The direct iodination of arenes with chromium(VI) oxide as the oxidant

An easy and cheap laboratory method is presented for the direct mono- and diiodination of a number of activated and deactivated arenes. The main iodination reactions occurred at the temperatures not exceeding 65 degrees C for 0.5--12 h in the anhydrous, strongly acidic liquid system, I-2/AcOH/Ac2O/H2SO4, in the presence of prior dissolved CrO3 used as the oxidant. The yields of the pure iodinated products varied from 31% (for 3,5-diiodobenzoic acid) up to 90% (for 4-iodoanisole). So far, benzonitrile and some oxidizable aromatics, e.g. naphthalene, fluorene, xanthene, and thiophene, have been found to be unsuitable for the effective iodination. Nevertheless, this novel, simple method of direct iodination is worthy to be extended to other appropriate aromatics.