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 more effective coupling agent reagents than benzoic acid because anisole has o-cH₃ an electron donating group whereas benzoic acid have a 2-oh group attached to the benzene ring that acts as electron withdrawing group. 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 ll 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

1. To answer this question consider the example below diazo coupling between phenol and an arene diazonium salt. но е a- BASE Only a base can help reaction Presence of an the diazotisation coupling acid will not of use. 2. Azo violet : The two starting compounds are : 4- nitroaniline and ribmas geood Resorcinol NH2 NaNO2 Nanozi, lol o NoH HU FOH for NO2 3. The to the para position changed tautomelication of aro violet leads color yellow in acidic medium. q OY NON -Noz -NO violet ph=13 Yellow Phall Scanned by CamScanner

4. The appearance of color is due to conjugation Due to the altanating double & single bonds areas of delocalication are formed below and above the moleculae plane. The energy lenes gaps are reduced due to delocalisation, le the amount of light required to excite the elections to a higher energy level decreases. Visible pourt of specta lies in lower frequency region and hence eve see color Scanned by CamScanner