Reaction of Ethanol to Acetaldehyde using CrO3 in an Anhydrous Medium

The reaction of ethanol with CrO3 in an anhydrous medium is a common method to obtain acetaldehyde. This reaction is known as the dehydrogenation of ethanol.

Reaction Mechanism:

1. In the presence of a strong oxidizing agent like CrO3, ethanol undergoes dehydrogenation to form acetaldehyde.
2. The CrO3 acts as an oxidizing agent and oxidizes the alcohol group of ethanol to form the aldehyde group in acetaldehyde.
3. The reaction involves the loss of two hydrogen atoms from ethanol, resulting in the formation of acetaldehyde.

Reaction Steps:

Step 1: Oxidation of Ethanol to Acetaldehyde

The first step involves the oxidation of the alcohol group of ethanol by CrO3. The CrO3 is reduced to Cr3+ in the process.

CH3CH2OH + CrO3 → CH3CHO + Cr3+ + H2O

Step 2: Formation of Chromic Acid

The chromic acid (H2CrO4) formed in the reaction reacts with excess CrO3 to form a complex called chromate ester.

CrO3 + H2CrO4 → CrO3(OH)2 + H2O

Step 3: Rearrangement and Hydrolysis

The chromate ester undergoes rearrangement and hydrolysis to form acetaldehyde.

CrO3(OH)2 + H2O → CH3CHO + CrO4^2- + H3O+

Key Points:

- CrO3 in an anhydrous medium acts as an oxidizing agent in the reaction with ethanol.
- The reaction involves the dehydrogenation of ethanol to form acetaldehyde.
- The reaction proceeds through the formation of chromic acid and a chromate ester intermediate.
- The chromate ester undergoes rearrangement and hydrolysis to yield acetaldehyde.
- This method is commonly used in the laboratory for the synthesis of acetaldehyde from ethanol.