1723-27-9

201004-08-2

1723-27-9

Lithium hydroxide monohydrate (17.8 kg, 662.4 mol, 1.47 eq.) with deionized water (440.0 kg) was added to a 2000 L autoclave under a nitrogen atmosphere and stirred until completely dissolved. Subsequently, ethyl thieno[3,2-b]thiophene-2-carboxylate (95.5 kg, 449.8 mol, 1.0 eq.) was pumped into the reaction mixture at room temperature and tetrahydrofuran (379.5 kg) was added. The reaction mixture was heated to reflux (about 100°C) and maintained for 3 hours. Upon completion of the reaction, it was cooled to 35-40°C and the tetrahydrofuran was removed by rotary evaporation under reduced pressure under nitrogen atmosphere. Deionized water (200 kg) was added to the reaction vessel and the temperature was controlled to be below 20°C. The reaction mixture was filtered and the filter cake was washed three times with cold water (20 kg) and the residual liquid was removed by centrifugation to give the final thieno[3,2-b]thiophene-2-carboxylic acid (146 kg, 100% yield).