Org. Synth. 1959, 39, 46
DOI: 10.15227/orgsyn.039.0046
3-METHYL-2-FUROIC ACID AND 3-METHYLFURAN
[2-Furoic acid, 3-methyl-]
[Furan, 3-methyl-]
Submitted by D. M. Burness
1
Checked by James Cason and Robert B. Hutchison.
1. Procedure
A.
3-Methyl-2-furoic acid. A mixture of
35 g. (0.25 mole) of methyl 3-methyl-2-furoate (p.649) and
80 ml. of aqueous 20% sodium hydroxide is heated under reflux for 2 hours. The solution is cooled, acidified with about
50 ml. of concentrated hydrochloric acid (sp. gr. 1.18), stirred vigorously for a few minutes to ensure freeing of the acid from its salt, then cooled to room temperature before the product is collected by suction filtration. The product is washed with about 25 ml. of water used in two portions, drained well on the funnel, then dried. The yield of essentially pure
3-methyl-2-furoic acid is
28.5–29.5 g. (
90–93%), m.p.
134–135° (Note 1).
B. 3-Methylfuran. A mixture of 25 g. of 3-methyl-2-furoic acid, 50 g. of quinoline (Note 2), and 4.5 g. of copper powder is placed in a 125-ml. round-bottomed flask attached by a ground joint to a 30-cm. simple Vigreux column which delivers to a water-cooled condenser. The condenser is connected to a small distilling flask which serves as receiver, with the tip of the condenser extending to the edge of the bulb of the flask. The receiver is cooled in an ice-salt bath (Note 3). The round-bottomed flask is heated by means of an electric mantle or liquid bath.
When the quinoline is heated to boiling by raising the bath temperature to about 250°, carbon dioxide is evolved at a moderate rate; the reaction is usually completed in 2–3 hours. Near the end of the reaction, heat is increased to about 265°, and the last distillate is collected until the temperature at the top of the column begins to rise rapidly above 65°. The contents of the receiver are decanted from any ice present and dried over about 1.5 g. of anhydrous magnesium sulfate, followed by Drierite, in a tightly closed flask. Redistillation yields 13.5–14.5 g. (83–89%) of colorless 3-methylfuran, b.p. 65.5–66°, nD25 1.4295–1.4315 (Note 4) and (Note 5).
2. Notes
1.
In a run thirty times the size described, the submitter obtained a yield of
85%.2.
The
quinoline should be dried by distillation from anhydrous
barium oxide.
3.
For larger runs, the side arm of the distilling flask should be attached to a cold
trap immersed in an ice-salt bath, for about 10% of the product is likely to pass through the first receiver.
4.
The product turns yellow on standing, even overnight. It can be stabilized with
0.1% hydroquinone or similar material.
25.
The submitter obtained similar results in runs about twenty times the size described. Over-all yields for the four steps starting with
4,4-dimethoxy-2-butanone (p.649) were consistently in the range
50–55%.
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3. Discussion
3-Methyl-2-furoic acid has been prepared by the oxidation of
3-methyl-2-furaldehyde3 and by the degradation of
3-methyl-2-isovalerylfuran (Elsholtzia ketone).
4 3-Methylfuran has been prepared by the present method
5 and more recently by a three-step method starting with
methallyl chloride and
ethyl orthoformate.
6 Circuitous routes from
citric acid7 and
malic acid8 have also been used.
Appendix
Chemical Abstracts Nomenclature (Collective Index Number);
(Registry Number)
Drierite
hydrochloric acid (7647-01-0)
sodium hydroxide (1310-73-2)
citric acid (77-92-9)
hydroquinone (123-31-9)
barium oxide
carbon dioxide (124-38-9)
copper powder (7440-50-8)
Ethyl orthoformate
Quinoline (91-22-5)
magnesium sulfate (7487-88-9)
malic acid (617-48-1)
3-Methyl-2-furoic acid,
2-Furoic acid, 3-methyl- (4412-96-8)
3-Methylfuran,
Furan, 3-methyl- (930-27-8)
Methyl 3-methyl-2-furoate (6141-57-7)
4,4-dimethoxy-2-butanone (5436-21-5)
3-methyl-2-furaldehyde
3-methyl-2-isovalerylfuran
methallyl chloride (563-47-3)
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