Organic Syntheses, CV 4, 543
Submitted by Herman Stone and Harold Shechter
1.
Checked by T. L. Cairns and V. A. Engelhardt.
1. Procedure
Forty-one grams (0.5 mole) of cyclohexene (Note
1) is added to a mixture of
250 g. (1.5 moles) of potassium iodide in
221 g. (2.14 moles) of 95% orthophosphoric acid (Note
2), (Note
3), and (Note
4) contained in a
1-l. three-necked flask equipped with a
reflux condenser, a sealed
mechanical stirrer, and a
thermometer. The mixture is stirred and heated at 80° for 3 hours, after which it is allowed to cool and treated with 150 ml. of water and
250 ml. of ether with continued stirring (Note
5) and (Note
6). The
ether extract is separated, decolorized with
50 ml. of 10% aqueous sodium thiosulfate solution, washed with
50 ml. of saturated sodium chloride solution, and dried with anhydrous
sodium sulfate (50 g.). The
ether is evaporated on a
steam bath, and the product is distilled from a
modified Claisen flask under reduced pressure. The portion boiling at
48–49.5°/4 mm. is collected. The yield of
iodocyclohexane is
93–95 g. (
88–90%),
nD20 1.551,
d420 1.625.
2. Notes
1.
Cyclohexene was obtained from Eastman Kodak Company.
3. Although
95% orthophosphoric acid is recommended for this method,
commercial phosphoric acid (85%) may be used, but the reaction proceeds more slowly and the yield is lower.
5. Excess
potassium iodide can be recovered by filtering the acid layer, after adding sufficient water to dissolve precipitated inorganic phosphates.
6. If the acid layer has an
iodine color, another extraction with
100 ml. of ether is recommended.
3. Discussion
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