Order of acidity is RCOOH > H2CO3 > C6H5OH > H2O > R – OH.
Phenol is more acidic than alcohols due to stabilisation of phenoxide ion through resonance. Presence of electron withdrawing group increases the acidity of phenol by, stabilising phenoxide ion while presence of electron releasing group decreases the acidity of phenol by destabilising phenoxide ion.
Thus. increasing acidic strength is
o-cresol < p-cresol < m-cresol < phenol < o-nitrophenol < 2, 4.6. trinitrophenol( picric acid)
Higher Ka and lower pKa value corresponds to the stronger acid.
( b) Esterification
The reaction with R’ COOH and( R’ CO) 2O is reversible, so cone, H2SO4 is used to remove water.
The reaction with R’ COCI is carried out in the presence of pyridine so as to neutralise HCI which is formed during the reaction.
The introduction of acetyl( CH3CO-) group in phenols is known as acetylation.
Acetylation of salicylic acid produces aspirin.