p-Phenylazo (CAS NO.: ), which is also known as Benzoyl chloride, p-phenylazo-, could be produced through the following synthetic routes.

Fifty grams (0.22 mole) of recrystallized p-phenylazobenzoic acid (p. 711) and 50 g. (0.47 mole) of anhydrous sodium carbonate are placed in a 1-l. flask and thoroughly mixed by shaking. To this mixture is added 250 ml. (3.5 moles) of chloride; a reflux condenser with a drying tube is fitted to the flask, and the mixture is refluxed for 1.5 hours. A condenser is set for distillation, and as much as possible of the thionyl chloride is distilled on a steam bath.

The acid chloride is dissolved by refluxing with 500 ml. of 90–100° ligroin, and the hot solution is decanted from the sodium carbonate onto a fluted filter. This process is repeated with three 150-ml. portions of ligroin. The combined filtrates are concentrated to 500 ml., filtered if necessary, and cooled to 0°. The acid chloride is collected on a Büchner funnel and pressed as dry as possible. It is washed twice with 30–60° petroleum ether and stored in a vacuum desiccator over phosphorus pentoxide and paraffin shavings. The yield of orange-red crystals melting at 94.5–95.5° is 48 g. (89%).