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 .