Org. Synth. 1960, 40, 29
DOI: 10.15227/orgsyn.040.0029
2,5-DIHYDRO-2,5-DIMETHOXYFURAN
[Furan, 2,5-dihydro-2,5-dimethoxy-]
Submitted by D. M. Burness
1
Checked by Alan E. Black and Henry E. Baumgarten.
1. Procedure
In a 3-l., three-necked flask equipped with a stirrer, thermometer, drying tube filled with Drierite, and a dropping funnel are placed 500 ml. of methanol, 500 ml. of benzene, 380 g. of anhydrous sodium carbonate, and 155 ml. (2.15 moles) of distilled furan (Note 1). The slurry is cooled to < −5° with a dry ice-acetone bath (maintained at −10 to −15° during the addition), and an ice-cold solution of 106 ml. (2.0 moles) of bromine in 1.0 l. of methanol (Note 2) is added dropwise or at such a rate as to maintain a reaction temperature of 0 to −5°. This requires about one hour; the mixture is stirred for an additional 2 hours at < 0° and filtered. The solids collected are washed in the funnel with two 100-ml. portions of benzene. The filtrate is stirred for 30 minutes with 100 g. of anhydrous magnesium sulfate and refiltered. The solvent is removed at reduced pressure (Note 3) to a volume of about 300 ml. Filtration and washing with benzene is repeated (Note 4), the filtrate is stirred for 15–20 minutes with anhydrous potassium carbonate, filtered, and distilled through a short packed column to give 195–205 g. (75–79%) of a clear oil, b.p. 80–82° (50 mm.), n25D 1.4333 (Note 5) and (Note 6).
2. Notes
1.
The
furan was distilled from anhydrous
potassium carbonate. Use of undistilled
furan gives a lower yield (
8–10%).
2.
The
methanol is cooled to about 0° before adding the
bromine, and the solution is kept cold during the addition.
3.
An
aspirator,
water bath, and short packed column are used, and distillation is continued until the temperature of the distillate begins to rise about 30°. Good stirring is needed here to prevent bumping and local superheating. The pot temperature never exceeds 25–30°.
4.
If an additional
500 ml. of methanol is used in lieu of the recommended
500 ml. of benzene, a small, heavier second phase, consisting mostly of
methanol, water, and salts, may separate at this point. This is removed before drying the filtrate. Later, in the early stages of distillation of the product, if drying has not been thorough enough, water may appear in the distillate. This necessitates further drying, preferably by azeotroping with
benzene.
The checkers observed a separation into two layers in some runs even in the absence of added methanol. The layers were filtered together and any solids in the funnel were washed with two 100-ml. portions of benzene. The combined filtrates were dried with a second 100 g. of anhydrous magnesium carbonate.
5.
The product from this procedure is yellow, due to
maleic dialdehyde, and occasionally gives a positive Beilstein test for
bromine, although its purity is better than 99.5% by glpc. A colorless product is reported
2 to be obtained by treatment with
sodium methoxide before the final distillation. Activated
alumina treatment of the distillate is also effective.
6.
If the product is not used promptly a peroxidation inhibitor should be used.
t-Butyl catechol (0.01%) is recommended.
2
3. Discussion
Numerous 2,5-dialkoxy-2,5-dihydrofurans have been prepared by electrolytic oxidation of
furan and substituted furans in alcoholic
ammonium bromide3,4,5 or by
bromine6,7 or
chlorine8 oxidation in the appropriate alcohol. The present method is a modification of the halogen oxidation procedures cited. It is more convenient and gives better yields (~5%) than with
chlorine, and halogen-containing byproducts are eliminated in the distillation.
The 2,5-dialkoxy-2,5-dihydrofurans are cyclic acetals of unsaturated dicarbonyl compounds and as such serve as sources thereof. They are also valuable intermediates in the synthesis of numerous types of heterocyclic compounds including those of the
tropinone series.
3Hydrogenation of the described product to tetrahydro-2,5-dimethoxyfuran is best accomplished with Raney nickel catalyst at 80–100° and 1700–2000 p.s.i. in 45–60 minutes.
This preparation is referenced from:
Appendix
Chemical Abstracts Nomenclature (Collective Index Number);
(Registry Number)
alumina
potassium carbonate (584-08-7)
Benzene (71-43-2)
methanol (67-56-1)
ammonium bromide (12124-97-9)
sodium carbonate (497-19-8)
bromine (7726-95-6)
Raney nickel (7440-02-0)
sodium methoxide (124-41-4)
chlorine (7782-50-5)
Furan (110-00-9)
magnesium sulfate (7487-88-9)
2,5-Dihydro-2,5-dimethoxyfuran,
Furan, 2,5-dihydro-2,5-dimethoxy- (332-77-4)
magnesium carbonate
maleic dialdehyde
tropinone (532-24-1)
tetrahydro-2,5-dimethoxyfuran (696-59-3)
t-Butyl catechol
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