Treatment with methyl chloride and \(\mathrm{AICI}_{3}\) at \(0^{\circ}\) converts toluene chiefly into o- and p-xylenes; at \(80^{\circ}\), however, the chief product is \(\mathrm{m}\) -xylene. Furthermore, either o- or \(\mathrm{p}\) -xylene is readily converted into \(\mathrm{m}\) -xylene.by treatment with \(\mathrm{AICI}_{3}\) and \(\mathrm{HCl}\) at \(80^{\circ}\). How do you account for this effect of temperature on orientation? Suggest a role for the HCl.

Temperature significantly impacts the Friedel-Crafts alkylation of toluene. At 0°C, the reaction primarily results in ortho and para forms of xylene, showing a preferential attachment of the methyl group to the sites ortho and para to the already existing methyl group on toluene. However, at higher temperature of 80°C, the reaction favors the formation of m-xylene, presumably due to 'thermal equilibration', a process where situations of higher energy favor creating the most stable product. In this case, m-xylene is more thermodynamically stable than o-xylene and p-xylene due to a more evenly distributed electron cloud. In addition to temperature, \( \mathrm{HCl} \) also plays a significant role in the reaction. When o- or p-xylene is treated with \( \mathrm{AlCl}_{3} \) and \( \mathrm{HCl} \) at 80°C, a conversion to m-xylene occurs. It's likely that the \( \mathrm{HCl} \) in conjunction with the \( \mathrm{AlCl}_{3} \) catalyzes a process of demethylation and remethylation at the more thermodynamically stable meta position, thus favoring the transformation of o- or p-xylene into m-xylene. Therefore, both temperature and \( \mathrm{HCl} \) effectively control the orientation of the methyl groups in the products of these reactions.