Question

This is a Synthesis of Azo Dyes lab

EXPERIMENT 8: SUPPLEMENTARY LAB QUESTIONS 1. Would you expect benzoic acid or anisole to be a more effective coupling reagent? Why? Anisole would be moe cffectiue canpling agent rensents thanbezei acid becase anisole has o-eHz an elect/on donating grou whelcas burzoie aci el have n ing that acts as clection withdrawins group. OM fe attached te cbenzene 2. Most diazo coupling reactions do not work well in acidic solutions. Explain. 3. What two starting compounds would be used to prepare Azo Violet? Below pH 11 azo violet appears yellow in color. Above pH 13, the dye appears violet in color. Explain. 4. For most students, an instantaneous and dramatic color change occurs when the two coupling reagents are mixed together. Why does this occur? Most of our UV solutions have been prepared using isopropanol as solvent. Why are the azo dye UV solutions prepared under aqueous conditions?

Answer 1

Ams 2 ti Diazo coupling reactions are electrophilic substitution reactions wherein are ne diazonium iom acts as electrophile and highly activated aromatic compounds much as phemol on aniline act as the nucleophile 1. Generally compounds like phemol undongo diazodization reaction is basic medium [pH9-10] where as aniline need acidic pH (4-5) In cone of phemol ; activation initiated by the deprotomation of phemolic -oh group which needs a bonic medium NEN- N : 2 But in case of aniline, protomation of the NH, group is necessary in order to avoid unwanted reaction with the diaronium ion. Acidie condition activates the reaction by marking the -NH₂ of aniline we does not from the mñ e Want this — += ^- NON 2 Scanned with CamScanner

C - Amsg - The two starting compounds for the synthesis of Aza violet are on heats 4-mitro aniline and resoncino The first step for the synthesis of aza-violet is the insitw prep anation of i a diazonium, intermediate from 4-mitro aniline and nitrous aced .. . Naremico NO Step 2 is the azo-compling reaction of diazonium intermediate with Meroncino in ima sodium hydroxide solutim, ki Na Hoy" >NSTI NH₂ ta NaNO, HU 1. solution Naoh OH ho Azo-violet Scanned with CamScanner

Azo violet is commercially used as a basic pH indicator. The intense color of azo violet attributed to its azo group (-N=N-) and hydroxyl side groups. Normally, azo violet is most stable in the trans-configuration, due to steric crowding. But in acidic medium tautomerization take place at para position of azo violet which provides mechanical insight to undergo isomerization and leads to pH dependent color variation.

H NO2 ZI - No e scanne Tautomerization af Azo violet CamScanner