Glyoxal, atmosphere

Scheme 22.9 Intermolecular reductive aldol coupling of acrolein and phenyl glyoxal under a D2 atmosphere.a)...

Scheme 22.11 Reductive coupling of 1,3-cyclohexadiene and 2-naphthyl glyoxal under an atmosphere of D2(g).

Photolytic. Photolysis products include carbon monoxide, ethylene, free radicals, and a polymer (Calvert and Pitts, 1966). Anticipated products from the reaction of acrolein with ozone or OH radicals in the atmosphere are glyoxal, formaldehyde, formic acid, and carbon dioxide (Cupitt,... 

Photolytic. A photooxidation rate constant of 6 x 10 " cm /molecule-sec at room temperature was reported for the vapor-phase reaction of benzene with OH radicals in air (Atkinson, 1985). The reported rate constant and half-life for the reaction of benzene and OH radicals in the atmosphere are 8.2 x 10 M/sec and 6.8 d, respectively (Mill, 1982). Major photooxidation products in air include nitrobenzene, nitrophenol, phenol, glyoxal, butanedial, formaldehyde, carbon dioxide, and carbon monoxide (Nojima et al., 1975 Finlayson-Pitts and Pitts, 1986). 

Aldehydes—formaldehyde, acetaldehyde, and glyoxal (CHOCHO)—are present in the atmosphere because they are formed in the oxidation of hydrocarbons. These aldehydes are quite soluble. SO2 reacts with aldehydes, for example. 

In this contribution the re-evaluated yields from the OH-radical initiated oxidation of benzene, toluene, p-xylene, and initial results of new simulation chamber experiments on prompt glyoxal formation from isoprene oxidation are presented. A detailed discussion of sources, sinks and their uncertainties to model atmospheric concentrations of glyoxal is presented, and exemplifies how basic research in environmental simulation chambers besides giving input for photochemical models also triggers advancements with measurement techniques for field observations. The integration of laboratory and field observations by models in turn will guide future research on atmospheric chemical processes. 

As part of this MCMA-2003 campaign, glyoxal was detected for the first time directly in the atmosphere (Volkamer et al. 2005a). As is visible from the concentration time profile shown in Figure 1, the rapid variation of glyoxal was well resolved by these time resolved DOAS measurements, which present useful data to validate the performance of photochemical models that are used as tools for the design of control strategies to improve air quality in Mexico City. 

Letters indicate times of the corresponding atmospheric spectrum shown on the light. Spectra have been vertically shifted for clarity thick lines indicate scaled reference spectra of glyoxal error bars indicate 2-sigma level. Reproduced from (Volkamer et al. 2005a). 

Branching ratios for the different oxidation routes of aromatics have been adjusted to reflect the reported yields of glyoxal and of phenol-type compounds at NOx levels appropriate to the atmosphere (Volkamer et al., 2001 Volkamer et al., 2002). 

These compounds, exemplified by acrolein, crotonaldehyde, and methyl vinyl ketone, are known to react with ozone and with OH radicals. Photolysis and N03 radical reaction are of minor importance. Under atmospheric conditions the 03 reactions are also of minor significance (Atkinson and Carter, 1984), leaving the OH radical reaction as the major loss process. For the aldehydes, OH radical reaction can proceed via two reaction pathways OH radical addition to the double bond and H-atom abstraction from the -CHO group (Atkinson, 1989). For crotonaldehyde, for example, the OH reaction mechanism is given in Fig. 3. As can be noted from Fig. 3, these a,/3-unsaturated aldehydes are expected to ultimately give rise to a-dicarbonyls such as glyoxal and methylglyoxal. For the a,/3-unsaturated ketones such as methyl vinyl ketone, the major... 

Reductive N-N cleavage of hydrazines. A diastcreoselective synthesis of chiral a-amino aldehydes (4) from glyoxal involves an intermediate dimethylhydrazone (1), which reacts with an alkyllithium to provide an or-substituted N. N -dimcthylhydrazine (2). The mildest method for cleavage of hydrazines to primary amines (3) involves hydrogenolysis catalyzed by Raney nickel at 30-50. This Raney nickel reductive cleavage is markedly improved by sonication and proceeds at atmospheric pressure of H2 at 20 in CHjOH in yields of 66-84% with no raccmization or debenyzlation.1... 

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