The reaction of an aromatic heterocycle with a proton is called a protonation. One of articles about this theory is 《The synthesis of 1,6-naphthyridine》. Authors are Ferrier, B. M.; Campbell, Neil.The article about the compound:3-Pyridinepropionic acidcas:3724-19-4,SMILESS:OC(=O)CCC1=CC=CN=C1).COA of Formula: C8H9NO2. Through the article, more information about this compound (cas:3724-19-4) is conveyed.
Reduction of 4.5 g. 3-pyridylacrylic acid (I) in 100 ml. water with 0.5 g. PtO2 by shaking in H 30 min., filtering, resuspending the insoluble portion in water and repeating the process until all insoluble I had disappeared, gave, on vacuum distillation of the combined water solutions, 2.92 g. 3-pyridylpropionic acid (II), cubes, m. 161-2° (EtOH). Under similar conditions reduction of I in one step until no more H was absorbed gave 3-piperidylpropionic acid, isolated as its hydrochloride (1.1 g.) from EtOH, prisms, m. 225°. II (1 g.) was heated 3 hrs. with 5 ml. 100-volume H2O2 and 25 ml. HOAc, the volume reduced to 10 ml. in vacuo, 25 ml. water added, and the process repeated until 0.8 g. 3-pyridylpropionic acid N-oxide (III) separated, prisms m. 144-53° (EtOH). III (0.5 g.), 10 ml. fuming HNO3, and 10 ml. H2SO4 were boiled 1 hr., poured on 50 ml. ice, the solution brought to pH 5 with NH4OH, and 0.36 g. 4-nitro-3-pyridylpropionic acid 1-oxide (IV), yellow plates, m. 169-71° (EtOH), extracted with EtOAc. IV (0.2 g.), 0.5 g. reduced Fe powder, and 6 ml. HOAc were heated 0.5 hr., poured into water, filtered, and the filtrate made alk. with NH4OH and extracted with EtOAc to give 0.05 g. 1,2,3,4-tetrahydro-2-oxo-1,6-naphthyridine, needles, m. 208° (C6H6). III (0.3 g.) in 5 ml. HCl was treated with 0.75 g. Zn dust until colorless, boiled with 0.25 g. more Zn for 2 min., made alk. with NH4OH, and the 1,2,3,4-tetrahydro-1,6-naphthyridine (V) which separated sublimed in vacuo and recrystallized to give 0.05 g. needles, m. 208°; picrate, orange-yellow prisms m. 175° (EtOH). Heating 0.03 g. V 2 hrs. at 220-30° with 0.025 g. 13.5% Pt/C gave, on EtOH extraction, an oil. The picrate of this oil (m. 211°) was dissolved in concentrated NH4OH, extracted with petr. ether, cooled, and after decanting an oil which separated, chilled in ice to give 3 mg. 1,6-naphthyridine, needles, m. 29-30°. 3-Ethylpyridine (3 g.) was oxidized and nitrated (as II above) to give 1.4 g. 3-ethyl-4-nitropyridine 1-oxide, yellow needles m. 63-4° (petr. ether), of which 0.38 g. was reduced (H, PtO2 in HOAc or Zn-HCl) to 4 mg. 4-amino-3-ethylpyridine, needles m. 42-3° (petr. ether); picrate m. 202-3°. Ultraviolet spectra were reported for the naphthyridines and compared with those of the corresponding pyridine derivatives
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Reference:
Imidazole – Wikipedia,
Imidazole | C3H4N2 – PubChem