Synthetic dyes

331 Pages·2009·11.903 MB·English

by  Gurdeep R Chatwal

SYNTHETIC DYES
GURDEEP R. CHATWAL
M.Sc., Ph.D., M.I.A.H.P.S.
Formerly Reader in Chemistry, Oyal Singh College
University of Delhi, New Delhi - 110003
Edited by
M.ARORA

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CONTENTS
1
Introduction to Dyes .............................................................................................. 1·1 - 1'9
General InfOl'mation About Fibres and Dyeing Methods .............................. 2·1 - 2·12
3
Classification of Dyes on the Basis of Mode of Application ........................... 3·1 - 3'6
4
Chemical Classification of Dyes ......................................................................... 4·1 - 4·10
5
Colour and Chemical Constittition .........•.•........................................•.......••...... 5·1 - 5·22
-6
Chemistry of Dyestuff Intermediates ..............................•. ~ .............................. 6·1 - 6·66
7
Nitro Dyes .................•.............•.............•......................•.•......................................... 7·1 - 7'4
8
,Nitroso Dyes ............................................................................................................ 8·1 - 8·3
9
Azo Dyes ................................................................................................................ 9·1 - 9·41
10
.<\zoic Dyes (I ngrain Azo Dyes) .................................•....................................... 10·1 - 10'3
'11
Diphenylmethane Dyes ..............•.......•....•...............•..................................•...•..... 11·1 - 11'3
12
Triphenylmethane Dyes ........................................................ ;. .......................... 12·1 - 12·11
13
Phthaleins ............................................................................................................ 13·1 - 13·3
14
Xanthene Dyes .................................................................................................... 14·1 - 14·7
15
Heterocyclic Dyes ............................................................................................. 15·1 - 15·14
16
Thioindigos and Indigos .................................................................................... 16'1 - 16·9
17
Anthraquinone Dyes .......................................................................................... 17·1 - 17·10
18
PhthaJocyanincs .................................................................................................. 18'1 - 18·3
19
Sulphur Dyes ....................................................................................................... 19,) - 19·2
20
Reactive Dyes ...................................................................................................... 20'1 - 20'5
21
Pigments ............................................................................................................. 21·1 - 21'12
n
0
Fluorescent Brightening Agents ........................................................................ 22,) - 22'5
23
Non-Textile Uses of Dyestuffs ......................................................................... 23·J - 23·13

24
Acridine Dyes ...................................................................................................... 24'1 - 24·1
25
Thiazole Dyes ......................... _ ........................................................................... 25-1 - 25-2
26
I ngrain Dyes ........................................................................................................ 26·1 - 26'1
17
Solubilised Vat Dyes ........................................................................................... 27·1 - 27'1
28
Sulphurise«J Vat Dyes ......................................................................................... 28·1 - 28·1
29
Lactone, Amino Ketone and Hydroxy Ketone Dyes ..................................... 29') - 29'1
3(}
Indamines and Indopbenols .............................................................................. 30·1 - 30·2
31
Azincs .. ~ ................................................................................................................ 31·1 - 31·2
32
Oxazines ..................•........••..•..................•................•..................•...................•.... 32'1 - 32·1
33
Thiazines .............•....•...........................•...............................•............................. ,. 33·1 - 33·1
34
Cyanine Dyes ....................................................................................................... 34·1 - 34'2
35
Dyes for Synthetic Fibres ................................................................................ 35'1 - 35·12
. 36
Synthesis of Some Specific Dyes .................................................................... 36·1 - 36·10
37
Important Questions ........................................................................................ 37·1 - 37'14
,
CHAPTER
INTRODUCTION TO DYES
I-I I I I I,I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I
1.1. Definitions
Dye 'or Dyestuff: A dye or a dyestuff is usual(v a coloured organic compound or mixture
that may be used for imparting colour to a substrate such as cloth, pape/: plastic or lea tIler in
a reasonably permallent fashioll. In other words, a dyed substrate should be resistant to a normal
laundry or cleansing procedures (washjast) and stable to light (lightfast). All the dyes may not
necessarily be coloured substances. Therefore, optical brighteners or whiteners which may be
called white dyes may be included in the term dye.
A dye is a coloured substance but all coloured substances are not dyes. Thus a dye should
fix itself on the substrate to give it a permanent coloured appearance. Thus, azobenzene is not
a dye even though it has red colour, as it cannot be attached to substrate. However, congo red
is a dye as it can be applied on cotton and retained by it. Thus, the dyes should have certain
groups which help the attachment to the fibre.
@-N=N-<Q)

Azobenzene (Red coloured hut not a dye)
White Dye : Some colourless compounds are used as the optical brighteners. They may
also be called as the white dyes. They have the special property of absorbing ultraviolet light and
re-emitting the visible light so that the fabric appears bright.
Pigment: The coloured substance which is insoluble in water or other solvents is called
a pigment. Thus the application of dye and pigment will he different. A dye is applied in the form
of a solution, whereas the pigment is applied in the form of a paste in a drying oil, in which it
is insoluble.
Requisites of a True Dye : All coloured substances are not dyes. However, the requisites
of a true dye are as follows :
(i) It must have a stable colour.
(if) It must have an attractive c%ur i.e., it should no! undergo struc/ura/changes readiZ)'·
(iii) It must be able to attach itself to material frol1l solution or to be capahle to fixed it.
01/
For example, azobenzene is coloured but cannot fix itself to a fabric. Therefore. azobenzene
is not a dye. Further, a dye may not be able to dye all types of substrates. For example,
(1.1)
1.2 Synthetic Dyes
picric acid is able to dye silk or wool a permanent yellow but not cotton. Thus, a dye
either forms a chemical union with the substrate being dyed or it may get associated with
it an intimate physical union.
(iv) It must be solu!J.le in water or must form a stable and good di:.persion in watel: Alter
natively, it mu;l be soluble in the medium other than water. However, it is to be remem
bered that the pick lip ~f the dye from the medium should he good.
"
(v) The substrate to be -(tved must have a natural affinity for an appropriate dye and must
be able to absorb it from solution or aqueous dispersion. If necessllIJ', in the presence
~f alcdliary ~\'Ubstan('es under suitahle conditions of concentratioll. temperatllre and pH.
(vi) When a dye isfixed to a substrate. it must be filst to washing, dry cleaning. perspiration.
light, heat and other agencies. It must be resistant to the action of water, acids or alkalis.
particularly the latter due to the alkaline nature of washing soda and washing soap.
There is probahly no dye which can be guaranteed not to alter shade under all conditions.
(vii) The shade and fastness of a given dye may vary depending on the substrate due to different
interactions of the molecular orbitals of the dye with the substrate, and the ease with which
the dye may dissipate its absorbed energy to its environment without itself decomposing.
1.2. Historical Development from Natural to Synthetic Dyes
Era of Natural Dyes: These have been used since ancient times for colouring and printing
fabrics. Until the middle of last century most of the dyes were derived from plants or animal
sources by long and elaborate processes. A ncient Egyptian hieroglyphs contain a thorough de
scription of the extraction of natural dyes and their application in dyeing. Further developments
extending over many thousands of years led to rather complicated dyeing processes and high
quality dyeings. Among these the following deserve special mention :
(i) Indigo: It is one of the earliest natural dyes and it originated in India. The art of dyeing
with this bluish indigo dye was practised in this country, using primitive fermentation
methods. Then the use of this dye spread to Egypt. Indigo occurs in the indigo-pm/e
species of plants as a glucoside called indican. This is extracted with water, when it gets
hydrolysed by the enzyme into indoxyl and dextrose. In al.1<aline medium indoxyl gets
oxidized into indigo, which is precipitated.
W OH
I I
+C(.H,pc.
~ N
H
Indican Indoxyl (tmol) Dextrose
03c=<=o
°
2~
~N)
H H II
°
Indoxyl (keto) Indigo
lll{roduction 10 Dyes 1.3
Ancient Britons obtained a dye called woad from the plant called isalis tincfOria. The
active compound is calIed indigotin from which indigo was prepared. Indigotin i~ in
soluble and hence it was reduced by fem1cntation and thcn applied.
(ii) 1j;rian Purple : It is a natural dye which originated in the ancient city of Tyre in
Phoenicia. This dye was extracted from certain kinds of shell-fish. However, at that time
the dye was so expensive that it was called Royal purple.
Later, Friedlander showed that it was a derivative of indigo.
l? ~l
B
''c=(t-(V
~
r
~N' 'C~
Br H II
o
Tyrian purple (6. 6'-Dibromo indigo)
(iii) Alizarin: It is extracted from the roots of madder plant. It occurs as a glycoside called
ruberythric acid. On hydrolysis with dilute acid it gives dextrose, rhamnose and alizarin
which is 1,2-dihydroxy anthraquinone. The extract also contains a dye called purpurine
(l, 2, 4-trihydroxy anthraquinone). Alizarin is a natural mordant dye and it produces
various colours using different compounds of the metals AI, Cr, Cu, etc.
o OH o Oil C)·lll(\
OC H 0 ~OH + D-glucose
II 19 9 Dil.llCI
+
~ ~
CsHII.os
o o D-Xylose
Ruberythric acid Alizarin
(iv) Cohineal: It was extracted from the insect coccus Cacti which is found mainly in South
America and Mexico. The active dye is called carminic acid which is a derivative of
antraquinone. It is also a natural mordant dye and gives ditferent shades of purpl,,: by
using compounds of Cr, AI, Fe, etc. It is used for dyeing of wool and silk and also as
non-poisonous food colourant.
011 0 OH
HO
BOOC o OH
Carminic acid
(v) Logwood: It is the only natural dye which is still isolated on a large scalc from the wood
of the tree Haematoxylon Cllmpechianu11l. It is cultivated and also grows wild in the
central America. The fermentation of the wood of this tree contains a glucoside of
haematoxyIin which on oxidation yields a colouring matter called haematin.