Experiment 23

Objective: Electrophilic Aromatic Substitution, Acidic Azo Dyes

Introduction:

An Azo coupling is an organic reaction between a diazonium compound and another aromatic compound that produces an azo compound. In this electrophilic aromatic substitution reaction, the aryldiazonium cation acts as the electrophile, while the activated arene serves as the nucleophile. Typically, both the diazonium compound and the arene are aromatic compounds, as demonstrated in the experiment below.

Chemicals Required:

Sulfanilic acidPhenol1-Naphthol2-NaphtholEthanol 96%2 N Acetic acidSodium nitrite (NaNO₂)

Pre-prepared Solutions:

Phenol: 15.06 g (160 mmol) dissolved in 400 mL ethanol 96%1-Naphthol: 17.3 g (120 mmol) dissolved in 400 mL ethanol 96%2-Naphthol: 11.54 g (80 mmol) dissolved in 400 mL ethanol 96%Reagent Solution (Diazo component): 40 mL of 0.5% aqueous NaNO₂ solution mixed with 40 mL of 0.5% sulfanilic acid solution in 2 N acetic acid.

Glassware Required:

3 conical measures, graduated, 500 mL3 glass stirring rods5 beakers, 50 mL3 beakers, 500 mLGraduated cylinder, 200 mL

Procedure:

1.    Prepare three conical measures. Each should be filled with one of the following alcoholic solutions:

o   Conical Measure 1: 400 mL of phenol solution

o   Conical Measure 2: 400 mL of 2-naphthol solution

o   Conical Measure 3: 400 mL of 1-naphthol solution

2.    To each conical measure, add 20 mL of the prepared reagent solution (diazo component) while stirring.

Observations:

Conical Measure

Alcoholic Solution

Reagent Solution Added

Resulting Color

1

400 mL of phenol

20 mL of reagent solution

Lemon-yellow

2

400 mL of 2-naphthol

20 mL of reagent solution

Orange

3

400 mL of 1-naphthol

20 mL of reagent solution

Intensely orange

Discussion Questions:

1.    What is Electrophilic Aromatic Substitution? Explain the concept and mechanism behind electrophilic aromatic substitution, focusing on how the diazonium cation acts as an electrophile in this reaction.

2.    Why is this Experiment Important? Discuss the significance of electrophilic aromatic substitution reactions and how azo dyes are widely used in various industries, such as textiles and pigments.

3.    How is an Acidic Azo Dye Formed? Explore the role of the diazonium compound and the nucleophilic arene in forming an azo dye, with particular attention to the acidic conditions required.

4.    What Colors Identify the Substitution? Based on the observations, describe how the color changes (lemon-yellow, orange, and intensely orange) indicate the occurrence of substitution reactions.