Pyridines Reactions and Synthesis

Pyridine and its simple derivatives are stable and relatively unreactive liquids, with strong penetrating odours that are unpleasant to some people. They are much used as solvents and bases, especially pyridine itself, in reactions such as N- and 0-tosylation and -acylation. Pyridine and the monomethylpyridines (picolines) are completely miscible with water. 

Pyridine was first isolated, like pyrrole, from bone pyrolysates the name is constructed from the Greek for fire, pyr , and the suffix idine, which was at the time being used for all aromatic bases - phenetidine, toluidine, etc. Pyridine and its simple alkyl derivatives were for a long time produced by isolation from coal tar, in which they occur in quantity. In recent years this source has been displaced by synthetic processes pyridine itself, for example, can be produced on a commercial scale in 60-70% yields by the gas-phase high-temperature interaction of crotonaldehyde, formaldehyde, steam, air and ammonia over a silica-alumina catalyst. Processes for the manufacture of alkylpyridines involve reaction of acetylenes and nitriles over a cobalt catalyst. 

The pyridine ring plays a key role in several biological processes, most notably in the oxidation/reduction coenzyme nicotine adenine dinucleotide (NADP) the vitamin niacin (or the corresponding acid) is required for its biosynthesis. Pyridoxine (vitamin Bg) plays a key role as the coenzyme in transaminases. Nicotine, a highly toxic alkaloid, is the major active component in tobacco, and the most addictive drug known.  

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This chapter describes in general terms the types of reactivity found in the typical six- and five-membered aromatic heterocycles. We discuss electrophilic addition (to nitrogen) and electrophilic, nucleophilic and radical substitution chemistry. This chapter also has discussion of orf/to-quinodimethanes, in the heterocyclic context. Organometallic derivatives of heterocycles, and transition metal (especially palladium)-catalysed chemistry of heterocycles, are so important that we deal with these aspects separately, in Chapter 4. Emphasis on the typical chemistry of individual heterocyclic systems is to be found in the summary chapters (7, 10, 13, 15, 19 and 23), and a more detailed examination of typical heterocyclic reactivity and many more examples for particular heterocyclic systems are to be found in the chapters - Pyridines Reactions and Synthesis , etc. 

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