Org. Synth. 1962, 42, 12
DOI: 10.15227/orgsyn.042.0012
ALLENE
Submitted by H. N. Cripps
1 and E. F. Kiefer
2.
Checked by W. E. Russey, R. D. Birkenmeyer, and F. Kagan
3.
1. Procedure
A 1-l. three-necked flask is equipped with a Hershberg stirrer operating in a ground-glass bearing (Note 1), a 250-ml. pressure-equalizing dropping funnel, and a coil condenser. The exit from the condenser is connected to a train consisting of a trap (of at least 50-ml. capacity below the bottom of the inlet tube) cooled in ice, a drying tube (about 6 in. long by 1 in. I.D.) filled with indicating Drierite and calcium chloride, an efficient trap of at least 150-ml. capacity cooled in Dry Ice-acetone to −70° or below, and a drying tube containing Drierite. A mixture of 95% ethanol (400 ml.), water (80 ml.), and 300 g. (4.6 g. atoms) of zinc dust is placed in the reaction flask. The addition funnel is charged with 260 g. (2.34 moles) of 2,3-dichloropropene (Note 2), the reaction mixture is stirred and heated to reflux, and the 2,3-dichloropropene is added dropwise at such a rate that reflux is maintained without external heating (2–3 hours). After the addition is complete, heating is resumed for 1 hour. The ice-cooled trap is warmed to about 25°, and the residual allene is purged from the reaction flask with a very slow stream of nitrogen.
The trap cooled in Dry Ice-acetone contains about 105 g. of crude product which, when distilled through a column packed with glass helices (Note 3), yields about 75 g. (80%) of allene (Note 4). No external heat is needed during the distillation. The distillation flask is allowed to warm to room temperature, the distillation beginning at a liquid temperature of −34° and virtually stopping at about 10°. The distilled product contains no detectable ethanol, water, 2,3-dichloropropene, or methylacetylene as determined by gas-liquid chromatography (Note 5).
2. Notes
1.
The stirrer should be smooth running and gas-tight. The stirring motor (air-driven) should have a high torque because the reaction mixture tends to agglomerate as the reaction proceeds.
2.
2,3-Dichloropropene from Distillation Products or Columbia Chemicals was employed.
3.
A
vacuum-jacketed column 1 ft. long by 1 in. I.D. packed with glass helices (4 mm. O.D.) is satisfactory for this distillation. It is fitted with a cold finger in the top of the column cooled by means of
acetone that has been cooled in a
Dry Ice bath. The fraction cutter is jacketed and similarly cooled. A small circulating pump is used to circulate
acetone successively through
copper coils in a Dry Ice bath, the fraction cutter, and the cold finger. When the fraction cutter is full, the bottom may be attached to a
cooled, evacuated gas cylinder and the
allene sucked into the cylinder.
4.
The
allene contains up to
3% of
2-chloropropene, determined by its vapor-phase infrared spectrum and by vapor-phase chromatography
(Note 5).
5.
The checkers used an F and M Model 500 gas chromatographic apparatus (F and M Scientific Corporation, P. O. Box 245, Avondale, Penn.) equipped with a polyester column (
pentaerythritol adipate, 20% W/W on Chromasorb P, LAC-2-R446) 1 ft. by ¼ in. O.D.,
helium flow 45 cc. per minute, column temperature 50°, block temperature 215°, injector temperature 225°. This system was able to separate
allene from
methylacetylene and
2-chloropropene.
3. Discussion
Although many routes to
allene are described in the literature, most preparations give a mixture of
allene and
methylacetylene. The virtue of the present preparation, which is essentially that described by Gustavson and Demjanoff,
4 is that it gives
allene in a reproducible manner with
2-chloropropene as its only impurity.
Allene is an extremely useful reagent for cycloaddition reactions giving cyclobutane derivatives.
5 Allene dimer is also a useful and versatile starting material.
6
This preparation is referenced from:
Appendix
Chemical Abstracts Nomenclature (Collective Index Number);
(Registry Number)
ethanol (64-17-5)
nitrogen (7727-37-9)
copper (7440-50-8)
acetone (67-64-1)
zinc (7440-66-6)
2,3-dichloropropene (78-88-6)
Allene (463-49-0)
methylacetylene (74-99-7)
2-chloropropene (557-98-2)
pentaerythritol adipate
helium (7440-59-7)
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