Synthetic Dyes

Synthetic Dyes

1. B.Sc. SEM-VI
Paper-II
Organic Chemistry
Unit-IV
Dr. N. G. Telkapalliwar
(M.Sc., NET, SET, Ph.D., PGD-NSNT)
Associate Professor
Department of Chemistry,
Dr. Ambedkar College, Deekshabhoomi, Nagpur
SYNTHETIC DYES

2. A)SYNTHETICDYES:
Colourandconstitution(Witttheory,electronicconcept)ClassificationofDyes
basedonchemicalconstitution.SynthesisandusesofCongored,Crystalviolet,
PhenolphthaleinandAlizarindye.
B)SYNTHETICDRUGS:
Definition,Classification,Preparation,propertiesandusesof:Aspirin,
paracetamol,Dettol,Chloroquine,Phenobarbitone,Chloramphenicol,
ChloramineT.
C)SYNTHETICPOLYMERS:
Additionorchaingrowthpolymerization,freeradical.Vinylpolymerization,
Ionicvinylpolymerization,Ziegler-Nattapolymerization.Condensationorstep
growthpolymerization.Polyesters,polyamides.
Unit-IV (Syllabus)

3. RELATION BETWEEN COLOR AND CONSTITUTION
Likethephysicalandchemicalpropertiesoforganiccompounds,
thereisadefiniterelationshipbetweenthecolorandconstitution
e.g.,Benzeneiscolorless,whereasitsisomer,fulveneiscolored.
Thevarioustheorieshavebeenproposedtoexplaintheobserved
generalrelationshipsexistingbetweencolorandconstitutions.
•Dyesarecolouredorganiccompoundsthatareusedtoimpartcolourto
varioussubstrates,includingpaper,leather,hairs,drugs,cosmetics,waxes,
greases,plasticsandtextilematerials.
•Adyeisacolouredcompound,normallyusedinsolution,whichis
capableofbeingfixedtofabrics.
What are dyes?

4. 1) Classification based on the source of material
A very common classification of the dye is based on the source of
material
a) Natural Dyes
b) Synthetic Dyes
a)Natural Dyes
Natural dyes are dyes or colourants derived from Plants,Invertibrates
or Minerals.
The majority of natural dyes are Vegetable dyes from plant sources.
Example-Roots,Berries,Bark,Leaves ,Wood,etc.
Other organic sources include fungi and lichens.

5. b) Synthetic Dyes:-
Almost all the coloursthat you see today are synthetic dyes.
Synthetic dyes are used everywhere in everything from
clothes to paper, from food to wood.
These is because they are cheaper to produce, brighter and
easy to apply on fabrics.
Example-Acid dyes, Azo dyes, Basis dyes, Mordant dyes

6. Otto WittsTheory
(Chromophore-auxochrometheory)
In1876, a German scientist Otto Witt put forward a theory known as
“ChromophoreAuxochrometheory” or Otto Witt theory.
•It is also called as chromophore auxochrometheory
•The intrinsic colour of a compound is due to presence of certain groups
containing multiple bonds which are called chromophores
•More is the number of chromophore higher is the probability of colour
•Certain groups have a capacity to intensify the colour produced by
chromophore and called as auxochromes
•Combination of chromophore and auxochromeleads to enhanced colour

7. Some important points of this theory are:
(i) The colourof a substance is mainly due to the presence of unsaturated groups
known as chromophores. The important chromophoresare:
−C=C−, −C=N−, −C=O−, −N=N−, −NO
2​, Quinonoidrings
(ii) The compounds possessing chromophoresare referred to as chromogens. The
higher the number of chromophoresin a chromogenhigher is the colourbearing
capacity. The chromosphericgroups are of the following two types:
1. When a single chromophoreis sufficient to impart colourto the compound.
Example:NO, NO
2​,N=N, =N=N, N=NO,p –quinonoidetc.
2. When more than one chromophoresare required to impart the colour.
Example:>C=O, >C<etc.
3. Certain groups, which do not produce colourthemselves when present along with a
chromophorein an organic substance, intensify the colour. Such colourassisting groups
are called auxochromes. They make the colourdeep and fast.
Examples: -OH, -NH
2, -CHO

8. Modern Theory
TheOtto-Witt’stheorywasdiscussingtherelationship
betweencolorandconstitutionarefoundtobeonly
empirical.
Thenexttwoimportanttheories,whichexplainplausibly
therelationbetweencolorandconstitution,require
somewhattheoreticalbackgroundabouttheeffectof
lightonthemolecule.
–Valencebondtheory
–Molecularorbitaltheory

9. Electronic Concept of Modern Theory
The various postulates of this theory are as follows:
•Chromophoresaregroupsofatoms,theπ‐electronsofwhich
maygettransferredfromgroundstatetoexcitedstatebythe
absorptionofradiation,thusproducingthecolor.
•Auxochromesaregroups,whichtendtoincreaseresonanceby
interactingtheunsharedpairofelectronsonnitrogenoroxygen
atomsoftheauxochromeswiththeπelectronsofthearomatic
ring.Thisincreaseinresonanceincreasestheintensityof
absorptionoflightandalsoshiftstheabsorptionbandtolonger
wavelength.Hencethereoccursthedeepeningofthecolor.
Fromthisitisevidentthatincreaseinresonancemustdeepen
thecolorandactuallyithasbeenfoundtobeso.

10. Types of Electronic Transition

12. Chemical classification of dyes
1)Nitro Dyes
Ex: Picric acid
2) NitrosoDyes
Dyes may be classified according to the type of chromophoresand
auxochromespresent in their structure.
3)Azodye
Ex: Congo red
3)Triphenylmethane dye
Ex: Crystal violet

13. Chemical classification of dyes
5) Antraquinonedyes
Ex: Alizarin
6) Indigoid Dyes
Example: Indigo
7)Phthaleindyes
Ex: Phenophthalein

16. 1)It is a direct dye which can be used for dying cotton
2)It is used as indicator in acid base titration

17. •It has achemical formulaC
20H
14O
4.
•It is written as “phph” or HIn”.
•It is used in acid base titration as an indicator. As an indicator it turns pink to
red in alkaline and is colourlessin acid solutions.
•It is dissolved with alcohol for experiment purpose and it is slightly soluble in
water.
•It does not have taste and smell
•This chemical compound is widely used as PH indicator and laboratory agent.
•It is a weak acid and belong to class of dyes called Pthaleindyes.
Uses of Phenolphthalein
•It is used in acid base titrations as an indicator
•It is used in Kastle-Meyer test
•It was before used as a laxative
Phenolphthalein

18. Preparation of Phenolphthalein

19. Preparation of Alizarin
Alizarin