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Dyeing Of Cotton Fabric With Azoic Dyes


Dyeing Of Cotton Fabric With Azoic Dyes


  1. To dye a material practically.
  2. To observe the practical advantages and disadvantages of this dye.
  3. To compare the theoretical idea with practical experiment.


Azoic dyes are not ready-made dyes but are produced by reaction of two components-Diazocomponent or Base/Salt and 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 coloured substance formed Azoic dye from these essentially colourless compound is insoluble in water and the washing fastness of the shade is excellent.

Chemistry of dyeing:

Dyeing process of azoic dyes includes three main stages. They are-

  1. Naphtholation
  2. Diazotisation
  3. Coupling

(1). Naphtholation : Naphthols are insoluble in water and converted into soluble form by treating with alkali. The fabric is in pregnated with ß-naphthol and NaOH Soln and converted into ß-Naphthol Na-ß-Naphtholate.

(2) Diazotisation : A base containing amino group reacts with sodium nitrite to a soln of the hydro chloride of the base in the presence of excess of HCl at 0o-5o

(3) Coupling: The impregnated mtl is treated in a bath containing diazonium soln to carry out coupling and azoic colour is produced.

Process Sequence For dyeing with Azoic dyes:

Textile mtl is prepared

Fabric/textile mtl is treated with Naphthol Soln

Preparation of base salt soln

Naphthol treated fabric is treated with


Colour developed


For Naphtolation:     For Base solution:  
Napthol 5% owf   Base 5% owf
Glycerine 2%  “   HCl 3% “
Caustic soda 6% “   NaNO2 2% “
Common salt 15% “   CH3COONa 15% “
Temperature Room temp.   Acetic acid 0.5% “
Time 20-30 min   Temperature 0-5O C
M:L 1:20   Time 20 min
      M:L 1:20



For Naptholation For Base Solution
Caustic Soda = 0.6 gm Base = 0.5 gm
Common Salt = 1.5 gm HCL = 0.3 gm
Napthol =0.5 gm NaNO2 = 0.2 gm
Glycerine = 0.2 gm CH3COONa = 1.5 gm
Water= 200 ml  


Description of the process:

Naphthol preparation:

  1. The required amount of alkali and common salt was taken to a bath.
  2. The Naphthol and Glycerine are taken in a bath and stir it until dissolve.
  3. Then the above two liquor are added in a bath with the required water.
  4. The fabric of required weight is taken and impregnated in the naphthol solution and squeeze it until dry otherwise premature reaction may occur.

Base colour preparation:

  1. The required amount of base color, HCl, acetic acid, Na acetate,   are added in a bath.
  2.  Then add the required amount water (at 0-5°C) to make the liquor.
  3. Finally add the required amount of NaNO to complete the diazotisation.


  1. Then the  squeezed fabrics are mixed in the bath of base colour one by one and within 2-3 minute the magic color is obtained.

After treatment:

  1. Cold wash.
  2. Hot wash.
  3. H2O2 (3 g/L) at
  4. Acid wash (1-2 g/L) at room temperature.
  5. Hot wash.
  6. Cold wash.
  7. Drying.


The sample of the dyed material seems to have correct shade and it shows good fastness especially wash fastness. So it is proved that maintaining proper temperature and time does the experiment.


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