This document provides information about organic chemistry concepts including synthetic dyes, synthetic drugs, and synthetic polymers. It discusses the classification of dyes based on their chemical constitution and provides examples of important synthetic dyes like Congo red, Crystal violet, Phenolphthalein, and Alizarin. It also summarizes theories on the relationship between color and chemical structure, including Witt's theory and the modern electronic concept. Classification of dyes as natural or synthetic is described.

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) SYNTHETIC DYES:
Colour and constitution (Witt theory, electronic concept) Classification of Dyes
based on chemical constitution. Synthesis and uses of Congo red, Crystal violet,
Phenolphthalein and Alizarin dye.
B) SYNTHETIC DRUGS:
Definition, Classification, Preparation, properties and uses of: Aspirin,
paracetamol, Dettol, Chloroquine, Phenobarbitone, Chloramphenicol,
Chloramine T.
C) SYNTHETIC POLYMERS:
Addition or chain growth polymerization, free radical. Vinyl polymerization,
Ionic vinyl polymerization, Ziegler - Natta polymerization .Condensation or step
growth polymerization. Polyesters, polyamides.
Unit-IV (Syllabus)

3. RELATION BETWEEN COLOR AND CONSTITUTION
Like the physical and chemical properties of organic compounds,
there is a definite relationship between the color and constitution
e.g., Benzene is colorless, whereas its isomer, fulvene is colored.
The various theories have been proposed to explain the observed
general relationships existing between color and constitutions.
• Dyes are coloured organic compounds that are used to impart colour to
various substrates, including paper, leather, hairs, drugs, cosmetics, waxes,
greases, plastics and textile materials.
• A dye is a coloured compound, normally used in solution, which is
capable of being fixed to fabrics.
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 colours that 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 Witts Theory
( Chromophore-auxochrome theory)
In 1876, a German scientist Otto Witt put forward a theory known as
“Chromophore Auxochrome theory” or Otto Witt theory.
• It is also called as chromophore auxochrome theory
• 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 auxochrome leads to enhanced colour

7. Some important points of this theory are:
(i) The colour of a substance is mainly due to the presence of unsaturated groups
known as chromophores. The important chromophores are:
−C=C− , −C=N− , −C=O− , −N=N− , −NO2​ , Quinonoid rings
(ii) The compounds possessing chromophores are referred to as chromogens. The
higher the number of chromophores in a chromogen higher is the colour bearing
capacity. The chromospheric groups are of the following two types:
1. When a single chromophore is sufficient to impart colour to the compound.
Example: NO, NO2​,N=N, =N=N, N=NO, p – quinonoid etc.
2. When more than one chromophores are required to impart the colour.
Example: >C=O, >C< etc.
3. Certain groups, which do not produce colour themselves when present along with a
chromophore in an organic substance, intensify the colour. Such colour assisting groups
are called auxochromes. They make the colour deep and fast.
Examples: -OH, -NH2, -CHO

8. Modern Theory
The Otto-Witt’s theory was discussing the relationship
between color and constitution are found to be only
empirical.
The next two important theories, which explain plausibly
the relation between color and constitution, require
somewhat theoretical background about the effect of
light on the molecule.
– Valence bond theory
– Molecular orbital theory

9. Electronic Concept of Modern Theory
The various postulates of this theory are as follows:
• Chromophores are groups of atoms, the π‐electrons of which
may get transferred from ground state to excited state by the
absorption of radiation, thus producing the color.
• Auxochromes are groups, which tend to increase resonance by
interacting the unshared pair of electrons on nitrogen or oxygen
atoms of the auxochromes with the π electrons of the aromatic
ring. This increase in resonance increases the intensity of
absorption of light and also shifts the absorption band to longer
wavelength. Hence there occurs the deepening of the color.
From this it is evident that increase in resonance must deepen
the color and actually it has been found to be so.

10. Types of Electronic Transition

12. Chemical classification of dyes
1)Nitro Dyes
Ex: Picric acid
2) Nitroso Dyes
Dyes may be classified according to the type of chromophores and
auxochromes present in their structure.
3)Azo dye
Ex: Congo red
3)Triphenyl methane dye
Ex: Crystal violet

13. Chemical classification of dyes
5) Antraquinone dyes
Ex: Alizarin
6) Indigoid Dyes
Example: Indigo
7) Phthalein dyes
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 a chemical formula C20H14O4.
•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 colourless in 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 Pthalein dyes.
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