Organic Syntheses, Coll. Vol. 5, p.1043 (1973); Vol. 42, p.97 (1962).
A 3-l., three-necked, round-bottomed flask
is equipped with a glass paddle stirrer
, a condenser containing a mixture of acetone and solid carbon dioxide, and a gas inlet tube
. The outlet of the condenser is protected from the atmosphere by a T-tube through which a slow stream of nitrogen
is passed. The flask is purged with nitrogen
, and about 1.5 l. of anhydrous liquid ammonia
is either poured or distilled into the flask. A small crushed crystal of ferric nitrate nonahydrate
is added, followed by 23 g. (1 g. atom) of freshly cut sodium
in small pieces (Note 1)
The solvent is removed as completely as possible by distillation on a steam bath
under water-pump vacuum. Two hundred milliliters of water is added, and the solid is dissolved by swirling the flask (Note 6)
. The solution is filtered if suspended solid is present. The aqueous solution is extracted twice with 100-ml. portions of ether
. The aqueous layer in a 1-l. Erlenmeyer flask
is then cooled in ice, and a mixture of 70 ml. of concentrated hydrochloric acid
and 200 g. of ice is added slowly with swirling. The acidified solution is continuously extracted with 200 ml. (or more) of ether
for 24–36 hours. The extract is evaporated in a stream of air or nitrogen
to give tetrolic acid
in the form of a mushy tan solid that is further dried in a vacuum desiccator
over concentrated sulfuric acid
for 2 days (Note 7)
. The product is a tan crystalline solid weighing 58–60 g.
based on sodium
) and melting at 71–75°
. It is purified further by addition to 700 ml. of boiling hexane
. As soon as the tetrolic acid
has dissolved, about 1 g. of activated carbon
is added, and the solution is filtered through a heated funnel (Note 8)
. The filtrate is refrigerated (5°) overnight and 42–50 g.
) (Note 9)
of tetrolic acid
is collected in the form of white needles, m.p. 76–77°
. A second recrystallization from hexane
gives tetrolic acid
melting at 76.5–77° (Note 10)
The first few pieces of sodium
should be converted to sodium amide
as evidenced by a color change from blue to gray. The rest of the sodium
is then added over a period of 30 minutes.
An excess may be used if the purity of the methylacetylene
is in doubt; however, a large excess will result in foaming when the liquid ammonia
is later evaporated. Methylacetylene of satisfactory purity is available from the Matheson Company
When a flow rate of 70–100 ml. per minute is used, the internal temperature does not rise above 30° and most of the carbon dioxide
is absorbed. A lower yield (50%
) of product is obtained when carbon dioxide
gas is generated by the slow evaporation of commercial solid carbon dioxide
. [Caution! See p. 976.]
The reaction is complete when the addition of a small amount of the solid to a few drops of water yields a solution with a pH below 10.
may separate as a second (upper) phase. It is removed by the ether
To avoid spattering of the solid the desiccator is evacuated slowly. If drying is incomplete, an aqueous layer will be left in the hexane
solution when the tetrolic acid
Prolonged boiling should be avoided since some tetrolic acid
is lost by volatilization.
The submitters obtained yields of tetrolic acid
as high as 67.2 g.
4. Merits of Preparation
The virtue of the present method is its convenience, especially when pressure equipment is not available. This method is probably generally applicable to the synthesis of acetylenecarboxylic acids from terminal acetylenes. Thus phenylpropiolic acid
was prepared from phenylacetylene
yield by the present procedure.
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