Benzene purification from thiophene

Benzene (C₆H₆) is a widely used chemical in chemical industries and analytical laboratories. Purity of benzene liquid is a critical factor considering the requirement, specially for research purposes. Commercial benzene may contain thiophene which cannot be separated by distillation or by fractional crystallization.

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Health hazards of Benzene

Benzene (C₆H₆) is a widely used chemical in chemical industries and analytical laboratories. But it has been identified as a carcinogenic chemical and have to use carefully avoid health issues. Therefore, all experiments and procedures involving benzene as a chemical must be carried out in a well-ventilated fume cupboard, and protective gloves and other personal protective equipment should be properly worn to avoid or minimize the contact with humans.

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Preparing dry benzene

The analytical reagent grade benzene is satisfactory for most purposes (including research experiments). If dry benzene is required, Benzene is first treated with anhydrous Calcium chloride (CaCl₂, filtered and then placed over Sodium wire or a Type 5A molecular sieve. Phosphorus pentoxide (P₂O₅), Lithium aluminium hydride (LiAl₄) or Calcium hydride (CaH₂) may be used as alternatives to sodium wire.

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Thiophene in benzene

Commercial benzene may contain thiophene (C₄H₄S), (boiling point. 84⁰C), which cannot be separated by distillation or by fractional crystallization.

Testing the presence of Thiophene in benzene

Thiophene's presence can be detected by shaking 3 ml of benzene with a solution of 10 mg of isatin in 10 ml of concentrated Sulfuric acid and allow the mixture to stand for a short time period. You can observe a bluish-green colouration is produced if thiophene is present in the benzene solution.

Removing of Thiophene from Benzene

Thiophene is somewhat more polar than benzene due to the presence of Sulfur atom and that factor is used to remove Thiophene from benzene.

Steps of removing Thiophene from benzene

1. The Thiophene can be removed from benzene by mixing and shaking with concentrated sulfuric acid. The benzene is shaken repeatedly with about 15 per cent of its volume of concentrated sulfuric acid in a stoppered separatory funnel until the acid layer is colourless or very pale yellow on standing, or until the thiophene test becomes negative.
2. After each shaking lasting a few minutes, the mixture is allowed to settle and the lower layer is drawn off.
3. The benzene is then shaken twice with water in order to remove most of the acid (Sulfuric acid is highly soluble in water)
4. As the next step, Benzene solution is mixed and shaken with 10 per cent sodium carbonate solution.
5. Again mix and shake with water
6. Finally, dry with anhydrous calcium chloride.
7. After filtration, the benzene is distilled through an efficient column and the fraction. Benzene is collected at boiling point of 80-81⁰C in the distillation column.

Drying of distilled benzene

If you require dry the distilled benzene furthermore, distilled Benzene be stored over sodium wire or left in the presence of a Type 5A molecular sieve. Pure benzene has boiling point of 80⁰C at pressure of 760 mmHg.

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