Org. Synth. 1956, 36, 36
Submitted by R. J. Harrisson and M. Moyle1
Checked by James Cason and W. N. Baxter.
A 1-l. flask (Note 1) is fitted with a condenser, an efficient stirrer, two dropping funnels, a thermometer extending well into the flask, and a delivery tube which extends far enough to be below the surface of the stirred liquid.
To the flask is added 250 ml. of a 2.5% solution of sodium hydroxide and a cuprous oxide-silver oxide catalyst (Note 2). In the two dropping funnels are placed, respectively, 96 g. (1.0 mole) of furfural (Note 3) and a solution of 40 g. (1.0 mole) of sodium hydroxide in 100 ml. of water. The contents of the flask are heated to about 55°, vigorous stirring is started, and a rapid stream of oxygen is bubbled through as the contents of the two funnels are added simultaneously (Note 4) to the reaction mixture at such a rate (20–25 min.) as to maintain the temperature at 50–55° (Note 5) without external heating. After the additions have been completed, vigorous stirring and passage of oxygen are continued until the temperature drops below 40° (15–30 min., depending on the rate of oxygen flow).
The catalyst is separated by filtration, and the aqueous solution is extracted with three 30-ml. portions of ether (Note 6), acidified with 30% sulfuric acid, boiled for 45 min. (Note 7) with 6–7 g. of carbon, then filtered hot. The filtrate is cooled to 0° and allowed to stand at this temperature for 1 hour or longer. The 2-furoic acid, which separates as pale pink needles, m.p. 130–132°, is collected by suction filtration and washed with small portions of ice water (Note 8). The yield is 96–101 g. (86–90%).
is passed through the solution at 55°, it is best to operate under a reflux condenser
. Ground joint fittings are not essential but convenient. The checkers used a 4-necked flask with ground joints
; the thermometer was hung through the condenser, and one neck was arranged for attachment of the gas delivery tube
and one of the separatory funnels.
The catalyst used is commercial cuprous oxide (9.6 g., 10% of the weight of the furfural)
and commercial silver nitrate (0.5 g., 0.5% of the weight of the furfural)
in 15 ml. of water. The cuprous oxide
is suspended in the rapidly stirred 2.5% sodium hydroxide
solution, and the solution of silver nitrate
is added to give a dark brown suspension of cuprous oxide
and silver oxide
which is used directly. So long as oxygen
is being passed through the reaction mixture, the life of the catalyst appears to be unlimited.
A sample of commercial furfural
is purified by simple distillation or steam distillation immediately before use. The submitters have carried out this reaction on an 8-mole scale following the same procedure except that a total reaction time of about 4 hours was required.
The simultaneous addition of furfural
and sodium hydroxide
maintains the concentration of sodium hydroxide at about 2.5%
, at which concentration only a small percentage of furfuryl alcohol
is formed in the accompanying Cannizzaro reaction.
Below 50°, the reaction is too slow; above 55°, the reaction becomes violent and cooling becomes necessary. Frothing may be checked by addition of small amounts of benzene
extraction at this stage removes furfuryl alcohol (about 12 g.)
. If this is not removed, the reaction mixture becomes resinous on acidification and heating.
During the period of boiling in acid solution a small amount of polymeric material forms, and this is separated when the charcoal is removed by filtration.
The solubility of 2-furoic acid
in water is 2.8 g. per 100 ml. at 0°; however, its solubility in the salt solution resulting from the reaction is quite low. Usually it is not possible to obtain further material from the filtrate by salting out with sodium chloride
; however, in case a lowered yield is obtained in the first crop it may be profitable to investigate the possibility of obtaining additional material from the filtrate.
has been made by oxidation of lactose
followed by pyrolysis, by the oxidation of 2-acetylfuran
, or furfuryl alcohol
using potassium ferricyanide
in alkaline medium, and by other methods already listed.2
In addition, furfural
has been oxidized to furoic acid
by air in the presence of sodium hydroxide
and silver nitrate
by hydrogen peroxide
in the presence of pyridine
by sodium or potassium hypochlorite
by means of sodium hydroxide
or sodium hydroxide
followed by hydrogen peroxide
and by sodium hydroxide
in the presence of a copper oxide
Chemical Abstracts Nomenclature (Collective Index Number);
sulfuric acid (7664-93-9)
sodium hydroxide (1310-73-2)
sodium chloride (7647-14-5)
silver oxide (20667-12-3)
silver nitrate (7761-88-8)
hydrogen peroxide (7722-84-1)
furoic acid (88-14-2)
copper oxide (1317-38-0)
Furfuryl alcohol (98-00-0)
sodium hypochlorite (7681-52-9)
potassium ferricyanide (13746-66-2)
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