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Sodium hydroxide, 10.05 kg of 50% solution (125.6 mole) in 30 kg of ice was treated with bubbling chlorine gas while stirring until 2.22 kg (31.3 mole) of chlorine was taken into the solution. To the resulting basic sodium hypochlorite solution was added 4.26 kg (30 mole) of 2-hydroxynicotinic acid. External cooling with tap-water was used to keep the temperature between 20°-35° C. Stirring was continued over the weekend (72 hr) after which time 13CNMR analysis showed that about 70% of the 2-hydroxynicotinic acid was chlorinated. Another solution of basic sodium hypochlorite solution was prepared by the above procedure by absorbing 1.05 kg (14.8 mole) of chlorine gas in a mixture of 3.0 kg of 50% solution (37.5 mole) of sodium hydroxide and 8.3 kg of ice. This hypochlorite solution was added to the main reaction mixture and stirring was continued for about 12 hr, after which time 13CNMR indicated no 2-hydroxynicotinic acid remained. A solution of 104 g (1.0 mole) of sodium bisulfite in 300 ml of water was added to destroy the remaining sodium hypochlorite. The reaction mixture was added gradually to 9.9 liters (119 mole) of concentrated hydrochloric acid containing 2 liters of isopropyl alcohol (to control foam), keeping temperature between 13°-23° C. The mixture was cooled and the precipitate was collected by filtration, washing with a small amount of water followed by 2 liters of acetone. The precipitate was dried to give 4.44 kg (85%) of the title compound, m.p. starts at 245° C. and decomposes at 250° C. Analysis of the 1HNMR chart showed that approximately 4% of the product was 3,5-dichloro-2-hydroxypyridine. This was done by 1HNMR (DMSO-d6 ppm), integrating the area under the curves to determine relative amounts under the appropriate signals which are for 2-hydroxy-5-chloronicotinic acid: 8.25 (multiplet) and for 3,5-dichloro-2-hydroxypyridine: 7.90 to 7.60 (quartet).

1. custombetween 20°-35° C
2. customwas continued over the weekend (72 hr)
3. stirringstirring
4. customto destroy the remaining sodium hypochlorite
5. custombetween 13°-23° C
6. temperatureThe mixture was cooled
7. filtrationthe precipitate was collected by filtration
8. washwashing with a small amount of water
9. customThe precipitate was dried