Chemical Properties
Transparent flake crystal. soluble in water. 1-Hydroxynaphthalene- 4 -sulfonic acid [84-87-7]. (4-hydroxynaphthalene-1-sulfonic acid), Nevile and Winther’s acid, NW acid, C10H8O4S, Mr 224.23, and its salts are water soluble, but the sodium salt may be precipitated from solution by salting out. Coupling with diazo compounds takes place in the 2-position. Nitration yields 2,4-dinitro-1-naphthol, whereas nitrosation gives 2-nitroso-1-hydroxynaphthalene-4-sulfonic acid. Sulfonation leads to a mixture of 1-hydroxynaphthalene-2,4-di- and 2,4,7- trisulfonic acids.
Uses
1-Naphthol-4-sulfonic acid is used as an intermediate of azo dyes to prepare dyes such as direct copper blue BR and 2R, direct violet RB, acid red B and acid medium jujube red B
Preparation
After drying under vacuum, the resulting filter cake contains 1-naphthol-4-sulphonic acid in a yield of 92% of theory and <0.5% 1-naphthol-2-sulphonic acid and 3% of 1-naphthol-2,4-disulphonic acid based on the weight of 1-naphthol-4-sulphonic acid.
Synthesis
1-Naphthol-4-sulfonic acid was synthesized by addition, hydrolysis and acid precipitation of sodium 1,4-aminonaphthalene sulfonate.
