Step 3-Acid Catalyzed Condensation8. 9 Cis-dibenzoylethene (0.1 g) is dissolved

Question

Step 3-Acid Catalyzed Condensation8. 9 Cis-dibenzoylethene (0.1 g) is dissolved in 1 mL of acetic anhydride and cooled in an ice bath followed by the slow addition of three drops of concentrated sulfuric acid. (Some procedures include a 5-minute heating at 100 °C.) After 5 minutes, the reaction mixture is poured into 20 mL of water to precipitate the product. Upon crystallization, the final 3-acetoxy-2,5-diphenylfuran is isolated by vacuum filtration. Recrystallization may be performed using isopropanol.

Explanation / Answer

cis-dibezoylethene is dissolved in acetic anhydride, here cis-dibezoylethene is a starting material while acetic anhydride is a solvent and starting material for it.

Cooled by the ice bath and followed by slow addition of three drops concentrated sulphuric acid, it because of very much heat producing during this process. the concentrated sulphuric acid will work as a dehydrating agent and due to which water will come and it may react with acetic anhydride which will produce much heat, to avoid any cracking and danger it is better to cool it.

when the temperature of the reaction system reduced to room temperature the heating at 100 C will increase the yield by is the reaction of unreacted species of the solution.

Solution is quenched in 20 mL of water to neutralize the effect of the Sulphuric acid and acetic anhydride.

ppt can be collected and dried by vacuum filtration just to decrease the time of the filtration and to provide little drying of the ppt.  

Isopropanol is used as an eluent to recrystallize the ppt to get pure product.

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