A.
1-Methyl-3-p-tolyltriazene.
p-Toluidine (50.2 g., 0.47 mole) is added to a
2-l. flask equipped with a 200-ml. dropping funnel and an efficient stirrer, and the flask is immersed in an
ice-salt bath at
ca. −10°. A solution of
46.8 g. (0.55 mole) of potassium nitrite in 150 ml. of water is placed in the dropping funnel, and a mixture of 250 g. of crushed ice and
140 ml. of concentrated hydrochloric acid is added to the
p-toluidine with stirring. The
potassium nitrite solution is slowly added with continued stirring during 1–2 hours until a positive starch-potassium iodide test is obtained (Note
1), and the mixture is stirred for an additional hour to ensure the reaction of all the
toluidine.
The solution of
p-toluenediazonium chloride is then brought to pH 6.8–7.2 at 0° with cold, concentrated, aqueous
sodium carbonate, whereupon the solution becomes red to orange in color and a small amount of red material settles out. The cold, neutral solution is transferred to a dropping funnel and added slowly to a vigorously stirred mixture of
150 g. of sodium carbonate,
300 ml. of 30–35% aqueous methylamine (Note
2), and 100 g. of crushed ice in a
3-l. flask. The reaction mixture is kept at
ca. −10° during the addition, which requires about 45 minutes (Note
3). The solution is extracted with three
1-l. portions of ether. The ethereal extracts are dried with
anhydrous sodium sulfate and evaporated on a
rotary evaporator at room temperature to give
65 g. of crude
1-methy1-3-p-tolyltriazene (Note
4). This is placed in a water-cooled sublimer, and the
triazene is sublimed at 50° (1 mm.)
(Caution! See (Note 5));
43.3 g. (
0.29 mole,
62%) of a yellow, crystalline sublimate, m.p.
77–80°, is obtained (Note
6). The sublimate can be recrystallized from
hexane to give the
triazene as white needles, m.p.
80.5–81.5°. More conveniently, it is dissolved in the minimum amount of
ether, and the solution is diluted with
2 volumes of hexane and cooled to 0° to give flat plates with a slightly yellow cast; m.p.
79–81°. The yield of pure triazene is
33–37 g. (
47–53%) (Note
7).