Pyridine unreactivity towards nitration

The compounds which release NO3 radicals appear to be those in which the nitrate group is bonded in bidentate fashion. Thus the pyridine adduct Sn(N03)4(CsH5N)2, in which all of the nitrate groups are monodentate, is unreactive towards hydrocarbons and ether. 

An equally serious problem is that the nitrogen lone pair is basic and a reasonably good nucleophile—this is the basis for its role as a nucleophilic catalyst in acylations. The normal reagents for electrophilic substitution reactions, such as nitration, are acidic. Treatment of pyridine with the usual mixture of HN03 and H2SO4 merely protonates the nitrogen atom. Pyridine itself is not very reactive towards electrophiles the pyridinium ion is totally unreactive. 

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See also in sourсe #XX -- [ ]

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