( iv ) Substitution reactions in the hydrocarbon part α -hydrogen atoms in carboxylic acids are acidic in nature and can be easily replaced by halogen atoms in HVZ reaction
The reaction is known as Hell-Volhard-Zelinsky reaction .
( v ) Arndt-Eistert reaction It is method of converting lower carboxylic acids to their higher homologues
( vi ) Reducing property Among carboxylic acids , formic acid is the only acid that acts as reducing agent . It reduces , acidified KMnO4 to MnSO4 ,
HgCl2 to Hg , Tollen ‟ s reagent to silver mirror and Fehling ‟ s solution to red ppt . and itself gets oxidised to CO2 and H2O .
HCOOH + HgCl2→ Hg + 2HCI + CO2
( vii ) Electrophilic substitution reactions of aromatic acids -COOH group shows -R effect , therefore , acts as a deactivating and meta-directing group . Carboxylic acids do not undergo Friedel-Craft ‟ s reaction because the carboxylic group IS deactivating and the catalyst
AlCl3 ( anhy .) gets bonded to the carboxyl group .