Carboxylic acids are organic compounds that contain a carboxyl group (-COOH), which can act as an acid by donating a proton to a base. Carboxylic acids are widely used as chemical building blocks for synthesis, as they can undergo various reactions to form different functional groups and products. Some examples of carboxylic acid reactions are:

• Esterification: Carboxylic acids can react with alcohols to form esters, which are commonly used as fragrances, flavors, solvents and plasticizers.
• Amide formation: Carboxylic acids can react with amines to form amides, which are important components of proteins and polymers.
• Reduction: Carboxylic acids can be reduced to alcohols or aldehydes by using different reducing agents, such as lithium aluminum hydride (LAH) or borane (BH₃).
• Decarboxylation: Carboxylic acids can lose a carbon dioxide molecule to form alkanes or alkenes, depending on the structure of the acid. This reaction is often catalyzed by heat or base.
• Halogenation: Carboxylic acids can be converted to acyl halides by reacting with halogens or halogenating agents, such as phosphorus pentachloride (PCl₅) or thionyl chloride (SOCl₂). Acyl halides are highly reactive intermediates that can be used for further synthesis.