A solution of
107 g. (1 mole) of p-toluidine (Note
1) in
700 ml. of chlorobenzene is prepared in a
3-l. three-necked, round-bottom flask fitted with a stirrer,
reflux condenser,
thermometer, and
dropping funnel. Over a period of 5 minutes,
54 g. (29.3 ml., 0.55 mole) of concentrated sulfuric acid is added dropwise. To the finely divided suspension of
p-toluidine sulfate is added
90 g. (1.1 moles) of sodium thiocyanate, and the mixture is heated for 3 hours at 100° (inside temperature) in an oil bath (Note
2). The solution, which now contains the
thiourea, is cooled to 30°, and
180 g. (108 ml., 1.34 moles) of sulfuryl chloride is added over a period of 15 minutes, with care that the temperature does not exceed 50°. The mixture is kept at 50° for 2 hours (no further evolution of
hydrogen chloride), after which the
chlorobenzene is removed by filtration (Note
3).
The solid residue is then dissolved in 1 l. of hot water, and the remainder of the solvent is removed by a current of steam (Note
4). The solution is filtered from a little solid and is then made alkaline to litmus by the addition of
200 ml. of concentrated ammonium hydroxide (sp. gr. 0.90). The precipitated
aminomethylbenzothiazole is filtered and washed with 200 ml. of water. The solid, which melts over the range
123–128°, is dissolved in
300 ml. of hot ethanol (Note
5),
10 g. of Norit is added, and the hot suspension is filtered. The filtrate is diluted with 500 ml. of hot water, and the mixture is vigorously stirred and quickly chilled. After 30 minutes, the pale yellow granular product is filtered and washed with
150 ml. of 30% ethanol. After drying to constant weight, the product weighs
100–105 g. and melts at
135–136°, with preliminary shrinking at 130–131° (Note
6). On the addition of 200 ml. of water to the filtrate, a further
5–8 g. of product is recovered, making the total yield
105–110 g. (
64–67%).