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).
Methylacetylene (44–48 g., 1.1–1.2 mole) (Note
2) is bubbled in through the gas inlet tube with rapid stirring.
Sodium methylacetylide precipitates as a flocculent gray solid. The solid
carbon dioxide is removed from the condenser, and the
ammonia is evaporated overnight under a slow stream of
nitrogen. A hot
water bath may be used to drive off residual
ammonia.
One liter of dry tetrahydrofuran (Note
3) and
500 ml. of anhydrous ether are added, and with rapid stirring a slow stream of anhydrous
carbon dioxide from a cylinder is passed into the mixture (Note
4). After 8 hours the rate of absorption of
carbon dioxide is very slow. Any solid caked on the inside walls of the flask should be scraped off with the glass paddle stirrer. A very slow flow of
carbon dioxide is continued overnight (Note
5).
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. (
69–71% 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. (
50–59%) (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).