Org. Synth. 1927, 7, 40
DOI: 10.15227/orgsyn.007.0040
FURAN
Submitted by W. C. Wilson
Checked by Roger Adams and C. G. Gauerke.
1. Procedure
In a
200-cc. round-bottomed flask is placed
80 g. (0.68 mole) of crude 2-furancarboxylic acid (p. 276) (usually about 95 per cent pure). To the neck of the flask is fitted an
upright tube 2.5 cm. in diameter and 15 cm. long, with a side arm of the same diameter leading out about 2 cm. from the top of the tube. This side arm is extended into the bottom of an
efficient (25-cm.) soda-lime tower (Note 1) immersed in a
water bath held at 40° to prevent condensation of the
furan. From the top of the soda-lime tower an
outlet tube (0.5 cm. in diameter) is extended to the top of an
upright water condenser, to the lower end of which is attached a
receiving flask surrounded by ice and salt
(Note 2).
The top of the upright tube in the reaction flask is closed by a cork stopper holding a glass plunger which may be used for pushing back into the flask any sublimed 2-furancarboxylic acid.
The acid is heated just to its boiling point (200–205°) (Note 3), when it decomposes with the evolution of furan and carbon dioxide. The small amounts of 2-furancarboxylic acid that sublime are pushed back from time to time. The distillate is finally redistilled, when it is found to boil at 31–34°/745 mm. The yield is 33–36 g. (72–78 per cent of the theoretical amount based on 2-furancarboxylic acid of 95 per cent purity) (Note 4).
2. Notes
1.
The drying column removes
carbon dioxide, moisture, and some of the other by-products which are formed. The product which is collected is nearly pure, and the redistillation completes the purification.
2.
In a number of experiments a second
receiver was used in addition to the first one, but it was found that practically all of the
furan condensed in the first receiver.
3.
Care should be taken in heating
2-furancarboxylic acid. If the temperature is too low, decomposition takes place too slowly; if too high, much
2-furancarboxylic acid sublimes and causes difficulty. In one run a
thermometer was placed in the melted acid. It read
200–205° during the evolution of the
furan.
4.
In the preparation of considerable quantities of
furan it is desirable to pass the gas through one or two
wash bottles of potassium hydroxide before it reaches the soda-lime tower. The heat of absorption of
carbon dioxide keeps these bottles warm enough to prevent condensation of
furan. Also, the substitution of a
120–150 cm. column for the
15-cm. column allows greater volume and speed. By these modifications
200–300 g. of
furan can be prepared per hour without difficulty (F. N. Peters, private communication).
3. Discussion
Furan can be prepared by heating
2-furancarboxylic acid in a
sealed tube;
1 by the dry distillation of
barium 2-furancarboxylate;
1 and by heating
barium 2-furancarboxylate with
soda-lime.
2 Considerably improved yields have been reported to result from heating
2-furancarboxylic acid with a small amount of
copper sulfate or
copper oxide in a high-boiling coal-tar base
3 or in
quinoline.
4 Furan has also been prepared from
furfural by passing it over hot soda-lime or dropping it into a fused mixture of
sodium and potassium hydroxides.
5
This preparation is referenced from:
Appendix
Chemical Abstracts Nomenclature (Collective Index Number);
(Registry Number)
soda-lime
sodium and potassium hydroxides
copper sulfate (7758-98-7)
carbon dioxide (124-38-9)
Furan (110-00-9)
2-furancarboxylic acid (88-14-2)
barium 2-furancarboxylate
copper oxide (1317-38-0)
Quinoline (91-22-5)
Furfural (98-01-1)
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