Introduction to Carboxylic Acids

• Carboxylic acids contain the carboxyl group: a carbonyl with oxygen attached to the carbon that’s attached to a hydrogen

• Some common carboxylic acids are shown below:

Physical Properties of Carboxylic Acids

• They are the most polar functional group due to the carboxyl group

• They have the highest melting and boiling points of all the functional groups

• They tend to form dimers in the solid, liquid, and gaseous phases

  • this makes their apparent molar mass higher than their actual molar mass

• carboxylic acids up to 6 carbons long tend to be water soluble

  • benzoic acid (benzene ring attached to carboxyl group) is soluble in hot water

Chemical Properties of Carboxylic Acids

• Carboxylic acids are weak acids

• Most carboxylic acids have a pKa of approximately 5

• The dissociation reaction of acetic acid is shown below

  • it will be similar for all carboxylic acids

  • Acetic acid has a pKa of 4.74

• carboxylic acids are more acidic than alcohols because of

  • the resonance effect of the anion

  • inductive effect of the carbonyl group

• They can react with sodium hydroxide and sodium bicarbonate to form carboxylates (salts of carboxylic acids)

• The reaction of benzoic acid with sodium hydroxide is shown below