Heteroannelated 1,4-Naphthoquinones

A large number of quinones of the general structure 7 are known, where X corresponds to a heterocyclic residue containing one or more rings, and the chemistry of these has been reviewed extensively [6-8], If X consists of a benzenoid or aza-benzenoid ring system, then such compounds are best regarded as anthraquinone analogues. In the case of other heterocyclic residues, they may be considered as 1,4-naphthoquinone derivatives. 

The simplest members of this group are those in which X is a monocyclic residue, such as furan, thiophene, and pyrrole ring systems. Color may then be produced in the usual way by attaching auxochromes to the 5- and/or 8-positions. Few dyes of this type have been suggested for textile applications, presumably 

The brazanquinone system has also been used to provide disperse dyes by attaching auxochromes to the benzene ring of the naphthoquinone moiety. Thio- 

A different class of polycyclic naphthoquinone dyes is based on the n apht h 12,361 i ndolizine -6,11 -dione system 14, which is readily accessible by condensation of 2,3-dichloro-l,4-naphthoquinone with active methylene compounds in the presence of pyridine [22], or by reaction of 2-methoxy-3-pyridino-1,4-naphthoquinone with an active methylene compound [23], In 14, the bridgehead nitrogen atom acts as an effective auxochrome, and hence orange to red colors are observed without further substitution. Derivatives of 14 (R = amide group) are of particular value as vat dyes and pigments. Related isomeric heterocyclic structures have also attracted interest, e.g., 15, a yellow disperse dye for polyester [24], 

As with the simple 1,4-naphthoquinones, most recent research activity in the heteroannelated compounds has been directed towards the development of dyes that absorb in the near-infrared. Noteworthy is the dithiadinaphtho-1,4-naphthoquinone system 16 (X = S), which can be prepared by condensing 2,3-dichloro-5,8-dihydroxy-1,4-naphthoquinone with 2-aminothiophenol [25], The parent compound 16 (X = S) [96692-25-0] shows multiple absorption bands between 400 and 800 nm, with the most intense peak at 725 nm in chloroform (rmax 15 200 L mob1 cm-1) [25], Oxidation of the sulfur atoms to SO groups produces a large bathochromic shift, and 16 (X = SO) shows a peak at 827 nm (emax 17 600 L mol-1 cm-1) in chloroform [25], 

---