Submitted by C. F. H. Allen and G. H. W. McKee.
Checked by W. W. Hartman and A. Weissberger.
1. Procedure
(
A)
N-Phenylanthranilic Acid.—In a
1-l. round-bottomed flask fitted with an
air-cooled condenser, a mixture of
155 g. (1.66 moles) of aniline,
41 g. (0.26 mole) of o-chlorobenzoic acid (Note
1),
41 g. (0.3 mole) of technical anhydrous potassium carbonate, and
1 g. of copper oxide is refluxed for two hours, using an
oil bath. The excess
aniline is removed by distillation with steam (about three hours is required), and
20 g. of decolorizing carbon (Note
2) is added to the brown residual solution. The mixture is boiled for fifteen minutes and filtered by suction. The filtrate is added, with stirring, to a mixture of
30 cc. of concentrated hydrochloric acid and 60 cc. of water. The precipitated acid is filtered with suction when cold. After drying to constant weight in the air, the yield is
46–52 g. (
82–93 per cent of the theoretical amount) of a nearly white product; m.p.
179–181° with preliminary shrinking (Note
3), (Note
4), and (Note
5).
(
B)
Acridone.—In a
500-cc. flask a solution of
42.7 g. (0.2 mole) of N-phenylanthranilic acid (Note
6) in
100 cc. of concentrated sulfuric acid (sp. gr. 1.84) is heated on a boiling
water bath for four hours and then poured into 1 l. of boiling water. Spattering is minimized by allowing the solution to run down the wall of the
container. The yellow precipitate is filtered after boiling for five minutes, and the filtrate is saved (Note
7). The moist solid is boiled for five minutes with a solution of
30 g. (0.28 mole) of sodium carbonate in 400 cc. of water, collected with suction (Note
8), and washed well with water. After drying in the air the crude
acridone weighs
35.5–37.5 g. (
91–96 per cent of the theoretical amount) and melts at
344–346° (Note
9). This material is pure enough for many purposes; it may be recrystallized from a mixture of
aniline and acetic acid, using 10 cc. of aniline and 25 cc. of acetic acid for every 2 g. of solid. The recovery is about
90 per cent, and the recrystallized product melts at
348–352° (Note
10).
2. Notes
1.
Sixty grams of technical o-chlorobenzoic acid is dissolved in 200 cc. of hot water containing
20 g. of sodium carbonate,
10 g. of decolorizing carbon is added, and, after boiling for ten minutes, the mixture is filtered by suction. The filtrate is added to
hydrochloric acid prepared by diluting
31 cc. of the concentrated acid with an equal volume of water. The air-dried product weighs
41 g. and is used directly. This purification is essential to obtain a good yield and a product of good quality. If it is omitted, a blue to black acid results, from which the color is removed only with difficulty.
2. Ordinary animal charcoal and Darco gave equally good results.
3.
N-Phenylanthranilic acid decomposes slowly at elevated temperatures. Before the melting point is reached, there is considerable preliminary shrinkage. If the "dip method" is used, the melting point is
182–183°. The literature values vary from
181° to 184° for the pure acid.
4. This acid is pure enough for all ordinary purposes. The melting point is only slightly raised by dissolving
5 g. in 100 cc. of water containing
2.5 g. of sodium carbonate, adding
2.5 g. of decolorizing carbon, boiling for five minutes, filtering, and acidifying. The recovery is
4.6 g. If the product is colored this procedure must be followed to get
acridone of light color.
5. For recrystallization,
5 g. of the acid is dissolved in
25 cc. of boiling alcohol and 5 cc. of water added. The recovery is
4.8 g., and the melting point is
182–183°.
Acetic acid (2 cc. per gram) may be substituted for alcohol; it is more convenient for recrystallizing large quantities.
7. On standing overnight, the filtrate deposits
1 6 to 2 g. of a very impure product which melts at about
315°.
9. The crude
acridone shrinks in a
capillary tube at 330–335° and melts to a dark-colored liquid at
344–346°.
10.
Isoamyl alcohol may also be used for recrystallization;
1 g. of acridonerequires 120 cc. of solvent and yields
0.75 g. of material melting at
354°, using a
Berl-Kullman copper block.
1
3. Discussion
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