In organic chemistry, atoms other than carbon and hydrogen are generally referred to as heteroatoms. The most common heteroatoms are nitrogen, oxygen and sulfur. Now I present to you an article called X-ray contrast agents. II. Synthesis of iodine compounds of α-picoline, published in 1954, which mentions a compound: 22468-26-4, mainly applied to , Quality Control of 4-Hydroxypicolinic acid.
Two new x-ray contrast agents, 3,5-diiodo-4-hydroxy-α-picoline (I) and 2-methyl-3,5-diiodo-4-pyridone-1-acetic acid (II) were prepared from α-picoline. 4-Chloro-α-picoline (2.6 g.), 3 g. AcONa, and 15 ml. AcOH heated 8 hrs. at 200°, the solvent evaporated in vacuo, the residue heated 1 hr. with 10% HCl, the mixture evaporated to dryness, taken up in EtOH, mixed with 5 ml. saturated aqueous NaHCO3, again evaporated, and dissolved in benzene gave 1.7 g. 4-hydroxy-α-picoline (III), m.p. indefinite; picrate, m. 199-200° (from MeOH). III (0.5 g.) dissolved in 20 ml. hot H2O containing 3 ml. concentrated HCl, treated with 1.8 g. ClI in 10% HCl, heated 0.5 hr. on water bath, the mixture diluted with 100 ml. hot H2O, acid added, the mixture cooled, the precipitate dissolved in NaOH solution and precipitated with dilute HCl gave 1.6 g. I, decomposing 239-41°. I (1 g.) in 10 ml. 10% NaOH refluxed 3 hrs. with 0.3 g. CH2ClCO2H in 4 ml. 10% Na2CO3, cooled, filtered, and the filtrate neutralized with 10% HCl gave 1 g. II, decomposing 230-2° (from dilute pyridine). III (1.5 g.) in 5 ml. 10% NaOH treated portionwise with 4.4 g. KMnO4 in 200 ml. of H2O at 80° with stirring, stirring and heating continued, the MnO2 filtered off, the filtrate neutralized with HCl and AcOH, evaporated, and cooled gave 4-pyridone-2-carboxylic acid (IV), decomposing 249-57° (from EtOH-benzene). 3,5-Diiodo-4-pyridone-2-carboxylic acid, decomposing 250-5°, was prepared from IV by the procedure of Dohrn and Diedrich (C.A. 26, 3506) and in a smaller yield by oxidizing I with KMnO4. 2,5-Diiodo-2-carboxy-4-pyridone-1-acetic acid, decomposing 223-4°, and 3,5-diiodo-1-methyl-4-pyridone-2-carboxylic acid, m. 159°, were prepared from the appropriate intermediates by the method of D. and D. (loc. cit.).
Different reactions of this compound(4-Hydroxypicolinic acid)Quality Control of 4-Hydroxypicolinic acid require different conditions, so the reaction conditions are very important.