Acetic Acid → 4-Bromofuran-2-carboxylic acid

Participants

Reaction Steps

A 500 mL three-necked round-bottom flask fitted with an overhead mechanical stirrer and reflux condenser was charged with 4,5-dibromo-furan-2-carboxylic acid (57.0 g, 211 mmol), H2O (168 mL), and HOAc (42 mL). The third neck of the flask was stoppered and the suspension was heated to reflux with a temperature controlled heating mantle held at 125-130° C. Zn dust (24.9 g, 381 mmol) (previously ground in a mortar and pestle to break up lumps) was added portionwise over 50 minutes. Subsequent portions are added after most of the previously added portion has disappeared. After the first portions of the Zn were added, all of the 4,5-dibromofuran-2-carboxylic acid dissolves to give a pale brown solution. Twenty-five minutes after the conclusion of the zinc addition a thick grey-white slurry had formed. HPLC analysis of the reaction slurry at this time indicated complete consumption of the starting 4,5-dibromofuran-2-carboxylic acid and conversion to the desired product. After 35 minutes, heating was discontinued, and the slurry was allowed to cool to ambient temperature. After cooling to ambient temperature the reaction slurry was diluted with cold H2O (175 mL), cooled in an ice bath, and then filtered. The white and grey solids were rinsed with cold H2O, and dried on the filter for 3 hours. The product/Zn mixture was then pumped down under high vacuum with gentle heating to afford white-grey flakes. A portion of the resulting solids (37.3 g) was dissolved in warm acetone (1.8 L, solubility about 20 g/L). The resulting solution was filtered to remove residual zinc dust, and then concentrated under reduced pressure to afford 4-bromo-furan-2-carboxylic acid as a white powder. This material was carried on to the acid chloride formation without purification. 1H-NMR (400 MHz, DMSO-d6): δ 7.96 (1H, d, J=0.8 Hz), 7.04 (1H, d, J=0.8 Hz).

Provenance & Evidence