3.9 Carboxylic Acids
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Derivatives of carboxylic acids
• Esters RCOOR’ • Acyl chlorides RCOCl • Acid anhydrides (RCO)₂O • Amides RCONH₂ • N-substituted amides RCONHR’
General formula of carboxylic acids
CₙH₂ₙO₂
Functional group of carboxylic acids
RCOOH
Melting and boiling point of carboxylic acids
Relatively high due to hydrogen bonding
Why do carboxylic acids have higher boiling points than alcohols?
Carboxylic acids form dimers
Solubility of carboxylic acids
Carboxylic acids with a low Mr are soluble as they form hydrogen bonds with the water
Are carboxylic acids weak or strong acids?
Weak They only partially ionise in solution
Acid + Base →
Salt + Water
Acid + Carbonate →
Salt + Water + Carbon dioxide
Acid + Metal →
Salt + Hydrogen
What salts do carboxylic acids form?
Carboxylate salts
General formula of esters
CₙH₂ₙO₂
Functional group of esters
RCOOR’
How are esters formed from carboxylate acids?
Reaction with an alcohol
What is the prefix of an ester is named from?
The alcohol
What is the suffix of an ester named from?
The carboxylic acid
Properties of esters
• Sweet smelling liquids which occur in fruits • Lower boiling points than carboxylic acids • Less soluble than carboxylic acids • Do not form hydrogen bonds
Uses of esters
• Food flavorings • Solvents • Perfumes • Plasticisers
Methods for preparing esters
• Carboxylic acid + Alcohol • Acid anhydride + Alcohol • Acyl chloride + Alcohol (All condensation reactions)
Condensation reaction
A chemical reaction in which two molecules are joined together with the elimination of a small molecule
Products: Carboxylic acid + Alcohol
Ester + Water
Products: Acid anhydride + Alcohol
Ester + Carboxylic acid
Products: Acyl chloride + Alcohol
Ester + HCl
Conditions: Carboxylic acid + Alcohol
• Heat • Concentrated sulfuric acid catalyst