introduction to preparation and structure of some common dyestuffs

1. INTRODUCTION TOINTRODUCTION TO PREPARATION AND
STRUCTURE OF SOME COMMON DYESTUFFS
By Granch BerheBy Granch Berhe

2. Dyes are colored organic compounds that are
used to impart color to various substrates,
including
Paper
Leather
Hair
Drugs
Cosmetics
Waxes
Greases
Plastics and
Textile materials

3. Dyes may be classified according to their
chemical structure or by the method by
which they are applied to the substrate.
The dye manufacturers and dye chemists
prefer the former approach of classifying
dyes according to chemical type.
The dye users, however, prefer the latter
approach to of classification according to
application method.
Classification by application or usage is
the principal system adopted by the Color
Index (C.I.).

4. Azoic Dyes
Acid Dyes
Basic (Cationic) Dyes
Direct Dyes
Disperse Dyes
Reactive Dyes
Mordant Dyes
Sulfur Dyes
Vat Dyes

5. 1.1 Azo Dyes
Are:-
 Larger groups
 N=N
 NH2, NR2, OH
There may be more than one azo group
 Mono, Di, Tri, Tetrakis and poly
Prepared by Diazotization of primary
aromatic amines= Diazonium salt/diazo and
then coupled with phenol or amine

6. Diazotization
When aromatic amine is added on
aqueous acid medium by nitrous acid a
diazonium salt is formed and the amine is
said to be has been diazotized.
Rate determining step-nitration of amine
Ar. = aromatic hydrocarbon radical

7. Diazo CouplingDiazo Coupling
 Electrophilic substitution by diazonium salt.Electrophilic substitution by diazonium salt.
 Comparing withComparing with ++
NONO22 and SOand SO33
--
thethe diazoniumdiazonium
cation is a weak electrophile and powerfulcation is a weak electrophile and powerful
electron donating groups such as -OH, -NH2,electron donating groups such as -OH, -NH2,
-NR2 must be present in the aromatic system of-NR2 must be present in the aromatic system of
the coupling component for coupling to take place.the coupling component for coupling to take place.
Coupling Components areCoupling Components are
 Benzene Derivatives like amines at acidicBenzene Derivatives like amines at acidic
mediummedium
 Hydroxyl derivatives at alkaline mediumHydroxyl derivatives at alkaline medium
 Salicylic Acid at alkaline mediumSalicylic Acid at alkaline medium
 Naphthalene Derivatives at alkaline mediumNaphthalene Derivatives at alkaline medium

9. Examples of Diazotization and coupling on fiber

10. 1.2 Cationic Dyes( Mono Azo)
 Usually hydrochlorides of bases having
moderate solubility in water
 Drawing chiefly on Azo, Anthraquinone and
Triarylmethane and are now commercially
available.
water-soluble and produce colored cations in solution.
mostly amino and substituted amino compounds soluble in
acid and made insoluble by the solution being made basic.
attached to the fibers by formation of salt linkages (ionic
bonds) with anionic groups in the fiber.
used to dye paper, polyacrylonitrile, modified nylons, and
modified polyesters.

12. 1.3 Reactive dye
Main chromophores employed in this are
Azo, Metal Azo, Anthraquinone and
Phthalocyanin containing the groups which
can react directly with the fiber
react with the cellulose fiber to form a
covalent bond. This produces dyed fiber
with extremely high wash fastness
properties.
Cotton, rayon, and some nylons are dyed
by this relatively simple dye.

13. Reactive Azo DyesReactive Azo Dyes

14. 1.4 Vat Dyes
Commercial name
 Indathrene
 Cibanone
 Caledon
Divided into
 Dyes derived from Indigo: Include natural and synthetic
indigos and its Bromide and Thioindigo
 Dyes Derived from Anthraquinone
insoluble complex polycyclic
reduced with sodium hydrosulfite in a
strongly alkaline medium to give soluble
leuco forms that have a great affinity for
cellulose.
After the reduced dye has been absorbed
on the fiber, the leuco forms are reoxidized
to the insoluble keto forms.

16. Synthesis
Heumann Process
+ heat + KOH and NANH2

17. Sadamine Process
Alinine + heat + CS2= Thiocarbonilide + heat +
Lead carbonate + NaCN, S = Cyano
compound structure
+ Sodium Hydrosulphide
=thioisatin + Alkali=Indigo

18. 1.5 Disperse Dyes1.5 Disperse Dyes
Mono azo, Diazo,Mono azo, Diazo,
Anthraquinone, Methine,Anthraquinone, Methine,
Quinoline, Nitro,Quinoline, Nitro,
AroylenebenzimidazoleAroylenebenzimidazole
substantially water-insoluble
nonionic
application to synthetic hydrophobic
fibers from aqueous dispersions.
primarily used for polyester and
acetate fibers.

19. Presence of halogens, NO2,Presence of halogens, NO2,
CN or electron- withdrawingCN or electron- withdrawing
groups in the Diazogroups in the Diazo
component causes a shift ofcomponent causes a shift of
λλmaxmax to wards the longerto wards the longer
wavelengthwavelength bathometricbathometric
effecteffect..