TITLE PAGE

INTRODUCTION

DyeA dye can be defined as a colored substance that has an affinity to the substrate to which it is being applied.

A dye is mostly used as an aqueous solution and may require a mordant (an inorganic oxide, that combines with a dye or stain and thereby fixes it in a material) to improve the fastness of the dye on the fiber.

***Pigment as opposed to dye, has no affinity for the substrate and is insoluble.

COLORED COMPOUNDS AND DYES

Color has always fascinated humankind, for both aesthetic and social reasons. Throughout history dyes and pigments have been major article of commerce.

Manufactures of virtually all commercial products involve color at some stage, and some 8000 colorants with more than 40000 trade names are currently used. The large number is a consequence of the range of tints and hues desired, the chemical nature of the materials to be colored, and the molecular structure of the dye.

AZO GROUP

An azo group is,-N=N-, which links two sp2 hybridised carbon atoms.

These carbons can be part of aromatic as well as aliphatic systems.

Most azo dyes contain only one azo group, but some contain two (disazo), three (trisazo) or more.

In theory, azo dyes can supply a complete rainbow of colors.

However, commercially they tend to supply more yellows, oranges and reds than any other colors. But there are also some viable blue azo dyes on the market.

SYNTHESIS OF AZO DYES

An overview of azo dye synthesis is shown below:

DiazotizationThis involves a primary aromatic amine, called the diazo component. It is treated in low temperature, acid conditions with sodium nitrite to form an unstable diazonium salt.

Azo couplingThe diazonium salt is reacted with a coupling component (for example a phenol or an aromatic amine). This forms the stable azo dye.

AZO DYING TECHNIQUES

Azo dying is a technique in which an insoluble azoic dye is produced directly onto or within the fiber.

This is achieved by treating a fiber with both diazoic and coupling components.

With suitable adjustment of dye bath conditions the two components react to produce the required insoluble azo dye.

This technique of dying is unique, in that the final color is controlled by the choice of the diazoic end coupling components.

ADVANTAGES

The azo compound class accounts for 60-70% of all dyes.

They give bright, high intensity colours, much more so than the next most common dye class (anthraquinones).

They have fair to good fastness properties.

Their biggest advantage it their cost-effectiveness, which is due to the processes involved in manufacture.

The general formula for making an azo dye requires two organic compounds- a coupling component and a diazo component. Since these can be altered considerably, an enormous range of possible dyes are available, especially as the starting molecules are readily available and cheap.

Furthermore, the simplicity of the reactions means that the process can be scaled up or down very easily, which is always a key factor in the cost of chemicals.

Energy requirements for the reaction are low, since most of the chemistry occurs at or below room temperature.

The environmental impact is reduced by the fact that all reactions are carried out in water, which is easy and cheap to obtain, clean and dispose of.

EXPRIMENT

Aim:

To study and analyse the preparation of azodyes

Apparatus:

Boiling tubes Glass rod Ice Cubes Cloth Beaker Thermometer Test tubes

Reagents:

Aniline NaNO2

HCl β-Naphthol N,N Dimethyl Aniline.

Theory:

Aniline is mixed with a solution of NaNO2 and HCl at 0-5 degree Celcius to form benzene dizonium chloride.

Coupling reagents like aniline, B-naphthol, NNDimethylaniline, etc are added to form colorful complexes.

Preparation:

The first dye was prepared by adding aniline to a solution of NaNO2 and HCl maintained at a low temp.

Then a solution of B-Naphthol and NaOH was added to the solution.

The created dye was used to dye a piece of cloth.

The steps were repeated with different coupling reagents to obtain different products.

Observation:

B naphthol – Orange

Aniline – Yellow

NNDiMethyl Aniline – Dark Yellow

Phenol - Orange

Conclusion:

Multiple azodyes were prepared and analysed.