The reaction of an aromatic heterocycle with a proton is called a protonation. One of articles about this theory is 《The reaction with nitrous acid of certain derivatives of 4-aminopyridines, substituted in position 2 or 2 and 6. V. 4-Aminopicolinic acid and its amide and 2-cyano-4-aminopyridine》. Authors are Talik, Tadeusz; Plazek, Edwin.The article about the compound:4-Hydroxypicolinic acidcas:22468-26-4,SMILESS:O=C(O)C1=NC=CC(O)=C1).Reference of 4-Hydroxypicolinic acid. Through the article, more information about this compound (cas:22468-26-4) is conveyed.
cf. CA 53, 18954d. 4-Aminopyridine (I) derivatives with a CO2H, CONH2, or CN group in position 2 do not form stable diazonium compounds The 2-cyano derivative (II) of I, m. 145°, yield 92%, was prepared by heating 90 min. on steam bath 5 g. 4-aminopicolinic acid (III) amide (IV), m. 169°, 5 g. P2O5, 30 ml. POCl3, and 10 ml. PCl3, and crystallizing from water after addition of (NH4)2CO3. IV (63%) was prepared by reduction of 4-nitro-2-cyanopyridine N-oxide (V), m. 181°, with FeSO4 and aqueous NH3 solution V (62%) was obtained by boiling the resp. 2-iodo derivative with CuCN in pyridine. III m. 319° (decomposition) [260° as given by Graf (CA 31, 22149]. By action of HNO2 or gaseous N oxides on III, IV, or II in H2SO4 there was formed 4-hydroxypicolinic acid, m. 159°; amide m. 253°. An aqueous IV or II solution saturated with HCl reacted with NaNO2 to give 4-chloropicolinamide, m. 161°, 79% and 46%, resp.
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