Which reagents convert a carboxylic acid to the corresponding acid chloride?

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Multiple Choice

Which reagents convert a carboxylic acid to the corresponding acid chloride?

To turn a carboxylic acid into an acid chloride you need to replace the hydroxyl group of the carboxyl with chlorine. Thionyl chloride (SOCl2) does this efficiently: the carboxyl oxygen interacts with SOCl2, forming a reactive intermediate that collapses to give the acid chloride, while sulfur dioxide and hydrogen chloride are released as gases. This gas evolution helps drive the reaction forward. The result is the desired acyl chloride, R-COCl, ready for further conversions like forming esters or amides. The other options don’t achieve this transformation. An alcohol plus HCl would mainly convert alcohols to alkyl chlorides or promote ester formation with the carboxylic acid, not replace the OH on the carboxyl group. A base in aqueous solution deprotonates the carboxylic acid, giving a carboxylate, which is far less reactive toward chlorination. Water simply wouldn’t generate the acyl chloride and can even hydrolyze reactive intermediates instead.

To turn a carboxylic acid into an acid chloride you need to replace the hydroxyl group of the carboxyl with chlorine. Thionyl chloride (SOCl2) does this efficiently: the carboxyl oxygen interacts with SOCl2, forming a reactive intermediate that collapses to give the acid chloride, while sulfur dioxide and hydrogen chloride are released as gases. This gas evolution helps drive the reaction forward. The result is the desired acyl chloride, R-COCl, ready for further conversions like forming esters or amides.

The other options don’t achieve this transformation. An alcohol plus HCl would mainly convert alcohols to alkyl chlorides or promote ester formation with the carboxylic acid, not replace the OH on the carboxyl group. A base in aqueous solution deprotonates the carboxylic acid, giving a carboxylate, which is far less reactive toward chlorination. Water simply wouldn’t generate the acyl chloride and can even hydrolyze reactive intermediates instead.

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