A Publication
of Reliable Methods
for the Preparation
of Organic Compounds
Annual Volume
Org. Synth. 1945, 25, 86
DOI: 10.15227/orgsyn.025.0086
[Benzoic acid, p-phenylazo-]
Submitted by Harry D. Anspon
Checked by W. E. Bachmann and N. C. Deno.
1. Procedure
Fifty-four grams (0.39 mole) of p-aminobenzoic acid is dissolved in 390 ml. of warm glacial acetic acid in a 1-l. Erlenmeyer flask. The solution is cooled to room temperature, 42 g. (0.39 mole) of nitrosobenzene (p. 668) is added, and the mixture is shaken until the nitrosobenzene dissolves. The flask is stoppered, and the solution is allowed to stand for 12 hours at room temperature. The product begins to crystallize after about 15 minutes.
The p-phenylazobenzoic acid is collected on a Büchner funnel (Note 1) and washed with acetic acid and with water. The yield of air-dried acid melting at 245–247° cor. is 62 g. (70%). By recrystallization from 95% ethanol (60 ml. per g.) the acid is obtained as orange-gold plates which melt at 248.5–249.5° cor.; the yield is 54 g. (61%).
2. Notes
1. The solution is not cooled below room temperature before filtering; cooling below 20° brings down impurities.
3. Discussion
The method employed here is essentially the one described by Angeli and Valori.1
This preparation is referenced from:

References and Notes
  1. Angeli and Valori, Atti accad. Lincei, 22, I, 132 (1913) [C. A., 7, 2223 (1913)].

Chemical Abstracts Nomenclature (Collective Index Number);
(Registry Number)

ethanol (64-17-5)

acetic acid (64-19-7)

Nitrosobenzene (586-96-9)

p-aminobenzoic acid (150-13-0)

p-Phenylazobenzoic acid,
Benzoic acid, p-phenylazo- (1562-93-2)