Classification of acid dyes | Chemistry of Acid dyes

Classification of acid dyes

According to the chemical structure-

i. Nitro

ii. Nitroso

iii. Mono Azo

iv. Diazo

v. Triphenyl methane

vi. Xanthan

vii. Azin

viii. Quinoline

ix. Ketorenine

x. Anthraquinone

According to strength-

i. Strong acid dyes

ii. Weak acid dyes

iii. Neutral acid dyes

Strong Acid Dye

Strong acid dye requires a strong acid dye bath for dyeing. They have a simple molecular structure, low molecular weight, and contain a sulfonic acid group or carboxyl group. Solid water-based, poorly hydrophobic, good water solubility, low adhesion to wool, can transfer dyes on wool, can dye evenly, but the shade is not deep, and the wash fastness is weak, and when dyeing the wool is damaged and the wool looks bad after dyeing. It has a high dyeing rate, bright color, suitable for light dyeing in medium colors, and mainly needs to dye in a solid acid bath to use for dyeing wool.

Weak acid dyes

These are produced from strong acid dyes by increasing molecular weight and introducing groups like the aryl sulfone group, or long carbon sequences. The molecular structure is more complex, the proportion of sulfonic acid group in the molecule is relatively small, the solubility in hydroelectric, aggregate, and aqueous solutions is moderate, the solubility for wool is large, migration and level dyeing properties are slightly weak, and wet treatment is good and it has good fastness. It can dye the wool in a weakly acidic medium without any damage to the wool. The shade is darker and the fastness has improved, but the leveling properties are not good.

Neutral acid dyes

These dyes are applied in almost neutral dye baths, with acid salts like ammonium sulfate or ammonium acetate both as thick as white crystals. During the boil, these salts decompose slightly, releasing ammonia gas and leaving small amounts of sulfuric acid. Since the bath boil accumulates enough acid to promote proper fatigue. It’s pretty simple, you initially add some salt to the dye container and let it decompose slowly.

According to their dyeing behavior

Leveling acid dyes

This color has a relatively low molecular weight. As a result, they migrate more comfortably before settling and they show less wet fastness. They are generally not suitable for use as a clothing fabric. They require an acidic dye bath, often using sulfuric acid and sodium sulfate mixtures (pH 2-4) with leveling agents such as ethoxylated fatty amines.

Metal complex acid dyes

These dyes are made up of complex acid dye molecules with metal ions, usually chromium or cobalt. Metallic complex acid dyes have a high molecular weight which gives them low mobility and high wet fastness. For this reason, they are commonly used in nylon and synthetic polyamide fibers. Metallic complex acid dyes are economical, but they produce relatively dull shades. The metal complex takes up a large range of pH in acid dyebath (pH 2-7).

Chemistry of Acid dyes

Acid dyes are capable of producing metallic-complex dyes with chelating sites with identical or different functional groups such as O-O hydroxyl or carboxyl related to the azo chromophore. The chemical groups in these locations can be 2, 2, dihydroxy, 2-carboxy-2-hydroxy, or 2-amino-2 ′ hydroxy; although the ligands of the complex structure are insignificant and form three bonds to a converted metal ion.

The naming of the acid dye-metal product is more appropriately identified as ‘metallic-complex acid dyes. The complex formation occurs by the substitution of two protons by metallic ions, one by one from two substituting groups for a complex color of 1: 1. 1: 1 metal-complex copper, nickel, cobalt, or zinc, 5-cyano-6-methyl-2-2-bipyridine-containing zinc has been shown to be highly effective for protein fibers.

Formazans obtained by the reduction of water-soluble colorless tetrazolium salts are able to form very fast and intense reactions with metallic ions of different colors that replicate and disperse the asymmetric 1: 2 iron-complex formazan dyes, producing durability and excellent lightfastness without any adverse effects of dye.

Formazan dyes Co (II), Cr (III), and Cu (II) are used in industry in complex forms, but are environmentally hazardous; this has led to the development of several Iron (II) complex formazan dyes.