14.10:
Acid Halides to Carboxylic Acids: Hydrolysis
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.
14.10:
Acid Halides to Carboxylic Acids: Hydrolysis
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.