Azoic dyes are produced by reacting a diazo-component or base salt with a coupling component like naphthol. This reaction forms an insoluble azo group that produces the dye within the fiber, resulting in excellent washing fastness. Azoic dyes can be used to dye cellulose fibers like cotton. The dyeing process involves three steps: naphtholation, diazotization, and coupling. Azoic dyes form an insoluble color product within the fabric, making them different from azo dyes which use a soluble azo group.

1. Azoic Dye
Azoic dyes: Azoic dyes are not ready made dyes but are produced by reaction of two
components Diazo-component or base salt & coupling component (Naphthol).
Dye formation in fibre occurs on the basis of coupling reaction.
RN2Cl + R-ONa R- N=N-R-OH,
Azoic dye
The colored substance formed azoic dye from these essentially colorless compounds is insoluble
in water & the washing fastness of the shade is excellent.
Different name of Azoic dye:
1. (Icecolor)- The coupling component which is finally soluble in diazotization reaction the
ice water (0˚C- 5˚C) required to the process so it is called ice color.
2. Magic color
3. Naphthol color
4. Pigment color
Properties of Azoic dyes :
1. cellulose cotton but also jute, nylon, polyester, hemp, acetate, rayon, linen are dyeing by
azoic dyes.
2. Insoluble azo group present in it.
3. It is dercetly insoluble in water.
4. Color is formed from solubilesed component but the ultimate colored product in always
insoluble.
5. Alkali resistance: poor to good
6. Light resistance: poor to good
7. wash fastness: very good
8. Brightness of azoic dye is good
9. This dye is called developed dye due formation of dye in fabric during dyeing process.
10.Addition of salt increases substantivity.

2. Chemistry of dyeing-
Dyeing process of azoic dyes includes three main stages they are.
1. Naphtholation
2. Diazotisation insoluble
3. coupling soluble
1. Naphtholation:- Naphthols are insoluble in water & converted in soluble form by treating
with alkali, the fabric is pregnated with β- Naphthol & NaoH soluble & converted into β-
Naphthalin in NA-β- Naphtholate
ONa
OH + NaOH [30˚C – 40˚C]
+ H2o
insoluble β-Naphthol. Soluble
2. Diazotisation: – A base containing amino group reacts with sodium nitrite to a solution
of the hydrochloride of the bases in the presence of excess HCl at 0˚C -5˚C.
NH3 NH3+Cl
+ HCl
NaNo2+HCl HNO2+NaCl
NH3 N=N-Cl
HCl+ NaNO2 + NaCl+H2O
Diazoinium salt
0 C – 5 C
3. Coupling – The impregnated material is treated in a bath containing diazonium
solution to carry out coupling & azoic colour in produced.
ONa N=N-Cl OH N=N
+ coupling +NaCl

3. Naphtholated fabric Azoic base color
Process sequence for dyeing with Azoic dyes :
Textile mtl is perpared
Fabric /textile mtl treated with Naphthol soln
Preparation of base salt soln
naphthol treated fabric is treated with diazo solution
Colour developed
Dyeing of cotton fabric with Azoic dyes:
Dissolation method:
Naphthol is not easily dissolved in water. naphthol is dissolved in water by two process.
1. Hot dissolution method .
2. Cold dissolution method.
Hot dissolution method :
1. Naphthol
2. NaOH
3. TR-oil
4. Common salt.
5. Hot water.
6. HCHO
Procedure:
At first Naphthol is pasted with some water containing a suitable dispersing agent required
amount of boiling water is then added which is followed by addition of required quantity of
NaoH solution stirring in continued and it necessaryboiling is continued for afew minutes when
a clear solution should result for some Naphthol however a different required has to be
employed. In case of Naphthols AS-SW, AS-BR, AS-SG,& for Brenthols LIR & RB if is
necessary to paste the Naphthol with a dispersing agent required amount of NaoH is added &
stirring continued to get a smooth thick paste. The pasteis heated on a water bath after the thick
past in the heated to about (85-90)˚C required amount of boiling is added & the whole mass is
stirred & boiling continued for several minutes tile clear solution is obtained.

4. The solution is then cooled by adding cold water & required amount of formal dehyde is added
it necessary.
Cold dissolution method:
1. Azoic component .
2. Methyalted.
3. HCl
4. NaNO2
5. TR-oil.
6. HCHO.
7. Cold water.
Procedure :
This method in simpler than the hot method & given more satisfactory solution with less
readily solution Naphthol. Azoic component is placed in a container & required amount of
sprit is stirred into it. The required amount of NaNO2 and HCL solution is then added to
give a clear solution is diluted as required. It is known that the napthols impregnated
material is sensitive to prolonged exposureto air, particularly when the material is wet such
as exposure results is weak & streaky dyeing.
This effect can be prevented by adding formaldehyde to the naphthol solvent about 0.5 to
1 lit of 40% formaldehyde is added per kg of naphthol. The formaldehyde reacts with
naphthol to from a stable compound. It is desired to make use of formaldehyde while
preparing the stock solution. the solution should be cooled below 60 c before the addition
of formaldehyde because above the temp naphthol formaldehyde compound may be
converted to methylene compound which is no longer capable of coupling. Moreover,
formaldehyde should not be used when the naphthol solution is to be used hot & when the
naphthol impregnated material is to dried befor development.
**Factor considered for diazotisation :
1. Amount of HCl &NaNO2.
2. PH
3. Temp
4. Metal
*** Factor considered for coupling:
1. Conc. of naphthol solvent
2. Conc. of base solvent
3. Temp of base solvent
4. PH of base solvent for fast reaction PH should be less.
5. Strength of base &naphthol

5. 6. Base of water ratio 1:5.
Types of Naphthol:
According to substantivity:
1. Low substantivity Naphthol:
Exp-
Naphthol AS Naphthol AS-02
Naphthol AS-G
OH
CONH Naphthol –AS
2. Medium to substantivity Naphthol :
Exp-
Naphthol AS-BL Naphthol AS-BG
OH OCH3
CONH
Naphthol AS-BL
3. Higher substantivity Naphthol:
Exp-
Naphthol AS-BS
Naphthol AS-BI
OH NO2
CONH
Naphthol AS-BS

6. Different between Azoic dye & Azo dye :
Azoic dye Azo dye
1. Insoluble Azo group soluble Azo group
2. Insoluble in water soluble in water
3. It is not found in readymade dye Readymade dye
4. Needof diazotisation & coupling No need
5. Complicated& application Simple application
6. Less used Widely used
7. Comparatively costly Comparatively cheap