Org. Synth. 1954, 34, 73
DOI: 10.15227/orgsyn.034.0073
3-METHYLTHIOPHENE
[Thiophene, 3-methyl-]
Submitted by R. F. Feldkamp and B. F. Tullar
1.
Checked by Cliff S. Hamilton, Y. H. Wu, and William J. Raich.
1. Procedure
Caution! This preparation should be conducted in a well-ventilated hood to avoid exposure to hydrogen sulfide.
A 1-l. three-necked round-bottomed flask is fitted with a ground-glass-sealed stirrer, an immersed thermometer, a gas inlet tube, an addition funnel (Note 1), and a distilling head, wrapped with asbestos cloth, connected to a condenser arranged for distillation. The flask is charged with 150 ml. of mineral oil (Note 2), and the system is thoroughly swept out with a slow stream of carbon dioxide admitted through the gas inlet tube while the flask is heated with an electric heating mantle. When the temperature of the oil reaches 240–250°, a slurry of 90 g. (0.51 mole) of powdered anhydrous disodium methylsuccinate (Note 3) and 100 g. (0.287 mole) of phosphorus heptasulfide (Note 4) in 250 ml. of mineral oil is placed in the addition funnel. With efficient stirring and a slow continuous stream of carbon dioxide passing through the system, the slurry is added to the hot mineral oil at such a rate as to effect fairly rapid distillation of 3-methylthiophene accompanied by considerable gas evolution (mostly hydrogen sulfide). During the addition, which requires about 1 hour, the temperature is maintained at 240–250° (Note 5). The temperature is then raised to 275° and stirring continued in the inert atmosphere for an additional hour or until distillation ceases. The total distillate, amounting to 33–38 ml., is washed with two 50-ml. portions of 5% sodium hydroxide solution and finally with 50 ml. of water (Note 6). The crude 3-methylthiophene is then distilled (Note 7). A small fore-run is discarded, and the fraction boiling between 112° and 115° is collected. The yield is 26–30 g. (52–60%), n25D 1.5170 ± 0.0005 (Note 8), (Note 9), and (Note 10).
2. Notes
1.
A
gravity funnel fitted with a glass rod of suitable diameter is satisfactory for regulating the addition of the slurry.
2.
Dowtherm A may also be used as a solvent for this reaction. However, because the boiling point (about 265°) is close to the reaction temperature, considerable quantities of Dowtherm distil along with the
3-methylthiophene. The total distillate amounts to 60–75 ml., which after washing and fractionally distilling gives the same yield as with mineral oil. Dowtherm gives a more fluid slurry and final residue and can be easily recovered by distillation at reduced pressure.
3.
Disodium methylsuccinate was made by hydrogenating a concentrated solution of itaconic acid supplied by Chas. Pfizer and Company in aqueous sodium hydroxide (pH 8.7) over Raney nickel catalyst at 50 p.s.i. and 80–100°. After the catalyst was removed by filtration, the product was isolated by evaporation of the water and the residue was dried in a
vacuum oven at 70–80°.
4.
Phosphorous heptasulfide was obtained from the Oldbury Electrochemical Company. It has been shown
2 that the '
phosphorus trisulfide' used by earlier workers for such fusions was actually somewhat impure
phosphorus heptasulfide.
5.
The rate of addition of the slurry and the reaction temperature should be carefully controlled. About two-thirds of the crude
3-methylthiophene distillate is collected during the addition of the slurry. Further heating at 260–275° gives the remainder of the material.
6.
An emulsion may be obtained on further washing with water. A small amount of
sodium chloride (2–3 g.) dissolved in the wash water assists in breaking such emulsions.
7.
Rather violent foaming may occur during this distillation but is easily controlled in a
250-ml. flask. The distilling head and flask may be wrapped in asbestos cloth in order to increase the speed of distillation.
8.
When fresh mineral oil was used (first run), a yield of
52–54% was obtained. However, when the recovered mineral oil
(Note 9) was used, the yield increased to
60%.9.
The reaction residue is allowed to cool to room temperature and is filtered by suction. The dark mineral oil filtrate may be reused in the process. The malodorous filter cake is not pyrophoric and is almost completely soluble in water or dilute alkali with liberation of
hydrogen sulfide.
10.
The submitters obtained comparable yields on twice the scale described. They also applied the same procedure to
disodium succinate to give a
25% yield of
thiophene comparable to the yield obtained by dry fusion.
3
3. Discussion
3-Methylthiophene has been prepared by the dry fusion of a salt of
methylsuccinic acid and
phosphorus 'trisulfide.'4 This reaction was later investigated quite completely in respect to ratio of reactants, rate of heating,
carbon dioxide atmosphere, and dilution of reactants with sand.
5 An excellent technical method for preparing methylthiophenes has been described which involves a vapor-phase reaction of preheated
sulfur with pentanes.
6 3-Methylthiophene has also been prepared by adding
50% crude isoprene (amylenes) to molten
sulfur at 350°,
7 and by passing a mixture of
2-methyl-2-butene and
sulfur dioxide over a
chromium oxide-aluminum oxide catalyst at 450°.
8
Appendix
Chemical Abstracts Nomenclature (Collective Index Number);
(Registry Number)
phosphorus trisulfide
phosphorus heptasulfide
Phosphorous heptasulfide
phosphorus 'trisulfide.'
chromium oxide-aluminum oxide
sodium hydroxide (1310-73-2)
sodium chloride (7647-14-5)
hydrogen sulfide (7783-06-4)
sulfur dioxide (7446-09-5)
sulfur (7704-34-9)
carbon dioxide (124-38-9)
nickel (7440-02-0)
Thiophene (110-02-1)
Itaconic acid (97-65-4)
2-methyl-2-butene (513-35-9)
disodium succinate (150-90-3)
ISOPRENE (78-79-5)
Methylsuccinic acid (498-21-5)
3-Methylthiophene,
Thiophene, 3-methyl- (616-44-4)
disodium methylsuccinate
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