Organic Syntheses, CV 3, 811
Submitted by Kenneth B. Wiberg
Checked by Cliff S. Hamilton and J. L. Pauley.
1. Procedure
B.
2-Thiophenealdehyde. The
hexamethylenetetrammonium salt is placed in a
2-l. round-bottomed flask containing 400 ml. of warm water. The flask is fitted for steam distillation, and steam is passed in until all the aldehyde has distilled (Note
1). The distillate is cooled,
10 ml. of 6 N acetic acid is added (Note
2), and the aldehyde is extracted with two
100-ml. portions of ether. The
ether solution is dried over anhydrous
calcium chloride, and the
ether is evaporated on a
steam bath until the volume of the solution has decreased to about 50 ml. The solution is placed in a
100-ml. Claisen flask, the ether is removed by distillation, and the aldehyde distilling at 89–91°/21 mm.,
n25D 1.5880, is collected. The yield is
27–30 g. (
48–53%) of a colorless oily liquid which darkens slowly on standing (Note
3) and (Note
4).
2. Notes
1. About 1.5 l. of distillate is collected before all the
thiophenealdehyde is distilled over.
2. The
acetic acid is added to remove traces of amines that come over in the steam distillation. This method of purification must be used because of the high solubility of the bisulfite addition compound of the aldehyde.
3. If the aldehyde is to be stored for any period of time, the addition of a small amount of
hydroquinone is advisable.
4. It has been reported (S. J. Angyal and D. F. Penman) that the procedure for
1-naphthaldehyde [Org. Syntheses, 30, 67 (1950)] may also be followed with slight modification for the preparation of
2-thio-phenealdehyde. A mixture of
41.5 g. (0.31 mole) of 2-chloromethylthiophene,
88 g. (0.60 mole) of hexamethylenetetramine,
130 ml. of glacial acetic acid, and 130 ml. of water is swirled until, with considerable evolution of heat, the mixture has become homogeneous. The mixture is heated under reflux for 4 hours; at the end of this period,
125 ml. of concentrated hydrochloric acid is added, and heating under reflux is continued for 5 minutes. After cooling, the mixture is extracted with three
100-ml. portions of ether. The combined
ether extracts are dried (with anhydrous
sodium or magnesium sulfate), and the
ether is removed. The crude product is distilled through a
short column under reduced pressure; after a fore-run of
acetic acid the product is collected at 63–66°/6 mm. or 115–118°/65 mm. The yield is
25–26 g. (
71–74%).
3. Discussion
2-Thiophenealdehyde has been prepared by the decarboxylation of
2-thienylglyoxalic acid,
1 by the action of
2-thienylmagnesium iodide on
ethyl orthoformate followed by hydrolysis of the
acetal,
2 in small yields by the Rosenmund reduction of
2-thiophenecarboxylic acid chloride,
3 in small yields by the action of
hydrogen cyanide,
hydrogen chloride, and
aluminum chloride on
thiophene, using
benzene as a solvent,
4 by a series of reactions from
1-chloro-2,3-diketocyclopentane,
5 by the hydrolysis of
2-thenylmethylhexamethylenetetrammonium chloride in neutral solution,
6 by the action of
N-methylformanilide on
thiophene in the presence of
phosphorus oxychloride,
7 by the acid hydrolysis of
N-(2-thenyl)-2'-thenaldimine,
8 and by the oxidation of
N,N-di-(2-thenyl)hydroxylamine with alkaline
potassium permanganate.
9
This preparation is referenced from:
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