Acid-base interactions of diazaporphyrins in proton-donor media

Acid-base interaction of 3,7,13,17-tetramethyl-2,8,12,18-tetrabutyl-5,15-di azaporphyn and its copper complex (H(2)DAP and CuDAP) in CH2Cl2-CF3COOH, CF 3COOH-H2SO4, and CH3COOH-urea-H2SO4 proton-donor media was studied by spect rophotometric titration. The dissociation constants of the resulting acid f orms were determined; it was found that the pK(i) concentration values obta ined in CH2Cl2-CF3COOH coincided with the pK(ai) thermodynamic constants de termined by the Hammer equation for acetic acid media. In CH2Cl2-CF3COOH, b oth meso nitrogen atoms of CuDAP were involved in complete acid-base intera ction, which resulted in the formation of ionic associates of the protonate d CuDAPH(+) (pK(a1) = +3.32) and CuDAPH(2)(2+) (pK(a2) = +0.58) forms. H(2) DAP first formed an ionic associate of the H(2)DAPH(+) form monoprotonated at the meso nitrogen atom (pK(a1) = +3.1.5). Further, this associate transf ormed into the H(4)DAP(2+) symmetrical dication with protonated endocyclic nitrogen atoms (pK(a2) = +2.19). Complete acid-base interaction with the me so nitrogen atoms in the H(4)DAP(2+) dication was only possible in a medium more acidic than 100% CF3COOH; sequential formation of the H(4)DAPH(3+) tr ication (pK(a3) = -4.45) and H(4)DAPH(2)(4+) tetracation (pK(a4) = -8.10) w as observed in a CF3COOH-H2SO4 binary solvent. The electronic absorption sp ectra of the acid forms of diazaporphyrins are discussed.