Cationic azo dyes typically contain quaternary ammonium centers. The resulting diazonium salts are reagents in azo coupling reactions to give azo dyes. Industrially, aryldiazonium salts are important intermediates in the organic synthesis of azo dyes. Other uses include its conversion to specialty azo dyes and crosslinking agents. Primary aromatic amines are used as a starting material for the manufacture of azo dyes. Aniline Yellow was the first azo dye. The first azo dye was aniline yellow. Industrially, anthranilic acid is an intermediate in the production of azo dyes and saccharin. These are usually aromatic hydrocarbons, or azo dyes, made from petroleum. These chemicals include but are not limited to bleaching agents and azo dyes. Many are used as dyes (see azo dye). Studies with cyclodextrin-protected rotaxane azo dyes established this characteristic. Treatment of aromatic nitro compounds with metal hydrides gives good yields of azo compounds. Many azo dyes are produced by reactions from pre-existing azo compounds. The cadmium pigments have been partially replaced by azo pigments.