Indanthrene Brilliant Orange

Naphthalenetetracarboxylic acid and its anhydride react, similar to phthalic anhydride, with o-diamines to form intensely color bis-imidazoles. These compounds, in contrast to the corresponding derivatives of phthalic anhydride, have the properties of vat dyes. When o-phenylenedianiinc is used, a mixture of the two isomers, I ids) and II (trans), is formed. This mixture is known in the trade as indanthrene scarlet 2G. The trans isomer (II), isolated from the mixture, is known as indanthrene brilliant orange GR. 

The color of the dye indanthrene brilliant orange is evident from its name. In what wavelength range would you expect to find the maximum in the absorption spectrum of this molecule Refer to the color spectrum in Figure 4.3. 

Indanthrene Brilliant Orange can be synthesized by heating naphthalene-1,4,5,8-tetracarboxylic acid with 2 moles of o-phenylenediamine. The product is a scarlet mixture (which itself is useful as a vat dye) of Indanthrene Brilliant Orange and an isomer called Indenthrene Bordeaux (red-purple). Formulate a reasonable mechanism for the formation of Indanthrene Brilliant Orange from the reaction of the tetracarboxylic acid and the diamine with attention to the possible formation of isomeric products. 

Solution From the structure of Indanthrene Brilliant Orange, we can see how it can be synthesized from naphthalene-1, 4, 5-8- tetracarboxylic acid and o-phenylenediamine ... 

Cl vat orange 7 Indanthrene brilliant orange GR Vat brilliant orange... 

---