93795-06-3Relevant academic research and scientific papers
Phenylazo-Substituted Triphenylmethylium Systems
Hellwinkel, Dieter,Fritsch, Helmut
, p. 2207 - 2226 (2007/10/02)
Triphenylmethanols (or their ethers) bearing phenylazo groups react with trifluoroacetic acid to give deeply colored solutions of the tritylium ions 7(+) - 9(+), (RC6H4N=NC6H4)nC(+)(C6H5)3-n (R = H, Me, Cl, NO2, MeO, H2N, Me2N), whose long wavelengths VIS absorptions and lowfield 1H-NMR signals are consistent with the existence of through-conjugated ?-electron systems.After addition of trifluoromethanesulfonic acid significant hypsochromic shifts of the VIS bands as well as additional proton deshieldings in the 1H-NMR spectrum are observed, which are in accordance with the formation of proximally azo-protonated phenylazotritylium ions 7(+)*H(+), 8(+)*2H(+), and 9(+)*3H(+), (RC6H4N=N(+)H-C6H4)nC(+)(C6H5)3-n.Fully analogous acid-strength-dependent ionisation/protonation reactions result for the overall p-substituted ions 17(+), 18(+), (RC6H4N=NC6H4)C(+)(C6H4R')2 (R,R' = Me, MeO, Me2N), as well as for the azobistritylium system 10(2+), (C6H5)2C(+)C6H4N=NC6H4C(+)(C6H5)2, and its azoxy derivative 11(2+).The linearly extended bis- and trisazo systems 19(+), 22(+), MeC6H4N=N(C6H4N=N)1,2C6H4C(+)(C6H5)2 and the (phenylazo)styryl system 20(+), MeC6H4N=NC6H4CH=CHC6H4C(+)(C6H5)2 in trifluoroacetic acid do not show any significant color changes relativ to the corresponding monofunctional parent types.In trifluoromethanesulfonic acid, however, compounds 19(+), 22(+) exhibit the usual bathochromic shifts of the longest wavelenght VIS absorption accompanying the increasing protonation of the polyazo system.In the case of the tritylium ions containing azomethine bridges, 24(+), only for the methoxy derivative 24b(+) indications for the existence of the conjugatively extended tritylium system (MeOC6H4N=CHC6H4)C(+)(C6H5)2 are found.The amide derivatives 26(+)-29(+), on the other hand, presents no clues for the existence of through-conjugated systems of the kind ArC(OH)=NC6H4C(+)Ar2 and ArN=C(OH)C6H4C(+)Ar2, respectively.
