The reaction of an aromatic heterocycle with a proton is called a protonation. One of articles about this theory is 《Structure and reactivity of 2-aminopyridine 1-oxide》. Authors are Katritzky, A. R..The article about the compound:2-Chloropyridine 1-oxidecas:2402-95-1,SMILESS:ClC1=CC=CC=[N+]1[O-]).HPLC of Formula: 2402-95-1. Through the article, more information about this compound (cas:2402-95-1) is conveyed.
2-Aminopyridine 1-oxide (I) was prepared Comparison of its ultraviolet spectrum with those of 2-methylimino- and 2-imino-1-methoxy-1,4-dihydropyridine (II) showed that I does not exist mainly in the tautomeric imino form. Et 2-pyridinecarbamate (III), 72 cc. AcOH, and 43 cc. 30% aqueous H2O2 kept overnight at 70°, the solid (IV) filtered off, volatile material removed from the filtrate in vacuo, the residue and IV refluxed overnight with 40 cc. concentrated HCl, volatile material removed in vacuo, 50 cc. EtOH and alc. NaOEt (from 6 g. Na in 150 cc. EtOH) added followed by small pieces of solid CO2 until the solution was no longer alk., the mixture filtered, the filtrate evaporated, and the residue crystallized from EtOH-EtOAc gave 16.1 g. I, m. 157-62°, and when further recrystallized m. 163-4°, λ0.1N HCl 231, 301 mμ (ε 8080, 5230), λ0.1N NaOH 221,310 mμ (ε 23,300, 3900), inflection 239 mμ (ε 6900), λEtOH 227,251,321 mμ (ε 25,000, 5740, 4610). 2-Chloropyridine (22.6 g.), 150 cc. AcOH, and 50 cc. 30% aqueous H2O2 heated overnight at 80°, volatile material removed in vacuo, 140 cc. CHCl3 added, the mixture digested with 17 g. K2CO3 5 min. at 65°, the precipitate filtered off, washed with 60 cc. CHCl3, and filtrate and washings evaporated gave 19.75 g. 2-chloropyridine 1-oxide (V), m. 67-8.5° (from EtOAc). V (7 g.) and 40 cc. 25% aqueous MeNH2 heated 12 hrs. at 140°, 4 g. K2CO3 added, the whole evaporated to dryness in vacuo, the residue extracted with EtOH, the extracts evaporated, and the residue crystallized from EtOAc gave 5.5 g. 2-methylaminopyridine 1-oxide (VI), needles, m. 103-5°, or prisms, m. 68-70°, giving a dark blue color with FeCl3, λ0.1N HCl 236, 314 mμ (ε 7950, 4250), λ0.1N NaOH 226, 324 mμ (ε 18,700, 3640), inflection 246 mμ (ε 5500) [picrate (VII), needles, m. 155.5-7.0° (from EtOH); picrolonate (VIII), yellow needles, m. 201-3° (from EtOH); HCl salt, needles, m. 203-4° (from EtOH)]. To 0.3 g. VI was added 0.5 cc. Ac2O, the whole left overnight at 18°, EtOH added, the mixture evaporated in vacuo, treated with CHCl3 and K2CO3, filtered, and evaporated to give 0.28 g. Ac derivative, hygroscopic prisms, m. 95-7° (from EtOAc), giving no color with FeCl3. Prepared like VI in about 80% yield, 2-dimethylaminopyridine 1-oxide, b0.25 143-5° (bath temperature), nD20 1.6117, giving no color with FeCl3, λ0.1N HCl 243, 320 mμ (ε 7370, 4470), λ0.1N NaOH 236, 319 mμ (ε 16,500, 2690), inflection 261 mμ (ε 5400) [picrate, plates, m. 142.5-4.0° (from EtOH); picrolonate, orange-yellow prisms, m. 180-1° (decomposition) (from EtOH)]. Attempted preparation of II: I (5.5 g.) heated overnight at 100° with 9.3 g. p-MeC6H4SO3Me (IX) and the product crystallized from EtOH-EtOAc gave 12.66 g. 2-amino-1-methoxypyridinium p-toluenesulfonate (X), prisms, m. 127-9°, giving no color with FeCl3. X (0.6 g.) in EtOH treated with 5.5 cc. 0.4N NaOEt, the solid filtered off, and 0.46 g. picric acid in EtOH added gave 0.40 g. 2-amino-1-methoxypyridinium (XI) picrate (XII), yellow needles, m. 169.5-71° (from EtOH), its infrared spectrum quite distinct from those of VII and 2-aminopyridinium picrate, needles, m. 222-3° (from EtOH). Similarly to XI was prepared XI picrolonate, yellow prisms, m. 245-7° (decomposition), its infrared spectrum distinct from those of VIII and 2-aminopyridinium picrolonate, yellow prisms, m. 269-71° (decomposition) (from EtOH). X (1.48 g.) in 3 cc. EtOH treated with 0.8 cc. 60% HClO4 gave 0.95 g. perchlorate, laths, m. 182-4° (from EtOH), λ0.1N HCl 230, 299 mμ (ε 7670, 5870), λ0.1N NaOH 230, 291 mμ (ε 8890, 4400). X (0.6 g.) in 3 cc. pyridine and 0.4 g. 3,5-(O2N)2C6H3COCl (XIII) kept overnight at room temperature and treated with aqueous NaOH gave 2-(3,5-dinitrobenzoylimino)-1,2-dihydro-1-methoxypyridine, pale yellow needles, m. 219-20° (from EtOH). VI (1.24 g.) and 1.86 g. IX heated 24 hrs. at 100° gave 2.33 g. 1-methoxy-2-methylaminopyridinium p-toluenesulfonate, prisms, m. 98-100° (from MeCN-EtOAc), λ0.1N NaOH 237, 297, 302 mμ (ε 9400, 3390, 3370), inflection 236 mμ (ε 9650), λ0.1N HCl 235, 314 mμ (ε 10,900, 6590). I (1 g.), 6 cc. pyridine, and 2.4 cc. BzCl kept overnight, and H2O added, gave 1.57 g. 2-benzamidopyridine 1-oxide (XIV) benzoate (XV), needles, m. 94-5° (from C6H6-petr. ether). XV (0.75 g.) treated in CHCl3, with 1 g. K2CO3, the mixture filtered, and the filtrate evaporated gave 0.47 g. XIV, m. 122-4° (from EtOH), giving a red color with FeCl3. BzCl (0.6 cc.) and 0.55 g. I in 5 cc. hot MeCN kept overnight at room temperature gave 0.43 g. 1-benzoyloxy-1,2-dihydro-2-iminopyridine (XVI), needles, m. 158-9° (from EtOH), giving no color with FeCl3. XVI recrystallized from EtOH and left in the mother liquor for 4 days gave XIV. 2-Benzamidopyridine (0.32 g.), 6 cc. AcOH, and 0.2 cc. 30% aqueous H2O2 kept overnight at 70° and worked up gave XIV. I (0.55 g.) in 10 cc. hot MeCN treated with 0.5 cc. EtO2CCl and kept 2 days gave a low yield of Et 2-pyridinecarbamate 1-oxide. I (1.1 g.), 10 cc. MeCN, and 1 cc. Ac2O kept overnight gave 0.82 g. 2-acetamidopyridine 1-oxide, rods, m. and mixed m.p. 140.5-1.0°. I (1 g.) and 3 cc. (CO2Et)2 boiled 10 min. and EtOH added to the cooled solution gave 0.2 g. N,N’-di-2-pyridyloxamide 1,1′- dioxide, which separated from AcOH as the diacetate, plates, m. and mixed m.p. 270° (deompn.) (varying with rate of heating). PhNCO (0.6 g.) and 0.55 g. I in 10 cc. hot MeCN kept 2 days at room temperature gave 0.52 g. 2-N-phenylureidopyridine 1-oxide, needles, m. and mixed m.p. 212-13° to 220-0.5° (varying with the rate of heating). XIII (1.15 g.) added to 0.55 g. I in 10 cc. hot MeCN and worked up after 30 hrs. at room temperature gave 0.98 g. 2-(3,5-dinitrobenzamido)-pyridine 1-oxide, separating from AcOH as the acetate, needles, m. 216-17°. I did not react smoothly with (EtO)2CO, o-C6H4(CO)2O, α-naphthyl thiocyanate, or CS2. III (1.66 g. and 0.9 cc. morpholine refluxed 18 hrs., cooled, and recrystallized from C6H6-petr. ether gave 1.05 g. 2-morpholinocarbonylaminopyridine, needles, m. 91-2.5°. To 1.1 g. I in 2 cc. concentrated HCl was added 4 g. ice followed by dropwise addition of 0.9 g. KNO2 in 5 cc. H2O and the mixture gradually added to 1.44 g. β-naphthol in 12 cc. 10% aqueous NaOH and 6 g. ice gave 1.15 g. 2-(2-hydroxy-1-naphthylazo)pyridine 1-oxide, crimson plates, m. 215-16° (decomposition)(from EtOH), λEtOH 225, 292, 466 mμ (ε 12,100, 5800, 5600).
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Reference:
Isoxazole – Wikipedia,
Isoxazole | C3H3NO – PubChem