This document discusses the classification and synthesis of dyes. It begins by defining key concepts like chromophores, which are the parts of molecules responsible for color, and auxochromes, which increase the color intensity. It then describes several classes of dyes in more detail, including nitro dyes, azo dyes like methyl orange, triarylmethane dyes like malachite green, indigo dyes, anthraquinone dyes like alizarin, and fluorescein dyes. Other topics covered include benzenesulfonic acid, saccharin, chloramine-T, and sulfonamides. The document provides examples and reaction mechanisms to illustrate the synthesis of dyes from various

1. 1
Mr.M.RAGU
Assistant Professor of
Chemistry
Vivekananda College
Tiruvedakam West –
Classification and
Synthesis of Dyes

2.  Introduction
 Theory of color and constitution
 Chromophore and Auxochrome
 Nitro dyes and Naphthol yellow
 Azo dyes
 Methyl orange
 T-Chloramine
OutlineOutline

5. THEORY OF COLOR AND CONSTITUTION
CHROMOPHORE
A chromophore is the part of a molecule responsible for its color
It arises when a molecule absorbs certain wavelengths of visible light and
transmits or reflects others
The energy difference between two different molecular orbitals falls within
the range of the visible spectrum.
Visible light that hits the chromophore can thus be absorbed by exciting
an electron from its ground state into an excited state.
White light is a continuum of different colours.
If white light is passed through clouds or a prism, then it can be split up
into its constituent colours, each of which has a different wavelength.

7. Examples of Chromophores
If there is only conjugation, a long chain of conjugated bonds is needed to
reduce the HOMO/LUMO gap to energies that correspond to visible light.
Realize that it is continuous, extended conjugation that is important (i.e. the size
of the molecular orbital), not the total number of double bonds.
If we continue to increase the number of conjugated C=C bonds, then eventually
we reach a point where the compound will absorb visible light (β-carotene ~475
nm).
Keto group, Nitroso group, Quinonoid group, Ethylenic group, Nitro
group, azo group.

8. Chemical structure of beta-carotene. The eleven conjugated double bonds that
form the chromophore of the molecule are highlighted in red
An auxochrome (Gr. Auxanein: to increase, chroma:colour) is a group of
atoms attached to a chromophore
 They themselves fail to produce the colour; but when present along with
the chromophores increase in color
Acidic: -COOH, -OH, -SO3H ;
Basic: -NHR, -NR2, -NH2
AUXOCHROME

9. NITRO DYES
a group of dyes; aromatic compounds whose color results from the presence of nitr
o groups, NO2, and hydroxyl and iminogroups, OH and NHR (R is an alkyl or aryl
group).
They may also contain Cl, SO3H, and COOH substituent's.
Nitro dyes containing imino groups are more stable.
It is produced by the reaction of 2,4-dinitrochlorobenzene with p-aminophenol.

10. NAPHTHOL YELLOW
It is used in a number of countries as a food dye.
 It is produced by sulfonation of α-naphthol, with
subsequent nitration of the product.
Nitro dyes (for example, picric acid) were among the first industrial dyes. They
lost their practical importance as a result oftheir low stability.

11. diazotized
sulfanilic acid
+-O3S N N N(CH3)2
N,N-dimethylaniline
-O3S N N N(CH3)2
H
H+ transfer
-O3S N N N(CH3)2
HNaOH
helianthin (red)
NaO3S N N N(CH3)2
methyl orange
AZO DYES

12. It is a pH indicator frequently used in titrations because of its clear and
distinct colour change.
Its not an universal indicator
Colourless solid is soluble in nonpolar organic solvents and not in water.
METHYL ORANGE

13. i) It can be synthesized by Friedel-Crafts
reaction from benzene and chloroform with aluminium
chloridecatalyst:
3 C6H6 + CHCl3 → Ph3CH + 3 HCl
TRIPHENYLMETHANE DYES
Basic skeleton of many synthetic dyes called triarylmethane dyes

14. Examples of triarylmethane dyes are bromocresol green:
ii) Benzene may react with carbon tetrachloride using the same
catalyst to obtain the trityl chloride-aluminium chloride adduct,
which is hydrolyzed with dilute acid:
3 C6H6 + CCl4 + AlCl3 → Ph3CCl·AlCl3
Ph3CCl·AlCl3 + HCl → Ph3CH

15. It is prepared by condensing benzaldehyde and dimethylaniline in the
molecular ratio 1:2 in the presence of sulfuric acid
MALACHITE GREEN DYES

16. N-phenylglycine is treated with a molten mixture of sodium
hydroxide, potassium hydroxide, and sodamide. This highly sensitive melt
produces indoxyl, which is subsequently oxidized in air to form indigo.
INDIGO DYES

17. Alizarin is one of ten dihydroxyanthraquinone isomers.
Its molecular structure can be viewed as being derived fromanthraquinone by
replacement of two neighboring hydrogen atoms (H) by hydroxyl groups (-OH).
It is soluble in hexane and chloroform
ANTHRAQUINONE DYES

18. Derivatives of 9,10-anthraquinone include many important drugs
(collectively called anthracenediones).
Antimalarials such as rufigallol Antineoplastics used in the treatment
of cancer, such as mitoxantrone, pixantrone
Aloe emodin mitoxantrone
pixantrone

19. It can be prepared from phthalic anhydride and resorcinol in the presence
of zinc chloride via theFriedel-Crafts reaction.
FLUORESCEIN DYES

20. It is an organosulfur compound with the formula C6H5SO3H.
 It is the simplest aromatic sulfonic acid.
 It is often stored in the form of alkali metalsalts. Its aqueous solution
is strongly acidic
Preparation
Benzenesulfonic acid is prepared from the sulfonation of benzene using
concentrated sulfuric acid
BENZENESULFONIC ACID

21. of other aromatic sulfonic acids, forming sulfonamides, sulfonyl chloride, and
esters.
The sulfonation is reversed above 220 °C. Dehydration with phosphorus
pentoxide gives benzenesulfonic acid anhydride ((C6H5SO2)2O).
Conversion to the corresponding benzenesulfonyl chloride (C6H5SO2Cl) is
effected with phosphorus pentachloride.
It is a strong acid, being dissociated in water.
The alkali metal salt of benzenesulfonic acid was once widely used in the
production of phenol:
 C6H5SO3Na + 2 NaOH → C6H5ONa + Na2SO3
 C6H5ONa + HCl → C6H5OH + NaCl

22. It is an artificial sweetener with effectively no food energy which is about 300–
400 times as sweet as sucrose.
It starts with toluene; Sulfonation by chlorosulfonic acid gives
the ortho and para substituted sulfonyl chlorides. The ortho isomer is separated
and converted to the sulfonamide with ammonia. Oxidation of the methyl
substituent gives the carboxylic acid, which cyclicizes to give saccharin free acid
SACCHARIN

23. Anthranilic acid successively reacts with nitrous acid (from sodium
nitrite and hydrochloric acid), sulfur dioxide, chlorine, and then ammonia to
yield saccharin

24. CHLORAMINE-T
Chloramine-T is slightly basic (pH typically 8.5).
In water, it breaks down to the disinfectant hypochlorite.
It can be used as a source of electrophilic chlorine in organic synthesis.
Chloramine-T is prepared from p-toluenesulfonamide and sodium hypochlorite,
with the latter being produced in situfrom sodium hydroxide and chlorine (Cl2)

25. Applications
It is widely used for the incorporation of iodine to peptides and proteins.
Chloramine-T together with iodogen or lactoperoxidase is commonly used
for labeling peptides and proteins withradioiodine isotopes
Chloramine-T is available in tablet or powder form and has to be dissolved before
use.
The substance is also used for parasitecontrol and for drinking water
disinfection.
It reacts readily with mustard gas to yield a harmless crystalline sulfimide;
chloramine-T derivatives are being studied as protective agents againstpoison gas

26. SULFONAMIDE OR SULPHONAMIDE
 It is the basis of several groups of drugs.
The original antibacterial sulfonamides (sometimes called sulfa drugs or sulpha
drugs) are synthetic antimicrobial agents that contain the sulfonamide group.
Some sulfonamides are also devoid of antibacterial activity
Sulfonamides are prepared by the reaction of a sulfonyl chloride with ammonia
or an amine.
Hydrochlorothiazide Furosemide

27. 27
Mr.M.RAGU
Assistant Professor of
Chemistry
Vivekananda College
Tiruvedakam West –
Thank you