Oxidation-reduction reactions alcohols

CaniZZaro Reaction. Both 2- and 4-hydroxybenzaldehydes undergo this self-oxidation—reduction reaction, but much less readily than benzaldehyde the reaction requires metal catalysts such as nickel, cobalt, or silver to yield the corresponding hydroxybenzoic acids and hydroxybenzyl alcohols (47—48). 

Another method to hydrogenate butadiene occurs during an oxidation—reduction reaction in which an alcohol is oxidi2ed and butadiene is reduced. Thus copper—chromia or copper—2inc oxide cataly2es the transfer of hydrogen from 2-butanol or 2-propanol to butadiene at 90—130°C (87,88). 

Since many of the transformations undergone by metabolites involve changes in oxidation state, it is understandable that cofactors have been developed to act as electron acceptors/ donors. One of the most important is that based on NAD/NADP. NAD+ can accept what is essentially two electrons and a proton (a hydride ion) from a substrate such as ethanol in a reaction catalysed by alcohol dehydrogenase, to give the oxidized product, acetaldehyde and the reduced cofactor NADH plus a proton (Figure 5.2). Whereas redox reactions on metal centres usually involve only electron transfers, many oxidation/reduction reactions in intermediary metabolism, as in the case above, involve not only electron transfer but... 

Figure 10. Cyclic voltammetric response at the NPyeCME for the oxidation/ reduction reaction of benzyl alcohol (32 mM)/C10 in aqueous 4.1 mol NaOCl (A) and nonaqueous CH2CI2 (B) solutions at a scan rate of 50 mV/s. (C) Cartoon for the NPyeCME. Inset (A) corresponds to an enlarged version of the oxidation part without (a) and with (b) benzyl alcohol. In order to marntam the electrical conductivity, 0.1 M tetrabutylammonium bromide (TBAB) is added into the CH2CI2 solution.

This enzyme [EC 1.1.99.8], also referred to as alcohol dehydrogenase (acceptor) and methanol dehydrogenase, catalyzes the oxidation-reduction reaction of a primary alcohol with an acceptor to generate an aldehyde and the reduced acceptor. The cofactor for this enzyme is pyrroloquinoline qutnone (PQQ). A wide variety of primary alcohols can act as the substrate. See also Alcohol Dehydrogenase... 

A major class of enzymes that catalyze oxidation-reduction reactions. This class includes dehydrogenases, reductases, oxygenases, peroxidases, and a few synthases. Examples include alcohol dehydrogenase (EC 1.1.1.1), aldehyde oxidase (EC 1.2.3.1), orotate reductase (EC 1.3.1.14), glutamate synthase (EC 1.4.1.14), NAD(P) transhydrogenase (EC 1.6.1.1), and glutathione peroxidase (EC 1.11.1.9). 

RGURE 7 An oxidation-reduction reaction. Shown here is the oxidation of lactate to pyruvate. In this dehydrogenation, two electrons and two hydrogen ions (the equivalent of two hydrogen atoms) are removed from C-2 of lactate, an alcohol, to form pyruvate, a ketone. In cells the reaction is catalyzed by lactate dehydrogenase and the electrons are transferred to a cofactor called nicotinamide adenine dinucleotide. This reaction is fully reversible pyruvate can be reduced by electrons from the cofactor. In Chapter 13 we discuss the factors that determine the direction of a reaction. 

Acrolein is a highly reactive compound because both the double bond and aldehydic moieties partidpate in a variety of reactions, including oxidation, reduction, reactions with alcohols yielding alkoxy propionaldehydes,... 

The biochemistry of alcoholic fermentation involves a series of internal enzyme-mediated oxidation-reduction reactions m which glucose is degraded via the Embden-Meyerhof-Parnas pathway See also Carbohydrates and Glycolysis. 

In homogeneous chemistry, pure electron transfer reactions are seldom encountered. Indeed, with the exception of a few examples, electron transfers are often associated with atom or group transfers. This usually results in a confused notion of the nature of oxidation-reduction reactions. For example, the reaction of a ketone with sodium in alcohol to afford the corresponding alcohol, via the sequence in Eq. (1) [2],... 

Because of the involvement of transfer of electrons, the reaction between sodium metal and either water or an alcohol are examples of oxidation-reduction reactions. 

Panza et al. synthesized a C02-philic amphiphile from the coenzyme nicatinamide adenine dinucleotide (MW 664) and a covalently attached perfluoropolyether (MW 2500) (Figure 7B) (73). The fluorofunctional coenzyme (FNAD) was soluble up to 5 mM in CO2 at room temperature and 1400 psi. The C02-soluble FNAD was able to participate in a cyclic oxidation/reduction reaction catalyzed by the enzyme horse liver alcohol dehydrogenase (HLADH) in CO2 at room temperature and 2600 psi. 

Muonium has been observed in pure hydrocarbons ( ), alcohols (, 7 ), and water ( ). Because Mu reacts slowly with these pure liquids, giving observable reaction lifetimes of Mu up to 4us, they can be used as solvents to study various solutes of interest. As the free triplet Mu atom reacts with the solute its observed precession frequency is damped and a decay constant, X can be obtained. The concentration dependence of the decay constant provides second order chemical rate constants for Mu addition, abstraction, spin conversion, and oxidation-reduction reactions. When analogous hydrogen atom rate constants are available the kinetic isotope effect can also be calculated. 

Converting one functional group into another is called functional group interconversion. Our knowledge of oxidation-reduction reactions has greatly expanded our ability to carry out functional group interconversions. For example, an aldehyde can be converted into a primary alcohol, an alkene, a secondary alcohol, a ketone, a carboxylic acid, an acyl chloride, an ester, an amide, or an amine. 

How do these oxidation-reduction reactions take place All the chemistry of the pyridine nucleotide coenzymes (NAD, NADP, NADH, and NADPH) takes place at the 4-position of the pyridine ring. The rest of the molecule is important for binding the coenzyme to the proper site on the enzyme. If a substrate is being oxidized, it donates a hydride ion (H ) to the 4-position of the pyridine ring. In the following reaction, the primary alcohol is oxidized to an aldehyde. A basic amino acid side chain of the enzyme can help the reaction by removing a proton from the oxygen in the substrate. 

When is NAD, rather than FAD, used in a particular oxidation-reduction reaction It depends on the chemical properties of the electron donor and the enzyme catalyzing the reaction. In oxidation reactions, NAD accepts two electrons as a hydride ion to form NADH, and a proton (H ) is released into the medium (Fig 19.9). It is generally nsed for metabolic reactions involving oxidation of alcohols and aldehydes. In contrast,... 

There are several classes of alcohol dehydrogenases that catalyze the reversible oxidation/reduction reaction of alcohols to aldehydes (Testa and Kramer, 2007 ... 

It would be well to point out a few examples which illustrate the overlap of asymmetric reduction studies and molecular biochemistry. Diphosphopyridine nucleotide (DPN) and triphospho-pyridine nucleotide (TPN) are important coenzymes in biochemical oxidation reduction reactions. Certain enzymes function as catalysts for the reversible transfer of hydrogen between these nucleotides and a substrate for which the enzyme is specific. For example, DPN and the enzyme, alcohol dehydrogenase (ADH), form a redox system with ethanol. Using deuterium labeled reducing agent and substrate, Westheimer, Vennesland,... 

Like water, alcohols react with Li, Na, K, Mg, and other active metals to liberate hydrogen and to form metal alkoxides. In the following oxidation-reduction reaction, Na is oxidized to Na and is reduced to H2 ... 

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