Charles O. Okafor

The chemistry and applications of angular phenothiazine derivatives

Abstract Since 1883 when Bernthsen, the father of phenothiazine chemistry, synthesized the first compound in this series, several hundreds of derivatives have been made, including angular phenothiazine derivatives of varying structural types. The angular azaphenothiazines have wide industrial application, typified by their use as dyes and pigments, drugs, sensitizers for photocopying materials, polymerization retardants and particularly as antioxidants in gasoline, grease and other petroleum lubricants. In this paper, we present a review of the chemistry and uses of angular phenothiazine derivatives.

STUDIES IN THE HETEROCYCLIC SERIES. XIV. THE CHEMISTRY AND BIOLOGICAL ACTIVITY OF NEW AZA- AND THIA-PHENOTHIAZINES, AND RELATED DIBENZOTHIAZEPINES

Abstract Owing to increasing demand for phenothiazine compounds both in medicine and industry, novel rings in these series have been prepared and evaluated. The benzene rings have been replaced with pyrrole, pyrazole, pyridine, pyridazine, pyrimidine, pyrazine, thiazine and triazine rings or their combinations leading to twelve new polyaza- and thia-phenothiazines. Expansion of the central thiazine ring in these systems has also been carried out. This article therefore provides a survey of the chemistry and applications of new polyaza- and thia-phenothiazine systems and their related thiazepines and thiazocines.

Synthesis, properties and uses of angular phenoxazines

Abstract Since the first and prototype of angular phenoxazines, Meldola Blue, was reported over a century ago, several hundreds of derivatives have so far been made. These include the side-chain derivatives, isomeric structural types and the aza-, thia- and oxa-analogues. Some naturally occurring angular azaphenoxazines have also been isolated from arthropods. Most of the natural compounds in these series are intensely coloured and are responsible for the coloration in the wings, cuticle and eyes of insects. In general, angular phenoxazines constitute an important class of organic compounds because of their wide range of commercial uses. These include their uses as drugs, polymerization retardants, photosensitizers, acid-base indicators, redox indicators, biological stains, metal extradants and, most importantly, as dyes and pigments for the textile, paint and varnish industries. In this article, the first comprehensive report on the chemistry and industrial applications of angular phenoxazines is presented.

The first branched benzoxazinophenothiazine ring system and its aza-analogues

Abstract The synthesis of a branched benzoxazinophenothiazine heterocycle is described. The parent compound benzo [a]]1,4]-benzoxazino [3,2-c] phenothiazine ( 12 ), was obtained from 2,3-dichloro-1,4-naphthoquinone ( 6 ), 2-aminophenol and 2-amino-thiophenol. Monoaza-, diaza- and triaza- analogues of this novel heterocycle were also synthesized. The parent compounds, 16-oxa-15-thia-4,5,10-triazabenzo [ h ] pentaphene ( 18 ) and 16-oxa-15-thia-4, 5, 10,14-tetraazabenzo [ h ] pentaphene ( 22 , R=H) were also synthesized as well as 4-amino-16-oxa-15-thia-4, 5,10,12,14-pentaazabenzo [ h ] pentaphene (24). They are intensely coloured high-melting solids suitable for application as pigments. Their ease of reduction with Na2S2O4 and the ready oxidation of the reduced compounds to the quinoid forms by atmospheric oxygen suggest their applicability also as vat dyes.

Vat dyes from three new heterocyclic ring systems

Abstract The syntheses of a new angular azaphenoxazine and of two new angular azaphenothiazine ring systems are described and the dyeing properties of their derivatives studied. Thiocyanation of 2-amino-6-picoline ( 8 ) followed by hydrolysis and condensation with 2,3-dichloro-1,4-naphthoquinone ( 11 ) gave the purple-coloured 6-chloro-10-methylbenzo[a]-11-azaphenothiazin-5-one ( 12 ) in excellent yields. Similarly, from 4,6-diaminopyrimidine ( 15 ) and 2-amino-3-pyridinol ( 22 ), the compounds, 8-amino-6-chlorobenzo[a]-9,11-diazaphenothiazin-5-one ( 18 ) and 6-chlorobenzo[a]-11-azaphenox-azin-5-one ( 23 ), were obtained as bluish-purple and orange colourants, respectively. Elemental analysis, infrared, ultraviolet, NMR and mass spectroscopy agree with the assigned tetracyclic structures. Reduction with Na 2 S 2 O 4 and the ease of air oxidation of the reduced forms to the quinoid coloured materials make them applicable as vat dyes. Fastness to washing, light, acids and bases was also investigated, and also their toxicity in laboratory animals.

A new type of angular phenothiazine ring system

Abstract The first synthesis of monoaza- and diaza-analogues of benzo[a]phenothiazine ring system is achieved under anhydrous conditions by base-catalysed reaction of o -aminoheterocyclic thiones with 2,3-dichloronaphtho-1,4-quinone. If the reactions were carried out in methanol, 2-chloro-3-methoxynaphtho-1,4-quinone was also isolated. The ease of air oxidation of the Na 2 S 2 O 4 reduced compounds makes them suitable for consideration as vat dyes.

New non-linear polycyclic azaphenothiazine dyestuffs

Abstract The synthesis of some new angular and Y-shaped azaphenothiazine ring systems from simple heterocyclic compounds is described. 3-Nitration of pyridin-4[1H]-one (7) followed by reduction and thiation with P2S5 gave 3-aminopyridine-4 [1H]-thione (10) in good yields. Reaction of product 10 with 2,3-dichloro-1,4-naphthoquinone (12) gave a red dyestuff, 6-chloro-7-thia-10,12-diazabenz [a]anthracen-5-one (13) having a new angular azaphenothiazine ring system. Two facile methods were also proposed for the synthesis of 15,16-dithia-1,5,10-triazahenzo[h]pentaphene (26) from 3-aminopyridine-2[1H]-thione (25, R= H) and 2-aminothiophenol. The purple pigment 26, R= H is the parent compound of this Y-shaped azaphenothiazine. Reduction of these dyestuffs (13 and 26) and their derivatives led to loss of colour which reappeared on exposure to atmospheric oxygen. This property makes them applicable as vat dyes. Additionally they were found to be good colorants for soap, candle, polish, paint and plastic materials.

A new synthesis of ‘three-branched’ diazaphenothiazine dyes

A new and unequivocal synthesis of a ‘three-branched’ azaphenothiazine heterocycle is described. The parent compound. 15,16-dithia-3,5,10,12-tetra azabenzo[h]pentaphene was obtained by mononitration of pyridin-4[1H] one and thiation with P2S5 to give 3-nitropyridine-4[1H]-thione. Base catalysed condensation of this compound with 2,3-dichloro-1,4 naphthoquinone gave 2,3-bis(3-nitro-4-pyridylthio)-1,4-naphthoquinone which, on reduction with tin(II) chloride and glacial acetic acid, gave the parent compound, a purple-red dye. Also reported is the synthesis of a new angular diazaphenothiazine, 9-bromo-6-chloro-8,11,12-triazabenz[a]an thracen-5-one. Their intense colorations, ease of preparation in good yields and ready reduction with Na2S2O4. and reoxidalion by atmospheric oxygen make these compounds good vat dyes. These purple-red dyes and their derivatives were also found to be good colorants for paper, plastic, paint, ink, soap, polish, rubber, candle and cosmetic products.

New phenothiazine dyes and pigments

Abstract The synthesis of three new azaphenothiazine ring systems and an evaluation of their use as intermediates for new dyes and pigments is described. 2-Amino-5-bromopyrazine-3[4H]-thione ( 11 ) was prepared and converted to the novel 1,4,6,9-tetraazaphenothiazine ring system. The reaction of 4,5-diaminopyrimidine-6[1H]-thione ( 15 ) with 2,3-dichloropyrazines gave the isomeric 1,4,6,8-tetraazaphenothiazine ring system, another new heterocycle in this series. With 2,3-dichloroquinoxaline a previously unknown tetracyclic tetraazaphenothiazine ring system was isolated in satisfactory yields. The properties and reactions of these new heterocyclic systems are presented. Mixed nitric and sulphuric acids convert them to their 5-sulphoxides. Structural assignments were based on chemical evidence and their UV, IR, NMR and mass spectra. Mechanistic pathways to these compounds are also proposed.

Novel heterocyclic intermediates for new dyes and pigments

Abstract The synthesis of two new heterocyclic ring systems of the phenoxazine type is described. These are the 1,4,9-triazaphenoxazine and 1,4,6-triazabenzo[b]phenoxazine. The preparation of the parent ring of 1,4,9-triazaphenoxazine ring system is also reported. Spectroscopic data are in agreement with the assigned structures and the mechanistic pathway to these novel heterocycles is also presented. These ring systems provide a new framework for the development of novel dyes and pigments of the phenoxazine class.