Organic Syntheses, Coll. Vol. 3, p.438 (1955); Vol. 24, p.61 (1944).
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
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.
, based on the selenious acid
used) (Note 13)
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.
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.
This amount of paraldehyde
represents a considerable excess over the theoretical but was found to be most satisfactory.
appears to function both as an accelerator for the oxidation and an inhibitor of the rearrangement to glycolic acid
This is regulated by the temperature of the water bath, 65–80° being the required range.
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.
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.
A test sample is filtered, and the clear filtrate is treated with more of the reagent to determine the end point.
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."
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
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
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%
has been obtained by several methods, only a few of which are of preparative value. The most feasible are the oxidation of acetaldehyde
acid; the hydrolysis of dichlorodioxane
and the hydrolysis of the product resulting from the action of fuming sulfuric acid
This preparation is referenced from:
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