Hydrochloric Acid → 5,7,5',7'-Tetra-tert-butyl-[3,3']bibenzofuranylidene-2,2'-dione

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Reaction Steps

78.7 g of 5,7-di-tert-butyl-3-hydroxy-3H-benzofuran-2-one (prepared as in Ex. 2b) are placed in 150 ml of toluene, and 3 drops of dimethylformamide (DMF) and 45 ml of thionyl chloride are added thereto. The solution is then slowly heated to 373 K at such a rate that the evolution of HCl and SO2 remains vigorous yet controllable. It is then stirred at that temperature for a further hour. Approximately 150 ml of liquid are then distilled off in order to remove the excess thionyl chloride. The residue is diluted with 480 ml of toluene and, at room temperature, 42 ml of triethylamine are added dropwise. The thick, red reaction mixture is then heated under reflux for 15 min. After cooling to room temperature, the triethylamine hydrochloride which has precipitated is filtered off, and the filtrate is washed with water and concentrated NaCl solution and concentrated to an oily consistency using a rotary evaporator. The isoxindigo is crystallised out by adding 225 ml of acetonitrile, is filtered off, washed with acetonitrile and dried, yielding 57.7 g (78.7% of the theoretical yield) of 5,7,5′,7′-tetra-tert-butyl-[3,3′]bibenzofuranylidene-2,2′-dione of formula (LIa).

Provenance & Evidence