The reaction of an aromatic heterocycle with a proton is called a protonation. One of articles about this theory is 《5-Chloro- and 5,6-dichloronicotinic acids》. Authors are Graf, Roderich; Lederer-Ponzer, Ernst; Kopetz, Viktor; Purkert, Renato; Laszlo, Paul.The article about the compound:5-Hydroxynicotinic acidcas:27828-71-3,SMILESS:O=C(O)C1=CN=CC(O)=C1).Recommanded Product: 5-Hydroxynicotinic acid. Through the article, more information about this compound (cas:27828-71-3) is conveyed.
Nicotinic acid HCl salt (100 g.) and 180 g. SOCl2, gently boiled 5 days and then heated in tubes 12 hrs. at 180°, give 50-60% of a mixture of the 5-Cl and 5,6-di-Cl derivatives (I), in about equal amounts; more SOCl2 increases the proportion of the di-Cl acid. 5-Aminopyridine-3-carboxylic acid (II), m. 288-90° (decomposition). II through the diazo reaction gives the 5-Br derivative, m. 182-3°; chloride, m. 74-5°; Me ester, m. 98-9°; Ph ester, m. 86-7°. The chloride and N2H4.H2O in C6H6 give sym-bis(5-bromo-3-pyridoyl)hydrazine, m. 308° (decomposition). The Me ester gives 5-bromopyridine-3-carbonyl hydrazide, m. 193-4° (benzal derivative, m. 191-3°); the azide m. 88-9° (decomposition) and with absolute EtOH gives 5-bromo-3-carbethoxyaminopyridine, m. 150-1°; Me ester, m. 169-70°; heating the Et ester with 30% NaOH gives 5-bromo-3-aminopyridine (III), b12 149-50°, m. 66-7°; the intermediate Na 5-bromo-3-pyridylcarbamate was also analyzed; Ac derivative of III, m. 127-8° (dihydrate, m. 76-8°); picrate of III, deep yellow, m. 212-3°; chloroaurate, red-orange, m. 185-7°. 5-Iodopyridine-3-carboxylic acid, m. 220°; Ph ester, m. 100-1° Me ester, m. 121°; Et ester, m. 86-7°; amide, m. 221-2°. 5-Hydroxypyridine-3-carboxylic acid, m. 299° (decomposition). The Et ester of I and N2H4.H2O give Et 5-chloro-6-hydrazinopyridine-3-carboxylate (IV), m. 137-8°; the hydrazide, gray, m. 238-40°; the free acid m. 248-9° and was also obtained directly from I. IV on diazotizing yields Et 5-chlorobenzotetrazole-3-carboxylate, m. 95-6°; the free acid m. 195-6°; heating with HCO2H gives 5-chlorobenzotriazole-3-carboxylic acid, m. above 300°. I and concentrated NH4OH at 180-90° give 6-amino-5-chloropyridine-3-carboxylic acid, m. 323° (decomposition); Me ester, m. 163-5°; the Me ester of the 6-HO derivative m. 218°.
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Reference:
Chapter 1 An introduction to palladium catalysis,
Palladium/carbon catalyst regeneration and mechanical application method