Glyoxals from methyl ketones

The preparative importance of the acyloins depends on the fact that they are intermediate products, from which many 1 2-diketones can be obtained. The simplest aromatic member of this group is benzil (anisil and furil are analogous) like its aliphatic prototype diacetyl CH3.CO.CO.CH3 (and like anhydrous glyoxal) it is yellow in colour. Diacetyl is obtained from methyl-ethyl ketone via the monoxime of the former compound (von Pechmann). It is remarkable that diacetyl condenses to p-xyloquinone. (Formulate). 

Figure 5.6 Alcohols, aldehydes, ketones and acids 15, ethylene glycol 16, vinyl alcohol 17, acetaldehyde 18, formaldehyde 19, glyoxal 20, propionaldehyde 21, propionaldehyde 22, acetone 23, ketene 24, formic acid 25, acetic acid 26, methyl formate. (Reproduced from Guillemin et at. 2004 by permission of Elsevier)...

Methyl selenien-2-yl glyoxal,118 the simplest a-diketone of the selenophene series, has been obtained in two ways by oxidation of 2-propionylselenophene by selenium dioxide and by hydrolysis of the product resulting from nitrosation of that ketone. Its UV spectrum has three characteristic maxima (Amax 277, 283, and 310 mp). When... 

Figure 2. The isomerization reaction catalysed by triosephosphate isomerase. The enzyme takes the ketone dihydroxyacetone phosphate to the aldehyde D-glyceraldehyde-3-phosphate. Evidence for an enediol intermediate comes in part from the side-reaction that also occurs the enzyme produces methyl glyoxal and inorganic phosphate.

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... 

Dialdehydes are important, photochemically reactive intermediates, formed from a wide range of precursors, most importantly isoprene and aromatic hydrocarbons. Glyoxal is formed following reaction of OH with hydroxyacetaldehyde, an intermediate in isoprene oxidation, as discussed previously. Methylglyoxal is formed following reaction of O3 with both methyl vinyl ketone and methacrolein, major intermediates in isoprene oxidation, and following reaction of methacrolein with OH. 

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