Carboxylate ion is more stable than the phenoxide ion as the negative charge is evenly spread on the carboxylate ion,
In case of phenoxide ion, three contributing structures have a negative charge on the less electronegative carbon atom. Therefore their contribution towards the resonance stabilization of the phenoxide ion is very small.
In the carboxylate ion the negative charge is delocalized on the two oxygen atoms, while in phenoxide ion the negative charge remains localized on the oxygen atom only (considering the remaining two contributing structures of the phenoxide ion). Thus carboxylate ion is much more resonance stabilized than the phenoxide ion.Hence release of proton from carboxylic acid is much more easier than phenol.
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