SAL COLLEGE OF ENGINEERING SUBJECT.: ORGANIC CHEMISTRY AND UNIT OPERATIONS ( ) TOPIC.:DYES &PIGMENTS ALA PRESENTATION CHEMICAL ENGINEERING Guided BY: Dr. Monika Swami TUSHAR PATEL( ) DHAVALVAGAHASIYA ( ) TRILOKDAN VARASDA( )

colour  Definitions :  the property possessed by an object of producing different sensation on the eyes as a result of the way it reflects or emits light.  One or any mixture, of the constituents into which light can be separated in a spectrum or rainbow.

Electromagnetic radiation Light is a form of energy that travels through space like a wave and is characterized by its wavelength.

Electromagnetic radiation Only certain wavelengths of light can be detected by the human eye.

“White” light is actually composed of all colors in equal amounts. White Light

Dyes  Definitions :  A dye is a coloured compound, normally used in solution, which is capable of being fixed to a fabric.  Oxford English Dictionary (11 th edition):  A natural or synthetic substance used to colour something.

Classification of dyes Nitro & Nitroso dyes Azo dyes Triarylmethane dyes Anthraquinone dyes Indigo dyes  Direct dyes  Vat dyes  Mordant dyes  Azoic dyes  Disperse dyes Dyes By application

By structure 1. Nitro & nitroso : The NO 2 & NO groups are chromophores in this class of dyes.  Example is…..  Naphthol yellow s

2. Azo dyes : the azo dyes contain one or more azo groups, -N=N-, as the primary chromophore. Azo dyes form the largest &most important group of synthetic dyes.they are highly coloured & can prepared by diazotising an aromatic amine and subsequent coupling with a suitable aromatic phenol or amine. Examples are, (a) Para red : it was the first azo dye to be prepared. Para red is obtained by the reaction of diazotised p-nitroaniline with ɮ - napthol onfabric itself.

(b)Methyle orange : it is obtained from sulphanilic acid by the folowing steps:  Mithyl orange imparts orange colour to wool and silk but the colour is not fast to sunlight or washing. it is valuable indicator for acid- base titration s because it gives yellow colour in basic solution & red colour in acid solution.the change in colour due to the change in the structure of the ion.

(C) Congo red : it contains two azo groups. It is obtained by coupling tetrazotised benzidine (1) with two molecules of naphthionic acid (2).  It is a direct dye and its sodium salt is used for dyeing cotton red from aqueous solutions.  It is also used as an indicator, being red in alkali and blue in acid solution.

(d)Bismarck brown :it is brown dye used in boot polishes and for dyeing wool & cotton.

(3) Triarylmethane dyes : in this dyes, a central carbon is bounded to three aromatic rings, one of which is in the quinoid form.The auxochromes are -NH2,-NR2 & -OH. Ex.s are, (a) Malachite green : it has deep green colour. It is used as a direct dye for wool and silk.

(b) Phenolphthalein: It is also known as an acid-base indicator.

(c)Fluorescein : it is red powder insoluble in water. It dissolves in dilute alkali and the solution gives beautiful yellow-green flourescence. The sodium salt of it is known as URAINE which is used for dyeng wool or silk yellow.

(4) Anthraquinone dyes: the para quinoid chromophore is present in these type dyes. Alizarin is a typical anthraquinone dye.  Alizarin forms ruby red crystals which dissolve in alkali to give purple solutions. It is used to dye wool and cotton.

(5)Indigo dyes: it is an example of the type of dyes which contain carbonyl chromophore.  It is a dark blue crystalline compound, insoluble in water. It is used for dyeing cotton by the vat process.

BY application (1)Direct dyes : these can be applied to a fabric by immersion in a water solution of the dye.  A direct dye contains acidic or basic auxochrome which combines with the opp. Polar group present in the chemical structure of fibre.  Fibre –NH ₂ + HO- dye → Fibre- NH ₃⁺ ….O‾-dye

(2)Vat dyes  This dyes are insoluble in water. Indigo is a good example of a vat dyes.

(3)Mordant dyes  This class of dyeshave no natural affinity affinity for the fabric and are applied to it with the help of salts e.g., oxides of alluminium or chromium. This salts are called mordants. It is most suitaible for wool and nylon.

(4)Azoic dyes  In this method, the water soluble azo dye is produced in the fabric itself.  The azoic dyeing is particularly suitable for cotton and other cellulosic fibres but may also be used for nylon.

(5)Disperse dyes  Disperse dyes : these dyes are insoluble in water but can be dispersed in a colloidal form in water. The fabric is immersed in the colloidal dispersion of the dye.  Disperse dyes are used with morden synthetic fabrics such as nylon, orlon,polyester & cellulose acetate.

Pigments  Definition:  A substance used for colouring or painting, especially a dry powder which constitutes a paint or ink when mixed with oil or water.  Uses:  These are used for colouring paint ink plastic fabric, cosmatic food &other materials.

6/22/2016GCSE Chemistry Extension Module C Soluble transition metal compounds that are coloured can be used as... dyes and pigments Insoluble transition metal compounds that are coloured can be used as... DYESDYES PIMENTSPIMENTS

Pigments and Dyes Pigment particles Dye molecules  A dye is a colorant that goes into solution or dissolves. Dye particles break apart into single molecules  Pigment particles remain clustered together in suspension  Dyes have a chemical affinity for fiber but pigments do not

Pigments and Dyes  Dyes migrate out of the solution, are absorbed into the fiber, and diffuse from the surface of the fiber toward its center. There they either:  Bond chemically with fiber molecules OR  React chemically with fiber molecules to produce permanent, enlarged colored fiber molecules  Both situations are permanent  Pigment molecules carry their own color  They do not unite with fiber molecules chemically and must be fixed to the fibers with bonding agents  In man made fibers pigments can be mixed into the fiber solution before it is formed