PROJECT ON DYES

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PROJECT ON DYES:

PROJECT ON DYES ASHA SHARMA XII-A

CONTENTS:

CONTENTS INTRODUCTION ACKNOWLEDGEMENT BASIS OF COLOUR NATURAL DYES MAUVIENE COLOR FASTNESS DYE CLASIFICATION AZO DYES CERTIFICATE

ACKNOWLEDGEMENT:

ACKNOWLEDGEMENT I would like to thanks our chemistry teacher Mrs.Promila Kohly mam and our lab assistant Balbir sir. They helped me completing this project. She acted as a friend, philosopher and guide.

INTRODUCTION:

INTRODUCTION The basis of this project is the chemistry behind fabric dyes- what are they? What are the origins of dyes? How are they made? What affects the dyes have an affinity for the substrate ( fibre ) they are applied to.  Dyes are also either soluble, or dispersible in a solvent (the particles of a dispersed dyes are essentially aggregates of a few molecules) 1 . Pigments have no affinity for the substrate they are applied to, and tend to be present as an insoluble suspension in a drying oil or other resinous vehicle. Pigment particles also tend to be of the order of 1μm in diameter 1 . However, the boundary between pigments and dyes is not sharp. The method of application of some dyes requires them to form insoluble compounds within the fabric. See Protein Textile Dyes for a greater discussion of this effect way they attach to different fibres ?

BASIS OF COLOUR :

BASIS OF COLOUR The different colours of white light Everyone is familiar with rainbows- see the top picture for a well known example!  Sunlight is refracted by atmospheric water, producing bands of red, orange, yellow, green,  blue, indigo and violet.  These combined make up white light.  If a light source is deficient in any colour band, the light appears to be coloured in the complementary colour .  The table below shows wavelength, the corresponding colour , and its complementary colour 2

PowerPoint Presentation:

This image shows the effect on white light reflected off a solid object This image shows the effect on white light transmitted through a solution, or other transparent article

THE EFFECT OF MOLECULAR ENERGY LEVELS:

THE EFFECT OF MOLECULAR ENERGY LEVELS . Transition metal complexes are coloured due to the distortion of the metal's Simple molecular excitation, such as in a neon tube, may cause the appearance of colour .  This is due to rotation and/or vibration of the moleculesd -electron shell caused by ligands surrounding the metal ion. Electronic motion in conjugated organic systems, and charge transfer. Colour in crystalline solids arises from band theory- the blurring of many orbitals through-out the solid.  Solids are only coloured if the gap between the Highest Occupied Molecular Orbital (HOMO, the Fermi level) and the Lowest Unoccupied Molecular Orbital (LUMO) is small enough. Colour due to refraction, scattering, dispersion and diffraction- these are all due to the geometrical and physical dimensions of a solid or a solution.

The first four mechanisms all rely on some form of energy transfer to move either molecules or electrons from their ground state into some excited state.  However, only one of these effectively applies to dye molecules, since dye molecules are almost without exception organic conjugated systems.  The overlapping p-orbitals effectively mean that no one electron absorbs more energy than another, since all p-electrons in the conjugated system are smeared above and below the molecule.  Conjugated organic molecules absorb specific wavelengths of electro-magnetic radiation:

The first four mechanisms all rely on some form of energy transfer to move either molecules or electrons from their ground state into some excited state.  However, only one of these effectively applies to dye molecules, since dye molecules are almost without exception organic conjugated systems.  The overlapping p- orbitals effectively mean that no one electron absorbs more energy than another, since all p-electrons in the conjugated system are smeared above and below the molecule.  Conjugated organic molecules absorb specific wavelengths of electro-magnetic radiation If this absorption falls within the visible region, then the light reflected or transmitted is deficient in a particular colour , and the solid (or solution) appears coloured :

PowerPoint Presentation:

The energy of the electronic transition can be calculated from DE = hn where DE is the difference between the two electronic levels, h is Planck's constant and n is the frequency of the absorbed radiation.

NATURAL DYES :

NATURAL DYES Early dyes The earliest records of dyeing processes are Chinese, and date from about 2600BC 3 .  The drive to find new and interesting colours is understandable- most natural fibres such as cotton, linen, wool and leather are shades of white, black or brown:

Dyers Madder, Rubia tinctorum and R. peregrina, also gives a red dye, but this time, the main dye molecule is alizarin: :

Dyers Madder, Rubia tinctorum and R. peregrina , also gives a red dye, but this time, the main dye molecule is alizarin:

MAUVIENE:FIRST SYNTHETIC DYE:

MAUVIENE:FIRST SYNTHETIC DYE No dye story would be complete without some mention of mauveine .  It was first discovered in 1856 by a young chemist called William Henry Perkins, although it was not his intention! His aim was to synthesise quinine, a drug extracted from tree bark and used as a preventative against malaria.  Since very little was then known about the structure of quinine, or indeed any organic molecule, he took a stab in the dark and began by oxidising allyltoluidine 1 : 2C 10 H 13 N + 1½O 2 ----> C 20 H 24 N 2 O 2 + H 2 O Since we now know the structures of both quinine and allyltoluidine , it is easy to see why it didn't work 1 .  What he did notice, however, was a brown product

  This was sufficiently interesting for him to investigate further, and he repeated the experiment, but with aniline extracted from coal tar instead.  This resulted in a black product, which we now know to be Aniline Black.  But when he extracted this with alcohol, he obtained a purplish product which he called Aniline Purple1,2. When Aniline Purple was tested on silk at a dye works in Perth,  Scotland, it gave a rich purple colour.  He took out a patent on it and went into production2. :

This was sufficiently interesting for him to investigate further, and he repeated the experiment, but with aniline extracted from coal tar instead.  This resulted in a black product, which we now know to be Aniline Black.  But when he extracted this with alcohol, he obtained a purplish product which he called Aniline Purple 1,2 . When Aniline Purple was tested on silk at a dye works in Perth,  Scotland, it gave a rich purple colour .  He took out a patent on it and went into production 2 .

COLOR FASTNESS :

COLOR FASTNESS A definition of fastness "That property of a pigment or dye, or the leather, cloth, paper, ink, etc., containing the coloring matter, to retain its original hue, especially without fading, running, or changing when wetted, washed, cleaned; or stored under normal conditions when exposed to light, heat, or other influences." For example, linen is much harder to dye than silk or cotton (although indigo dyes both cotton and linen well- see later).  A dye which works well on leather will probably not be suitable for wool.

DYE CLASSIFICATION:

DYE CLASSIFICATION According to its chemical structure. According to how it is applied to materials. How Do we classify dyes? There are two practical ways to classify a dye:

on the basis of their structure:

on the basis of their structure Azo dyes are the most important of the dye classes, with the largest range of colours (see Basis of Colour ).  All azo dyes contain at least one -N=N- group.  See the Azo Dyes page for more explanation.  The next most important dye class contains carbonyl functions (-C=O).  This group includes anthraquinones 2

Azo dyes :

Azo dyes The azo compound class accounts for 60-70% of all dyes.  As you might expect, they all contain an azo group, -N=N-,  which links two sp 2 hybridised carbon atoms.  Often, these carbons are part of aromatic systems, but this is not always the case.  Most azo dyes contain only one azo group, but some contain two ( dis azo ), three ( tris azo ) or more 2 . Isomerism in azo dyes Geometrical isomerism As with any double bond, the planar -N=N- bond shows geometrical isomerism:

This change from trans (preferred) to cis can be effected by exposure to UV radiation.  This can lead to photochromism, a light-induced reversible colour change in some dyes, for example C.I. Disperse Red 1.  This effect was considered a nuisance and has largely been eliminated by careful development of more stable dyes.  But photochromic dyes are beginning to make a comeback in technology like sunglasses and sunroofs in cars2:

This change from trans (preferred) to cis can be effected by exposure to UV radiation.  This can lead to photochromism , a light-induced reversible colour change in some dyes, for example C.I. Disperse Red 1.  This effect was considered a nuisance and has largely been eliminated by careful development of more stable dyes.  But photochromic dyes are beginning to make a comeback in technology like sunglasses and sunroofs in cars 2

Tautomerism :

Tautomerism This involves the removal of a hydrogen from one part of the molecule, and the addition of a hydrogen to a different part of the molecule.  This is common when there is an -OH group ortho or para to the azo group: Tautomeric forms can be identified form their characteristic spectra. Ketohydrazones are normally bathochromic compared to their counterpart hydroxyazo forms. Ketohydrazones also have higher molar extinction co- efficients .  However, not all azo dyes show tautomerism , and some tautomeric forms are more stable than others 2 . Since we now know the structures of both quinine and allyltoluidine , it is easy to see why it didn't work 1 .  What he did notice, however, was a brown produc

. :

. An overview of azo dye synthesis is shown below: Stage 1- Diazotisation This involves a primary aromatic amine, called the diazo component.  It is treated in low temperature, acid conditions with sodium nitrite to form an unstable diazonium salt 2 . Stage 2- Azo coupling The diazonium salt is reacted with a coupling component (for example a phenol or an aromatic amine).  This forms the stable azo dye.

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