Dyes are colored substances that are used to add color to or change the color of other substances like fabrics, plastics, paper, leather, and food. Dyes work by absorbing certain wavelengths of visible light, which allows them to impart color. They contain structures called chromophores that have delocalized electron systems responsible for light absorption. Auxochromes are groups attached to chromophores that modify their light absorption properties and provide solubility and cohesiveness to dyes. There are many ways to classify dyes, including by their source (natural vs synthetic), chemical structure, intended application, and dyeing method used. Common types of dyes include direct, vat, sulfur

2. INTRODUCTION
What is Dye?

3. Plastic toys for children to that fabrics you wear, from food to wood; hardly there is any
industry where
coloring material that color commodities of our day to day use. Dyes are applied everywhere,
from a natural or synthetic substance used to add a color or to change the color of something.
Dyes are the dyes are not used commercially.
A dye is a colored substance that has an affinity to the substrate to which it is being applied. It
is an Ionising and aromatic organic compounds. The dye is generally applied in an aqueous
solution, and may require a mordant to improve the fastness of the dye on the fiber.
With the help of dyes we can easily manipulate things according to our liking. At the very basic
level the use of color in identifying individual components of tissue sections can be
accomplished primarily with dyes. Dyes are applied to numerous substrates for example to
textiles, leather, plastic, paper, food etc.
The rule that we apply to other chemicals is similarly applicable to dyes also. They also get
completely or atleast partially soluble in which it is being put to. For example certain kind of
dyes can be toxic, carcinogenic or mutagenic and can be hazardous to health.
What makes the Dyes colored?
Dyes are basically ionising and aromatic compounds, they have Chromophores present in them.
Their structures have Aryl rings that has delocalised electron systems. These structures are said
to be responsible for the absorption of electromagnetic radiation that has varying wavelengths,
based upon the energy of the electron clouds.
Chomophores make the dyes proficient in their ability to absorb radiation. Chromophores act
by making energy changes in the delocalised electron cloud of the dye. This alteration invariably
results in the compound absorbing radiation within the visible range of colors and not outside
it. Human eyes detects this absorption, and responds to the colors.
Electrons may result in loss of color, their removal may cause the rest of the electrons to revert
to the local orbits. A very good example is the Schiff's reagent. As Sulphurous acid reacts with
Pararosanilin, what happens is that a Sulphonic group attaches itself to the compound's central
carbon atom. This hampers the conjugated double bond system of the Quinoid ring, and causes
the electrons to become localised. As a consequence the ring ceases to be a Chromophore. As a
result, the dye becomes colorless.
To conclude chromophores are the atomic configurations which has delocalised electrons.
Generally they are represented as carbon, nitrogen, oxygen and sulphur. They can have
alternate single and double bonds.
What gives the Dyes Solubility and Cohesiveness?

4. Auxochrome, the only substance responsible for providing solubility and cohesiveness to dyes.
An auxochrome is a group of atoms attached to a chromophore which modifies the ability of
that chromophore to absorb light. Examples include the hydroxyl group (-OH), the amino group
(-NH2), and an aldehyde group (-CHO).
The presence of an auxochrome in the chromogen molecule is essential to make a dye.
However, if an auxochrome is present in the meta position to the chromophore, it does not
affect the color.
Auxochrome has the ability to intensify colors. It is a group of atoms which attaches to non-
ionising compounds yet has the ability to ionise. Auxochromes are of two types, positively
charged or negatively charged.
Classification of Dyes
Dyes can be classified in several ways, each class has a very unique chemistry, structure and
particular way of bonding. Some dyes can react chemically with the substrates forming strong
bonds in the process, and others can be held by physical forces. Some of the prominent ways of
classification are given below
 Natural / Synthetic
 Organic / Inorganic
 By area and method of application
 Chemical classification - Based on
the nature of their respective
chromophores.
 By nature of the Electronic
Excitation
 According to the dyeing methods
 Anionic (for Protein fibre)
 Direct (Cellulose)
 Disperse (Polyamide fibres)
US International Trade Commission has advocated the most popular classification of
dyes. This system classifies dyes into 12 types, which are given below:
Group Application
Direct Cotton, cellulosic and blended fibres
Vat dyes Cotton, cellulosic and blended fibres
Sulphur Cotton, cellulosic fibre
Organic pigments Cotton, cellulosic, blended fabric, paper
Reactive Cellulosic fibre and fabric
Disperse dyes Synthetic fibres
Acid Dyes Wool, silk, paper, synthetic fibres, leather
Azoic Printing Inks and Pigments
Basic Silk, wool, cotton

5. Type of Dyes
The Dyes are classified based on the products to which they can be applied and the chemical
nature of each dye. Dyes are complex unsaturated aromatic having characteristics like
solubility, intense color, sub-stansiveness and fastness. A dye-formulation is supposed to have
approximately 10-80% pure dyestuff. It is mostly observed that dyestuffs delivered in powder
form have a higher value. While a lower value is obtained for the liquid formulations.

6. MALACHITE GREEN
INTRODUCTION
Alternative titles: aniline green; benzaldehyde green; china green
Malachite green, also called aniline green, benzaldehyde green, or china
green, triphenylmethane dyeused medicinally in dilute solution as a local antiseptic. Malachite
green is effective against fungi and gram-positive bacteria. In the fish-breeding industry it has
been used to control the fungus Saprolegnia,a water mold that kills the eggs and young fry.
Malachite green also is used as a direct dye for silk, wool, jute, and leather and to dye cotton
that has been mordanted with tannin. Prepared from benzaldehyde and dimethylaniline, the
dye occurs as lustrous green crystals soluble in water and in alcohol.
PREPARATION
APPARATUS REQUIRED:
 Test tube
 Water bath
 Flask
 Beaker
 Watch glass
 China dish
CHEMICAL REQUIRED:
 3 ml of benzaldehyde
 6 ml of dimethylaniline
 3 g of Anhydrous ZnCl2
 2 g of PbO2
 4 g of sodium sulphatein cold water

7. PROCEDURE:
1. Place 3 g of anhydrousZnCl2 ina china dishand3 ml of benzaldehyde and6ml of dimethylaniline
to it.
2. Coverit withwatchglassandheatforabout 90 minute ona waterbath. Stirfrequentlyandif the
mixture becomesveryviscoustostir,add1 ml of hot water.
3. While the chinadishisstill onthe waterbath, add5 ml of water,stirthe contentswithaglass
rod to dissolve the maximumdye andtransferthe solutionto400ml beaker.
4. Add125 ml of ice coldwater.Leuco formof the dye isobtained.Withstirring,now adda
suspensionof 2g PbO2 in 20 ml of waterand then4 g of sodiumsulphate in20 ml of waterto it.
Warm and filter.
OBSERVATION: A dark green dye is obtained.
USES
Malachite green is traditionally used as a dye. Millions of kilograms of MG and related
triarylmethane dyes are produced annually for this purpose.[3]
MG is active against the protozoan Saprolegnia, which infects fish eggs in
commercial aquaculture, MG is used to treat parasites and is used as anantibacterial.] It is a
very popular treatment against Ichthyophthirius multifiliis in freshwater aquaria. The
principal metabolite, LMG, is found in fish treated with malachite green, and this finding is the
basis of controversy and government regulation. See also Antimicrobials in aquaculture.
MG has frequently been used to catch thieves and pilferers. The bait, usually money, is
sprinkled with the anhydrous powder. Anyone handling the contaminated money will find that
on upon washing the hands, a green stain on the skin that lasts for several days will result.

8. FLOURESCENT DYE
APPARATUS REQUIRED:
 Test tube
 Weighing balance
 Burner
 Conical flask
CHEMICALS REQUIRED:
 2g Resorcinol
 2g Phthalic anhydride
 5% NaOH
 2ml Conc. H2SO4
PROCEDURE:
1. Take 2g Resorcinol and 2g Phthalic anhydride and add 2ml conc. H2SO4 to it.
2. Heat the content on burner till the content turns black.
3. Cool the contents and add 20 ml of 5% NaOH in a conical flask.
4. Vary concentration of NaOH and water to obtain different intensities of colour.
OBSERVATION:
The dye formed shows fluorescence. It appears green from some angle and orangish yellow
from others. The dye when put in sink with a large amount of water turned into bright yellow
colour.