Acetic anhydride can be prepared by treating ethyl alcohol with __________?

Acetic anhydride ((CH₃CO)₂O) is an important reagent in organic synthesis, widely used for acetylation reactions in pharmaceuticals, dyes, and cellulose derivatives. One method to prepare acetic anhydride is by treating ethyl alcohol (C₂H₅OH) with a strong dehydrating agent such as phosphorus pentoxide (P₂O₅) or concentrated sulfuric acid (H₂SO₄).

Both P₂O₅ and H₂SO₄ remove water from the alcohol, enabling the condensation reaction that converts ethanol into acetic anhydride. The reaction can be simplified as follows:

C₂H₅OH + Dehydrating agent → (CH₃CO)₂O + H₂O

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  P₂O₅ (phosphorus pentoxide) acts as a powerful dehydrating agent due to its strong affinity for water, absorbing the water molecules produced during the reaction and driving it forward.

  
  


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  Concentrated H₂SO₄ (sulfuric acid) also serves as a dehydrating agent and promotes the esterification and condensation of alcohol molecules to form the anhydride.

  
  

In practice, the reaction is carried out under controlled conditions of temperature to maximize the yield of acetic anhydride and minimize side reactions. This method demonstrates a typical use of dehydrating agents in organic chemistry, where water removal is essential for driving condensation reactions.

Other options like PCl₅ (phosphorus pentachloride) are not used for this preparation; PCl₅ is mainly employed in converting carboxylic acids to acyl chlorides rather than forming anhydrides from alcohols.

Hence, the preparation of acetic anhydride from ethyl alcohol is achieved using both P₂O₅ and H₂SO₄, highlighting the importance of dehydrating agents in organic synthesis reactions.