Synthesis of 1-(4-Chlorophenylazo)-2-naphthol [10149-93-6]

1-(4-Chlorophenylazo)-2-naphthol [10149-93-6-A]            C16H11ClN2O

Procedure: 3.45 g (27.0 mmol) p-Chloroaniline are dissolved in a 100 ml Erlenmeyer flask in the mixture of 8.0 ml conc. hydrochloric acid and 8.0 ml water. Then, the flask is clamped, placed in an ice bath, and at an internal temperature of 0-5 °C, a solution of 2.00 g (29.0 mmol) sodium nitrite in 10 ml water is added portion-wise from a dropping funnel with stirring. 5 minutes after the addition is complete, excess acid is checked with potassium iodide/starch paper, and the excess is neutralized by adding a small amount of urea. The diazonium salt solution is cooled to 0 °C in the ice bath, stirred very intensively with a little activated carbon, quickly filtered through a fluted filter, and placed back in the ice bath until further use.
In a 250 ml beaker, 3.89 g (27.0 mmol) 2-Naphthol are dissolved in 22.5 ml of 10% sodium hydroxide solution (if necessary, warming). The solution is cooled to 5-10 °C in the ice bath, and then about 10 g of ice is added to the solution. The cold diazonium salt solution is then added slowly with stirring and further cooling from a dropping funnel. After the addition is complete, the mixture is left in the ice bath with occasional stirring for 15 minutes. The precipitate is suction-filtered on a Büchner funnel for about 15 minutes. Recrystallization is performed from glacial acetic acid. The product is dried in a desiccator over CaCl2/KOH. Yield: 5.34 g (70%).

Notes: 1. If the temperature during diazonium salt formation is kept at -5 to -3 °C, the yield is higher (about 76%).
2. The test for free acid and its neutralization with urea is not absolutely necessary.
3. About 150 ml of glacial acetic acid or about 300 ml of 94% ethanol is required for recrystallization.

Literature: OC Basic Practical Script of the Ruhr University Bochum
Delivered by: Kanonenfutter
Last update: 21/11/2007
Translated: 02/08/2024

Other name: 1-(4-Chlorophenylazo)-naphthalen-2-ol