Org. Synth. 1927, 7, 76
DOI: 10.15227/orgsyn.007.0076
2-PENTENE
Submitted by James F. Norris
Checked by Frank C. Whitmore
1. Procedure
To a cooled mixture of 200 cc. of water and 200 cc. of concentrated sulfuric acid in a 1-l. round-bottomed flask is added slowly 176 g. (214 cc., 2 moles) of pentanol-2 (b.p. 118–120°) (Note 1). The flask is connected with a long efficient condenser for distillation (Note 2). The end of the condenser is provided with an adapter which passes well into a receiver surrounded by ice water (Note 2). The flask is heated on a boiling-water bath as long as distillation takes place (two to three hours).
The distillate is shaken in the receiver with about 25 cc. of a 5 per cent solution of sodium hydroxide to remove any trace of sulfur dioxide that may be present. The hydrocarbon is separated and dried with 10 g. of anhydrous calcium chloride. It is then distilled, the fraction boiling at 35–41° (Note 3) being collected. The yield is 92–112 g. (65–80 per cent of the theoretical amount).
2. Notes
1.
Pentanol-2 is now manufactured on a large scale from petroleum. As the quality of the commercial alcohol varies, the product should be distilled before use and the proper fraction taken. The material was kindly supplied by the Petroleum Chemical Corporation, Cambridge, Mass. (A. D. Little, Inc.).
2.
Because of the volatility of the product, unusual precautions must be taken in its preparation to avoid loss.
3.
Most of the product distils at
36–37°. The product may contain a small amount of the isomeric
pentene-1. By redistilling it through a
25-cm. fractionating column containing small pieces of glass rod, the pure hydrocarbon can be readily obtained.
Pentene-2 boils at
36.39° ± 0.04°/760 mm., melts at
− 138° ± 2°, has the density
d15°4° 0.6555 and
n25D 1.3839.
3. Discussion
Pentene-2 can be prepared by the action of
alcoholic potash on
3-iodopentane1 or
3-bromopentane;
2 by dehydration of
pentanol-2,
3 or
pentanol-3;
4 by pyrolysis of the
acetate of pentanol-3;
5 and by the catalytic reduction of
pentine-2.
6
Appendix
Chemical Abstracts Nomenclature (Collective Index Number);
(Registry Number)
alcoholic potash
acetate of pentanol-3
calcium chloride (10043-52-4)
sulfuric acid (7664-93-9)
sodium hydroxide (1310-73-2)
sulfur dioxide (7446-09-5)
2-Pentene,
Pentene-2 (646-04-8)
pentanol-2 (6032-29-7)
pentene-1 (109-67-1)
3-iodopentane (1809-05-8)
3-bromopentane (1809-10-5)
pentanol-3 (584-02-1)
pentine-2 (627-21-4)
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