Chemical Properties
Off-white to reddish paste. Dissolved in water. 1-Hydroxynaphthalene-5-sulfonic acid [117-59-9]. (5-hydroxynaphthalene-1-sulfonic acid), oxy L acid, Azurin acid, C10H8O4S, Mr 224.2, and its salts are very soluble in water, but the sodium salt may be precipitated from solution by salting out. Coupling with diazo compounds normally occurs in the 2-position but takes place in the 4-position with stronger diazo compounds such as diazotized nitroanilines. Sulfonation yields 1-hydroxynaphthalene-2,5-disulfonic acid; vigorous alkali fusion gives 1,5-dihydroxynaphthalene. Bromination in acetic acid yields 2,3-dibromo-1,4-naphthoquinone-5-sulfonic acid.
Uses
1-Naphthol-5-sulfonic acid is used to prepare dyes and organic pigments, such as direct dark blue L, pigment purple sauce BLC, lake purple red CK, etc. It is also used to prepare photoresist sensitizer 215.
