Quaternary Nitrogen Heterocycles. VII. Reactions of some Tricyclic Heteroaromatic Cations in Basic Solutions

Abstract

Pseudobase formation and methoxide ion addition have been investigated spectroscopically for some N-methylacridinium, -phenanthridinium, and -benzoquinolinium cations. Susceptibility to nucleophilic attack decreases in the order 10-methylacridinium (pKnorr = 9.86) > 5-methylphenanthridinium (pKnoa = 11.94) > 1-methyl-5,6-benzoquinolinium = 1-methyl-7,8-benzoquinolinium (~Knorr > 14). A qualitative correlation of pKnorr with loss of resonance energy upon pseudobase formation is shown to exist. For the 9,lO-dimethylacridinium cation, the C-9 pseudobase (or methoxide adduct) is the kinetically preferred product in basic solutions but this is subsequently converted to the thermodynamically more stable anhydrobase. With the corresponding 9-ethyl-and 9-benzyl-10-methylacridinium cations, the pseudobase, rather than the anhydrobase, seems to predominate at equilibrium.On a examine B l'aide de la spectroscopie la formation de pseudobases et l'addition d'ion mtthylate pour quelques cations tels N-m&thylacridinium, phtnanthridinium et benzoquinoltinium. La susceptibilitt de I'attaque nucltophile diminue dans l'ordre mtthyl-10 acridinium (pKnorr = 9.86) > methyl-5 phtnanthridinium ( p K n o~ = 11.94) > mtthyl-1 benzoquinoltinium-5,6 z mtthyl-1 benzoquinoltinium-7,8 (pKno11 > 14).On a montrt qu'une relation existe entre le p K n o~ et la perte d'tnergie de rkonnance lors de la formation de pseudobases. En solution basique, la pseudobase C-9 (ou I'addition de mtthylate sur) du cation dimtthyl-9,10 acridinium est obtenue par contrble cinttique, mais elle est transformte en anhydrobase thermodynamiquement plus stable.Parcontre la pseudobase plutbt que l'anhydrobase semble &tre majoritaire B l'equilibre pour les cations tthyl-9 et benzyl-9 mtthyl-10 acridiniums.[ Although Hantzsch and Kalb (1) first recognized the formation of the pseudobase (2; R = H) by hydroxide ion addition to the 10-methylacridinium cation (1; R = H) in 1899, it was not both this cation and the 10-methyl-9-phenylacridinium cation (1; R = C,H,).Magrath and Phillips (5) have also reported equilibrium constants for pseudobase formation from the 5-methylphenanthridinium (3; R = H; pKRoH = 10.4) and 5,6-dimethylphenanthridinium (3; R = CH,; pKRoH = 10.1) cations which suggest that the N-methylphenanthridinium cation is only slightly less susceptible t o pseudobase formation than its acridinium isomer. pendence of the equilibrium constant for pseudoWe have now extended these studies t o a series base formation upon the structure of the hetero-of 9-substituted-10-methvlacridinium cations and cyclic cation andwe later measured (4) the rates some other tricyclic caiions that are isomeric of pseudobase formation and decomposition for with 1 (R = H). Owing to thegeneral insolubility of the pseudobases in aqueous solution at p.m.r.

Luminescent lanthanide sensors for pH, pO2 and selected anions

“…The pseudo-base adduct does not absorb at the chosen excitation wavelength and the observed emission intensity was zero above pH 13.5. An effective dissociation constant of 16 mM (9 2), equivalent to pK OH = 12.2 [34] is in good agreement with related literature values for ground-state ions, [46]. Thus the red europium emission is independent of pH over the range 2-9 but falls in intensity by a factor of \ 200 as the pH rises to over 13.…”

“…It has been established that N-methylphenanthridinium ions are attacked at C-6 by the hydroxide ion, in a reversible reaction [46] that leads to the disappearance of the longest wavelength absorption band as the conjugation length is reduced, ( 10). With [Eu 16a] + , addition of KOH over the pH range 10-13.5, led to a decrease in the europium emission intensity (u exc 380 nm, u em 594 nm) as reversible C O bond formation occurred.…”

Photophysical Property of Sanguinarine in the Excited Singlet State

“…It can be mentioned here that the C, position of sanguinarine iminium ion (structure I) is such a high electrophilic centre that even a very poor nucleophilic solvent can make an addition to that position. Similar studies have been reported by several workers (Bunting and Meathrel, 1974;Kano et al, 1986Kano et al, , 1987Zhou et al, 1988) who have found that the electrophilicity of 10-methylacridinium and 10methyl-9-phenylacridinium cations is so strong that nucleophiles such as hydroxide and alkoxide anions attack the carbon atom at the 9 position of the acridinium ring to give the corresponding pseudo bases. Reversibility of sanguinarine from structure 11,111 and IV to structure I also has been confirmed by spectrophotometric (Figs.…”

10-Methylacridinium ion as a fluorimetric probe measuring the activity of halide anions in aqueous solutions of cationic surfactants

“…Bunting and Meathrel [8] report the same value for λ max and a value of log ε = 4.28. Fluorescence of the MA + cation is strongly quenched by I − , Br − , and SCN − ions.…”