Organic Syntheses, Coll. Vol. 2, p.509 (1943); Vol. 15, p.67 (1935).
In a 1-l. three-necked, round-bottomed flask
, fitted with a liquid-sealed stirrer
and a reflux condenser
, are placed 600 cc. of dioxane(Note 1)
, 111 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 95–97°/25 mm.
collected (Note 6)
. The yield is 93–96 g.
per cent of the theoretical amount) (Note 7)
The aldehyde sets to a stiff gel on standing, probably as the result of polymerization. It may be recovered without appreciable loss by distillation. Phenylglyoxal
may be preserved also in the form of the hydrate, which is conveniently prepared by dissolving the yellow liquid in 3.5–4 volumes of hot water and allowing crystallization to take place (Note 8)
Ethyl alcohol (95 per cent)
can also be used as solvent. The reaction can be carried out with an excess of acetophenone (2 moles)
as solvent, but the results are less satisfactory. The dioxane
can be recovered and used in later runs.
For the preparation of selenium dioxide
, 200 g. (141 cc.) of concentrated nitric acid
is heated in a 3-l. beaker
on a hot plate under a good hood
and 100 g. of selenium is added in portions of 5–10 g.
A glass mechanical stirrer
to break the foam hastens the process of oxidation. The resulting solution is transferred under the hood to a large evaporating dish
and heated on a hot plate at a temperature not exceeding 200° until the selenious acid
is completely dehydrated. The crude product is purified by sublimation. A 50-g. portion of the oxide
is transferred to a 7-cm. porcelain crucible
upon which is placed a 250-cc. filter flask
through which a stream of cold water is run from the tap. The crucible is protected with asbestos and heated with a low flame until sublimation is complete (20–30 minutes). When the crucible has cooled, the sublimed selenium dioxide
will be found wedged against the condenser. Extreme care should be used when working with selenium dioxide
because of its poisonous properties.
An alternative procedure for the oxidation of selenium
to the dioxide has been described by Hahn and Schales.1
After about two hours the solution becomes clear and little further precipitation of selenium
Several grams of the hydrate may be obtained by adding the fore-run to an equal volume of warm water and allowing the product to crystallize.
Boiling points reported in the literature are 120°/50 mm.
and 142°/125 mm.
may be used in place of acetophenone
is obtained in a similar manner from propiophenone
, and many other compounds containing a methylene group adjacent to a carbonyl group may be oxidized by means of selenium dioxide
to the corresponding α-ketoaldehyde or α-diketone.2
The solubility of the hydrate at 20° is given in the literature as one part in about thirty-five parts of water. The melting points recorded range from 73° to 91°
; the difference is said to be due to varying degrees of dryness of the samples.4
The hydrate crystallizes well from water; chloroform
, carbon disulfide
, alcohol, or ether-ligroin
also may be used for the purpose. Phenylglyoxal
can be recovered from the hydrate by distillation in vacuum.
This preparation is referenced from:
Copyright © 1921-, Organic Syntheses, Inc. All Rights Reserved