Oxygen oxidation over charcoal

A particularly useful preparation of DHA, described by Ohmori and Takagi, uses oxygen oxidation over a charcoal catalyst (6). The use of oxygen and charcoal to convert AA to DHA is a well-known reaction that has been used in AA assays for many years. The oxidation can be made in ethanol, methanol, water, or various mixtures of these solvents. We carry out this procedure as follows ... 

In 1775, Lavoisier published his paper on the composition of the air. In this historically interesting memoir, Lavoisier refers first to the action of heat upon a mixture of iron calx (oxide) and charcoal in giving fixed air, and to the similar action of mercury precipitate and charcoal. He then describes an experiment, in which he subjected the mercury precipitate to strong heat by itself and collected the expelled gas over water. This gas on examination gave properties familiar to us as those of oxygen. 

The assignment of proton chemical shifts is also supported by carbon-13 chemical shifts obtained for the 5,6-isopropylidene derivatives of DHA, iherythro-DHA and 6-bromo-6-deoxy-L-DHA. All the dehydro compounds were prepared by oxidation using oxygen over charcoal in 95% ethanol. The preparation of the isopropylidene derivatives follows. 

Guyton then reported that the gaz oxide de carbone is oxidised in the cold by chlorine in presence of water, forming carbonic acid. Desormes and Clement were not acquainted with Cruickshank s paper, which had not then reached Paris, but their results confirmed his. They obtained the gas by heating zinc oxide with charcoal or graphite, or barium carbonate with charcoal, and found that it could be exploded with oxygen over oil or mercury in a eudiometer (it exploded only weaWy), giving no water but only carbonic acid gas, completely absorbed by lime water. An important experiment was... 

The Kestner-Johnson dissolver is widely used for the preparation of silver nitrate (11). In this process, silver bars are dissolved in 45% nitric acid in a pure oxygen atmosphere. Any nitric oxide, NO, produced is oxidized to nitrogen dioxide, NO2, which in turn reacts with water to form more nitric acid and nitric oxide. The nitric acid is then passed over a bed of granulated silver in the presence of oxygen. Most of the acid reacts. The resulting solution contains silver at ca 840 g/L (12). This solution can be further purified using charcoal (13), alumina (14), and ultraviolet radiation (15). 

It not unfrcquently happens that carbonio oxide is formed by the combustion of carbon when the supply of oxygen Is inadequate to the production of carbonic acid hence the lambent blue flame which sometimes plays upon a coke or charcoal fire, or is seen to issue from certain furnaces this is, in fact, equivalent to passing carbonio acid over red-hot charcoal so that 0 0( -J- C becomes 2 C O. 

An improved synthesis of dehydroascorbic acid has been reported (42). The oxidation of ascorbic acid in absolute methanol with oxygen over activated charcoal catalyst is reported to aflFord 28 in 95% yield. Dehydroascorbic acid has been characterized in solution as the monomer, 28 (43), and as the dimer (44,45) and its tetra acetyl derivative 29 (46). Several studies of mono- and di-hydrazone (48-53) and osazone (54) derivatives of dehydroascorbic acid have been reported. Hydrazone derivatives of dehydroascorbic acid have been used in the reductive synthesis of 2,3-diaza-2,3-dideoxy- and 2-aza-2-deoxyascorbic acid derivatives 30, 31, and 32 (55,56). Recently the reaction product of dehydro-L-ascorbic acid and L-phenylalanine in aqueous solution has been isolated and identified as tris(2-deoxy-2-L-ascorbyl)amine, 33, based on spectral and chemical data and its symmetry properties (57). 

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