~1H and ~(13)C NMR detection of the carbocations or zwitterions from rhodamine B base, a fluoran-based black color former, trityl benzoate, and methoxy-substituted trityl chlorides in the presence of alkali metal or alkaline earth metal perchlorates

摘要

The cleavage of C-O bonds in two fluoran-based dyes by the addition of alkali metal (M~+ = Li~+, Na~+) and alkaline earth metal (M~(2+) = Mg~(2+), Ba~(2+)) perchlorates in acetonitrile solution was examined by means of UV-visible absorption and ~1H and ~(13)C NMR spectroscopy at room temperature. Although the ~1H NMR signals of the xanthene part of Rhodamine B base (3',6'-bis(diethylamino)fluoran) were shifted toward lower fields, those of the isobenzofuran (of the benzoate) part were not shifted much upon the addition of M~+ and M~(2+). The appearance of ~(13)C signals at 163.6 and 162.4 ppm (vs TSM) in the presence of Li~_ and Ba~(2+), respectively, confirmed the formation of the zwitterions from Rhodamine B base. The assignments of the ~1H and ~(13)C signals were performed by the HMBC method. The colored zwitterion of a practical black color former, 2'-anilino-6-dibutylamino-3'-methylspiro[3H-isobenzofuran-1,9'-(9H)xanthene]-3-one, was produced by the addition of M~+ and M~(2+). The ~(13)C NMR signals at 162.2 and 159.8 ppm in the presence of 2.0 mol dm~(-3) Mg(ClO_4)_2 and Ba(ClO_4)_2, respectively, gave conclusive evidence of the formation of the sp~2-hybrid carbon center for the black color former. The interaction between the metal ions and the zwitterions from the fluoran-based dyes decreased as Mg~(2+) > Bs~(2+) < Li~+ > Na~+. The 1:1 complex formation constants with the metal ions for both dyes were evaluated based on the UV-visible absorption data. The smaller formation constants of the black color former, compared with those of Rhodamine B base, indicate some more difficulty in the cleavage of the gamma-lactone ring, which is probably based on the asymmetric structure of the compound, i.e., only a single dibutylamono-group at the 3'-and 6'-positions. The evidence for the formation of both the trityl cation and the benzoate ion was obtained by the ~1 H NMR signals from trityl benzoate in the presence of Mg(ClO_4)_2 in CD_3CN containing a small amount of CF_3SO_3D. The C-Cl bond cleavage of 4-methoxy, 4,4'-dimethoxy, and 4,4',4"-trimethoxytrityl chlorides, through the chemical interaction between Ba~(2+) and Cl~- in acetonitrile soluition, was justified by our ~(13)C NMR results.