Checked by William E. Parham and Gerald E. Stokker.
1. Procedure
In a
5-l. three-necked flask fitted with
reflux condenser,
mechanical stirrer,
thermometer, and
nitrogen gas inlet is placed a solution of
80.0 g. (43.5 ml., 0.82 mole) of concentrated sulfuric acid in 3 l. of water. The solution is stirred under
nitrogen, and
740.0 g. (2.49 moles) of reagent mercuric sulfate is added to form a suspension of deep-yellow, basic
mercuric sulfate. The mixture is stirred and heated to 55° under
nitrogen, and
82.0 g. (101 ml., 1.0 mole) of cyclohexene (Note
1) is added at once. A temperature of 55–65° (Note
2) is maintained for 1 hour. During this time the color of the reaction mixture changes from a deep yellow to the cream color of the
cyclohexene-mercuric sulfate complex.
At the end of 1 hour the condenser is set for distillation. The temperature of the reaction mixture is raised (Note
3), the mixture is stirred while a slow current of
nitrogen is continued, and 300 ml. of a mixture of crude
cyclopentanecarboxaldehyde and water is distilled over a period of approximately 2 hours. The crude product is removed in a
separatory funnel from the aqueous layer, which is extracted with three
50-ml. portions of ether. The extracts are combined with the product and dried over anhydrous
sodium sulfate. The solution is filtered into a
250-ml. Claisen flask set for vacuum distillation, the pressure is gradually reduced to 100 mm. to distil
ether, and the
cyclopentanecarboxyaldehyde is distilled rapidly (Note
4) at
74–78° (100 mm.). The yield of aldehyde (
n20D 1.4420–1.4428) is
45–52 g. (
46–53%).
Unless the aldehyde is to be used immediately, it is stored in a
brown bottle at 0° after the addition of
0.1 g. of hydroquinone and a blanket of
nitrogen (Note
5).
2. Notes
1.
Cyclohexene from an unopened bottle or freshly distilled material (b.p.
82–84°) is used.
2. This is the optimal temperature range to form the
cyclohexene-mercuric sulfate complex.
2,3
The regeneration procedure is as follows:
The water and sludge of
mercurous sulfate and
mercury, which remain after the distillation of
cyclopentanecarboxyaldehyde, are filtered with suction, washed with three 100-ml. portions of boiling water, three
100-ml. portions of acetone, and finally with three 100-ml. portions of boiling water. The gray-black solid is sucked dry.
To the solid in a
3-l. Erlenmeyer flask is added 270 ml. of water, then
90 g. (65 ml., 1.0 mole) of concentrated nitric acid slowly (
Hood!). The contents of the flask are swirled and allowed to stand until frothing and evolution of reddish brown
oxides of nitrogen subsides. Dow-Corning Antifoam A helps to control frothing.
The mixture is heated
cautiously on a hot plate to avoid excess frothing. When the frothing has almost subsided, additional concentrated
nitric acid is added, 90 g. (65 ml., 1.0 mole) at a time, with swirling and intermittent heating to control the vigorous reaction. The solid changes from gray-black to a cream color after six
90-g. portions of concentrated nitric acid have been used.
Six hundred milliliters of concentrated nitric acid is then added with heating to form a clear, deep-orange solution of
mercuric nitrate. This mixture is allowed to cool and is then filtered with suction through sintered glass to remove a small amount of solid.
Four hundred and sixty grams (250 ml., 4.7 moles) of concentrated sulfuric acid is added to the filtrate to precipitate
mercuric sulfate. The mixture is boiled under the hood for 1 hour, cooled to 10–25°, and filtered with suction through sintered glass.
The solid
mercuric sulfate is washed with three
100-ml. portions of approximately 40% aqueous sulfuric acid solution (110 ml. of concentrated sulfuric acid mixed with 300 ml. of water). The solid is sucked dry, transferred to an
evaporating dish, broken up, and dried in the hood under a heat lamp.
4.
Cyclopentanecarboxyaldehyde may trimerize if heating is prolonged; hence a fast, simple distillation is done. When the distillation residue is cooled, a solid may appear. This solid can be distilled above 78° (100 mm.) as a clear liquid which solidifies when allowed to stand. Recrystallization of this material from
95% ethanol gives a white solid melting at 122–124°. This product was shown to be cyclopentanecarboxaldehyde trimer by a mixed melting-point determination with trimer prepared from
cyclopentanecarboxyaldehyde and
85% phosphoric acid.
4
5. During storage there is a slow formation of cyclopentanecarboxaldehyde trimer.
3. Discussion
4. Merits of the Preparation
This procedure uses readily available starting materials and in one operational step generally gives higher yields of
cyclopentanecarboxaldehyde than other preparations described in the literature. Because
mercuric sulfate is an expensive reactant, a method of regenerating the
mercury products is given.
Cyclopentanecarboxaldehyde is a useful intermediate for many cyclopentane derivatives.
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