What is Benzenesulfonic Acid used for? Preparation, Properties, and uses

Benzenesulfonic acid Preparation

Benzenesulfonic acid is obtained from sulphonation of benzene. For this, benzene is heated with concentrated Sulfuric acid.

C₆H₆ + H₂SO₄(concentrated) → C₆H₅SO₃H + H₂O

Laboratory Method

To make Benzenesulfonic acid in the laboratory, take a mixture of one part banzene and two parts concentrated sulfuric acid in a round bottom flask. Attaches a reflux condenser to the flask. Heat the flask at 80 -100°C for about two hours by placing it on a water heater.

After this, the mixture is cooled and put in water. It contains barium carbonate. Unused sulfuric acid precipitates as barium sulfate. Filter it and separate it. Berium salt of Benzenesulfonic acid is filtered due to dissolution in water.

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On cooling after filtration, the cristal of Benzenesulfonic acid’s berium salt is obtained, separating these crystals and adding appropriate amounts of sulphuric acid. Berium sulfate precipitates and Benzenesulfonic acid is released.

The precipitates of berium sulfate are filtered and separated. Water containing crystals of Benzenesulfonic acid are obtained after cooling the filtrate. Anhydrous Benzenesulphonic(C₆H₅SO₃H.3/2H₂O) Acid is obtained after being isolated and heated.

Physical Properties

It is a colorless crystal solid. Its melting point is 65°C. Its water-containing crystals have a melting point of 47°C. It is more soluble in water.

Chemical Properties

Its chemical reactions can be divided into three parts.

• Reactions in which the -OH group of the -SO₃H group participates.
• Reactions in which the –SO₃H group is displaced.
• Replacement reactions of nuclei

Reactions in which the -OH group of the -SO3H group participates.

Acidic symptoms: It is an acid. Its aqueous solution is strongly acidic. The acid strength of its aqueous solution is as high as sulphuric acid. It reacts with bases to form salts.

example:

C₆H₅SO₃H + NaOH → C₆H₅SO₃Na + H₂O

Reaction with Phosphorus pentachloride: In the reaction of Benzenesulfonic acid and phosphorus pentachloride, the -OH group of -SO₃H group is displaced by the chlorine atom.

C₆H₅SO₃H + PCl₅ → C₆H₅SO₂Cl + POCl₃ + HCl

Reaction with alcohols: Like other acids it reacts with alcohols to form ester.

C₆H₅SO₃H + C₂H₅OH → C₆H₅ – SO₂ –O – C₂H₅ + H₂O

Reactions in which the –SO3H group is displaced.

Displacement by hydrogen atom: On decomposition of benzene sulphonic acid with superheated steam or heating with dilute HCl or dilute H₂SO₄, its water decomposition occurs and benzene is obtained.

C₆H₅SO₃H + H₂O → C₆H₆ + H₂SO₄

Displacement by Hydroxyl Group: Phenol is obtained by melting its sodium or potassium salts with solid NaOH or KOH.

C₆H₅SO₃Na + NaOH → C₆H₅OH + Na₂SO₃

Displacement by amines group: Aniline is obtained by melting its sodium or potassium salts with NaNH₂ or KNH₂.

C₆H₅SO₃Na + NaNH₂ → C₆H₅NH₂ + Na₂SO₃

Displacement by cyano group: Cyano benzene is obtained by melting its sodium or potassium salts with NaCN.

C₆H₅SO₃Na + NaCN → C₆H₅CN + Na₂SO₃

Displacement by carboxyle group: Its sodium or potassium salts are smelted with sodium phomate to obtain benzoic acid.

C₆H₅SO₃Na + HCOONa → C₆H₅COOH + Na₂SO₃

Displacement by -SN group: thaophenol is obtained by melting its sodium or potassium salts with KSH.

C₆H₅SO₃K + KSH → C₆H₅SH + K₂SO₃

Replacement reactions of nuclei

The sulphonic acid group is a meta director group. Hence meta products are obtained from its halogenation, nitration and sulphonation. Like all other meta director groups, it is also a deactivating group. This implies that its substitution reactions occur at a lower intensity than benzene. Following are its major nuclear substitution reactions.

Halogenation: When replicated with chlorine in the presence of halogen carrier, it forms meta chlorobenzene sulphonic acid.

Nitration: When heated with a mixture of concentrated NHO₃ and concentrated H₂SO₄, it forms m nitrobenzene sulphonic acid.

sulphonation: when heated at 200°C with gentle sulphuric acid, it forms meta benzene di sulphonic acid.

Benzenesulfonic acid Uses

• In the manufacture of dyes
• Sulpha drugs are prominent in the manufacture of drugs.
• In manufacture of saccharine
• In the manufacture of detergents