Acylated Oxazine Leuco Dyes

Benzoyl leuco Basic Blue 3 (2) is a typical cyan leuco oxazine used in carbonless copy paper. To satisfy the requirements of new applications such as electrolytic recording and Color Dry Silver, new oxazine leucos have been 

The reductive acetylation of Brilliant Cresyl Blue (29) yields 1,9-dimethyl-4-acetamido-8-diethylaminoimidazophenoxazine (30) which gives a purple image in electrolytic recording.12 Other similar oxazine leucos (31-34) have also been developed for electrolytic recording.13 The leucos 33 and 34 produce blue violet images. 

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As in the case of thiazine and oxazine leuco dyes described earlier, the reductive acylation of the phenazine dye 52 results in the acylation of the exocyclic amino group.18 The phenazine leuco obtained 53 retains the exocyclic amide group on oxidation resulting in the acylated phenazine dye 54, the color of which is different from the one intended. 

Phenazine leucos are generally more reactive and more susceptible to air oxidation than the thiazines and oxazines. Incorporation of electron-withdrawing groups on the acyl substituent at the 10-position of the leuco dye can provide a substantial improvement in the thermal and light stability of the leuco form and it is found that in general the stronger the electron-withdrawing character of the acyl substituents the more stable the leuco is.18... 

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