Checked by R. S. Schreiber, M. F. Murray, and A. C. Ott.
1. Procedure
A
5-l. three-necked flask is fitted with an
efficient stirrer, mounted through a short glass bushing, and a
long gas inlet tube which dips below the surface of the liquid
ammonia. The third neck carries a device for holding
sodium; this consists of a short piece of 10–12 mm. glass tubing, bent at a 45° angle, through which is passed a 12-in. piece of stout, flexible iron wire (picture wire is satisfactory). The lower end of the wire is attached to a stout iron fish-hook. (Sneck Hook No. 5/0 is satisfactory.)
The flask is charged with about
3 l. of liquid ammonia (Note
1), the stirrer is started, and a rapid stream of
acetylene gas (about 5 bubbles per second) is passed in for about 5 minutes to saturate the
ammonia. The
acetylene from a tank is sufficiently purified by passage through a
sulfuric acid wash bottle; a safety
trap also should be inserted in the line.
Sodium (92 g., 4 g. atoms) is cut in strips (about

by

by 3 in.) so that they can be inserted through the side neck of the flask. One of these pieces of
sodium is attached to the fish-hook and is gradually lowered into the liquid
ammonia while a rapid stream of
acetylene is passed in. The
sodium should be added at such a rate that the entire solution does not turn blue. If it does, the
sodium should be raised above the level of the
ammonia until the color is discharged (Note
2). The rest of the
sodium is added in a similar manner; the addition requires about 45 minutes, depending on the rate of passage of the
acetylene.
The
acetylene is shut off, and the gas inlet tube and iron wire are removed, but not the bent glass tubing. A
potassium hydroxide tower (Note
3) is attached to the end of this tubing, and a
dropping funnel (Note
4) is mounted in the other neck of the flask.
n-Butyl bromide (548 g., 428 ml., 4.0 moles) is added dropwise with stirring over a period of 45–60 minutes (Note
5). The mixture is stirred for an additional 2 hours.
Ammonium hydroxide (500 ml.) is then added dropwise, followed by about 1–1.5 l. of distilled water. When the frost on the outside of the flask is loose and can be pulled off easily, the contents of the flask are transferred to a
large separatory funnel, and the lower aqueous layer is removed. The organic layer is washed with 100 ml. of distilled water, then with about
100 ml. of 6N hydrochloric acid (the aqueous layer should be tested to make sure that it remains acid; if not, another washing with acid should be carried out), and finally with about
100 ml. of 10% sodium carbonate solution. The material is dried over
potassium carbonate, a small amount of solid
sodium carbonate is added, and the liquid is fractionated through a
helix-packed column of about 10–14 plates. The yield of pure
n-butylacetylene is
230–252 g. (
70–77%); b.p.
71–72°,
n20D 1.3984–1.3990 (Note
6) and (Note
7).
2. Notes
1. More liquid
ammonia should be added from time to time to maintain approximately the same level. Liquid
ammonia can be handled in ordinary apparatus, and it is not necessary to use a
Dewar flask or to cool the reaction flask in a
Dry Ice bath, as a thick frost forms on the outside and partially insulates the contents. In making very volatile alkylacetylenes, such as
ethylacetylene and
propylacetylene, it is advisable to cool the apparatus in a Dry Ice bath, to minimize loss by entrainment, and to use a
Dry Ice condenser. With the higher alkylacetylenes the use of a Dry Ice condenser, as recommended by Henne and Greenlee,
2 does not improve the yields enough to justify the extra trouble.
2. In order to see inside the flask a little alcohol may be poured over the outside.
3. This is not absolutely necessary except in damp weather, for the
ammonia escaping through the outlet tube prevents the entrance of appreciable amounts of moisture.
4. A
calibrated funnel is convenient, as the rate of addition may be judged better.
5. If the addition is carried out more slowly, the yield of product is lowered, unless a Dry Ice condenser is used.
6. The reaction may be carried out on a smaller scale without much loss in yield.
7. Other alkylacetylenes can be made in the same way from primary alkyl bromides. With
n-propylacetylene the time of addition of
n-propyl bromide should be about 45–60 minutes, and the yield is lower (
40–50%), owing to losses by entrainment unless a Dry Ice condenser is used (b.p.
39–40°;
n20D 1.3850).
n-Amylacetylene (b.p.
98°;
n20D 1.4088) and
isoamylacetylene (b.p.
91–92°;
n20D 1.4060) can be prepared in 70–80% yields by this method; the time of addition of the halide is 1.5–2.0 hours.
n-Hexylacetylene (b.p.
76–77° /150 mm.;
n20D 1.4157) can be obtained in
65% yields if a
1-mole excess of sodium acetylide is used. The halide is added during the course of 1 hour, and the mixture is stirred for an additional 3 hours before hydrolysis.
The method is not satisfactory for methyl- and ethylacetylenes or with secondary and tertiary alkyl halides or with primary alkyl halides above hexyl.
3. Discussion
The method described here is a modification of the one published by Vaughn, Vogt, Hennion, and Nieuwland.
3
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