Org. Synth. 1954, 34, 46
DOI: 10.15227/orgsyn.034.0046
ETHOXYACETYLENE
[Ether, ethyl ethynyl]
Submitted by E. R. H. Jones, Geoffrey Eglinton, M. C. Whiting, and B. L. Shaw
1.
Checked by Arthur C. Cope and Ronald M. Pike.
1. Procedure
Caution! This preparation should be conducted in a hood to avoid exposure to ammonia, and thorough shielding of the apparatus is recommended.
A solution of
sodium amide in liquid ammonia is prepared according to a procedure previously described
(Note 1) in a
1-l. three-necked flask (Note 2) equipped with a
cold-finger condenser (cooled with Dry Ice) attached through a
soda-lime tower to a
gas absorption trap2 and an inlet tube. Anhydrous
liquid ammonia (500 ml.) is introduced from a commercial cylinder through the inlet tube, and
0.5 g. of hydrated ferric nitrate is added, followed by
38 g. (1.65 g. atoms) of clean, freshly cut sodium (Note 3). The inlet tube is replaced with a
100-ml. dropping funnel, and the mixture is agitated manually
(Note 2) until all the
sodium is converted into
sodium amide, after which
76.5 g. (0.50 mole) of diethylchloroacetal (Note 4) is added over a period of 15–20 minutes. The mixture is swirled for an additional period of 15 minutes, after which the
ammonia is evaporated in a stream of pure
nitrogen. The flask is cooled to −70° in a
Dry Ice-trichloroethylene bath (Note 5), and
325 ml. of a saturated solution of sodium chloride which has been cooled to −20° is added all at once and as rapidly as possible with vigorous agitation
(Note 6). The flask is then fitted with a still head connected to a trap cooled to −70° with Dry Ice, and the contents of the flask are slowly heated to 100° on a
steam bath (Note 7). The condensate is allowed to warm to 0°, after which the trap is again cooled to −70° and the mixture is neutralized by the dropwise addition of a saturated aqueous solution of
sodium dihydrogen phosphate. The aqueous layer is frozen by cooling with Dry Ice, and the supernatant liquid is decanted and dried over about
4 g. of anhydrous calcium chloride. The drying agent is removed by filtration, and the filtrate is distilled
(Note 8) through a
column containing a 20-cm. section packed with glass helices at partial reflux, yielding
20–21.2 g. (
57–60%) of
ethoxyacetylene, b.p.
49–51°/749 mm.,
nD25 1.3790
(Note 9),
(Note 10),
(Note 11), and
(Note 12).
2. Notes
1.
One of the procedures for converting
sodium to
sodium amide described in
Organic Syntheses is used
(p. 763).
32.
The flask is clamped to the free end of a long (30-in.) Duraluminium rod which is fixed at the other (top) end to a rigid frame. The rod is clamped in a vertical position, and by moving the free end the contents of the flask can be swirled very conveniently.
The submitters used a 1-l. round-bottomed flask mounted in the same way, without provision for cooling or a condenser cooled with Dry Ice, and were successful in preparing sodium amide and adding diethylchloroacetal before excessive loss of liquid ammonia occurred. Conversion of sodium to sodium amide sometimes requires a considerable period of time, in which case use of the apparatus specified avoids difficulty and the necessity of adding more liquid ammonia.
3.
More liquid
ammonia should be added through the inlet tube if vaporization reduces the liquid volume to less than 300 ml.
4.
Diethylchloroacetal (chloroacetaldehyde diethylacetal) supplied by Eastman Kodak Company is satisfactory.
5.
Important! This sodium derivative is extremely pyrophoric, and at this point and during the addition of the saturated sodium chloride solution it is essential that the contents of the flask be kept out of contact with air. When the flask is immersed in the Dry Ice bath the
nitrogen stream is increased to counteract the diminution in pressure due to rapid cooling.
6.
The checkers found that a dropping funnel equipped with a
pressure-equalizing tube provided the most satisfactory mode of addition.
7.
It is advisable to allow the mixture to warm to room temperature gradually before applying heat.
8.
The distillation should be conducted in a hood since the product has lachrymatory properties.
9.
Others have reported b.p.
28°/300 mm.,
nD20 1.3812,
4 and b.p.
48–50°/760 mm.510.
The submitters have used a similar procedure for the preparation of
methoxyacetylene, b.p.
22.5–23.5°,
nD16 1.3693, from commercial
dimethylchloroacetal in
60% yield.
Caution! Minor explosions have been reported to occur during the addition of saturated sodium chloride solution to the sodium derivative of methoxyacetylene. They may have resulted from ignition of the methoxyacetylene by particles of sodium which adhered to the walls of the flask. It is recommended that all apparatus be shielded during the preparation of methoxyacetylene.11.
Ethoxyacetylene has proved to be a useful reagent for the conversion of ketones to acetylenic carbinols:
which can be converted to α,β-unsaturated aldehydes, esters, and acids:
6It has been used in the synthesis of vitamin A aldehyde
7 and in the preparation of an intermediate in one of the total syntheses of
cortisone.
812.
It has been reported
9 that the following modified procedure eliminates the dangers associated with the preparation of
ethoxyacetylene.
The initial operations were the same as described above except that 46 g. (2 g. atoms) of sodium was employed (per 76.5 g. of chloroacetal), and the reaction mixture was stirred mechanically for 2 hours after the addition of the diethylchloroacetal. The dropping funnel and stirrer were removed and the flask was closed with a stopper provided with a wide plastic tube that came within 1 mm. of the bottom. The other end was placed near the bottom of an open 2-l. flask which contained 1 kg. of finely crushed ice.
When the stopper was fitted, the contents of the reaction flask were transferred to the ice by the ammonia pressure. The walls of the flask were rinsed with a little liquid ammonia and the washings also were forced onto the ice. The cold hydrolysis mixture was shaken repeatedly with 50-ml. portions of high-boiling petroleum (b.p. > 160°). The combined extracts were washed with ice water and dried over anhydrous sodium sulfate. Distillation afforded 21–23 g. (60–66%) of material which boiled at 49–55°/760 mm., nD20 1.3820.
3. Discussion
Ethoxyacetylene has been prepared from
β-bromovinyl ethyl ether4 or
β-chlorovinyl ethyl ether10 and
potassium hydroxide; from
α,β-dibromoethyl ethyl ether and
potassium hydroxide;
5 and from
diethyl chloroacetal,
diethyl bromoacetal,
α,β-dichloroethyl ethyl ether, or
α,β-dibromoethyl ethyl ether and
sodium amide.
11
Appendix
Chemical Abstracts Nomenclature (Collective Index Number);
(Registry Number)
diethyl bromoacetal
diethylchloroacetal
dimethylchloroacetal
sodium derivative of methoxyacetylene
petroleum
diethyl chloroacetal
calcium chloride (10043-52-4)
ammonia (7664-41-7)
sodium chloride (7647-14-5)
sodium sulfate (7757-82-6)
nitrogen (7727-37-9)
potassium hydroxide (1310-58-3)
sodium (13966-32-0)
sodium amide (7782-92-5)
ferric nitrate
α,β-Dibromoethyl ethyl ether (2983-26-8)
Ethoxyacetylene,
Ether, ethyl ethynyl (927-80-0)
sodium dihydrogen phosphate (7558-80-7)
chloroacetaldehyde diethylacetal (621-62-5)
methoxyacetylene (6443-91-0)
cortisone
β-bromovinyl ethyl ether
β-chlorovinyl ethyl ether
α,β-dichloroethyl ethyl ether (623-46-1)
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