Dyes and their classification

Walchand College of Arts & Science, Solapur
Dr. S. N. Battin
(shankarbattin@gmail.com)
Associate Professor, Head, Dept. of Chemistry
Walchand College of Arts and Science, Solapur
(www.wcas.org)
Dyes and Their Classification
1

Learning Objectives
After this session, you will be able to explain-
• Meaning and Qualities of a Dye and
• Classification of Synthetic Dyes
2

Contents
• Meaning of a Dye
• Qualities of an Ideal Dye
• Witt’s theory- Chromophore-Auxochrome Theory
• Classification of Dyes
3

Meaning of a Dye
• Dye- A coloured organic substance having the
property of imparting colour to other substrates like
fibre, paper, leather, plastic, hair, foodstuff etc.
• Colour imparted should not wear out easily with
water, soap or sunlight
• Also used as indicators, in colour photography, in
histological and bacteriological studies
4

Qualities of an Ideal Dye
Dyes must have attractive colour and offer wide range of
shades
Must be permanent and able to fix itself or being fixed
to the substrate
Should not be affected by water, soap, acid and sunlight
Must be cheap and easy to handle
Easily soluble and must form a stable and good
dispersion in water
Should not be harmful to skin or body
5

Witt’s Theory
 Chromophore- Auxochrome theory
 Explains relation between colour and chemical structure of a substance
 A dye molecule must possess chromophore and auxochrome
 Chromophore- unsaturated group responsible for colour of a dye e.g. nitro,
nitroso, azo, o-or p- quinonoid, ethylenic, carbonyl group etc.
 Auxochrome-acidic or basic group which deepens the colour and also fixes dye
to the substrate e.g. –OH, SO3H, -COOH, -NH2, -NHR, -NRR, -OCH3, -OCOCH3 etc.
6

• Identify 1. Chromophore 2. Auxochrome in following dyes-
Picric acid Malachite green
7

Answers
Dye Chromophore Auxochrome
Picric acid Nitro Hydorxyl
Malachite green Para-quinonoid N,N-Dimethyl
8

Classification of Dyes
1. On the basis of Chemical structure-It is further based on the
chromophoric group present in the molecule of dye molecule
2. On the basis of Methods of Application- It is based on the mode
of dyeing of the substrate.
9

Classification on the basis of Chemical
Structure
10
Sr. No. Type of Dye Chromophore Examples
1 Nitro Dyes -NO2 Picric Acid, Manchestor
Yellow
2 Nitroso Dyes -N=O Gambine-R, Gambine-Y
3 Azo Dyes -N=N- Methyl Orange, Congo
Red
4 TPM Dyes TPM Quinonoid Malachite Green, Para-
rosaniline
5 Anthraquinone
Dyes
Anthraquinone
Quinonoid
Alizarine, Alizarine Orange

Classification based on the Chemical
Structure
Sr.No. Type of Dye Chromophore Examples
6 Indigo Dye >C=C< and >C=O Indigo,Royal Purple
7 Thiazine Dyes >C=S and >C=O Methylene Blue, Lauth’s Violet
8 Sulphur Dyes =C-S-C= and =C-S-S-C= Sulphur Black-T
9 Phthalocyanine Dyes Chelated metals Monastral Fast Blue
10 Stilbene Dyes >C=C< and –N=N- Sun Yellow, Mikado Orange
11

Classification based on methods of
Application
Dyes- I. Ready made Dyes II. Ingrain Dyes
I. Readymade Dyes- 1.Water Soluble 2.Water Insoluble
1.Water Soluble Dyes- a)Acid b)Base c)Direct d)Mordant
e)Reactive f)Optical Whitener
2.Water Insoluble Dyes- a)Vat b)Sulphur c)Disperse
II. Ingrain Dyes- 1. Oxidation
2. Azoic a) Ice colour b)Developed Dye
12

• I.Ready made Dyes- Dyes ready for use by dissolving in suitable
solvent.
• Water Soluble Dyes- contain polar groups such as COOH, -SO3H, -
NH2, -NHR etc.
a)Acid Dyes- contain acidic groups like –COOH, -SO3H, -OH etc
e.g. Orange-II, Manchestor Yellow
b)Basic Dyes- contain basic groups like –NH2, -NHR, -NRR etc
e.g. Malachite Green, Crystal Violet
13

c)Direct Dyes- these dyes are directly used to dye fibre swollen in
hot water (salt dyes) e.g. Congo Red, Brilliant Yellow
d)Mordant Dyes- fixed to fabric by using some binding material
e.g. Alizarine, EB-T
e)Reactive Dyes-these dyes get fixed to fibres by covalent bond
formation e.g. Chlorinated Triazines
f)Optical Whiteners-water soluble dyes which make fabric look
whiter e.g. Pyrazolones, Stilbenes
14

• 2. Water Insoluble Dyes
a) Vat Dyes- insoluble in water but on reduction become water
soluble lueco-bases and fixed to fibre by hydrogen bonding
e.g. Indigo, Indanthrene Blue
b)Sulphur Dyes- sulphur containing, water insoluble hence made
water soluble leuco-bases by reduction. e.g.Sulphur black-T
c)Disperse Dyes- these dyes are applied on the synthetic fibres
in the form of colloidal dispersions e.g. Disperse red- G
15

• II. Ingrain Dyes- These dyes are formed on the fibre itself.
• 1.Oxidation Dyes-these dyes are formed on the fibre after their
oxidation. e.g. Aniline black
2.Azoic Dyes-
a)Ice Colours- developed on the fibre at 0-5⁰C e.g. Para red
b)Developed Diazotised Dye-diazotisation is done on the fibres
16

References
1.Dyeing by Dr. V. Shenai
2.Advanced Organic Chemistry by B. S. Bahl and Arun Bahl
S. Chand and Co. N. Delhi
3.Organic Chemistry Volume I and II by I. L.Finar, ELBS, London
17

Thank you…
18

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