Nitrobenzene (Fluka)

Trichloroisocyanuric acid (Fluka)

A mixture of nitrobenzene (1.25 g, 10 mmol) and sulfuric acid (96%, 10 ml) was stirred on an oil bath at room temperature while trichloroisocyanuric acid (5.0 g, 20 mmol) was carefully added. After 15 min of stirring a short air condenser was set on the flask and the temperature of the oil bath slowly increased to 180°C during the period of 2 h. The reaction mixture was left stirring for 4 h at that temperature. The organic layer solidified during cooling and was extracted directly from the sulfuric acid with dichloromethane (40 ml), the extract washed with water (3 × 40 ml), dried over anhydrous Na₂CO₃ and evaporated in vacuo (Caution: The waste acid is still concentrated and should be carefully quenched and disposed). The resulting 2.58 g of greenish crystals were triturated in hot methanol and filtered when cold to give white crystalline 2,3,4,5,6-pentachloronitrobenzene (1.86 g, 62 %).

The use of trichloroisocyanuric acid in sulfuric acid for electrophilic aromatic chlorination was first described by Rosevear and Wilshire. Perchlorination of some deactivated aromatic substrates like phthalic anhydride and 4-alkylnitrobenzenes with this reagent combination at about 100°C is published in two Japonese patents. Mendonça et al published a thorough study of chlorination with trichloroisocyanuric acid in sulfuric acid.

mp = 141–143°C (lit.  145–146 °C). IR (KBr)  3500, 1559, 1364, 1333, 1223, 928, 785, 676, 656 cm^-1. MS (EI) m/z (%) 295 (M+, 68), 249 (83), 237 (100), 214 (75), 142 (83); the isotopic distribution is consistent with 5 Cl atoms.

Maraš, N.: Funkcionalizacija alkenov in aromatov s trikloroizocianurno kislino (diploma). University of Ljubljana, Ljubljana, 2006.