Organic Syntheses, CV 3, 14
Submitted by Alvin I. Kosak and Howard D. Hartough.
Checked by George T. Gmitter, F. Lee Benton, and Charles C. Price.
1. Procedure
In a
1-l. three-necked flask fitted with a mechanical stirrer, a thermometer, and a reflux condenser are placed
168 g. (2 moles) (Note 1) of thiophene (Note
2) and
107 g. (1 mole) of 95% acetic anhydride (Note
3). The solution is heated to 70–75°, the source of heat is removed, and
10 g. (6 ml.) of 85% phosphoric acid is added with stirring. After 2–3 minutes an exothermic reaction occurs, and it is necessary to immerse the flask in a cold
water bath to control the reaction. The boiling subsides in a few minutes; heat is again applied, and the mixture is refluxed for a total of 2 hours. The cooled mixture is washed successively with one 250-ml. portion of water and two
100-ml. portions of 5% sodium carbonate and is dried over anhydrous
sodium sulfate. The orange-red liquid is distilled through a
short fractionating column. After the removal of
76–80 g. of unchanged thiophene (b.p.
83–84°) by distillation at atmospheric pressure the residue is distilled under reduced pressure. The yield of
2-acetothienone, b.p.
89–90°/10 mm. (m.p.
9.2–10.5°;
n20D1.5662), is
93–100 g. (
74–79%).
2. Notes
1.
Acetic anhydride rather than
thiophene may be used in excess, but the unchanged reagent cannot be recovered by the procedure given. With a 3:1 mole ratio of
thiophene to anhydride the yield is of the order of
85%.
3. The use of an equivalent amount of freshly distilled
100% acetic anhydride does not improve the yield.
3. Discussion
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