A catalytic effect by silica gel on electrophilic aromatic chlorinations by sulfuryl chloride was recently described.' We wish to report that this technique is synthetically useful for side-chain electrophilic chlorination of highly substituted aromatic compounds. Our results also bear on the recent controversy over whether such reactions occur by an electron-transfer2 or electrophilic3 mechanism. A solution of hexamethylbenzene (I, 1.62 g, 10 mmol) in Ccl4 (25 ml) to which was added 0.35 g of silica gel4 and 1.35 g (10 mnol) of sulfuryl chloride was stirred at room temperature for 8 hr. Work-up by washing with saturated NaHC03 solution, drying (Na2S04) and removing the solvent gave 1.9 g (96%) of pentamethylbenzyl chloride 5, mp 79-81" (hexanes).5 Under similar i $ (96%) conditions, but with the silica gel omitted, no chlorination occ;;r;d (~1% in 72 hr). In view of the demonstration that SC/SG acts by an electrophilic mechanism, ' our results support the conclusions of Baciocchi and Illuminati3 that polar a-chlorination of 1 occurs by an ionic rather than electron-transfer mechanism. Chlorination of octamethylnaphthalene (3)' by SC/SG can be controlled to give excellent yields of mono-, di-or tetrachloro derivatives, depending on the reagent/substrate mol ratio.