Hydrogen Bromide → 1H-2-Benzopyran-1,4(3H)-dione

Participants

Reaction Conditions

Reaction Steps

A stirred mixture of 2-acetylbenzoic acid (compound of formula (XI)) (1.00 Kg, 6.09 mol) and chlorobenzene (10.0 L) was treated with 5.5 molar hydrobromic acid in acetic acid (55 mL) and bromine (310 mL) then warmed to approximately 30° C. After 3 hours water (10.0 L) was added and the reaction heated to reflux. After 3 hours the reaction was cooled to 60° C. and the organic layer removed. The aqueous layer was extracted with chlorobenzene (2.0 L) and the combined organic layers concentrated under reduced pressure to approximately 3.0 L. Propan-2-ol (5.0 L) was charged and the slurry cooled to 0° C. before being filtered and washed with propan-2-ol (2.0 L). The resulting solid was dried in vacuo at 50° C. to give the title compound (736 g, 75%); 1H NMR (400 MHz, CDCl3): δ 5.14 (2H, s, H-9), 7.82-7.91 (2H, m, H-2 and 3), 8.08-8.10 (1H, m, H-1), 8.28-8.30 (1H, m, H-4); 13C NMR (100 MHz, CDCl3) δ 73.4, 125.6, 128.0, 130.9, 131.8, 134.7, 135.9, 161.4 and 189.5.

Provenance & Evidence