoclaving at 121°C/250°F for 15 min. 

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Manufactured by the liquid-phase oxidation of ethanal at 60 C by oxygen or air under pressure in the presence of manganese(ii) ethanoate, the latter preventing the formation of perelhanoic acid. Another important route is the liquid-phase oxidation of butane by air at 50 atm. and 150-250 C in the presence of a metal ethanoate. Some ethanoic acid is produced by the catalytic oxidation of ethanol. Fermentation processes are used only for the production of vinegar. 

Many biological processes involve oxidation of alcohols to carbonyl compounds or the reverse process reduction of carbonyl compounds to alcohols Ethanol for example is metabolized m the liver to acetaldehyde Such processes are catalyzed by enzymes the enzyme that catalyzes the oxidation of ethanol is called alcohol dehydrogenase... 

Both the fermentation of hexose sugars to ethanol and carbon dioxide and the oxidation of ethanol to acetic acid are exothermic (heat yielding) processes (see Sugar). The first reaction is expressed as foUows ... 

It has also been proposed that under the acidic conditions found ia whiskeys, ethanol reacts with lignin (qv) to reduce an alcohol-soluble form of lignin (ethanol lignin). This can be converted into coniferyl alcohol, which can be oxidized to coniferaldehyde. The partial oxidation of ethanol lignin can produce siaapic and coniferyl alcohols that can be converted to syfingaldehyde and vanillin, respectively (8). 

There are two ways to produce acetaldehyde from ethanol oxidation and dehydrogenation. Oxidation of ethanol to acetaldehyde is carried out ia the vapor phase over a silver or copper catalyst (305). Conversion is slightly over 80% per pass at reaction temperatures of 450—500°C with air as an oxidant. Chloroplatinic acid selectively cataly2es the Uquid-phase oxidation of ethanol to acetaldehyde giving yields exceeding 95%. The reaction takes place ia the absence of free oxygen at 80°C and at atmospheric pressure (306). The kinetics of the vapor and Uquid-phase oxidation of ethanol have been described ia the Uterature (307,308). 

According to the proposed mechanism for biological oxidation of ethanol, the hydrogen that is transferred to the coenzyme comes from C-1 of ethanol. Therefore, the dihydropyridine ring will bear no deuterium atoms when CD3CH2OH is oxidized, because all the deuterium atoms of the alcohol are attached to C-2. 

However, the reaction occurring in the acetaldehyde/ethanol half-cell is the oxidation of ethanol ... 

A problem often encountered in the oxidation of primary alcohols to acids is that esters are sometimes produced as by-products. For example, oxidation of ethanol yields acetic acid and ethyl acetate ... 

Balance the half-reaction involved in the oxidation of ethanol to acetic acid. Compare the number of electrons released per mole of ethanol with the number per mole of methanol in the equivalent reaction (73c). How many electrons would be released per mole of propanol in the oxidation to propionic acid ... 

Alcohol dehydrogenase is a cytoplasmic enzyme mainly found in the liver, but also in the stomach. The enzyme accomplishes the first step of ethanol metabolism, oxidation to acetaldehyde, which is further metabolized by aldehyde dehydrogenase. Quantitatively, the oxidation of ethanol is more or less independent of the blood concentration and constant with time, i.e. it follows zero-order kinetics (pharmacokinetics). On average, a 70-kg person oxidizes about 10 ml of ethanol per hour. 

Acetic acid, CH,COOH(l), could be produced from (a) the reaction of methanol with carbon monoxide (b) the oxidation of ethanol (c) the reaction of carbon dioxide with... 

Formally, in redox reactions there is transfer of electrons from a donor (the reductant) to the acceptor (the oxidant), forming a redox couple or pair. Oxidations in biological systems are often reactions in which hydrogen is removed from a compound or in which oxygen is added to a compound. An example is the oxidation of ethanol to acetaldehyde and then to acetic acid where the oxidant is NAD. catalyzed by alcohol dehydrogenase and acetaldehyde dehydrogenase, respectively. 

Alcoholism leads to fat accumulation in the liver, hyperlipidemia, and ultimately cirrhosis. The exact mechanism of action of ethanol in the long term is stiU uncertain. Ethanol consumption over a long period leads to the accumulation of fatty acids in the liver that are derived from endogenous synthesis rather than from increased mobilization from adipose tissue. There is no impairment of hepatic synthesis of protein after ethanol ingestion. Oxidation of ethanol by alcohol dehydrogenase leads to excess production of NADH. 

Dobereiner Selective oxidation of ethanol to acetic acid on platinum... 

Induced oxidation of alcohols by hydrogen peroxide was studied by Kolthoff and Medalia . According to their measurements the value of F-, increases with the increase in the concentration of ethanol, while it decreases with increase in the acid concentration (see Table 16). In acetic acid medium the value of F[ is considerably lower. Chloride ions effectively suppress the induced oxidation of alcohols. The main product of the oxidation of ethanol is acetaldehyde which can be further oxidized to acetic acid. The data on the induced oxidation of alcohol (H2A) can be interpreted by reactions (53), (98), (99) and (57). 

Frimmer U, F Widdel (1989) Oxidation of ethanol by methanogenic bacteria. Growth experiments and enzymatic studies. Arch Microbiol 152 479-483. 

Such improvements in conversion were reported for the oxidation of ethanol by hydrogen peroxide to acetic acid. This is a well-studied reaction, carried out in a continuous stirred-tank reactor (CSTR). Near-complete conversion (> 99%) at near-complete selectivity (> 99%) was found in a micro-reaction system [150]. Processing in a CSTR resulted in 30-95% conversion at > 99% selectivity. 

Oxodedihydro Bisubstitution - Catalyzed Oxidation of Ethanol with HjOj to Acetic Acid... 

The catalyzed oxidation of ethanol to acetic acid is a well-studied reaction, carried out in continuous stirred tank reactors (CSTR) [51]. Hence it is a good test reaction for benchmarking micro reactor results. 

Organic synthesis 84 [OS 84] Catalyzed oxidations of ethanol with hydrc en peroxide to acetic acid... 

Kraut, M., Nagel, A., Schubert, K., Oxidation of ethanol by hydrogen peroxide, in Proceedings of the 6th International Conference on Microreaction Technology, IMRET 6, 11-14 March 2002,... 

Bio-ethanol is attracting growing interests in relation to the shift of raw materials from petroleum to biomass. A pioneering work by Christensen is that over MgAl203 support gold is much more selective to acetic acid than palladium and platinum in the aerobic oxidation of ethanol in water in a batch reactor. Figure 32 shows that selectivity to acetic acid exceeds 80% [99]. In contrast, Au/Si02 catalysts prepared by deposition reduction... 

Similar considerations apply to the oxidation of ethanol, although one must take into account the breaking of the C—C bond, and the formation and involvement of different intermediates and side products. Ethanol oxidation will be the topic of Section 6.5. Section 6.6 will briefly summarize our main conclusions and discuss the relation of our surface science approach to real catalysts. 

Gold is generally considered a poor electro-catalyst for oxidation of small alcohols, particularly in acid media. In alkaline media, however, the reactivity increases, which is related to that fact that no poisoning CO-hke species can be formed or adsorbed on the surface [Nishimura et al., 1989 Tremihosi-Filho et al., 1998]. Similar to Pt electrodes, the oxidation of ethanol starts at potentials corresponding to the onset of surface oxidation, emphasizing the key role of surface oxides and hydroxides in the oxidation process. The only product observed upon the electrooxidation of ethanol on Au in an alkaline electrolyte is acetate, the deprotonated form of acetic acid. The lack of carbon dioxide as a reaction product again suggests that adsorbed CO-like species are an essential intermediate in CO2 formation. 

In acidic media, the reactivity of ethanol on Au electrodes is much lower than in alkaline media. The main product of the oxidation of ethanol on Au in an acidic electrolyte was found to be acetaldehyde, with small amounts of acetic acid [Tremiliosi-FiUio et al., 1998]. The different reactivities and the product distributions in different media were explained by considering the interactions between the active sites on Au, ethanol, and active oxygen species absorbed on or near the electrode surface. In acidic media, surface hydroxide concentrations are low, leading to relatively slow dehydrogenation of ethanol to form acetaldehyde as the main oxidation pathway. In contrast, in alkaline media, ethanol, adsorbed as an ethoxy species, reacts with a surface hydroxide, forming adsorbed acetate, leading to acetate (acetic acid) as the main reaction product. 

Lai SCS, Koper MTM. 2009. Electro-oxidation of ethanol and acetaldehyde on platinum single-crystal electrodes. Faraday Discuss 140 399-416. 

Tamowski DJ, Korzeniewski C. 1997. Effects of surface step density on the electrochemical oxidation of ethanol to acetic acid. J Phys Chem B 101 253. 

Xia XH, Liess HD, Iwasita T. 1997. Early stages in the oxidation of ethanol at low index single crystal platinum electrodes. J Electroanal Chem 437 233-240. 

Considering as an example a DEFC, electro-oxidation of ethanol takes place at the anode (negative pole of the cell),... 

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