After-treatments of direct dyes

What is the main purpose of after-treatments of direct dyes?

Why is it important for the preliminary deposition to be achieved with a soluble and comparatively small molecule?

What group in the dye molecule allows it to be diazotized during the in situ reaction?

In what year was the oldest method of improving fastness by an in situ reaction discovered?

Direct dyes exhibit good wet-fastness properties without any additional treatments.

The oldest method of improving fastness involved diazotizing the primary amino group attached to the aromatic nucleus.

What causes a complete alteration in shade when added to a dye molecule?

After diazotization, the dye molecule is coupled with phenols or aromatic amines to form new azo dyes in situ on the fiber.

The addition of another chromophore to the dye molecule during the in situ reaction does not affect the shade of the dye.

If the dye molecule is too large, it will not enter the fiber, resulting in uneven dyeing.

The preliminary deposition of the dye should be achieved with a soluble and comparatively large molecule.

The diazotization reaction is carried out in a hot solution containing sodium nitrite and excess hydrochloric acid.

The dye molecule Primuline, discovered by A.G. Green, exhibited good fastness to both light and washing before any after-treatments.

The in situ reaction increases the molecular weight of the dye, rendering it less soluble in water and more fast to wet treatments.

$\text{The primary amino group in the Primuline dye molecule is represented by the structure } -NH_2$.