Azoic colours

DYEING WITH AZOIC COLOURS

INTRODUCTIONIt 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)

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

How is colour formed?OH

NH

NO

2

2

Β naphtholP-nitroaniline

2

2

NO

NH

NO 2

N NCl-

OH

OH

N=N NO2

Diazotised p-nitro anilineOn coupling, colour is formed

NAPHTHOLSOH 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

NAPHTHOLS….contd

Naphthol ASHas affinity for cotton and so drying is not

required. It is a naphthol developed from BON acid

OH

CONH

NAPHTHOLS….contd

Anilides of BON acid (RED naphthols)

By changing amine different naphthols can be obtained.

CONH

OH

H N2

+COOH

OH

NH

CH3

NH

NO2

NH

Naphthol ASD Naphthol ASBS Naphthol AS-SW

NAPHTHOLS….contd

Anilides of Anthracene and Carbazole hydroxy carboxylic acids

OH

CONH

CH3

NH

OH

CONH

OCH

CH

3

3

Green naphthol

Brown naphthol

NAPHTHOLS….contd

Acyl acetic acid anilides

Only naphthol where coupling takes place as aliphatic CarbonProduces Yellow colourLow substantivity

CH - C - CH - C - NH - NH - C - CH - C - CH3 22 3

CH CH3 3

DIAZOTIZABLE BASES

Aniline derivatives

Examples

Red OrangeGC Bordeaux GP

A base will give only 1 colour but can have tonal changes

NH2

R

2NH

NO2

2NH

Cl

2NH

NO

OCH

2

3

DIAZOTIZABLE BASES...contd

Amino Azo derivatives

N=N NH2

R R1 2

This class will have 2 azo groups in their structure (Bisazo)

Garnet GBC base

Garnet, Bordeaux and Corinth shades are produced using this class

N=N

CH CH

NH

3 3

3


Substituted p-Benzoyl Amino Anilines

CO-NH NH2

R

R

1

2

NH2CO-NH

OCH

OCH

3

3

3OCH

CO-NH NH2

CH3O

Fast Blue RR

Fast Violet B

Bases are banned now as potential carcinogens

Diamines


NH NHH N2 2

Cl

Cl

NHH N 22

Black B

Brown 2R

Cheap ways of producing brown shades is by using this base with carbazole based or Naphthol AS base


Colour Coupling component Diazo component

Yellow Amides of acetoacetic acid (Ex - Naphthol ASG)

Aniline derivativeRed Anilides of Bon acid (Red

naphthol)

Bordeaux

6-methoxy derivative of Bon acid OR

Red acid Aminoazo benzene derivative

Violet Red naphthol p-Benzoyl amino anilinesGreen Green naphthol Violet/Blue BB base

Brown Anthracene derivative (Brown naphthol)

Various fast bases or salts

BlackRed naphthol Black bases

OR Black naphthol Red base or salt

APPLICATION OF AZO DYES

1. Treatment with naphthol2. Diazotization of base3. Coupling of naphthol4. After treatment

Naphthols are not soluble in water. Dissolution -

Can be done by 2 methods - 1. Hot dissolution method

2. Cold dissolution method

Treatment with Naphthols

OH

CONH

NaOH

CONH

O-Na+

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

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

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

• Naphthol can react with carbon dioxide and get precipitated. To protect it formaldehyde is added as a stabiliser.

• 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.

OH

CONH

R

HCHO

R

CONH

OH

CH OH2

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

Substantivity of naphtholate ion

Naphthols AS-D, AS, AS-OL have low substantivityNaphthols AS-BR, AS-LC, AS-L3G have high substantivity

Diazotization of base

O N NH 2 2 + HCl

2O N N Cl

+

H H H

NaNO2 + HCl HNO2 + NaCl

HHH

+N ClO N

2HNO2

2O N N - N =OCl

H H

+ -

-+

H

O N2 N=N-OHCl2

O N N_ _ Cl+ -

• 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

Diazotization of base

Diazotization of base1. Base is pasted with TRO. HCl added and solution is heated so

that base dissolves2. Water and ice added to bring down the temperature to 5-10oC3. In separate vessel, NaNO2 is dissolved and added to base

solution gradually with stirring4. Presence of nitrous acid is checked with starch iodide paper5. 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

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

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 acid2.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.

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

Fast Red Salt RC

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

2

+- -

2ZnCl

3OCH

Cl

N_ _ N

Alternative options

OCH

N_ _ NO N

3

2

+

SO

HSO

3

3

-

+

2

3

O N N_ _ N

OCH

BF4

Fast Red Salt B

Fast Red RL

Alternative options

2. Rapid Fast Colours – Mixture of naphthol and stabilised base

Syn-Diazotate Anti-DiazotateStabilized 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.

N

NO- -ON

N

Alternative options3. Rapidogen Colours – Naphthol + stabilized base.

Base is stabilized by reacting it with an amino compound called diazo compound. Colour is developed by acid steaming.

4. Rapidozols – Not used much

Cl

CH

N_ _ N

R

H-N

COOH

SO H

3

3CH

Cl

+3

3SO H

COOH

N N N

R

Derivative of sulphoanthranilic acid

Diazoamino compound

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.

Disadvantages of azoic colours

• Colour range/ gamut is limited – only orange, red, yellow, blue, brown & blacks produced

• Poor rubbing fastness

Azoic colours

Education

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