The reaction of an aromatic heterocycle with a proton is called a protonation. One of articles about this theory is 《Nitration of isoquinoline 2-oxide》. Authors are Ochiai, Eiji; Ikehara, Morio.The article about the compound:Isoquinolin-5-amine hydrochloridecas:152814-23-8,SMILESS:NC1=CC=CC2=C1C=CN=C2.[H]Cl).Electric Literature of C9H9ClN2. Through the article, more information about this compound (cas:152814-23-8) is conveyed.
Isoquinoline 2-oxide (I) (5 g.) in 20 g. concentrated H2SO4 and 5 g. KNO3, heated 3 hrs. at 60°, the mixture poured into ice water, made alk. with Na2CO3, and the product recrystallized from Me2CO give 4.5 g. 5-nitroisoquinoline 2-oxide (II), yellow needles, m. 220°. Chromatographic separation of the mother liquor in C6H6 gives 0.1 g. C9H6O3N2 (III), m. 179-80°. III (0.1 g.) in 10 ml. CHCl3 heated 10 min. at 50° with 1 ml. PCl3, let stand 3 hrs., the product poured into ice water, and the mixture made alk. with Na2CO3 and extracted with CHCl3 gives 0.1 g. C9H6O2N2 (IV), needles, m. 70°; catalytic reduction of 70 mg. IV in 10 ml. alc. with Pd-C (1 ml. 1% PdCl2 and 0.2 g. C) gives 70 mg. sirupy product (IVA), which, diazotized in 2 ml. 15% HCl at 0-2° with 20 mg. NaNO2 in 0.5 ml. water, and the solution poured into Cu2Cl2 (0.2 g. CuCl2, 1 ml. water, 0.5 ml. concentrated HCl, and 0.1 g. Zn), made alk. with Na2CO3, and extracted with Et2O, gives 8-chloroisoquinoline (V), needles, m. 55°; picrate, m. 190°. Catalytic reduction of 0.5 g. II in 40 ml. alc. with 0.2 g. Pd-C (60%), 10 ml. 10% HCl, and H gives 0.3 g. 5-aminoisoquinoline (VI), needles, m. 124-5°; picrate, m. 226-8°; VI.HCl, m. 270° (decomposition); VI acetate, m. 145-6°. The mother liquor from VI in C6H6 passed through Al2O3 gives a small amount of 5-amino-1,2,3,4-tetrahydroisoquinoline (VII), prisms, m. 150-1°; HCl salt, m. 308-9°, picrate, m. 205-6° (decomposition). VII (50 mg.) in 1 ml. Ac2O and a small amount of AcONa heated 2 hrs. at 100°, the Ac2O removed in vacuo, and the residue made alk. with Na2CO3 and extracted with Et2O gives 40 mg. 5-acetamido-2-acetyl-1,2,3,4-tetrahydroisoquinoline, needles, m. 155-6° (from C6H6). Catalytic reduction of 0.5 g. II in 40 ml. alc. with 0.2 g. Pd-C (60%) and H 70 min. gives 0.4 g. VI and 0.1 g. 5-aminoisoquinoline 2-oxide (VIII), needles, m. 225°. VIII (0.1 g.) in 10 ml. CHCl3 and 1 ml. PCl3 refluxed 30 min. on a water bath, and the mixture cooled, made alk. with Na2CO3, and extracted with CHCl3 gives 70 mg. VI. VI (0.2 g.) in 5 ml. 20% NaHSO3 heated 6 hrs. at 150° in a sealed tube, the product made alk. with NaOH, extracted with C6H6, the aqueous layer acidified with HCl, evaporated to dryness, the residue taken up with a small amount of water, the solution saturated with Na2CO3, and the precipitate recrystallized from alc. gives 0.1 g. 5-hydroxyisoquinoline, prisms, m. 230° (decomposition).
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Reference:
1,8-Naphthyridine – Wikipedia,
1,8-Naphthyridine | C8H6N2 – PubChem