In a
500-ml. flask (Note
1), fitted with a
mechanical stirrer, are placed 36 ml. of water and
25 g. (0.078 mole) of finely crystalline alloxantin dihydrate (p. 42). The flask and contents are heated on a
steam bath to 50°, and
3.6 ml. of fuming nitric acid (sp. gr. 1.62) is added in a fine stream while vigorous stirring is maintained and the temperature is not allowed to rise above 60° (Note
2). After all the fuming
nitric acid has been added, the temperature is brought to 55° and the stirrer is stopped. In a few minutes a vigorous reaction begins, and large quantities of oxides of
nitrogen are evolved. The stirrer is again started, and, if the reaction becomes too violent, the mixture is cooled somewhat; otherwise, the reaction is allowed to take its course. The reaction is complete when a current of air, introduced into the flask above the mixture, does not produce much color due to formation of
nitrogen tetroxide (Note
3). The mixture is then heated to 60–65° for 10–15 minutes, whereupon practically all the solid dissolves. The reaction mixture is poured into a
glass (Pyrex) tray and cooled overnight at 0° or below. The large triclinic, colorless crystals of
alloxan tetrahydrate are broken up, filtered with suction, washed with ice water, and pressed as dry as possible. The crystals are then added to 25–26 ml. of
hot water (Note
4), and the mixture is shaken until solution is complete. The solution is filtered immediately, and the filtrate is cooled overnight in a tray at 0°. The crystals are broken up, filtered, washed with ice water, and pressed as dry as possible. These moist crystals of the tetrahydrate, which weigh
22–24 g., are dried to constant weight in a glass tray over concentrated
sulfuric acid. The resulting product is a fine white powder (Note
5) which weighs
16 g.
The mother liquor from the recrystallization is placed in a
250-ml. flask and is concentrated to a volume of 8–10 ml. under reduced pressure at not over 30–40° (Note
6). The concentrate, when cooled overnight at 0°, deposits a solid which is filtered, recrystallized from its own weight of boiling water, and dried over
sulfuric acid. This solid weighs about
2 g. The mother liquors from the two crystallizations are combined with the original mother liquor from the oxidation, and the whole is evaporated to dryness under diminished pressure at not above 30–40°. This solid residue is somewhat yellow and possesses a strong odor of
nitric acid. It is kept on a tray for several days until the odor of
nitric acid disappears, and then it is dissolved in its own weight (
2–3 g.) of boiling water, and the solution is cooled for several days below 0° (Note
7). The solid is removed, recrystallized from water, and dried over
sulfuric acid (Note
8). This crop weighs about
0.5 g. The total yield of
alloxan monohydrate is
18–19 g. (
72–76%) (Note
9).