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.