Dioxazine synthesis

Dioxazine synthesis involves two distinct stages dianil formation and dianil cycliza-tion. 

Inositols, ie, hexaliydrobenzenehexols, are sugars that have received increasing study and are useful in the treatment of a wide variety of human disorders, including vascular disease, cancer, cirrhosis of the Hver, frostbite, and muscular dystrophy (269). Myoinositol esters prepared by reaction with lower fatty acid anhydrides are useful as Hver medicines and nonionic surfactants the aluminum and ammonium salts of inositol hexasulfate are useful anticancer agents (270). Tetraarjloxybenzoquinones are intermediates in the preparation of dioxazine dyes (266,271). The synthesis of hexakis(aryloxy)benzenes has also beenpubUshed (272). 

Benzil, 3 594 14 594 Benzilonium bromide, 4 359t Benzimidazoles, microwave-assisted synthesis of, 16 574-575 Benzimidazolethiols, 25 197 Benzimidazolone dioxazine, 19 446 Benzimidazolone pigments, 19 432 433 Benzimidazolone Violet, pigment for plastics, 7 367t Benzine, 3 597... 

Pigment Violet 23 may serve as an example to illustrate the synthesis of dioxazine pigments in general. The technique has not changed much since it was first developed [4],... 

Derived from tribenzodioxazine (79), coloured compounds of this type have been known since 1928 and have been used as reddish-blue direct dyes for cotton. An important violet, Carbazole Dioxazine Violet (80), was prepared by condensation of 3-amino-A-ethylcar-bazole with chloranil followed by cyclization of the intermediate diimine and pigmentary conditioning (56GEP946560). A second useful synthesis involves condensation of an o-alkoxyarylamine with chloranil followed by cyclization (65C242). 

Because of the symmetrical nature of the chloranil condensation product 7, all the syntheses described so far afford exclusively symmetrical triphenodioxazines i.e., the two phenyl rings fused onto the dioxazine skeleton bear the same substituents. An elegant synthesis for an asymmetric chloranil condensation product has not yet been developed. 

Acylnitroso compounds are best recognized for their ability to participate as dependable 2ir components of Diels-Alder reactions with dienes, and these observations have found substantial application in the total synthesis of natural products (Chapter 3).81 However, Mackay and coworkers have detailed the isolation of 5,6-dihydro-1,4,2-dioxazine 9a (10%) from the reaction of acylnitroso 7a with cyclopentadiene [Eq. (39)]. ... 

Synthesis by Cycloaddition. Earlier reports have shown that acylnitroso-com-pounds add efficiently to dienes. Now a full paper describes the oxidation of hydroxamic acids to give acylnitroso-compounds which can act both as dienophiles or as hetero-dienes with respect to cyclopentadiene. Heating the bridged oxazine adducts causes partial rearrangement to dioxazines (Scheme 1). 

PCBs and PCDDs. In Diarylide Yellow manufacture, the use of formate buffer to enhance pigment transparency for offset ink was discontinued in the nineteen seventies, when it was realized that polychlorinated biphenyls were being produced as an undesirable by-product of the coupling reaction. In Phthalocyanine Blue crude synthesis, the commonly used solvent, trichlorobenzene, was also discontinued in the US, as a potential source of poly-chlorinated biphenyls. More recently, use of chloranil, manufactured from chlorinated phenols, has been discontinued in the synthesis of dioxazine violet crude and sulfonated dioxazine acid dyes, so as to minimize by-product formation of polychlorinated dibenzodioxins and dibenzofurans (PCDDs/PCDFs). A new grade ofhigh purity chloranil is now produced from hydroquinone for dye and pigment manufacture. 

The universally applicable dioxazine pigment, especially Pigment Violet 23, which is distinguished by good color strength, is commercially important. It is produced by the reaction of 3-amino-N-ethylcarbazole and chloranil in o-dichloro-benzene at temperatures between 130 and 150 °C followed by oxidative ring closure to the dioxazine in the presence of benzenesulfonyl chloride. The 3-amino-N-ethylcarbazole required for the synthesis is produced from carbazole by N-alkyla-tion, e.g. with diethyl sulfate or ethyl chloride, and nitration followed by the reduction to the amine. 

Arylsulfonyl chlorides are typically employed as the cyclization agents in the oxidative route to dioxazines. In the manufacture of Pigment Violet 23 crude the most commonly employed agents are benzene- or p-toluene-sulfonyl chloride. Some literature articles describing the synthesis of dioxazines refer to the sulfonyl chlorides... 

Preparation of the benzimidazolone-dioxazine pigments usually involves a multi-step synthesis followed by finishing. A typical reaction scheme depicting the synthesis of the unsubstituted derivative, but which can be generalized for all other substituents, is shown in Figure 20-15. 

Figure 20-15 Typical synthesis of benzimidazolone-dioxazine pigments.

The synthesis of key intennediate 360 bearing unnsnal fragment of 5,6-dihydro-1,4,2-dioxazin was developed by Bayer in 2002. Synthesis started from... 

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