Alkalinity And Salt Formation Of Pyridine

Unshared electron pairs on pyridine nitrogen atoms accept protons and become alkaline. The conjugate acid of pyridine (pyridine after accepting a proton on the N atom) has a pKa of 5.25, which is more acidic than ammonia (pKa9.24) and fatty amines (pKa 10-11) (the smaller the pKa, the more acidic it is). The reason is that the unshared electron pair on the nitrogen atom in pyridine is in sp2 hybrid orbital, and its s orbital component is more than sp3 hybrid orbital, close to the nucleus, the electron is strongly bound by the nucleus, and the tendency to give electrons is small, so it is difficult to combine with the proton and the alkalinity is weak. However, pyridine is slightly more basic than aromatic amines (such as aniline, pKa 4.6).
Pyridine and strong acids can form stable salts, and some crystalline salts can be used in separation, identification and refining. The alkalinity of pyridine is used as a catalyst deacidifier in many chemical reactions. Due to its good solubility in water and organic solvents, the catalysis of pyridine is often inaccessible to some inorganic bases.
Pyridine can form salts not only with strong acids, but also with Lewis acids.
In addition, pyridine also has some properties of tertiary amines, and can react with halogenated hydrocarbons to form quaternary ammonium salts, and can also react with acyl halides to form salts.