DETERMINATION OF MOLAR ABSORPTIVITIES OF RADICALS OF 18 PHENOTHIAZINE-DERIVATIVES

A new colorimetric method is described for the quantification of 18 different phenothiazine derivatives. The phenothiazine derivatives changed immediately to various different colored radicals following their oxidation with 2,3-dichloro-5,6-dicyano-p-benzoquinone in 47% or 66% perchloric acid solution. The radicals produced were very stable. The extent of color fading after 1 h was less than 2% for all 18 radicals, and that after 24 h was less than 2% for 16 radicals. The absorption maxima of the 18 radicals in the visible region showed a linear concentration dependence in the range 0.5-10-mu-g/ml phenothiazine. The molar absorptivities of these radicals were determined in the ultraviolet and visible regions. With the exception of two derivatives studied, these radicals exhibited one prominent peak in the wavelength range 280-300 nm having a molar absorptivity approximately 40 000 while the other peak occurred between 500-640 nm having a molar absorptivity approximately 10 000. These 18 phenothiazine derivatives were classified into seven groups according to the wavelength of the absorption maximum in the visible region.