Pyridine, C6H5N, resembles benzene in many points:
1. It is even more stable than benzene, and yields substituted derivatives with sulphuric and nitric acids or the halogens, but not so readily as
benzene. Sulphonic acids are obtained at very high temperatures only, and only a few chloro- and bromo-pyridines have been prepared. Pyridine and its
carboxylic acids are not affected by oxidizing agents.
2. Its derivatives resemble those of benzene. Thus its homologues (and also quinoline, &c.) are transformed into pyridine carboxylic acids when
oxidised, and these acids yield pyridine when distilled with lime, just as benzoic acid yields benzene.
3. The isomeric relations are also precisely analogous to those of the benzene derivatives. Thus the number of the isomeric mono-derivatives of
pyridine is the same as that of the isomeric bi-derivatives of benzene, viz. three; and the number of the bi-derivatives of pyridine, containing the
same substituents, the same as that of the benzene derivatives, C6H3X3, viz. six.
4. Just as two benzene nuclei can form naphthalene, so can a benzene and a pyridine form the compound quinoline.
5. The products of reduction are likewise analogous. Pyridine like benzene yields a hexahydro derivative, C5H11N, only somewhat more readily; this is
known as piperidine. Quinoline yields a tetrahydro-derivative, C12H11N, which is analogous to anthracene dihydride. In these latter compounds further
combination with hydrogen my take place, but there is likewise a tendency to the reproduction of the original bases.
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