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

15 March 1974

journal article
Published by Canadian Science Publishing in Canadian Journal of Chemistry

Vol. 52 (6) , 981-987
https://doi.org/10.1139/v74-157

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 (pK_ROH = 9.86) > 5-methylphenanthridinium (pK_ROH = 11.94) > 1-methyl-5,6-benzoquinolinium ≈ 1-methyl-7,8-benzoquinolinium (pK_ROH &([a-z]+); 14). A qualitative correlation of pK_ROH with loss of resonance energy upon pseudobase formation is shown to exist. For the 9,10-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.

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