" Into a 3 L round bottomed flask compound (XIX)
from step-III (40 g) and dimethyl formamide (200 ml) were
charged. Potassium carbonate (96.9 g) and isobutyl bromide
(48.3 g) were added and the reaction mass was heated to
80-85° C. Reaction mass was maintained at the same tem
perature for five hours and brought to room temperature.
Water (2 L) was charged to reaction mass and stirred for one
hour. Reaction mass was filtered and washed with water
(2x500 ml). The wet compound was dissolved in Ethyl
acetate (1000 ml) and ethyl acetate layer was washed with
water (400 mlx3). Ethyl acetate layer was dried over sodium
sulphate and distilled off completely under vacuum. Metha
nol (240ml) was added to the residue and heated to 50–55°C.
and maintained at the same temperature for 15 minutes. Reac
tion mass was brought to room temperature and maintained
for one hour. The compound (XX) was filtered and dried at
50-60° C. "
Here, de reaction is a nucleophilic sustitution from a phenol to an Br-bencene (one step to the formation of febuxostat). DMF is hardazous, that is the reason that makes me wonder it...