In a
nitrogen atmosphere the reaction mixture is heated to 80°
on a water bath over a period of 40 minutes with stirring. The solids slowly dissolve, and a yellow-orange solution results (Note
3). The reaction mixture is cooled to 5°, and the reflux condenser is turned downward for distillation. The condenser is cooled with a circulating fluid maintained at −20° to −40° (Note
4). The
receiver is immersed in dry ice and
acetone. At 1–3 mm. pressure, 1.5 l. of distillate is collected while the distillation flask is kept in a
water bath maintained at 50° (Note
5). A
capillary tube is used to bubble
nitrogen through the reaction mixture to ensure good agitation. The distillation residue is dissolved in
1 l. of t-butanol, the solution scratched to encourage crystallization, and it is refrigerated overnight. The crystals are collected by filtration (Note
2). The filter cake is washed with a minimum volume of
t-butanol and then with
Skellysolve B (Note
6) or
hexane. The moist cake is slurried with Skellysolve B or
hexane under a
nitrogen atmosphere (Note
7), filtered, and dried to constant weight under vacuum at ambient temperature. The yield of light buff to yellow crystals, m.p.
89–92°, is
320–328 g. (
66–68%).