Q 56E - Organic Chemistry (Mcmurry)

Question

Azo dyes are the major source of artificial color in textiles and food. Part of the reason for their intense coloring is the conjugation from an electron-donating group through the diazo bridge $\left(-N=N-\right)$ to an electron-withdrawing group on the other side. For the azo dyes below, draw a resonance form that shows how the electron-donating group is related to the electron-withdrawing group on the other side of the diazo bridge. Used curved arrows to show how the electrons are reorganized.

a.

Methyl orange

b.

C.I. Acid Red 74

Step-by-Step Solution

Answer

a.

Methyl orange

b.

C.I. Acid red 74

Step 1: Azo dyes

These are the organic compounds bearing the functional group $\mathbf{R}\mathbf{-}\mathbf{N}\mathbf{=}\mathbf{N}\mathbf{-}\mathbf{R}$ in which R and R' are generally the aryl group. In this, the movement of electrons from one group to another results in the formation of a specific color.

Step 2: a) Methyl orange

The movement of electrons from the electron-donating group to the electron-withdrawing group through the aromatic framework of methyl orange and C.I. Acid red 74 is as shown: