Twenty-five grams (0.18 mole) of salicylic acid (m.p.
159–160°) is dissolved in
225 cc. of glacial acetic acid in a
2-l. beaker provided with a
mechanical stirrer (Note
1). To this is added with stirring a solution of
62 g. (0.38 mole) of iodine monochloride (Note
2) in
165 cc. of glacial acetic acid; then 725 cc. of water is added. A yellow precipitate of
diiodosalicylic acid appears. The reaction mixture is gradually heated with stirring on a hot plate to 80° and kept at approximately that temperature for twenty minutes. The entire period of heating should be about forty minutes. Toward the end of the reaction the mixture becomes rather difficult to stir because of the voluminous precipitate. After cooling to room temperature (Note
3), the precipitate is filtered on a
Büchner funnel and washed with
acetic acid and then with water. When no more water is removed by suction, the solid (75 g.) is dissolved in
100 cc. of warm acetone and filtered by gravity. To the filtrate 400 cc. of water is slowly added with shaking. The fine, flocculent precipitate is filtered by suction, washed with water, and dried. The yield of
diiodosalicylic acid melting at
235–236° is
64–64.5 g. (
91–92 per cent of the theoretical amount) (Note
4).