Chemistry, Manufacture, and Properties

Pigment synthesis follows the typical route to azo pigment lakes the aniline derivative or the aniline sulfonic acid is diazotized with sodium nitrite in an acidic medium (hydrochloric acid), followed by coupling on the Naphthol AS derivative, which is initially dissolved in an alkaline solution and then precipitated by adding inorganic or acetic acid. If a Naphthol AS sulfonic acid is used as a coupling component, it must be neutralized with alkali for dissolution and coupled directly. 

The resulting alkali salts (usually sodium salts) of the sulfonated Naphthol AS pigments are treated as described in Sec. 2.7.1.1 and reacted with calcium or barium salts. 

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