Question

These questions refer to an organic dye lab that was done in organic chemistry.

1; Discuss what features a molecule needs to possess in order to be classified as a dye, and explain the different means in which they adhere to fabrics.

2; Describe how indigo and azo dyes differ from each other, both in how they are prepared and their mechanism of action for dyeing clothing, be sure to include structures/mechanisms.

Answer 1

1.The following features a molecule needs to classify as a dye-

-It has a suitable colour. These are coloured organic compounds which are used to impart colour to various substrates including paper, leather, fur, hair, drugs, cosmetics, waxes, greases, plastics and textile materials.

-It fixes itself to fabrics.

-It has fastness properties, such as fastness to light. Resistance to the action of water, diluted acids, alkalis and various organic solvents used in dry cleaning.

The dye adhere to fabrics due to physical bonding between fabric and dye. There are different forms of dyeing. Common forms are the package form and hanks form. Cotton yarns are mostly dyed at package form and acrylic or wool yarn are dyed at hank form. In continuous filament industry, polyester or polyamide yarns are always dyed at package form, while viscouse rayon yarns are partly dyed at hank form.

2. Difference in indigo and azo dyes-Indigo dye is used for denim but azo dyes are used for cotton fabrics.

Indigo dye converted into soluble form by which affinity to fibre is increased. Soluble form is leuco form by reduction.

Azo dyes are compounds containing azo function (N=N- bond). Azo function is bound to aromatic ring which broken down to aromatic amine.