Submitted by Anthony R. Ronzio and T. D. Waugh.
Checked by C. F. H. Allen and J. Vanallan.
1. Procedure
In a
2-l. round-bottomed flask, attached to an efficient reflux condenser (Note
1) and set in a hot
water bath, are placed
222 g. (1.72 moles) of selenious acid (Note
2),
270 ml. of paraldehyde (Note
3),
540 ml. of dioxane, and
40 ml. of 50% acetic acid (Note
4), and the mixture is refluxed for 6 hours (Note
5). The solution is then decanted from the inorganic material (Note
6), which is washed with two 150-ml. portions of water. The combined solutions are steam-distilled through a
still head (p. 65) until the
paraldehyde and
dioxane have been removed; this requires about 3.5 hours (Note
7). The mixture is decanted from a little
selenium (Note
6), and to the solution, without filtration, is added a slight excess of
25% lead acetate solution (Note
8) and (Note
9). The
lead selenite is removed by filtration, and the filtrate is saturated with
hydrogen sulfide in a
hood (Note
8). Then
20 g. of Norit is added; the whole is warmed to 40° in a hood and filtered with suction. The water-clear solution is concentrated on a
hot water bath under reduced pressure to about 150 ml. in the usual apparatus (Note
10).
This concentrate is added to a previously prepared and filtered solution of
sodium bisulfite in
40% ethanol (Note
11) contained in a
4-l. beaker provided with a mechanical stirrer (Note
12). The mixture is stirred for 3 hours, and the addition product then is filtered with suction on an
18-cm. Büchner funnel and washed, first with two
150-ml. portions of ethanol and then with
150 ml. of ether. The yield of air-dried product is
350–360 g. (
72–74%, based on the
selenious acid used) (Note
13).
2. Notes
1. The loss of large quantities of
acetaldehyde is avoided by use of a
spiral condenser, with sufficient heating so that a vapor lock is formed–the entrapped liquid should fill about two-thirds of the spiral. In cold weather, the tap water is usually cold enough so that any efficient long condenser, or two in series, is sufficient.
2. The
selenious acid does not need to be freshly prepared. A larger amount does not increase the yield. The submitters specified
selenium dioxide as the oxidizing agent, but the checkers prepared their material by evaporating an aqueous solution to dryness on the water bath. They, therefore, have considered the oxidizing agent to be
selenious acid and have calculated the yield on this basis. If this product is in reality
selenium dioxide, then the yield is
62–64%, and
222 g. is 2.0 moles.
3. This amount of
paraldehyde represents a considerable excess over the theoretical but was found to be most satisfactory.
4.
Acetic acid appears to function both as an accelerator for the oxidation and an inhibitor of the rearrangement to
glycolic acid.
5. This is regulated by the temperature of the water bath, 65–80° being the required range.
6. This material, impure
selenium, may be reoxidized,
1 and then it is suitable for a subsequent preparation. About 130 g. is recovered at this point, and 8–10 g. after the concentration.
7. Alternatively, direct distillation may be employed; this requires only 2.5 hours but demands more attention. The volume is reduced to 200–300 ml., and then 800 ml. of water is added.
8. A test sample is filtered, and the clear filtrate is treated with more of the reagent to determine the end point.
10. This volume of solution is most easily handled. Should
glyoxal itself be desired, the solution may be evaporated to dryness in a
desiccator. The product thus obtained is identical with that sold as "polyglyoxal."
11. The solution is prepared by dissolving
312 g. of technical sodium bisulfite in 2.1 l. of warm (about 40°) water, and adding
1.4 l. of 95% ethanol.
12. Alternatively, this may be done in a flask, which is shaken by hand frequently to prevent formation of a solid cake. The use of a stirrer results in a granular product. The mother liquor retains about
7 g. of
glyoxal bisulfite per liter.
13. This product is pure enough for most purposes. It can be recrystallized by dissolving it in water and adding enough alcohol to make a 40% solution. The recovery is
90–92%.
3. Discussion
Copyright © 1921-2002, Organic Syntheses, Inc. All Rights Reserved