English: Synthesis of β-naphthol orange

1.35 g of Na₂CO₃ are dissolved with 50 ml of H₂O in a 250 cm₃ Erlenmeyer flask. Afterwards, 5.35 g of sulfanilic acid was added to the solution. If necessary, the solution should be heated on a stove until a clear solution is obtained. In doing so, sulfanilic acid is converted into Na-sulfonate, which is soluble in water. The solution is cooled to 10-15 °C. To this, 1.85 g of NaNO₂ dissolved in 5 ml of H₂O (dissolved in the cold) was added slowly with stirring. 5 ml of HCl and 10 ml of H₂O (T = 10-15 °C) were placed in a 200 ml beaker. The previously prepared solution in the erlenmeyer flask was added to this mixture for 15 min with constant stirring. Mixing is continued until crystals of diazobenzenesulfonic acid (diazo salt) are formed.

In a 200 ml beaker, 3.6 g of β-naphthol were dissolved in 20 ml of 10% NaOH. The solution was cooled to approximately 5 °C. The solution thus prepared was added to the previously obtained diazo salt. During this coupling reaction, a solid product is formed. After 10 min, the mixture was heated to dissolve the solid product. 10 g of NaCl was added to this solution and heated again (5 min). The solution was allowed to cool and crystals form which are filtered through a vacuum filtration system, rinsed with water and dried.

Demonstrated by Asst. MSc Marija Proševa. Planned and prepared by Prof. PhD Vesna Dimova and laboratory technician Maja Senčeva Petrevska, Institute of Organic Technology, Faculty of Technology and Metallurgy, SCMU, Skopje, Macedonia.