N-heterocyclic pigments

Non-Polymeric N-Heterocyclic Pigments (Other than Tetrapyrroles... 

NON-POLYMERIC N-HETEROCYCLIC PIGMENTS (OTHERTHAN TETRAPYRROLES AND BETALAINS)... 

Several non-polymeric N-heterocyclic pigments other than betalains will be briefly presented in this chapter, even if they do not belong to a unique class of chemical compounds. 

Figure 2.5.2 illustrates the chemical structures of some N-heterocyclic non-polymeric pigments. 

Betalains are N-heterocyclic water-soluble pigments deposited in vacuoles. Their common precursor is betalamic acid consisting of a 1,7-diazaheptamethin system, an extended Jt-electron system exhibiting a canary yellow color. Betalamic acid may condense with cyc/o-dopa to yield betanidin, the common precursor aglycon of the red betacyanins. Betanidin in turn may be glycosylated and/or acylated, yielding 29... 

In the second pathway, dehydration of 3-deoxyhexosones leads to hydroxymethyl furaldehydes. The reactions which follow the formation of these intermediates are complex and result finally in the formation of dark brown nitrogen-containing pigments and also N-heterocyclic compounds such as pyrazines and pyrroles, which appear to be mainly responsible for the roasted, bready and nutty flavours of heated foods. 

Honda, T. and Saito, N., Recent progress in the chemistry of polyacylated anthocyanins as flower color pigments. Heterocycles, 56, 633, 2002. 

The fifth volume of Advances in Heterocyclic Chemistry surveys the chemistry of four well-defined groups of compounds pyrrolizidines (N. K. Kochetkov and A. M. Likhosherstov), aromatic quinolizines (B. S. Thyagarajan), 1,2,4-thiadiazoles (F. Kurzer), and the amino-chrome pigments (R. A. Heacock). 

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],... 

Isochromans result from the intramolecular C-H insertion reactions of contributing singlet and triplet states of 2-(alkoxymethyl)phenylcarbenes (94TL1699). The cyclisation of both the 2-ally 1 and the 2-prop-T-enyl substituted 3-(l-hydroxyethyl)naphthalene derivatives (9), (10) leads stereoselectively to the trans-n htho[2,3-c]pyrans (11), the heterocyclic moiety of some aphid pigments (94JCS(P1)859). The alkylation of 2-acetylnaphtho-... 

Two other amide-type solvents are the cyclic five-member heterocyclic 2-pyrrolidone and N-methyl 2-pymolidone. As shown in the solvent-resin solubility profile in Table 10.8 these two solvents dissolve a wide variety of resins. Both 2-pyiTolidone and N-methyl 2-pyirolidone are used as coalescent aids in floor polish formulations [11]. N-methyl 2-pyirolidone is an important component in many paint stripper formulations as well as a solvent for the removal of polymeric residues from reactor vessels. The solvent is used as a reaction medium for high molecular weight polymers, a synthetic fiber spinning medium, and as an aid in pigment dispersions. In the petrochemical industry N-methyl... 

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