What molecule am I?
Naphthalene is an aromatic organic compound that consists of two fused benzene rings. Diazanaphthalenes have the naphthalene structure with nitrogen atoms in place of two of the CH groups. There are two structural classes of diazanaphthalenes: benzodiazines, in which both nitrogen atoms are in the same ring, and naphthyridines, with one nitrogen atom in each ring.
Six naphthyridine isomers exist, based on the positions of the nitrogen atoms; they can be in the 1,5, 1,6 (shown here), 1,7, 1,8, 2,6, or 2,7 positions. All are white solids with a surprisingly wide span of melting points: 1,6-Naphthyridine’s is the lowest at <40 ºC; 2,6-naphthyridine’s is the highest at 114–115 ºC.
Quinoline derivatives such as naphthyridines that have nitrogen atoms in the 1-position are usually synthesized via the Skraup reaction, in which an aminopyridine and a glycerol derivative are heated in the presence of an oxidizing agent (e.g., nitrobenzene) and sulfuric acid. This is often a violent, runaway reaction, so it is perhaps fortunate that the synthesis of 1,6-naphthyridine from 4-aminopyridine was not originally successful.
Refinements of the Skraup reaction, however, did eventually lead to preparations of 1,6-naphthyridine in modest yields. One modification used 4-aminopyridine-N-oxide as the starting material; the resulting 1,6-naphthyridine-N-oxide was then reduced to the free base.
1,6-Naphthyridine and some of its derivatives have been reported to have medicinal, electronic, and catalytic properties. But none of these investigations has yet resulted in any practical applications.
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