8/13/2019 1252004_634571154791887500

1/23

PROJECT ONDYESASHA SHARMAXII-A

8/13/2019 1252004_634571154791887500

2/23

8/13/2019 1252004_634571154791887500

3/23

CONTENTS INTRODUCTION ACKNOWLEDGEMENT BASIS OF COLOUR

NATURAL DYES MAUVIENE COLOR FASTNESS DYE CLASIFICATION AZO DYES CERTIFICATE

8/13/2019 1252004_634571154791887500

4/23

ACKNOWLEDGEMENT I would like to thanks our chemistry teacher Mrs.Promila

Kohly mam and our lab assistant Balbir sir. They helped mecompleting this project. She acted as a friend, philosopher and

guide.

8/13/2019 1252004_634571154791887500

5/23

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? Whataffects the dyes have an affinity for the substrate (fibre) they are appliedto. Dyes are also either soluble, or dispersible in a solvent (the particles ofa dispersed dyes are essentially aggregates of a few molecules)1.

Pigments have no affinity for the substrate they are applied to, and tendto be present as an insoluble suspension in a drying oil or other resinousvehicle. Pigment particles also tend to be of the order of 1m in diameter1.

However, the boundary between pigments and dyes is not sharp. Themethod of application of some dyes requires them to form insolublecompounds within the fabric. See Protein Textile Dyesfor a greaterdiscussion of this effect way they attach to different fibres?

http://www.chm.bris.ac.uk/webprojects2002/price/protein.htmhttp://www.chm.bris.ac.uk/webprojects2002/price/protein.htm

8/13/2019 1252004_634571154791887500

6/23

BASIS OF COLOURThe different colours of white lightEveryone is familiar with rainbows- see the top picture for a wellknown 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 isdeficient in any colour band, the light appears to be coloured in thecomplementary colour. The table below shows wavelength, thecorresponding colour, and its complementary colour2

8/13/2019 1252004_634571154791887500

7/23

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

8/13/2019 1252004_634571154791887500

8/23

THE EFFECT OF MOLECULARENERGY LEVELS.

Transition metal complexes are coloured due to the distortion of the metal'sSimple molecular excitation, such as in a neon tube, may cause the appearanceof 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 theHighest Occupied Molecular Orbital (HOMO, the Fermi level) and theLowest 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.

8/13/2019 1252004_634571154791887500

9/23

THEFIRSTFOURMECHANISMSALLRELYONSOMEFORMOFENERGYTRANSFERTOMOVEEITHERMOLECULESORELECTRONS

FROM

THEIR

GROUND

STATE

INTO

SOME

EXCITED

STATE. HOWEVER, ONLYONEOFTHESEEFFECTIVELYAPPLIESTODYEMOLECULES, SINCEDYEMOLECULESAREALMOSTWITHOUTEXCEPTIONORGANICCONJUGATEDSYSTEMS. THEOVERLAPPINGP-ORBITALSEFFECTIVELYMEANTHATNOONEELECTRONABSORBSMOREENERGYTHANANOTHER, SINCEALLP-ELECTRONSINTHECONJUGATEDSYSTEMARESMEAREDABOVEANDBELOWTHEMOLECULE. CONJUGATEDORGANICMOLECULESABSORBSPECIFICWAVELENGTHSOFELECTRO-

MAGNETICRADIATIONIfthis absorption falls within the visible region, then the light reflected ortransmitted is deficient in a particular colour, and the solid (or solution)appears coloured:

8/13/2019 1252004_634571154791887500

10/23

The energy of the electronic

transition can be calculated fromDE = 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.

8/13/2019 1252004_634571154791887500

11/23

NATURAL DYESEarly dyesThe earliest records of dyeing processes are Chinese, and date from about2600BC3. 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:

8/13/2019 1252004_634571154791887500

12/23

DYERSMADDER RUBIATINCTORUMANDR.PEREGRINA ALSOGIVESAREDDYE BUTTHISTIME THEMAINDYEMOLECULEISALIZARIN:

8/13/2019 1252004_634571154791887500

13/23

MAUVIENE:FIRST SYNTHETIC DYENo dye story would be complete without some mention of mauveine. It wasfirst 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 usedas a preventative against malaria. Since very little was then known aboutthe structure of quinine, or indeed any organic molecule, he took a stab in thedark and began by oxidising allyltoluidine1:

2C10H13N + 1O2----> C20H24N2O2

+ H2OSince we now know the structures of both quinine and allyltoluidine, it iseasy to see why it didn't work1. What he did notice, however, was a brownproduct

8/13/2019 1252004_634571154791887500

14/23

THISWASSUFFICIENTLYINTERESTINGFORHIMTO

INVESTIGATEFURTHER, ANDHEREPEATEDTHEEXPERIMENT,BUTWITHANILINEEXTRACTEDFROMCOALTARINSTEAD. THISRESULTEDINABLACKPRODUCT, WHICHWENOWKNOWTOBEANILINEBLACK. BUTWHENHEEXTRACTED

THISWITHALCOHOL, HEOBTAINEDAPURPLISHPRODUCTWHICHHECALLEDANILINEPURPLE1,2.WHENANILINEPURPLEWASTESTEDONSILKATADYEWORKSINPERTH, SCOTLAND, ITGAVEARICHPURPLECOLOUR. HETOOKOUTAPATENTONITANDWENTINTOPRODUCTION2.

8/13/2019 1252004_634571154791887500

15/23

COLOR FASTNESSA 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 undernormal conditions when exposed to light, heat, or other influences."

For example, linen is much harder to dye than silk or cotton (although indigodyes both cotton and linen well- see later). A dye which works well on leatherwill probably not be suitable for wool.

8/13/2019 1252004_634571154791887500

16/23

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 toclassify a dye:

8/13/2019 1252004_634571154791887500

17/23

ONTHEBASISOFTHEIRSTRUCTURE

Azo dyes are the most important of the dye classes, with the largest rangeof colours (see Basis of Colour). All azo dyes containat least one-N=N- group. See the Azo Dyes page for more explanation. The next

most important dye class contains carbonyl functions (-C=O). Thisgroup includes anthraquinones2

8/13/2019 1252004_634571154791887500

18/23

AZODYESThe azo compound class accounts for 60-70% of all dyes. As you might expect, they allcontain an azo group, -N=N-, which links two sp2hybridised carbon atoms. Often,these carbons are part of aromatic systems, but this is not always the case. Most azodyes contain only one azo group, but some contain two (disazo), three (trisazo) ormore2.Isomerism in azo dyesGeometrical isomerism

As with any double bond, the planar -N=N- bond shows geometrical isomerism:

8/13/2019 1252004_634571154791887500

19/23

THISCHANGEFROMTRANS(PREFERRED) TOCISCAN

BEEFFECTEDBYEXPOSURETOUV RADIATION. THISCANLEADTOPHOTOCHROMISM, ALIGHT-INDUCEDREVERSIBLECOLOURCHANGEINSOMEDYES, FOREXAMPLEC.I. DISPERSERED1. THISEFFECTWASCONSIDEREDANUISANCEANDHASLARGELYBEENELIMINATEDBYCAREFULDEVELOPMENTOFMORESTABLEDYES. BUTPHOTOCHROMICDYESAREBEGINNINGTOMAKEACOMEBACKINTECHNOLOGYLIKESUNGLASSESANDSUNROOFSINCARS2

8/13/2019 1252004_634571154791887500

20/23

TAUTOMERISMThis involves the removal of a hydrogen from one part of the molecule, and theaddition of a hydrogen to a different part of the molecule. This is common when thereis an -OH group ortho or para to the azo group:

Tautomeric forms can be identified form their characteristicspectra. Ketohydrazones are normally bathochromic compared to their

counterpart hydroxyazo forms. Ketohydrazones also have higher molarextinction co-efficients. However, not all azo dyes show tautomerism, andsome tautomeric forms are more stable than others2.

Since we now know the structures of both

quinine and allyltoluidine, it is easy to seewhy it didn't work1. What he did notice,

however, was a brown produc

8/13/2019 1252004_634571154791887500

21/23

.

An overview of azo dye synthesis is shown below:

Stage 1- Diazotisation

This involves a primary aromatic amine, called the diazocomponent. It is treated in low temperature, acid conditions with

sodium nitrite to form an unstable diazonium salt2.

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.

8/13/2019 1252004_634571154791887500

22/23

8/13/2019 1252004_634571154791887500

23/23