Azo dyes are organic compounds bearing the functional group R−N=N−R′, in which R and R′ are usually aryl. They are a commercially important family of azo compounds, i.e. compounds containing the linkage C-N=N-C. Azo dyes are widely used to treat textiles, leather articles, and some foods.

1. AZO DYES

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CONSULTANTS
SUBMITTEDTO
MD.RAIJULISLAM
SUBMITTED BY
Arafat Islam Pranto
ID:172-010-0-155
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CONSULTANTS
WHAT ISAZO DYES?
The dyes containing azo group (-N=N) in
chemical constitution (nucleous) are known as
azo dyes.
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EXAMPLE OFAZO DYES
• Blue Br
• Yellow 2G
• Yellow 4G
• Orange 2R
• Reactive Red
• Reactive violet
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CLASSIFICATION OFAZO DYES
• AZO DYES are further classified according to presence of azo group
(-N=N) In the chemical constitution.
• A. Mono Azo Dyes
• B. Bis (Dis) Azo Dyes
• C. Tris Azo Dyes
• D. Tetra Azo Dyes
E. Poly Azo dyes
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PROPERTIES OFAZO DYES
• Azo dyes are insoluble in water.
• They are not ready made dyes. The colour is formed in the
fibre by two components usually referred to as “napthols” and
“bases .
• The dyed goods have very good to excellent light fastness .
• The dyed goods have good washing fastness .
• The dyed goods suffer from poor rubbing fastness and this can
be overcome by proper soaping treatment .
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BOND INAZO COMPOUNDS
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MECHANISM OF DYEING
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• The steps involved in dyeing cotton is stated below -
• Impregnation with solution of napthol. This step is called
“naptholation”
• Development of the chromophore (azo group). This is the
“diazotisation” step
• Development of coloured compound. This is the “coupling”
step
• Removal of the surface colour from the dyed fibre. This step
is called “soaping”

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NAPTHOLSARE INSOLUBLE IN WATER
• They can be dissolved in water by converting them into sodium
compounds, which are soluble in water
• For this caustic soda is used
• Napthol – OH + NaOH Napthol – ONa
(Insoluble in water) (Sodium salt of napthol – soluble in hot water )
• Treat the material with the napthol solution in room
temperature for 20 – 30 minutes.
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TIME OF IMPREGNATION
• • Temperature– Affinity of napthol is more at lower
temperature and decreases with increase in temperature – The
best temperature of impregnation is 20 – 250C
• Addition of common salt / glauber salt.
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COUPLING OR DEVELOPMENT
• The naptholated material is entered and developed in the base solution
for 15 – 20 minutes at room temperature
• This process is called “coupling” or “developing”
• The pH should be maintained 5 to 6 during this step
• Napthol – ONa + Base – N=N-Cl Napthol + HCl
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N=N-Base
ONa

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SOAPING
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• After dyeing, the material is rinsed in cold water to which 1
g/l HCl is added and then it is soaped at the boil for 30
minutes to remove unfixed dye.
• • The soaping process is important to increase the rubbing
fastness of the dye

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FASTNESS PROPERTIES OFAZO DYES
• Azoic dyes have good to very good to excellent light fastness
which is attributed to the very stable electron arrangement of
the dyes
• Their washing fastness is also very good due to the fact that
azoic dyes are insoluble in water
• Azoic dye suffer from poor rubbing fastness due to the
formation of insoluble azoic dye on the surface of the fibre
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ADVANTTAGE AND DISADVANTAGE
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15. THANK YOU
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