Yield:334708-05-3 83%

Reaction Conditions:

with sulfuric acid at 50 - 140; for 13 h;

Steps:

4.a (a)

(a) 2-Hydroxy-5-sulfonicotinic acid 2-Hydroxynicotinic acid (27 Kg, 194.2 mol) was added portionwise to 30% oleum (58.1 Kg) at 50° C. over 1 hr.. This caused an exotherm to 82° C. The reaction mixture was heated further to 140° C. After maintaining this temperature for 12 hrs the reactor contents were cooled to 15° C. and filtered.. The filter cake was then re-slurried with acetone (33 Kg) at room temperature, filtered and dried to afford the title compound (35.3 Kg, 83%) as a white solid..

References:

US6350751,2002,B1 Location in patent:Page column 12