Benzoin Condensation


Benzoin condensation is a coupling reaction or addition reaction which involves two aldehydes. It was first observed by Justus von Liebig and Friedrich Wohler in 1832 during their research on bitter almond oil. While use of cyanide as catalyst in the reaction was developed by Nikolay Zinin in the 1830s. Condensation reactions are organic addition reactions which produce an additional product and a water molecule. As it produces water molecules that’s why known as condensation. In benzoin condensation addition product benzoin is produced and water molecules are released.

Benzoin Condensation Reaction

The benzoin condensation reaction is a condensation (or addition) reaction between two aromatic aldehydes such as benzaldehydes in presence of nucleophilic catalysts such as cyanide or thiamine to produce benzoin. Reaction is given below – 

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Mechanism of Benzoin Condensation Reaction

Benzoin condensation reaction mechanism was proposed by A. J. Lapworth in 1903. 

  • In the first step cyanide anion reacts with aldehyde in nucleophilic addition reaction. Now rearrangement of intermediate results in polarity reversal of the carbonyl group. Which then adds to the second carbonyl group in the second nucleophilic addition. 

  • In the second step proton transfer and elimination of the cyanide ion takes place which results in removal of water molecules and formation of benzoin. 

  • In this reaction both protonation and deprotonation takes place, one aldehyde donates a proton and one aldehyde accepts a proton. 

 

Reactions involved are as follows – 

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Benzoin condensation reaction can also be executed by aliphatic aldehydes with base catalysis in presence of thiazolium salts. 

Benzoin Condensation Reaction and Benzoin Uses 

  • Tincture of benzoin is made by using benzoin. 

  • Benzoin is used under adhesive bandage. 

  • Benzoin is applied on skin to protect it from allergy. 

  • Benzoin is used by athletes for toughening skin. 

  • Benzoin is used by orthopedists under a cast. 

  • Benzoin can be applied skin fissures, fever blisters as an antiseptic. 

  • Benzoin is used for treatment of asthma, bronchitis and common colds. 

  • Benzoin is used in alternative medicine. 

  • Benzoin is used in military also to prevent loss of skin. 

  • Benzoin condensation reaction is used for the synthesis of various organic compounds and in reactions. 

  • It is used to extend aliphatic form of aldehydes. 

  • This reaction is used in synthesis of heterocyclic compounds. 

  • This reaction is used in polymer chemistry. 

 

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