Hydrolysis of acid halides is a nucleophilic acyl substitution reaction in which acid halides react with water to give carboxylic acids. The reaction occurs readily and does not require acid or a base catalyst.
As shown below, the mechanism involves a nucleophilic attack by water at the carbonyl carbon to form a tetrahedral intermediate. This is followed by the reformation of the carbon–oxygen π bond along with the departure of a halide ion. A final proton transfer step yields carboxylic acid as the substitution product.
The reaction produces a very strong acid, HCl, as a by-product. Therefore, a base such as pyridine is used in the reaction, which reacts with HCl to form pyridinium chloride. This process neutralizes the acid and prevents undesired side reactions.
Hydrolysis of acid halides is a nucleophilic acyl substitution reaction, where an acid halide reacts with water to form a carboxylic acid.
Since acid halides are very reactive, the hydrolysis does not require an acid or a base catalyst.
The mechanism proceeds in three steps. The first step is the nucleophilic attack by water at the carbonyl carbon to form a tetrahedral intermediate.
In the second step, the carbon-oxygen π bond is re-formed, and the chloride ion departs as a leaving group.
Lastly, deprotonation forms the corresponding carboxylic acid as the final substitution product.
In this reaction, hydrochloric acid is formed as a by-product, which often leads to unwanted side reactions.
So, a weak base like pyridine is added to the reaction mixture to neutralize the hydrochloric acid, thereby preventing any side reaction.
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