Which reagent converts a carboxylic acid to an acid chloride?

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Multiple Choice

Which reagent converts a carboxylic acid to an acid chloride?

Activating a carboxylic acid to an acid chloride is done with thionyl chloride. The carboxyl hydroxyl group is replaced by chlorine when it reacts with SOCl2, giving the acyl chloride and releasing SO2 and HCl gas. This makes the carboxyl group far more reactive for further acylation steps, such as forming esters or amides. Other reagents don’t perform this transformation. NaBH4 is a hydride donor that reduces carbonyls to alcohols, not convert carboxylic acids to acid chlorides. Water would simply react with or hydrolyze reactive intermediates rather than form an acid chloride. Ammonia would attack an acid chloride line after it’s formed to make an amide, but it won’t convert a carboxylic acid to an acid chloride by itself.

Activating a carboxylic acid to an acid chloride is done with thionyl chloride. The carboxyl hydroxyl group is replaced by chlorine when it reacts with SOCl2, giving the acyl chloride and releasing SO2 and HCl gas. This makes the carboxyl group far more reactive for further acylation steps, such as forming esters or amides.

Other reagents don’t perform this transformation. NaBH4 is a hydride donor that reduces carbonyls to alcohols, not convert carboxylic acids to acid chlorides. Water would simply react with or hydrolyze reactive intermediates rather than form an acid chloride. Ammonia would attack an acid chloride line after it’s formed to make an amide, but it won’t convert a carboxylic acid to an acid chloride by itself.

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