2. INTRODUCTION
It is called azoic colour and not a dye as there is
no dye present. The dye is formed on the
substrate itself i.e. on fibre, yarn or fabric.
To have a azoic colour we require 2 components
– Naphthol (coupling component) and Base or
salt (Diazo component)
3. INTRODUCTION
• There are 34 naphthols and 50 bases/ salts
• The combinations can produce about 2000
shades but only a few of them are used as
either they are very expensive and there are
cheaper substitutes for them, or
they have poor reproducibility and brightness
4. How is colour formed?
NH 2
OH
Β naphthol
P-nitroaniline
NO 2
NH 2 N NCl- N=N NO 2
OH
OH
NO2 NO2 On coupling, colour is formed
Diazotised p-nitro aniline
5. NAPHTHOLS
OH OH
COOH
β naphthol BON acid (β oxy
napthoic acid)
β naphthol has no affinity so then the cloth has to be dried and
then coupled. This was a limiting factor as drying is a costly process
and during dyeing the naphthol even migrates
6. NAPHTHOLS….contd
OH
CONH
Naphthol AS
Has affinity for cotton and so drying is not
required. It is a naphthol developed from BON
acid
7. NAPHTHOLS….contd
Anilides of BON acid (RED naphthols)
OH OH
+ HN
2
COOH
CONH
By changing amine different naphthols can be obtained.
NH
NH NH
CH NO2
3
Naphthol ASD Naphthol ASBS Naphthol AS-SW
9. NAPHTHOLS….contd
Acyl acetic acid anilides
CH - C - CH2 - C - NH - NH - C - CH - C - CH
3
2 3
CH CH3
3
Only naphthol where coupling takes place as aliphatic Carbon
Produces Yellow colour
Low substantivity
10. DIAZOTIZABLE BASES
NH2
Aniline derivatives
R
Examples NH2 NH2 NH2
NO
2
NO 2
Cl OCH3
Red OrangeGC Bordeaux GP
A base will give only 1 colour but can have tonal changes
11. DIAZOTIZABLE BASES...contd
Amino Azo derivatives
N=N NH 2
R1 R2
This class will have 2 azo groups in their structure (Bisazo)
N=N NH3 Garnet GBC base
CH CH
3 3
Garnet, Bordeaux and Corinth shades are produced using this class
12. DIAZOTIZABLE BASES...contd
Substituted p-Benzoyl Amino Anilines
R1
Bases are banned now as
CO-NH NH2 potential carcinogens
R2
OCH3
CO-NH NH 2 Fast Blue RR
OCH3
O CH 3
CO-NH NH 2 Fast Violet B
OCH3
13. DIAZOTIZABLE BASES...contd
Diamines
H2N NH NH 2 Black B
Cl
Brown 2R
H2N NH 2
Cl
Cheap ways of producing brown shades is by using this base with carbazole based or
Naphthol AS base
14. DIAZOTIZABLE BASES...contd
Colour Coupling component Diazo component
Yellow Amides of acetoacetic acid
(Ex - Naphthol ASG)
Anilides of Bon acid (Red Aniline derivative
Red
naphthol)
6-methoxy derivative of
Bon acid OR
Bordeaux
Red acid Aminoazo benzene derivative
Violet Red naphthol p-Benzoyl amino anilines
Green Green naphthol Violet/Blue BB base
Brown Anthracene derivative Various fast bases or salts
(Brown naphthol)
Red naphthol Black bases
Black
OR Black naphthol Red base or salt
15. APPLICATION OF AZO DYES
1. Treatment with naphthol
2. Diazotization of base
3. Coupling of naphthol
4. After treatment
16. Treatment with Naphthols
Naphthols are not soluble in water.
Dissolution -
OH O-Na+
NaOH
CONH CONH
Can be done by 2 methods -
1. Hot dissolution method
2. Cold dissolution method
17. Hot dissolution Method
• Naphthol is pasted with a wetting agent such as TRO (sulphonated
castor oil) and a fine paste prepared.
• Soft water is added and dispresion is heated to near boil. If hard
water is used it may result in precipitation of the naphthol or alkali
• If soft water is not available, a sequestering agent is added
• Then calculated amount NaOH is added with stirring
• Naphthol dissolves slowly to give olive green to light brown colour
• Solution is then cooled and diluted to required amount
18. NaOH required
Naphthol AS 1.5 L NaOH (27.8%) /kg
Naphthol ASBR 2.5 L NaOH (27.8%) /kg
Naphthol AS-G 3.0 L NaOH (27.8%) /kg
Quantity of NaOH used is more than stoichiometric
quantity required
19. Cold dissolution method
• Paste is prepared with TRO & NaOH & then alcohol (ethyl
alcohol) (1.5-2 times quantity of naphthol) added
• Then cold water is added to get required concentration of
naphthol
• Generally used in printing where small quantity of liquor is
required to be used
20. • Naphthol can react with carbon dioxide and get precipitated.
To protect it formaldehyde is added as a stabiliser.
CH2OH
OH OH
HCHO
CONH CONH
R R
• Temporary bonding only as it is on coupling site.
• It should not be added when the fabric dyed is to be
subsequently discharge printed or when naphtholation of
substrate is to be carried out at high temperature as at high
temperature naphthol forms crosslinks with formaldehyde.
21. Substantivity of naphtholate ion
• For exhaust/ batch method high substantive naphthol should
be used
• For continuous method, low substantive naphthol should be
used
• Direct dyes are negatively charged and salt is added for its
exhaustion. Naphtols are also negatively charged and hence in
exhaustion method salt is added
• Within very short of time most of the naphthol and
subsequently only a small amount of naphthol is absorbed
22. Substantivity of naphtholate ion
Naphthols AS-D, AS, AS-OL have low substantivity
Naphthols AS-BR, AS-LC, AS-L3G have high substantivity
23. Diazotization of base
+
O2N NH 2 + HCl O2N N Cl
H H H
NaNO2 + HCl HNO2 + NaCl
+
O2N N Cl HNO2 + -
O2N N - N =OCl
H H H
H H
+ -
O2N N_ _ Cl +
O2N N=N-OHCl -
H
24. Diazotization of base
• Diazotization reaction is carried out at 5-10oC which is obtained
by adding ice. Hence these colours are also called as ice colours
• To diazotise 1 mole of amine, 2 moles of hydrochloric acid and 1
mole os sodium nitrite is required
• In practise amount of hydrochloric acid added is more than 2
moles
25. Diazotization of base
1. Base is pasted with TRO. HCl added and solution is heated so
that base dissolves
2. Water and ice added to bring down the temperature to 5-10oC
3. In separate vessel, NaNO2 is dissolved and added to base
solution gradually with stirring
4. Presence of nitrous acid is checked with starch iodide paper
5. Presence of HCl checked with congo red paper
6. Excess HCl is neutralized by adding sodium acetate which
reacts with HCl forming acetic acid and sodium acetate mixture
which acts as buffer of pH 4-5
Cloth is worked in naphthol for half an hour, squeezed and then
passed through base solution to produce colour
26. Coupling energy of diazo component
Group Coupling energy pH range
I High 4-5
II Medium 5.5-6.5
III Low 6-7
IV Very low 7-8.2
27. Residual alkali from naphthol application can pass
onto the base solution. To avoid this alkali-binding
agents are so as to maintain pH.
Alkali binding agents are –
1.Acetic acid
2.Aluminium suphate (in the form of alum)
3.Zinc sulphate
After naphtolation and coupling, the fabric is washed
with water and then soaping treatment is given.
Soaping improves the wash fastness as well as the
light fastness.
28. Alternative options
Since the whole naphtolation, diazotization and coupling is a
lengthy process, the following different systems were developed –
1.Fast Colour salts – Stabilised diazotised bases
Cl
+
--
Fast Red Salt RC
N_ _ N ZnCl2
OCH3
2
All are formed by dyeing diazotised base under vacuum and then
treating with required chemical which results in stabilised salt.
Most common chemical is zinc chloride
29. Alternative options
OCH3
HSO3
+
O2N N_ _ N - Fast Red Salt B
SO 3
OCH3
+ BF
O2N N_ _ N 4 Fast Red RL
30. Alternative options
2. Rapid Fast Colours – Mixture of naphthol and stabilised base
N N
-
O
-
N N O
Syn-Diazotate Anti-Diazotate
Stabilized base is prepared by treating base with NaOH at high
temperature . Anti diazotate is stabilized form of base.
This is used extensively by small scale printers. On printing,
fabric is left in sunlight. The CO2 neutralizes the alkali & then
base reacts with naphthol to give colour.
31. Alternative options
3. Rapidogen Colours – Naphthol + stabilized base.
Cl
R
N_ _ N + H-N SO3H
CH3 COOH Derivative of sulpho
anthranilic acid
Cl
R
N N N SO3H
CH3 COOH
Diazoamino compound
Base is stabilized by reacting it with an amino compound called diazo
compound. Colour is developed by acid steaming.
4. Rapidozols – Not used much
32. Advantages of azoic colours
• Does not have any solubilising group so have
good wash fastness. The colour is
mechanically entrapped and so cannot be
removed easily
• Bright shades produces
• Cheap to apply
• In deep shades, light fastness is also good
• Choice of application of colours is taken
advantage off in printing – batik, tie and dye
etc.
33. Disadvantages of azoic colours
• Colour range/ gamut is limited – only orange,
red, yellow, blue, brown & blacks produced
• Poor rubbing fastness
