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| Flavianic acid |
Picric acid is a common constituent of charge-transfer complexes with aromatic hydrocarbons at least as large as naphthalene. It also forms salts with amines. Unfortunately, its explosiveness is a problem working at scale.
Flavianic acid (8-hydroxy-5,7-dinitro napthalene-2-sulfonic acid) contains the same phenolic aryl nucleus with three strong electron-withdrawing substituents as in picric acid. For picric acid, there are three nitro groups. For flavianic acid, there are two nitro groups and one vinylogous sulfonic acid as substituents.
Like picric acid, flavianic acid is known to form insoluble salts with amines, but unlike picric acid flavianic acid forms these by donating a proton from the sulfonic acid moiety rather than the acidic phenol. As a consequence, the electron-poor aromatic ring remains substantially electron-deficient even after the transfer.
My hypothesis is that flavianic acid may form a preferred precipitant for organic amine compounds that also comprise an electron-rich aromatic ring because there are those two binding motifs. Simplistically thinking this could produce larger intermolecular attractions and higher melting points.
Like picric acid, flavianic acid is known to form insoluble salts with amines, but unlike picric acid flavianic acid forms these by donating a proton from the sulfonic acid moiety rather than the acidic phenol. As a consequence, the electron-poor aromatic ring remains substantially electron-deficient even after the transfer.
My hypothesis is that flavianic acid may form a preferred precipitant for organic amine compounds that also comprise an electron-rich aromatic ring because there are those two binding motifs. Simplistically thinking this could produce larger intermolecular attractions and higher melting points.
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