Sodium Hydroxide → 5-Hydroxybenzo[b]thiophene-3-carboxylic acid

Participants

Reaction Conditions

Reaction Steps

The methoxybenzo[b]thiophene carboxylic acid from Step 5 was slurried in toluene (35 L) and then warmed to 50° C. To an addition funnel containing toluene (9 L) was added boron tribromide (4.3 kg) and then the solution added over 1 hr to the slurry of 5-methoxy-3-benzo[b]thiophenecarboxylic acid. The mixture was aged for 8 hr. The reaction mixture was cooled to room temperature and 15%NaOH was slowly added (16 kg). To the three phase mixture was added 2 kg Solka Flok (filter aid) and then filtered to remove boric acid. The layers were then cut. To the aqueous layer was added 27 L THF and 4.5 kg NaCl, and then acidified to pH=1-3 with concentrated HCl (2.7 L). The layers were cut and the bottom layer extracted again with 15 L THF. The combined THF layers were then concentrated to a minimum stirred volume and solvent switched into toluene (kf<1000 ug/ml). The slurry was then cooled to 2-5° C., aged one hour and filtered, washing with cold toluene (10 L). The cake was dried on the filter pot with a nitrogen sweep under vacuum.

Provenance & Evidence