When carboxylic acids react with chlorine or bromine  in the presence of red phosohorous, the alpha-hydrogen atoms are replaced by halogen atoms. It is called Hell-Volhard-Zelinsky(H.V.Z) reaction. Ex:-    acetic acid reacts with chlorine in presence of red phosphorus to form chloro acetic acid, dichloro acetic acid or trichloro acetic acid depending on the quantity of chlorine … Read more