Carboxylic acids — common mistakes

It is crucial to remember the specific reagents and conditions. For reduction, you must state LiAlH₄ (or lithium tetrahydridoaluminate) and the condition of 'dry ether'. The reaction is followed by an aqueous workup step. Remember that the weaker reducing agent NaBH₄ cannot reduce carboxylic acids.

The acidity of a compound depends on the stability of the conjugate base formed after donating a proton (H⁺). When an alcohol (R-OH) loses a proton, it forms an alkoxide ion (R-O⁻), where the negative charge is localised on the single oxygen atom. This is relatively unstable. When a carboxylic acid (R-COOH) loses a proton, it forms a carboxylate ion (R-COO⁻). The negative charge in the carboxylate ion is delocalised over two oxygen atoms through resonance. This spreading out of the charge makes the carboxylate ion much more stable than the alkoxide ion. A more stable conjugate base means the parent acid is more willing to donate its proton, making it a stronger acid.

No. Oxidation of a secondary alcohol produces a ketone. Ketones are resistant to further oxidation under typical laboratory conditions. Only primary alcohols can be oxidised to form carboxylic acids (via an intermediate aldehyde).