Organic Syntheses, Coll. Vol. 2, p.349 (1943); Vol. 19, p.52 (1939).
The iodine monochloride
solution at 5° is stirred rapidly into the anthranilic acid
solution at 20°. 5-Iodoanthranilic acid
separates almost immediately as a granular, tan to violet precipitate, and the reaction temperature rises to 18–22°. The mixture is stirred for an hour, while warming to room temperature, then filtered on a 13-cm. Büchner funnel
. The acid is pressed as dry as possible, washed with three 100-cc. portions of cold water, and then dried at 90–100°. There is obtained 185–189 g.
per cent of the theoretical amount) of brown to purple acid which melts at 185–190°
, with decomposition (Note 2)
is best purified by recrystallization of its ammonium salt, as follows: To 100 g. of the acid in a 400-cc. beaker
is added 200 cc. of hot water, and the acid is dissolved by stirring in concentrated ammonia
(sp. gr. 0.9) until solution is complete at 60° and there is a slight excess of ammonia
. About 40 cc. of concentrated ammonia
is required. Sodium hydrosulfite
is added in about 1-g. portions until no further bleaching action is observed, about 5 g. of decolorizing charcoal is added, and, after stirring three minutes, the mixture is filtered with suction on a preheated Büchner funnel into a preheated flask. The filter is washed with 10 cc. of boiling water.
The combined filtrate and washings are transferred to a 400-cc. beaker, allowed to cool slowly without agitation until crystal formation appears complete, then cooled to 5°. The crystalline ammonium salt is then removed by suction filtration on a large Büchner funnel
, washed with 15 cc. of ice water, sucked as dry as possible, and spread in a thin layer on an enameled or glass tray
and allowed to dry in air at 35–50°. The yield of yellow to violet ammonium salt
is 80–89 g.
, representing a recovery of 76–84
per cent (Note 3)
and (Note 4)
The ammonium salt is dissolved in three parts of hot water, ammonia
is added if necessary to effect complete solution at 60°, the solution is again treated with sodium hydrosulfite
and 3–4 g. of decolorizing charcoal, filtered hot, and the 5-iodoanthranilic acid
is precipitated by adding c.p. hydrochloric acid
in 3- to 5-cc. portions, stirring thoroughly after each addition, until the reaction mixture is just faintly acid to Congo red. Ice is then added until the temperature is reduced to 20°, and the precipitated acid is removed by suction filtration, washed freely with cold water, and dried at 100–110° (Note 5)
. 5-Iodoanthranilic acid
is almost quantitatively precipitated from its ammonium salt solution and is obtained as a yellow powder, m.p. 190–195°
(decomp.) (Note 6)
Commercial "Acid Anthranilic Sublimed" is satisfactory.
The decomposition point varies with the method of determination. The values given herein were determined by placing the sample in a capillary tube
, inserting the tube in the bath at a temperature 25° below the decomposition point, and heating at the rate of 2–3° per minute.
The ammonium salt is not stable under the drying conditions. The dry product is a mixture of 5-iodoanthranilic acid
and its ammonium salt. Contact with air may change its color from yellow to violet.
Crude 5-iodoanthranilic acid
is recovered from the mother liquor by carefully making it just acid to Congo red, using a spot plate, with concentrated hydrochloric acid
, cooling to 20°, filtering, washing freely with cold water, and drying at 90–110°. This acid can be added to crude acid in further crystallizations or worked up alone.
The drying oven must have good air circulation and uniform temperature control; drying at 120° causes the evolution of considerable amounts of free iodine
This product is sufficiently pure for conversion to m-iodobenzoic acid (p. 353)
. If greater purity is desired the ammonium salt can be recrystallized from twice its weight of water, between 45° and 5°, with 85–90
per cent recovery. When the salt remains nearly white after drying, the acid precipitated from it melts with decomposition at a temperature above 210°. Four or five recrystallizations may be required.
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