Quinolines amino-, basicity

The presence of certain substituents e.g., the amino group) may markedly affect the solubibty and other properties of the sulphonic acid or carboxylic acid. Thus such sulphonic acids as the aminobenzenesul-phonic acids, pyridine- and quinoline-sulphonic acids exist in the form of inner salts or zwitter-ions that result from the interaction of the basic amino group and the acidic sulphonic acid. Sulphanilic acid, for example, is more accurately represented by formula (I) than by formula (II) ... 

In a similar way, 3-amino-1,2,4-triazino[6,5-c]quinoline 4-oxides 127 were synthesized by the reaction of 4-chloro-3-nitroquinoline 128 with guanidine, followed by the cyclization of intermediate arylguanidines under basic conditions (81JHC1537). 

This will increase the basicity of the quinoline system from about pATa 5, but almost certainly not as far as represented by pATa 10.8. However, it solves our problem, since it means the 4-amino substituent is donating its lone pair into the aromatic ring system and is not, therefore, available for bonding to a proton. This site is going to be less basic than a tertiary amine. pATa 10.8 must represent the terminal -NEt2. 

Autoxidation of indoles under basic conditions leads to the chemiluminescent ring cleavage of the heterocyclic ring (65MI30500, 65MI30501, 66CC522) which, in the case of 3-methylindole, can lead to a subsequent base-catalyzed formation of 2-(2-amino-phenyl)quinoline (77H(8)743>. 

Alkaloids are basically nitrogen bases. The amino acids act as building blocks for the biosynthesis of alkaloids. Majorities of the alkaloids contain a pyridine, quinoline, and isoquinoline or tropane nucleus and are responsible for physiological effects in man or in animal. The side chains in alkaloids are derived from terpene or acetate. Alkaloids have basic properties and are alkaline in reaction, turning red litmus paper blue. 

The most common basic group is the amino group, present either as a primary, secondary or tertiary amino grouping. Other possible basic groups are those present in heterocyclic nitrogen-containing compounds such as pyridine, quinoline and pyrrole. These bases are very weak, e.g. pyrrole has p Tb = 14. 

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