A
200-ml. three-necked flask is fitted with a
mercury-sealed glass stirrer, a
reflux condenser, and a
gas inlet tube and
thermometer, both of which extend into the lower half of the flask. The top of the condenser is connected to a
mercury bubbler tube, and the gas inlet tube is attached to the inlet tube of a
gas-washing bottle which serves as a safety trap to prevent liquid from being drawn into the
hydrogen sulfide source. The gas-washing bottle is connected through a drying tube containing anhydrous
calcium sulfate (Drierite) to a T-tube. The vertical arm of the T-tube dips into
mercury and forms a safety valve; the other arm is connected to a commercial cylinder (Note
1) or other source of
hydrogen sulfide. To the flask are added
107 g. (100 ml., 1 mole) of 95% acetic anhydride and
1 g. (0.025 mole) of powdered sodium hydroxide. The assembly of the flask, condenser, inlet tube, and thermometer is weighed and arranged so that the amount of
hydrogen sulfide introduced can be determined by subsequent weighing. The stirrer is started, and
hydrogen sulfide is passed into the mixture as rapidly as possible without much loss of the gas through the bubbler connected to the top of the condenser. The temperature of the mixture rises to 55° within 30 minutes and is kept at 50–55° by intermittent cooling. The temperature begins to drop after
14–17 g. of hydrogen sulfide has been absorbed and is maintained at 50–55° by external heating. After a total reaction period of 6 hours,
hydrogen sulfide ceases to be absorbed and the gain in weight amounts to about 31 g.
The reaction mixture is transferred to a
250-ml. Claisen flask (Note
2) and distilled rapidly at 200 mm. in order to separate the sodium salts (Note
3). The distillate of
thiolacetic acid and
acetic acid, b.p. 35–82°/200 mm., amounts to 120–124 g. It is fractionally distilled at atmospheric pressure through an efficient, variable take-off type
column2 with a
30- to 40-cm. section packed with glass helices. The fraction boiling at
86–88°,
n25D 1.4612, is nearly pure
thiolacetic acid and amounts to
55–57.5 g. (
72–76%) based on the
acetic anhydride (Note
4) and (Note
5). The residual liquid is mainly
acetic acid. If distillation is continued after separation of the
thiolacetic acid, the vapor temperature rises rapidly to the boiling point of
acetic acid.