Acetaldehyde from alcohol

Since 1960, the Hquid-phase oxidation of ethylene has been the process of choice for the manufacture of acetaldehyde. There is, however, stiU some commercial production by the partial oxidation of ethyl alcohol and hydration of acetylene. The economics of the various processes are strongly dependent on the prices of the feedstocks. Acetaldehyde is also formed as a coproduct in the high temperature oxidation of butane. A more recently developed rhodium catalyzed process produces acetaldehyde from synthesis gas as a coproduct with ethyl alcohol and acetic acid (83—94). 

Acetaldehyde.—The formation of aldehyde from alcohol probably occtiis by the Liddition of oxygen and bubsetpiem ciimination of water,... 

Apparent activation energies for the catalytic reactions were as expected about 80 kJ/mol for the formation of formaldehyde and 60 kJ/mol for the formation of acetaldehyde from the respective alcohols (Figure 3). The turnover rates of the samples were calculated either on the basis of the number of vanadiums (all of which could be assumed to be accessible) or by assuming that oxygen uptake counted the catalytic sites ... 

Fig. 29. Decrease in intensity of nitroxide ESR signal npon addition of deuterated ethanolamine to ethanolamine ammonia lyase containing spin labeled cobinamide coenzyme. The two curves are for different concentrations of coenzyme to enzyme. The arrows indicate the point at which alcohol dehydrogenase and NADH was added to remove acetaldehyde from the enzyme. Note that full intensity is regained...

The second category of aldehyde dehydrogenases are efficient catalysts of the oxidation of both aryl and alkyl aldehydes to the corresponding carboxylic acids. The most well known and common of such reactions is the oxidation of acetaldehyde, derived from alcohol, to acetic acid. 

The conversion of ethyl alcohol by way of acetaldehyde into acetic acid is the chemical expression equivalent to acetic fermentation. In this process the acetic bacteria utilise atmospheric oxygen in order to bind the hydrogen. That the hydrogen which has to be removed is activated, and not the oxygen (as was formerly thought), is shown by experiments in which oxygen is eaxluded and replaced by quinone the bacteria produce acetic acid from alcohol as before and the quinone is reduced to hydroquinone. 

Small amounts of acetaldehyde (from acetylene) are converted industrially into alcohol by catalytic hydrogenation, and large amounts are transformed into acetic acid by catalysed autoxidation (with oxides of manganese). 

Disulfiram is the generic name for Antabuse, a drug used in the treatment of chronic alcoholism. Disulfiram potentiates the toxic and carcinogenic effects of 1,2-dibromoethane in experimental animals. Presumably, this occurs by blocking conversion of the aldehyde metabolite as with acetaldehyde from ethanol. There is no evidence that similar effects occur in humans. Based on animal data, however, Ayerst Laboratories, producers of Antabuse (disulfiram), recommended the following in the package insert "Patients taking Antabuse tablets should not be exposed to ethylene dibromide or its vapors" (PDR 1991). 

The formation of acetaldehyde from the w-olefin complex was shown to involve intramolecular migration of a hydrogen atom from one carbon of the ethylene to the other, rather than 0H attack on a vinyl group generated by hydride abstraction with Pd (CH2=CH+ + OH -> CH2=CH0H) followed by rearrangement of the vinyl alcohol to acetaldehyde, since hydrolysis in DgO yielded acetaldehyde free of deuterium (59). 

Aldol condensation reaction may be either acid or base catalysed. However, base catalysis is more common. The product of this reaction is called an aldol, i.e. aid from aldehyde and ol from alcohol. The product is either a P-hydroxyaldehyde or P-hydroxyketone, depending on the starting material. For example, two acetaldehyde (ethanal) molecules condense together in the presence of an aqueous base (NaOH), to produce 3-hydroxybutanal (a P-hydroxyaldehyde). 

During conversion of ethanol by ADH to acetaldehyde, hydrogen ion is transferred from alcohol to the cofactor... 

Much of the acetaldehyde formed from alcohol is oxidized in the liver in a reaction catalyzed by mitochondrial NAD-dependent aldehyde dehydrogenase (ALDH). The product of this reaction is acetate (Figure 23-1), which can be further metabolized to C02 and water, or used to form acetyl-CoA. 

CH2 CH.CH CH2 which, in turn, can be obtd in 70% yield, by modified Russian Process from alcohol and acetaldehyde C2H5QH+CH3COH.- -CH2 CH.CH CH2+H20 This process is used now by Carbide and Carbon Chemical Corp... 

Developments in the production of acetaldehyde from acetylene have focussed attention on this reaction. Alcohols may also be formed from olefines. Sulphuric acid (20—4 5%), phosphoric acid 30—35%), or acetic acid (96%), in presence of a mercury salt may be employed. Selenium dioxide has been used for a similar purpose. (J. C. S., 1932, 2342.) See also, A. C. R 1934,123. 

Fulminate can be prepared from acetaldehyde instead of from alcohol, and from substances which are convertible into acetaldehyde, such as paraldehyde, metaldehyde, dimethyl- and diethyl-acetal. Methyl alcohol, formaldehyde, propyl alcohol, butyralde-hyde, glycol, and glyoxal do not yield fulminate. ... 

Upon conversion from alcohol to ketone/aldehyde the active site contains a reduced NADH molecule, which, in conjunction with the hydrophobic nature of the active-site cavity, is believed to raise the pKa of Tyrl51 to above 10. Evidence is provided by studies demonstrating pH-independent binding of acetaldehyde to the E-NADH complex so that the pKa value for the amino acid responsible for interaction with acetaldehyde is higher than 10. 

During conversion of ethanol to acetaldehyde, hydrogen ion is transferred from alcohol to the cofactor nicotinamide adenine dinucleotide (NAD+) to form NADH. As a net result, alcohol oxidation generates an excess of reducing equivalents in the liver, chiefly as NADH. The excess NADH production appears to underlie a number of metabolic disorders that accompany chronic alcoholism. 

Polyethylene (PEI. In an unpublished study, pouches were made from paper/foil/PE laminates, and headspace gas was taken from the bag after incubation at 60° C for 20 minutes and analyzed by a gas chromatograph. Three major components were identified as acetaldehyde, allyl alcohol and acrolein. When odorous bags were compared with non-odorous bags, there showed a direct correlation between odor, acetaldehyde and allyl alcohol levels. Those compounds were considered to be thermal oxidative decomposition products of polyethylene (Baxter, J. A., W. Grayson and Assoc., Ltd., unpublished data). 

This column must be capable of separating acetaldehyde from ethyl alcohol with the greatest completeness. A very efficient type is that of Hahn,2 in which the column is kept at a constant temperature by means of boiling methyl alcohol in a central tube, the vapors passing up an outer annular space. It is necessary that the lower part of the condenser employed be sufficiently broad (say 2 cm. in diameter) so that when in... 

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