A solution of alcoholic caustic potash, prepared by dissolving
59.3 g. of 85% potassium hydroxide (0.90 mole) in
400 ml. of absolute ethanol with warming, is divided into two equal portions, one of which is saturated with
hydrogen sulfide at room temperature (Note
1). The recombined solutions are placed in a
1-l. three-necked flask fitted with a
Hershberg stirrer (Note
2), a
gas delivery tube (Note
3), and a
reflux condenser carrying a
dropping funnel (Note
4). The air is displaced from the apparatus by passing a stream of
nitrogen through the stirred liquid (Note
5). The solution is warmed to approximately 45–50°, and
49 g. (35 ml., 0.25 mole) of benzotrichloride is added dropwise through the condenser from a dropping funnel at a rate to maintain the temperature of the reaction mixture at approximately 60°; this requires 1–1.5 hours (Note
6). The reaction mixture turns deep red soon after the addition is started. When all the
benzotrichloride has been added, the stirred deep-red suspension is refluxed gently for 30 minutes. A solution of
33.1 g. (0.35 mole) of chloroacetic acid in 200 ml. of water, neutralized with
29.4 g. (0.35 mole) of solid sodium bicarbonate, is next rapidly added through the condenser, the stirred mixture heated to boiling as rapidly as possible and refluxed (Note
5) for 5 minutes.
The resulting brownish red suspension is added to 750–1000 g. of ice contained in a
2-l. beaker (Note
7) and the turbid orange solution slowly acidified (to Congo red) with good stirring (Note
8) by the addition of approximately
50 ml. (Note 9) of concentrated hydrochloric acid. The deep-scarlet crystalline precipitate is collected at the pump after 30 minutes at 0° and rinsed with small quantities of water.
The air-dried product is crystallized by dissolving it in
chloroform (approximately 120 ml.), followed by dilution of the filtered boiling liquid (Note
10) with hot
petroleum ether (boiling range 60–80°, 60–80 ml.). The crystalline product, which separates rapidly, is collected at 0°, rinsed on the filter with a mixture of
chloroform and
petroleum ether (1:3), and dried. The yield of magnificent deep-scarlet lustrous prisms, m.p.
127–128°, varies between
28.9 and 30.4 g. (
54–57% of the theoretical). Concentration of the combined filtrates and wash liquids under reduced pressure to a small volume (50–80 ml.) yields an additional small quantity (
1.5–3.0 g.,
3–6%) of material of satisfactory purity, m.p.
121–124°.