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

Participants

Reaction Conditions

Reaction Steps

22 g of 7-tert-butyl-3-hydroxy-5-methyl-3H-benzofuran-2-one (prepared as described in Example 2 of U.S. Pat. No. 5,614,572) are introduced in 50 ml of toluene as initial charge and admixed with 3 drops of DMF and 15 ml of thionyl chloride. The solution is then gradually heated to 100° C. so that the evolution of HCl and SO2 remains lively but still controllable. Thereafter the reaction mixture is stirred at 100° C. for a further 1 h. About 50 ml of liquid are subsequently distilled off to remove excess thionyl chloride. The residue is diluted with 160 ml of toluene and admixed at room temperature with 14 ml of triethylamine added dropwise. The thick red reaction mixture is then refluxed for 30 min. The precipitated triethylamine hydrochloride is filtered off after cooling to room temperature and the residue is concentrated in a rotary evaporator to an oily consistency. The isoxindigo is crystallized out by addition of 200 ml of acetonitrile, filtered off, washed with acetonitrile and dried to leave 11.6 g (57% of theory) of 7,7′-di-tert-butyl-5,5′-dimethyl[3,3′]bibenzofuranylidene-2,2′-dione of the formula:

Provenance & Evidence