Organic Syntheses, Coll. Vol. 1, p.276 (1941); Vol. 6, p.44 (1926).
One kilogram (862 cc., 10.2 moles) of furfural (Note 1)
is placed in a 4-l. copper can (Note 2)
provided with a mechanical stirrer
and surrounded by an ice bath
. The stirrer is started and the furfural
is cooled to 5–8°. When the temperature has fallen to this range, 825 g. of 33.3 per cent technical sodium hydroxide
solution (Note 3)
is added from a separatory funnel
at such a rate that the temperature of the reaction mixture does not exceed 20°. This requires twenty to twenty-five minutes. The rate of addition will depend on the efficiency of the cooling. The stirring is continued for one hour after the addition of the sodium hydroxide
During the reaction considerable sodium 2-furancarboxylate
separates in fine scale-like crystals. The reaction mixture is allowed to come to room temperature and just enough water is added to dissolve this precipitate. This requires about 325 cc. The solution is then placed in a continuous extraction apparatus (Fig. 16) and the 2-furylcarbinol
is extracted with 1500–2000 cc. of ether (Note 4)
. The extraction is complete after six to seven hours (Note 5)
When extraction is complete the ether
solution of 2-furylcarbinol
is distilled until the temperature of the liquid (not the vapor) reaches 95°. Then the residue is distilled under diminished pressure. Some ether
and water come over first, and the temperature then rises rapidly to the boiling point of 2-furylcarbinol
. The yield of 2-furylcarbinol
boiling at 75–77°/15 mm.
is 310–325 g.
per cent of the theoretical amount) (Note 6)
The water solution containing the sodium 2-furancarboxylate
is made acid to Congo red paper with 40 per cent sulfuric acid
. This requires about 400 cc. On cooling, the 2-furancarboxylic acid
crystallizes and is filtered with suction. The crude acid contains considerable sodium hydrogen sulfate
and is deeply colored. For purification it is dissolved in 2300 cc. of boiling water containing about 60 g. of decolorizing carbon (Norite)
and the solution is boiled for about forty-five minutes. It is then filtered and cooled with stirring to 16–20° (Note 7)
and the 2-furancarboxylic acid
which crystallizes is filtered by suction. The product thus obtained is light yellow in color but darkens somewhat on standing. The yield is 360–380 g.
per cent of the theoretical amount) (Note 8)
. This acid melts at 121–124°
and by titration is 93–95 per cent pure. It is pure enough for many purposes.
For further purification the material may be recrystallized from hot water, or dissolved in alkali and reprecipitated, or distilled under reduced pressure or sublimed. Each of these operations involves considerable loss of product, either through solubility or through decomposition by heat. The best-appearing product is obtained by distillation under reduced pressure. The crude acid is distilled from a Claisen flask
with a delivery tube
set low in order that the acid need not be heated much above the boiling point. The product boiling at 141–144°/20 mm.
is pure white and melts at 125–132° (Note 9)
. The yield of distilled acid is about 75–85
per cent of the weight of the crude acid.
(sp. gr. 1.15) (p. 280)
was used in this preparation. It boiled over a range of 140–160° and contained about 2 per cent water.
A 1-gallon (4-l.) ice-cream freezer
is a very convenient apparatus to use for the reaction, and a copper container
is not necessary.
The apparatus shown (Fig. 16) is a very convenient form of continuous extractor
for the laboratory. In the flask F is placed two-thirds of the solvent to be used for the extraction. The remainder is placed in the bottle, which should be just large enough to accommodate the solution to be extracted and the rest of the solvent. The flask is heated on a bath, causing the vapors to pass through E into the condenser
, and the liquid therefrom flows through B into the bottom of the bottle, the contents of which must be mechanically stirred during the extraction in order to obtain efficient contact of the liquids. The stirrer and mercury seal
are represented by C. For emptying and filling the bottle without disconnecting the apparatus, the tube A with pinchcock
is provided. The only precaution to be mentioned is that occasionally the solution in the flask F becomes too concentrated, and consequently so hot that the ether
cannot flow back through D owing to its rapid vaporization. If this happens, the contents of the flask must be removed and replaced by fresh solvent.
It is reported that the necessity of extracting the carbinol with ether
after completion of the Cannizzaro reaction can be avoided and the yields improved if the excess alkali is neutralized with furoic acid
or ammonium sulfate
or if a slight deficiency of alkali is used in the first place.1
thus obtained is entirely soluble in water and has only a slight yellow tinge. If it is to be stored, about 0.5 to 1 per cent of its weight of urea
should be added as a stabilizer.
The low yields of 2-furancarboxylic acid
are due partly to the formation of tarry by-products and partly to loss through water solubility. The mother liquors contain about 2.5 g. of 2-furancarboxylic acid per 100 cc.
This may be recovered by extraction with ether
The melting point of the 2-furancarboxylic acid
is not very sharp. The distilled acid which titrates 100 per cent softens noticeably at 125° and melts completely at 132°.2
It is suggested that the 2-furancarboxylic acid
is satisfactorily purified by recrystallizing from carbon tetrachloride
. A few cubic centimeters of water should be added to coagulate and float the dark impurities. The clear lower layer is separated and deposits colorless crystals of correct melting point. It has also been suggested that the addition of water be omitted and the carbon tetrachloride
solution be heated with Norite
and then filtered.
can be prepared from furfural
by oxidation with dichromate,3
or oxygen in an alkaline solution
in the presence of a suitable catalyst;5
and by condensation using sodamide6
or concentrated alkali.7
This preparation is referenced from:
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