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Glyoxal, irradiation

Oxidation. Acetaldehyde is readily oxidised with oxygen or air to acetic acid, acetic anhydride, and peracetic acid (see Acetic acid and derivatives). The principal product depends on the reaction conditions. Acetic acid [64-19-7] may be produced commercially by the Hquid-phase oxidation of acetaldehyde at 65°C using cobalt or manganese acetate dissolved in acetic acid as a catalyst (34). Liquid-phase oxidation in the presence of mixed acetates of copper and cobalt yields acetic anhydride [108-24-7] (35). Peroxyacetic acid or a perester is beheved to be the precursor in both syntheses. There are two commercial processes for the production of peracetic acid [79-21 -0]. Low temperature oxidation of acetaldehyde in the presence of metal salts, ultraviolet irradiation, or osone yields acetaldehyde monoperacetate, which can be decomposed to peracetic acid and acetaldehyde (36). Peracetic acid can also be formed directiy by Hquid-phase oxidation at 5—50°C with a cobalt salt catalyst (37) (see Peroxides and peroxy compounds). Nitric acid oxidation of acetaldehyde yields glyoxal [107-22-2] (38,39). Oxidations of /)-xylene to terephthaHc acid [100-21-0] and of ethanol to acetic acid are activated by acetaldehyde (40,41). [Pg.50]

French researchers [38c] have investigated the /zetero-Diels-Alder reaction of methylglyoxylate and glyoxal monoacetal with 2-methyl-1,3-pentadiene in a microwave oven under various reaction conditions (Table 4.9). The microwave (MW) irradiation does not affect the diastereoisomeric ratio of adducts trans/cis = 70 30) but dramatically reduces the reaction time. The glyoxal monoacetal, for instance, gives 82 % adducts after 5 minutes when submitted to irradiation with an incident power (IP) of 600 W in PhH and in the presence of ZnCL (Table 4.9, entry 1), while no reaction occurs if carried out for 4h at 140 °C in sole PhH. Similarly, methylgloxylate in water at 140 °C gives 82% adducts after 3h, whereas microwave irradiation reduces the reaction time to 8 minutes (Table 4.9, entry 5). [Pg.158]

Irradiation of ///-xylene isomerizes to p-xylene (Calvert and Pitts, 1966). Glyoxal, methylglyoxal, and biacetyl were produced from the photooxidation of ///-xylene by OH radicals in air at 25 °C (Tuazon et al, 1986a). The photooxidation of ///-xylene in the presence of nitrogen oxides (NO and NO2) yielded small amounts of formaldehyde and a trace of acetaldehyde (Altshuller et al, 1970). ///-Tolualdehyde and nitric acid also were identified as photooxidation products of ///-xylene with nitrogen oxides (Altshuller, 1983). The rate constant for the reaction of ///-xylene and OH radicals at room temperature was 2.36 x 10 " cmVmolecule-sec (Hansen et al., 1975). A rate constant of 1.41 x 10" L/molecule-sec was reported for the reaction of ///-xylene with OH radicals in the gas phase (Darnall et ah, 1976). Similarly, a room temperature rate constant of 2.35 x 10"" cmVmolecule-sec was reported for the vapor-phase reaction of ///-xylene with OH radicals (Atkinson, 1985). At 25 °C, a rate constant of 2.22 x 10"" cm /molecule-sec was reported for the same reaction (Ohta and Ohyama, 1985). Phousongphouang and Arey (2002)... [Pg.1157]

The lowest excited triplet states of a-dicarbonyl compounds are considerably less energetic than those of simple carbonyls. For instance the energy of the vibrationally relaxed triplet of glyoxal is 55 kcal,366 as compared to 72 kcal for formaldehyde. Irradiation of glyoxal at 4358 A populates the lowest vibrational levels of the first excited singlet, 30% of which fluoresce and 70% of which cross over to the triplet manifold.388 Almost all of the triplet molecules then decompose to formaldehyde and carbon monoxide, the phosphorescence yield being only 0.1%. [Pg.108]

The proposed reaction mechanism for the destruction of aqueous solutions of TCE or PCE predicts the formation of stable oxidized polar organic compounds. These compounds consist of acids, aldehydes, and possibly halo-acetic acids. Three possible mechanisms have been proposed for the formation of by-products due to the irradiation of aqueous solutions containing TCE and PCE. The first is for the formation of formaldehyde, acetaldehyde, and glyoxal, which are formed at a concentration of approximately two orders of magnitude less than the influent solute concentration. Second, the formation of formic acid decreased with increasing radiation dose. The formic acid concentration was found to be higher for PCE than TCE. These results are most probably due to the slower reaction rate constants of PCE with e and OH, compared to TCE. The third possible reaction is the formation of haloacetic acids when TCE and OH react. The mechanism of decomposition of PCE by OH is shown in Equation (12.30) to Equation... [Pg.485]

Light enhances decarboxylation activity by proteinoids, with pyruvic acid, glucuronic, acid, glyoxalic acid, citric acid or indole-3-acetic acid as substrates 22,23). In a typical experiment, 20 mg of proteinoid is incubated with 20 pmoles of radioactive substrate for 2-3 days in 10 ml of buffer pH 4.5 (or 7.0) at 37 °C, under the irradiation of a tungsten filament bulb with a filter of 10 % CuS04 solution the COa evolved is trapped as sodium carbonate 22). [Pg.65]

Figure 2 The by-products of trichloroethylene irradiation O formic acid, dichloroacetic acid, glyoxalic acid, and oxalic acid. [Pg.326]

Trichloroethylene and PCE have also been irradiated on a process scale at the EBRF [55]. Unlike in the aromatic solute experiments above, increasing pH necessitated increased radiation requirements. Formic acid and smaller amounts of formaldehyde, acetaldehyde, and trace glyoxal were the detectable products. No detectable chloroacetic acids were reported, indicating that if produced they were decomposed by continued irradiation. [Pg.338]

The reaction of amines with 1,2-diketo substrates led to a variety of substituted imidazole derivatives. Treatment of various substituted anilines 88 with glyoxals 89 gave the imine intermediate 90, which was then cyclized to the 1-arylimidazoles 91 with paraformaldehyde and ammonium chloride under acidic conditions <0382661>. A one-pot, three-component condensation of benzil 92, benzonitrile derivatives and primary amines on the surface of silica gel under solvent-free conditions and microwave irradiation provided tetrasubstituted imidazoles 93<03TL1709>. [Pg.208]

One of the key steps used in a new synthesis of the bis(tetrahydrofuran) moiety of Asteltoxin (94) is the photoaddition of the propanal (95) to 3,4-dimethylfuran, yielding the adduct (96). This cycloaddition is a common outcome of the irradiation of aldehydes or ketones with furans. An analogous adduct (97) results from the photoreaction of butyl glyoxalate with 2-methylfuran. Two other products [(98) and (99)] are also formed, the first of which is presumably the result of ring opening of the isomeric oxetane (100), while (99) is produced by a hydrogen abstraction radical coupling pathway. [Pg.227]

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]

Reactions of 1,2-Diketones and other 1,2-Dicarbonyl Compounds. - 1,2-Dicarbonyl compounds such as glyoxal and biacetyl have been irradiated under direct sunlight. A study has examined the wavelength dependence for fission of glyoxal into the CHO radical on irradiation in the 290-420 nm range. a-Fission is the principal photochemical reaction of vicinal cyclic tricarbonyl compounds such as indanetriones. ... [Pg.42]

Figure 5. HPLC chromatograms of carbonyl compounds formed during the Irradiation of fllter-sterlllzed seawater containing added photosensitizers A. 1 pM of riboflavin, B. 10 mg/L of humic acid and, C. no addition. C. - formaldehyde, C. -acetaldehyde, GXL - glyoxal, LC - lumfchrome, R - excess IllIPH reagent. Figure 5. HPLC chromatograms of carbonyl compounds formed during the Irradiation of fllter-sterlllzed seawater containing added photosensitizers A. 1 pM of riboflavin, B. 10 mg/L of humic acid and, C. no addition. C. - formaldehyde, C. -acetaldehyde, GXL - glyoxal, LC - lumfchrome, R - excess IllIPH reagent.
Galloway, M. M., P. S. Chhabra, A. W. H. Chahn, J. D. Surrat, R. C. Flagan, J. H. Seinfeld and F. N. Keutsch (2009) Glyoxal uptake on ammonium sulphate seed aerosol Reaction products and reversibility of uptake under dark and irradiated conditions. Atmospheric Chemistry and Physics 9, 3331-3345... [Pg.633]


See other pages where Glyoxal, irradiation is mentioned: [Pg.91]    [Pg.369]    [Pg.883]    [Pg.1153]    [Pg.487]    [Pg.489]    [Pg.397]    [Pg.249]    [Pg.280]    [Pg.280]    [Pg.338]    [Pg.181]    [Pg.213]    [Pg.158]    [Pg.34]    [Pg.35]    [Pg.36]    [Pg.123]    [Pg.228]    [Pg.208]    [Pg.158]    [Pg.374]    [Pg.121]    [Pg.575]    [Pg.258]    [Pg.258]    [Pg.8]    [Pg.103]    [Pg.196]    [Pg.17]    [Pg.14]   
See also in sourсe #XX -- [ Pg.108 ]




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