Summary of Reactions

• The most important derivatives of carboxylic acids are acyl halides, anhydrides, esters, and amides. These are listed in order from most reactive (least stable) to least reactive (most stable).

ACYL HALIDES:

• can be formed by adding RCOOH + SOCl₂, PCl₃ or PCl₅, or PBr₃
• undergo many different nucleophilic substitutions; H₂O yields carboxylic acid, while ROH yields an ester and NH₃ yields an amide
• can participate in Friedel-Crafts acylation to form an alkyl aryl ketone
• can be reduced to alcohols or, selectively, to aldehydes

ANHYDRIDES:

• can be formed by RCOO⁻ + RCOCl (substitution) or by RCOOH + RCOOH (condensation)
• undergo many nucleophilic substitution reactions, forming products that include carboxylic acids, amides, and esters
• can participate in Friedel-Crafts acylation

ESTERS:

• formed by acid chlorides or anhydrides + ROH or by RCOOH + ROH
• hydrolyze to yield acids + alcohols; adding ammonia yields an amide
• undergo transesterification with alcohol to exchange alkoxy functional group
• react with Grignard reagent (2 moles) to produce a tertiary alcohol
• Claisen condensation, analogous to the aldol condensation, combines two molecules of ester acting both as nucleophile and target
• very important in biological processes, particularly phosphate esters, which can be found in membranes, nucleic acids, and metabolic reactions

AMIDES:

• can be formed by acid chlorides + amines, acid anhydrides + ammonia, or ester + ammonia
• hydrolysis yields carboxylic acids or carboxylate anions
• can be transformed to primary amines via Hofmann rearrangement or reduction
• very important in formation of proteins because all amino acids are linked by amide bonds known as peptide bonds