In a
1-l. flask, equipped with a
mechanical stirrer and
thermometer for reading low temperatures, and immersed in an
ice bath, are placed
150 ml. of concentrated hydrochloric acid (sp. gr. 1.18) and 150 g. of crushed ice. The stirrer is started, and
80 g. (0.75 mole) of m-toluidine (b.p.
92–93°/15 mm.) is slowly added. The mixture is cooled to 0°, and a cold solution of
55 g. (0.8 mole) of sodium nitrite in 125 ml. of water is slowly added, the temperature being kept below 4°.
In a
2-l. flask equipped with a thermometer,
dropping funnel, and stirrer is placed a solution of
140 g. of potassium ethyl xanthate (Note
1) in 180 ml. of water. This mixture is warmed to 40–45° and kept in that range during the slow addition of the cold diazonium solution (Note
2); about 2 hours is required (Note
3). After an additional 30 minutes at this temperature to ensure complete decomposition of the intermediate compound, the red, oily
m-tolyl ethyl xanthate is separated and the aqueous layer is extracted twice, using
100-ml. portions of ether. The combined oil and extracts are washed once with
100 ml. of 10% sodium hydroxide solution (Note
4) and then with several portions of water until the washings are neutral to litmus. The
ether solution is dried over
25 g. of anhydrous calcium chloride, and the
ether is removed by distillation. The crude residual
m-tolyl ethyl xanthate is dissolved in
500 ml. of 95% ethanol, the solution brought to boiling, and the source of heat removed. To this hot solution is added slowly
175 g. of potassium hydroxide pellets so that the solution keeps boiling, and the mixture is refluxed until a sample is completely soluble in water (about 8 hours). Approximately
400 ml. of ethanol is then removed by distillation on a
steam bath, and the residue is taken up in the minimum of water (about 500 ml.). The aqueous solution is extracted with three
100-ml. portions of ether, the extract being discarded. The aqueous solution is now made strongly acid to
Congo red paper, using
6 N sulfuric acid (Note 5) (625–650 ml.). The acidified solution is placed in a
3-l. flask,
2 g. of zinc dust is added, and the
m-thiocresol is distilled with steam. The lower layer of the
m-thiocresol is separated; the aqueous layer is extracted with three
100-ml. portions of ether, the extracts being added to the oil. After drying with
50 g. of Drierite, the
ether is removed by distillation, and the oily residue is distilled under reduced pressure. The yield of colorless
m-thiocresol, b.p.
90–93°/25 mm., is
59–69 g. (
63–75%) (Note
6) and (Note
7). It is best preserved in sealed glass bottles because of its disagreeable odor.