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Pure phenothiazine dyestuff cpds. prepn. from phenothiazine cpds. - by nitration with recovery of nitrite and nitrate from nitrous gas, redn., oxidn., amide formation using aq. base and reaction with amine
Pure phenothiazine dyestuff cpds. prepn. from phenothiazine cpds. - by nitration with recovery of nitrite and nitrate from nitrous gas, redn., oxidn., amide formation using aq. base and reaction with amine
Prepn. of pure phenothiazine dyestuffs (I) involves: (a) nitrating phenothiazine (derivs.) (II); (b) reducing the nitro cpd. to an amino cpd. (III); (c) oxidising (III) to a basic cpd. (IV); (d) converting (IV) to amide (V) with methane- or toluene-sulphonyl halide in the presence of an organic base in anhydrous medium; and (e) substituting (V) with amines to give (i). The novel features are that: (a1) the nitrous gases formed in (a) are converted to nitrites and/or nitrates in the presence of O2 and alkali; and (d1) amide formation is carried out in the presence of an aq. (in)organic base or a strong inorg. base. USE/ADVANTAGE - (I) are used for staining samples in medical tests, e.g. tissue sections, blood and bone samples. The process is environmentally friendly and gives (I) of the required high purity. Stage (d) is more economical and convenient than usual.
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