Phenylglyoxal from 2- acetophenone

In a i-l. three-necked, round-bottomed flask fitted with a liquid-sealed stirrer and a reflux condenser are placed 600 cc. of dioxane (Note 1), in g. (1 mole) of selenium dioxide (Note 2), and 20 cc. of water (Note 3). The mixture is heated to 50-55° and stirred until the solid has gone into solution, 120 g. (1 mole) of acetophenone is added in one lot, and the resulting mixture is refluxed with continued stirring for four hours (Note 4). The hot solution is decanted from the precipitated selenium, and the dioxane and water are removed by distillation through a short column. The phenylglyoxal is distilled at diminished pressure from a 250-cc. Claisen flask (Note 5), and the fraction boiling at 95-97V25 mm. collected (Note 6). The yield is 93-96 g. (69-72 per cent of the theoretical amount) (Note 7). 

Phenylglyoxal has been prepared from isonitrosoacetophenone through the bisulfite compound 2,3 or by treatment with nitro-sylsulfuric acid 4 or with nitrous acid.3 It also has been prepared by the oxidation of benzoylcarbinol with copper acetate,6 by heating bromophenacyl acetate,7 and by the oxidation of acetophenone with selenium dioxide.1... 

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