Aldehydes, unsaturated, oxidation with silver oxide

Further studies on the photochemistry of friedelin have led to the isolation of the unsaturated aldehyde (130).105 Silver oxide oxidation of (130) gave the known putranjivic acid. Irradiation of friedelin in the presence of acetone afforded the hydroxy-ketone (131).106 Photochemically initiated reaction of 7/3-hydroxyfriedelane and 3/3,7/3-dihydroxyfriedelane with lead tetra-acetate-iodine... 

The results of the oxidation of C2—C5 olefins over copper(i) oxide, silver, and gold catalysts are summarized in Table 1. We have excluded data from studies where additives have been deliberately included in the catalyst, or process gas stream, in order to improve the performance. Where several studies have been carried out we have quoted the best selectively obtained. While copper(i) oxide and gold give unsaturated aldehydes as the major product of partial oxidation, silver gives the epoxide. Copperfii) oxide is not a selective catalyst for olefin oxidation. The difference in behaviour between copper(i) and copper(ii) oxides is in line with the general trend in oxide catalysis. The selective catalysts tend to be those with either a full or an empty tZ-shell, i.e. the oxides of Groups IVA, VA, and VIA, and IB, IIB, IVB, VB, and VIB. ... 

Catalysts of 10 per cent copper-90 per cent silver, and silver gauze were found to be most effective with ethanol oxidation 50 per cent copper-50 per cent silver and 99 per cent silver-1 per cent bismuth were most effective with isopropanol copper wire and silver gauze were most effective with butanol.00 Yields of better than 70 per cent of aldehyde or ketone were obtained under the conditions of operation. The catalyst was supported in an externally heated tube half a meter long and seven millimeters iuside diameter. The air rate was 83 liters (standard conditions) of air per hour and the alcohol rate very nearly 0.8 mols per hour, a ratio of air to alcohol of very nearly mol per mol. After reaction had begun the heat of reaction was sufficient in most cases to maintain the catalyst at red heat. The conversion in each case may be made more efficient by allowing a smaller conversion of alcohol per pass over the catalyst. With these metal catalysts, three times as much ethanol and twice as much isopropanol break-down to carbon dioxide as butanol. Butanol, however, produced a larger amount of unsaturated hydrocarbons than either of the two other alcohols. The ratio of break-down to carbon dioxide is independent of the kind of metal catalyst and even of the oxide mixtures that remained hot. 

It may be seen from comparison of results on ethylene oxidation over silver and vanadium pentoxide that with both catalysts the oxidation of unsaturated hydrocarbons will proceed by the same mechanism. C02 generation is not accelerated in the presence of aldehydes and these cannot be intermediates in ethylene combustion. When aldehydes are introduced into the reactant mixture, the ratio of ethylene oxide to C02 formation rates undergoes a change, due to strong adsorption of aldehydes on the catalyst surface. Ethylene oxide will form on silver and is in fact absent on vanadium oxides. It was shown experimentally that the absence of acetaldehyde and formaldehyde in the products of oxidation over silver, and the low absolute content of these substances for vanadium oxides is due to the fact that they are not formed at all, or formed at a low rate, and not to their oxidation or decomposition. 

The oxidation of unsaturated a-aldehydes in an aqueous solution with a controlled basic pH (12 < pH < 13), catalyzed by silver, leads to the formation of the corresponding acids, which are stabilized in the form of salts, viz. 

Oxidative hydrolysis of 2-alkyl- and 2-acyl-l,3-dithians by iV-halogeno-succinimides is recommended as a high-yield method of carbonyl regeneration the combination of iV-chlorosuccinimide and silver(i) ion is suitable for reaction with unsaturated 1,3-dithians. In a related oxidative procedure, ketones and aldehydes can be readily regenerated from their ethylene thio- or hemithio-acetals by treatment with aqueous chloramine-T. 

Both oxides of silver, Ag20 and AgO, have been used for aldehyde oxidations. The silver]I) reagent has mainly been applied in transformations of aliphatic [83] and aromatic aldehydes [84], less so in oxidations of organometallic complexes bearing an aldehyde function [85] or a,P-unsaturated compounds [86]. Use of the silver(II) oxide is less common [70, 87], probably due to its limited availability and high cost Cyanide ions catalyze this oxidation in methanol leading to carboxylic acids (and not to esters as compared with manganese) [70]. In reactions with a,p-unsaturated aldehydes, double bond isomerizations have been observed [70]. Less common silver re-... 

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