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Azo Pigment Production Guide

The azo pigment group represents the largest and most important class of pigments. They contain one or more azo groups that form bridges between aromatic rings. Their preparation involves two steps - first, diazotization produces a diazonium ion from an aryl amine and nitrous acid. Second, coupling joins two aryl compounds with an azo group. This process yields different colored pigments and involves various equipment for mixing, filtering, drying, and packaging the final product.

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62 views9 pages

Azo Pigment Production Guide

The azo pigment group represents the largest and most important class of pigments. They contain one or more azo groups that form bridges between aromatic rings. Their preparation involves two steps - first, diazotization produces a diazonium ion from an aryl amine and nitrous acid. Second, coupling joins two aryl compounds with an azo group. This process yields different colored pigments and involves various equipment for mixing, filtering, drying, and packaging the final product.

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Techn Tec
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© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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Azo Pigment:

The azo Pigment represents the largest and the most important group of Pigments. They are
characterized by the presence of one or more azo groups (–N=N–), which form bridges between two or
more aromatic rings.

Preparation of azo pigments involves the following two steps.

Step 1. Diazotization

Azote is an old word for nitrogen. Hence, the presence of azo in the name of a chemical denotes that
nitrogen is present in the structure. Therefore, diazo means two nitrogen atoms. When combined with
onium, we have diazonium, which means two nitrogen atoms and a positive charge. A diazonium ion is
the cation of a salt. It is a reactive intermediate that undergoes substitution or coupling reactions.

Diazotization is the production of Diazonium ion from primary aryl amine and cold nitrous acid. Nitrous
acid is unstable and is generated in situ from sodium nitrite and strong acid such as hydrochloric acid or
sulfuric acid at 0-5°C.

Step 2. Coupling

In coupling reaction two aryl compounds are joined by an AZO group. Compounds such as aniline,
phenol and naphthol are (couplers) can undergo the coupling reaction with diazonium ion and produced
different color pigments.
HCl Tank,
Caustic soda Tank

Aromatic Amine,
Coupler
Reactor
Filter press with Trolley

Tray & Trolley Dryer


Pulverizer
Packaging
Kneader

High speed mixer

Pearl Mill, Dyno Mill


Filter

Packaging

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