Organic Syntheses, CV 5, 341
Submitted by Pasco Santurri, Frederick Robbins, and Robert Stubbings
1.
Checked by Max Tishler, Earl M. Chamberlin, and William Harrison.
1. Procedure
In a
1-l. three-necked round-bottomed flask equipped with an
efficient stirrer, a
reflux condenser, and a
thermometer (Note
1) are placed
500 ml. of glacial acetic acid (Note
2),
29.0 g. (0.19 mole) of p-aminoacetanilide (Note
3),
40 g. (0.26 mole) of sodium perborate tetrahydrate, and
10 g. (0.16 mole) of boric acid. The mixture is heated with stirring to 50–60° and held at this temperature for 6 hours. Initially the solids dissolve but, after heating for approximately 40 minutes, the product begins to separate. At the end of the reaction period, the mixture is cooled to room temperature and the yellow product is collected on a
Büchner funnel. It is washed with water until the washings are neutral to pH paper (Note
4) and then dried in an
oven at 110°. The yield of
4,4'-bis(acetamido)azobenzene, m.p.
288–293° (dec.), is
16.5 g. (
57.7%). It is used as such for the hydrolysis step (Note
5).
In a
500-ml. round-bottomed flask equipped with a reflux condenser and a
magnetic stirrer (Note
6) are placed
150 ml. of methanol,
150 ml. of 6N hydrochloric acid, and the total yield of
4,4'-bis(acetamido)azobenzene. The mixture is heated under reflux for 1.5 hours. The reaction mixture is cooled and the violet solid collected on a Büchner funnel (Note
7). The damp product is suspended in 500 ml. of water in a
1-l. beaker equipped with a stirrer, and the mixture is slowly neutralized by the addition of 2.5
N sodium hydroxide. In the course of the neutralization, the salt dissolves and the free base separates. The
4,4'-diaminoazobenzene is collected on a Büchner funnel, washed with water, and dried under reduced pressure. The yield of yellow product, m.p.
238–241° (dec.), is
11–12 g. The over-all yield from
p-aminoacetanilide is
52–56%.
2. Notes
1. The submitters carried out the reaction in a 1-l. beaker. The checkers found that considerable evaporation of
acetic acid occurs when a beaker is used.
3.
Technical grade p-aminoacetanilide (m.p. 158–160°) obtained from Eastman Kodak Company (T-13) was used.
4. If the product is not washed well, the dried material will turn violet, indicating unreacted
p-aminoacetanilide.
5. Witt and Kopetschni
2 report a melting point of 295–296° (dec.). This compound may be recrystallized from glacial
acetic acid or
ethanol.
6. The submitters did not stir the hydrolysis mixture. The checkers found that, if stirring was omitted, bumping occurred during the reflux period.
7. This product is probably the monohydrochloride salt. The dihydrochloride is reported to be red.
3
3. Discussion
The general method used by the submitters has been reported by others
8 for the preparation of other azo compounds.
The product is useful as a model compound for studies of the chemistry of derivatives of colored diamines. Specifically, the submitters used the compound for the preparation of colored diisocyanates.
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