1.2.4- Dioxazine ring

Without additional reagents 1,2,4-Dioxazine ring from N-alkylideneamines... 

The dioxazine ring system is the source of some valuable violet pigments, such as Cl Pigment Violet 23 (6.211). This colorant is obtained by condensing 3-amino-9 ethylcarbazole with chloranil. Sulphonation of the pigment gives the dye Cl Direct Blue 108. Triphenodioxazines have recently been the source of some blue reactive dyes [241-Examples are known of symmetrical bifunctional structures (6.212 NHRNH = alkylenediamine, Z = haloheterocyclic system) and unsymmetrical monofunctional types such as 6.213 [37]. 

Another alternative is attaching the reactive anchor to the dioxazine ring via sulfonamide or carboxamide groups instead of via amine groups, as in 33 [62], [63] ... 

Other similar fiber-reactive triphenodioxazines are prepared by replacing the sulfonic acid group in 26 with a 2-hydroxyethylsulfonyl group. The starting material here is 4-chloro-3-(2-hydroxyethylsulfonyl) nitrobenzene (35), which leads to products containing a VS group bound directly to the dioxazine ring (36) [64,66] (Scheme 3.3). 

Triisothiocyanatophosphane reacts with HFA, with complete isomerization of all ligands and formation of three dioxazine rings, in the presence of triethylamine as a catalyst 240). 

HFA has been reacted with a series of dicyanosulfanes NCS CN (n = 1 -4) under the catalytic action of triethylamine. The monosulfane produces a red oil which shows extensive decomposition during attempts of purification (176). Spectral data suggest formation of a A -l,3,5-dioxazine ring system as has been found in the reactions of the homologous dicyanoselenane [Eq. (116)] and thiocyanogen with HFA, which results in compound 140. The X-ray structure has been reported. A remarkable feature is the stability of the... 

Involvement of the catalyst has been observed in the reaction of excess HFA with dicyanoselenane. A bicyclic compound is formed with one dioxazine ring attached to selenium, the other ring being generated by complete dehydrogenation of an ethyl group (240). The X-ray structure of 141 has been reported. 

II. 7 0.2 kcal mol"1 (-33.5°C) and AG 10.2 0.2 kcal mol"1 (-64°C)340 were identified as nitrogen inversion (N-Meax -> transition state) and ring inversion, respectively, from a study of 2-methyl-6-alkyltetrahydro-1,4,2-dioxazines.341... 

Although very few detailed studies have been carried out, the acid-base properties of polyheteroatom six-membered rings are fairly predictable. The fully reduced systems behave as typical secondary amines, although the inclusion of extra heteroatoms often reduces their basicity. Thus the reduced dithiazines (68) (thialdine) and (69), and the related thiadiazine (70), are weak bases with pKz values of 2.7, 2.8 and 2.0 respectively (58JCS2893). The weak basicity is due to the inductive effect of the /3-heteroatoms. This inductive effect of /3-heteroatoms is also apparent in the dioxazine (71), which exhibits no tendency to... 

By varying the substituents on the orange parent substance 19, particularly in the positions para to the imino groups, its color can be modified. Red to red-violet shades result when X=OH or O R, and blue colors when X=NH2 or NHR. A blue shade also results if the external phenyl groups of the dioxazine system are part of an annulated and highly condensed aromatic ring system, for example, pyrene (C.I. Direct Blue 109, [33700-25-3]). 

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. 

Some bright blue direct dyes with good lightfastness are sulfonated dioxazine compounds, mostly synthesized by condensation of chloranil with amines followed by ring formation and sulfonation, e.g.,C.7. Direct Blue 106,51300 [6527-70-4] (14). 

In summary, the obvious refusal of 1,4,2-dioxazines to exist as fully unsaturated species can be explained by considering the anP -Hiickel aromaticity of an 871-electron system destabilizing the heterocyclic ring. 

There are several significant preparative procedures for dioxazines, oxathiazines and diathiazines that are based on transformation of other heterocyclic systems. Most, but not all, involve ring expansion of five- or, less frequently, four-membered systems. The synthetic methods employed in the preparation of the precursor heterocycles are not covered in this section as they are dealt with in the appropriate chapters elsewhere in this edition. 

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