Azo Coupling

Demonstration Experiment on Video

Azo Coupling

Objective: Electrophilic Aromatic Substitution, Acidic Azo Dyes

Peter Keusch

German version

Chemicals:

sulfanilic acid

phenol

1-naphthol

2-naphthol

ethanol 96 %

2 N acetic acid

NaNO₂

The following solutions are prepared in advance:

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 %

The solutions should be colorless; if needed a "spatula-tip" full of activated charcoal powder is added. After shaking, the suspension is filtered.

Reagent solution (Diazo component): 40 mL of 0.5 % aqueous NaNO₂ solution + 40 mL of 0.5 % solution of sulfanilic acid in 2 N acetic acid

Glass wares:
	3 conical measures, graduated, 500 mL
	3 glass stirring rods
	5 beakers 50 mL
	3 beakers 500 mL
	graduated cylinder 200 mL

Safety precautions:

Azo dyes are toxic and may cause genetic mutations.
Phenol is acute poisoning by ingestion, inhalation or skin contact may lead to death. Phenol is readily absorbed through the skin. Highly toxic by inhalation.

NaNO₂ is toxic if swallowed. Severe eye irritant. Respiratory and skin irritant. May act as a carcinogen for chronic exposure.

1-naphthol: Eye, skin and respiratory irritant. Causing liver damage.
2-naphthol is harmful if swallowed or inhaled. May be harmful in contact with the skin. Eye, skin and respiratory irritant.
Sulfanilic acid may act as a skin, eye or respiratory irritant.

Ethanol is highly flammable.

Safety goggles and gloves must be worn. Good ventilation required. The ethanolic solution of phenol and the reagent solution (diazo component) should be made under a fume hood!

Experimental procedure:

Each of three conical measures is filled with alcoholic solutions of phenol, 2-naphthol and 1-naphthol, respectively. Afterwards the diazo component is added while stirring.

conical measure 1	400 mL of alcoholic phenol solution	20 mL of reagent solution
conical measure 2	400 mL of alcoholic 2-naphthol solution	20 mL of reagent solution
conical measure 3	400 mL of alcoholic 1-naphthol solution	20 mL of reagent solution

Results:

	Color of the solution
conical measure 1	lemon-yellow
conical measure 2	orange
conical measure 3	intensively orange

Video clip (Download RealPlayer .rm file)

Discussion:

· Diazotized sulfanilic acid (1) reacts with phenol and the naphtholes forming acid azo dyes (2) The reaction proceeds according to the mechanism of electrophilic aromatic substitution.

Reference:
Projection Experiment: Basic and acid Azo Dyes

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