The reaction of an aromatic heterocycle with a proton is called a protonation. One of articles about this theory is 《The chlorination of methyl derivatives of pyridine. Part I. 2-Methylpyridine》. Authors are Sell, William James.The article about the compound:3,4,5-Trichloropyridinecas:33216-52-3,SMILESS:C1=NC=C(C(=C1Cl)Cl)Cl).Recommanded Product: 3,4,5-Trichloropyridine. Through the article, more information about this compound (cas:33216-52-3) is conveyed.
Based on the basic character of trichloropyridine, chlorine atoms may occupy the positions 3, 4, 5, and thus, experimental verification of this assumption was carried out. The substance 3:4:5-trichloro-2-aminopyridine was used for comparison. This compound should be obtained from the trichloropicolinic acid by converting it into its amide, and the latter by the Hoffmann reaction into the 3:4:5-trichloro-2-aminopyridine. Chlorine had no reactions the ordinary temperature, even in the presence of chlorine carriers as iodine or ferric chloride. However, when temperature of the hydrochloride was increased to 100°, fumes of hydrochloride were formed. As the chlorination proceeded, a heavy layer was formed in the liquid, which increased in quantity until the upper layer disappeared and no increase in weight occurred. At > 130°, a good deal of trichloropicolinic acid was decomposed into trichloropyridine, which remained in solution in sulfuric acid. Samples of the double salts with mercuric chloride from the different sources showed identical melting points and general characteristics. Traces of crystalline product was observed during the steam-distillation, and when recrystallized from an alcohol, it formed a mass of fine needles melting at 160°-161°.
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Reference:
Bromide – Wikipedia,
bromide – Wiktionary