The “positive halogen” reaction between benzotrichlorides and potassium iodide

Aromatic and Alkaromatic Chlorocarbons

“…[72], could be accounted for either in terms of shielding of the a-hydrogen in the heptachlorotoluene by the two ortho chlorines towards the attacking chlorine, or by electronic deactivation (-I effect) due to the chlorine atoms. As shown later, the perchlorobenzyl radical-the pertinent intermediate in the substitution of the last hydrogen-can easily be formed from perchlorotoluene, and it is sufficiently stable to give a strong esr signal [273] and to dimerize in solution, even in the presence of toluene [274]. Therefore, steric inhibition of resonance in the radical does not seem to be important.…”

“…The conversion into perchlorobenzene of benzotrichloride [15,69,77], oH-heptachlorotoluene [9], and perchlorotoluene [9] with reagent BMC under forcing conditions has also been reported. The remarkable chlorinolyses of alkylbenzenes mentioned above are set out:…”

“…It is not surprising, therefore, that in spite of many previous attempts as far back as 1869 [16] no alkylaromatic chlorocarbon with a side-chain flanked by two ortho chlorines was synthesized until 1954 [15]. The steric strain not only hinders the formation of the alkylaromatic chlorocarbons (or perchloroarylalkanes) but also assists their fragmentation (chlorinolysis and thermolysis).…”

“…The synthesis of perchlorotoluene was announced by Ballester and Molinet in 1954 [15] as a result of an unsuccessful experiment [249] and with it reagent BMC was discovered [9, 10] (Section 1.1). The chlorination of benzotrichloride with that reagent gives perchlorobenzene.…”

“…Reagent BMC has allowed the preparation of sterically strained chlorocarbons such as perchlorotoluene [15], which had already been attempted unsuccessfully by Beilstein (16,17] in 1869. Its efficiency is due to the high concentration of the active species present and the relatively low temperature (usually below 100°) which minimizes chlorinolysis, i.e., fragmentation of the carbon framework.…”