p-Chlorotoluene is treated with $\mathrm{NaNH}{}_2$ in liquid $\mathrm{NH}{}_3$. The amine products formed (in roughly equal amounts) are

The base removes a hydrogen ortho to Cl and chloride leaves, giving 4-methylbenzyne, whose triple bond joins the carbon that carried Cl (para to $\mathrm{CH}{}_3$) and the neighbouring meta carbon. The amide ion adds to either carbon of the triple bond. Addition at the original Cl carbon gives the para product and addition at the neighbouring carbon gives the meta product, so p- and m-toluidine form.