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Glyoxal, conversion

Results of these two electrolyses are summarized in Figure 5. In all cases, an increase of the selectivity is observed for the production of GA. The yield of GA, referred to glyoxal conversion, reaches nearly 70%. Smaller amounts of FA and COg (<1%), the C-C bond breaking products, are detected during these electrolyses and the amount of OA remains weak (= 5%). [Pg.469]

On the other hand, for the highest electrolysis potential (2.13 V/RHE), glyoxal conversion is more important, and the amount of oxalic acid increases, whereas the concentration of FA decreases. This confirms the selectivity dependence of the C-C bond breaking with the electrode potential, and shows that the optimal potential for a maximal selectivity towards GA production is close to 2.13 V/RHE. [Pg.469]

Conversion of ketone 80 to the enol silane followed by addition of lithium aluminum hydride to the reaction mixture directly provides the allylic alcohol 81 [70]. Treatment of crude allylic alcohol 81 with tert-butyldimethylsilyl chloride followed by N-b ro m o s u cc i n i m i de furnishes the a-bromoketone 82 in 84 % yield over the two-step sequence from a.p-unsaturated ester 80. Finally, a one-pot Komblum oxidation [71] of a-bromoketone 82 is achieved by way of the nitrate ester to deliver the glyoxal 71. It is worth noting that the sequence to glyoxal 71 requires only a single chromatographic purification at the second to last step (Scheme 5.10). [Pg.122]

One of the most common approaches to pyrazine ring construction is the condensation of diaminoethane and 1,2-dicarbonyI compounds such as 206 to provide pyrazines 207 after aromatization. Aromatization was accomplished by treating the dihydropyrazines with manganese dioxide in the presence of potassium hydroxide <00JCS(P1)381>. The N-protected 1,2-dicarbonyl compounds 206 were prepared from L-amino acids by initial conversion into diazoketones followed by oxidation to the glyoxal. [Pg.283]

Ytterbium triflate [Yb(OTf)3] combined with TMSG1 or TMSOTf are excellent reagents for the conversion of a-methyl styrene and tosyl-imines into homoallylic amides 32 (Equation (19)) (TMS = trimethylsilyl).29 These conditions produce the first examples of intermolecular imino-ene reactions with less reactive imines. Typically, glyoxalate imines are necessary. A comprehensive examination of the lanthanoid metal triflates was done and the activity was shown to directly correlate with the oxophilicity scale. The first report used preformed imines, and subsequently it was found that a three-component coupling reaction could be effected, bypassing the isolation of the intermediate imine.30 Particularly noteworthy was the successful participation of aliphatic aldehydes to yield homoallylic amines. [Pg.564]

Glutaronitrile, 3-hydroxy-, 46, 48 Glycerol chlorohydrin, 46, 24 Glycine (-butyl ester, 45, 47 conversion to acetamidoacetone, 45,1 Glyoxal, phenyl-, 48,109 Glyoxals from esters and the potassium salt of dimethyl sulfoxide, 48, 112... [Pg.75]

Glyoxalase, the glutathione-dependent enzyme which catalyzed the conversion of methyl glyoxal to lactic acid, was isolated by Neuberg and by Dakin and Dudley. [Pg.52]

The chemoselectivity can be strongly changed by the anode material. The oxidation of glycolaldehyde at a platinum anode affords mainly glyoxal while the conversion with a platinum anode modified by antimony or bismuth ad-atoms provides mainly glycolic acid (Fig. 29) [147]. [Pg.416]

An interesting example of the effectiveness of different reagents for 0-nitration can be seen during the synthesis of neo-inositol-based nitrate ester explosives. l,4-Dideoxy-l,4-dinitro-neo-inositol (15), a compound readily prepared from the condensation of nitromethane and glyoxal in the presence of base,undergoes conversion to the tetranitrate ester (16) on... [Pg.92]

Some other uses of silver metal include its applications as electrodes, catalysts, mirrors, and dental amalgam. Silver is used as a catalyst in oxidation-reductions involving conversions of alcohol to aldehydes, ethylene to ethylene oxide, and ethylene glycol to glyoxal. [Pg.833]

Results are shown in figure 4. The conversion reaches 66% after seven hours of electrolysis. The main product is FA (99%) and no selectivity i<. observed towards the formation of glyoxylic acid. Otherwise, conversely to the previous electrolysis in perchloric acid medium (pH=l), no trace of CO2, neither in the gas phase nor in solution as C03=, is observed. Therefore, the oxidation of glyoxal stops at the FA stage. This was confirmed by a voltammetric study, which showed that FA is not electroreactive above 1.0 V/RHE. The FA produced during the electrolysis at 1.9 V/RHE does not undergo further oxidation. [Pg.468]

The conversion of glyoxals to glyoxilic acids is a special case of the... [Pg.82]

It has also been suggested that glyoxal has a slow internal conversion pathway available. [Pg.44]

In summary, glyoxal photodecomposition studies are still in a state of disarray. A complete accounting of the photolysis products is necessary before definite conclusions can be drawn. Very low pressure work where —/vvv- -So internal conversion is... [Pg.51]

In connection with preliminary structural work on the hexitols, an unexpected result arose during attempted identification, by conversion into a (p-nitrophenyl)hydrazone, of the dialdehydes (8) or (9), formed by periodic acid oxidation of tbe anhydrodeoxyhexitols (6) and (7), or (21) and (22). The dialdehydes (8) were cleaved to form glyoxal and a 2-deoxytetrose [isolated as the (p-nitrophenyl)hydra-zone ]. [Pg.70]

The non-aqueous oxidation of various ketones and aldehydes to hydroxyaldehydes and hydroxy ketones has been carried out in two steps the first step is a bromination and the second a hydrolysis, or replacement of the bromine atoms by hydroxyl groups. Fischer and Landsteiner " brominated acetal in the presence of calcium carbonate (reaction 20). The bromoaldehyde Avas then treated with cold barium hydroxide solution (reaction 21) the resulting glycolic aldehyde was identified by conversion to glyoxal phenylosazone (reaction 22) and by the formation of calcium glycolate, after oxidation with bromine (reaction 23). [Pg.167]

The breakdown of the benzene ring to aldehydes is extremely rare and has been achieved only by ozone. A historical and classical example is the disintegration of o-xylene to a mixture of glyoxal, methyl glyoxal, and diacetyl (butanedione) in the predicted ratios [104]. From the preparative point of view, the conversion of phenanthrene into 0,0 -diformyl-biphenyl (diphenaldehyde) [1123] or o-formylbiphenyl-o -carboxylic (diphenaldehydic) acid [1124] is more important (equation 154). [Pg.96]

The l-ethyl-2,3-dimethylpyrrole whose nitrogen atom carries an ethyl group cannot be converted into a pyrrolenine form. Ozonolysis of this pyrrole derivative, however, not only yielded methylglyoxal (2.9%) but also dimethylglyoxal (8.6%). The ozonolysis of 1,2-dimethylpyrrole yielded glyoxal (5.1%) and methylglyoxal (8.3%). Here again, conversion of the pyrrole derivative in a pyrrolenine form is impossible. [Pg.156]

The prototype reaction is the conversion of glyoxal into glycolic acid (equation 2), and here the benzilic acid rearrangement mechanism coincides with that for an intramolecular Cannizzaro reaction. The reaction is observed with other purely aliphatic a-diketones such as f-butyl 2,3-dioxobutyrate and cyclohexane-1,2-dione (equations 3 and 4), but the scope is limited in the aliphatic series by competing (c.g. aldol) reactions. Suitably constructed heterocyclic systems also rearrange, and the conversion of alloxan (3) into alloxanic acid (4) was among the first of the benzilic acid rearrangements to be discovered (equation 5). ... [Pg.822]

Chlorinated phenols are common environmental pollutants, introduced as pesticides and herbicides. Studies have been carried out on the potential use of radiation to destroy these compounds as a means of environmental cleanup . While these studies were concerned with mechanisms (and are discussed in the chapter on transient phenoxyl radicals), other studies involved large-scale irradiation to demonstrate the decomposition of phenol in polluted water . Continuous irradiation led to conversion of phenol into various degradation products (formaldehyde, acetaldehyde, glyoxal, formic acid) and then to decomposition of these products. At high phenol concentrations, however, polymeric products were also formed. [Pg.1100]

Other catalytic systems have been employed to achieve high selectivity with more acceptable conversion. Thus, an Ag/Si-C catalyst was used for glyoxal production with 73% selectivity at 96% conversion [10] whereas, to the best of our knowledge, the most notable result in glycolic acid production from ethane-1,2-diol was claimed by using an Ir on carbon catalyst operating at 10 atm and 80°C (87% selectivity at 98% conversion) [11]. [Pg.510]

Glyoxylic acid is a raw material for various chemicals. It is generally produced by enzymatic or nitric acid oxidation of glyoxal, or electrolytic reduction of oxalic acid. It is also known that alkyl esters of glyoxylic acid are obtained by a vapor-phase oxidation of corresponding alkyl esters of glycolic acid [1]. The yield of ester reached 69 mol% at the conversion of 94%. [Pg.527]

The one-step conversion of diaminoethane into 2-imidazolines (89-%%) uses reaction with esters in the presence of trimethylaluminum <8UOC2824>. When 1,2-diamines are treated with glyoxal biimidazolidine (216) and azadecalin products are both formed <85JOC2365>. Other carbon sources which have proved useful include diphenyl A-sulfamoylcarbonimidate <918753), A-dichloro-methylenesulfonamides and arylcarbonimidates (Scheme 150) <828984,87864). [Pg.198]


See other pages where Glyoxal, conversion is mentioned: [Pg.315]    [Pg.1523]    [Pg.132]    [Pg.172]    [Pg.99]    [Pg.157]    [Pg.149]    [Pg.79]    [Pg.151]    [Pg.235]    [Pg.340]    [Pg.465]    [Pg.203]    [Pg.144]    [Pg.233]    [Pg.229]    [Pg.559]    [Pg.168]    [Pg.127]    [Pg.132]    [Pg.124]   
See also in sourсe #XX -- [ Pg.7 ]




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