⚗️ Carboxylic Acids
Reactivity order: acid chloride > anhydride > ester > amide
Carboxylic Acid Derivative Reactivity
Acyl substitution reactivity: acid chloride (most reactive) > anhydride > ester > amide (least reactive). More electronegative leaving group = more reactive. This order appears on every orgo exam.
⚗️ Carboxylic Acids
pKa ~5 for carboxylic acids vs pKa ~16 for alcohols
Carboxylic Acid Acidity
Carboxylic acids (pKa ~5) are much more acidic than alcohols (pKa ~16) because the carboxylate anion is resonance-stabilized. EWG groups lower pKa (stronger acid). EDG groups raise pKa (weaker acid).
⚗️ Carboxylic Acids
Fischer Esterification: acid + alcohol + H+ catalyst (reversible)
Ester Formation
RCOOH + R'OH ⇌ RCOOR' + H2O. Acid catalyzed, reversible. Drive equilibrium: excess alcohol, remove water (Dean-Stark), or use dehydrating agent. Mechanism goes through tetrahedral intermediate.
⚗️ Carboxylic Acids
Saponification = ester + NaOH → carboxylate salt + alcohol (irreversible)
Saponification
Base-catalyzed ester hydrolysis. Unlike acid hydrolysis, saponification is irreversible because the carboxylate salt cannot be re-protonated under basic conditions. This is how soap is made (fat + NaOH).
⚗️ Carboxylic Acids
LiAlH4 reduces COOH → primary alcohol (2 hydrides added)
Reduction of Carboxylic Acids
Carboxylic acids are resistant to NaBH4. Only LiAlH4 reduces them — through the aldehyde intermediate to primary alcohol. Two equivalents of hydride are added overall.