18 августа, 2015 
Malyar  |
Sulfonated triphenylmethane leuco dye 73 is prepared42 by sulfonating the leuco dye 74 with 20-30% of the theoretical amount of 20 — 65% oleum at 30 — 50°C. The dye, derived from leuco base 73 by oxidation, is used in the
production of black-and-white photographic film. Crystal Violet reacts with tributyl phosphite in chloroform to give Crystal Violet dibutyl phosphon — ate101 75 which is claimed to have improved light stability.
The leuco forms of Basic Fuchsin, Crystal Violet, and Malachite Green are prepared by reduction of the corresponding dyes using Na2S/H2SO4 at pH 8.2-9.6. Acid Fuchsine, Brilliant Green, and Malachite Green have been reduced by using H2S gas bubbled in ammonium hydroxide solution.102
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The reaction of 2,4,6-trihalophenols with tropylium perchlorates in the presence of triethylamine gives phenolate dye (Scheme 10) followed by acetylation to give dye 76 from which the leuco compounds 77 can be prepared103 by catalytic reduction using Pd-C/H2.
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(76) (77)
Scheme 10
4#-3,1-Benzothiazine derivatives 78 are synthesized according to Scheme 11. This process is carried out by reacting an o-amino-a, otdisub — stituted benzyl alcohol 80 to yield a thioisocyanate followed by ring closure
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Scheme 11
of the resulting o-thiourido-a, a-disubstituted benzyl alcohol 79 by means of hydrogen bromide or hydrogen chloride. Alternatively, they can also be prepared by the oxidation of thioamide derivatives of triarylmethanes 81 using manganese dioxide or lead dioxide. 104 Dyes prepared from these leuco compounds are resistant to light.
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