Potassium tert-butoxide reacts with halobenzenes on heating in dimethyl sulfoxide to give tert-butyl phenyl ether.
(a) o-Fluorotoluene yields tert-butyl o-methylphenyl ether almost exclusively under these conditions. By which mechanism (addition–elimination or elimination–addition) do aryl fluorides react with potassium tert-butoxide in dimethyl sulfoxide?
(b) At 100°C, bromobenzene reacts over 20 times faster than fluorobenzene. By which mechanism do aryl bromides react?