Nitrobenzene-azo-a-naphthol

The substance is employed under the name of Magneson II as a test for magnesium. 

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A solution of 5.91 g 4,6-dibromo-2-nitroaniline in 15 mL quinoline was diazotized with a mixture of 3 g NaN02 in 40 mL cone. H2SO4 and 15 mL water. Coupling took place when to the clear diazonium salt solution was added a solution of 2.88 g )0-naphthol in 10 mL quinoline. The coupled product was filtered, washed, and digested with 25% alcohol. The yield was quantitative. Recrystallization of the 4,6-dibromo-2-nitrobenzene-azo-)0-naphthol from toluene gave red crystals, m.p., 250°C. 

C22H13N707, mw 487.38, N 20.12% dk crysts (from benz or acet+w), mp 265- 5 mod sol in benz or toluene si sol in anisole or acet diffc sol in ale insol in alkalies dissolves in in coned H2S04 giving a green color was prepd by treating 4-nitrobenzene-5 -nitro-l-naphthol in ale soln with 4-nitro-benzene-l-diazoniumchloride. Its expl props were not investigated... 

In the stepwise synthesis of the unsymmetrical complex dye 13 [ 70236-60-1] [10], the azo dye made from diazotized l-amino-2-hydroxy-5-nitrobenzene and 1-phenyl-3-methyl-5-pyrazolone and the 1 1 chromium complex obtained from 6-nitro-l-diazo-2-hydroxynaphthalene-4-sulfonic acid and 2-naphthol are heated together at 80 °C for 5 h. The adduct is salted out with NaCl. A black powder is obtained that dyes wool and leather in dark brown shades. The resulting colors are fast, particularly on shrink-resistant wool. 

Sulfonation of 1-naphthol with sulfuric acid at 65 °C in nitrobenzene leads to l-hydroxynaphthalene-4-sulfonic acid (Nevile-Winther acid), which serves as a coupling component for azo dyestuffs such as Acid Orange 19. 

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