The Decarboxylation of Anthranilic Acid

Abstract

Anthranilic acid is known to decarboxylate on being heated above its melting point, v r on being boiled in water. We have found that the aqueous decomposition can be acid catalyzed, but that, after the concentration of added mineral acid approximates that of the anthranilic acid, the reaction rate decreases with increasing mineral acid concentration. A mass specirometer study of the carbon dioxide produced in the decomposition has shown that C12-carboxyl anthranilic acid decomposes a t the same rate as C13-carboxyl anthranilic acid. Thus, unlilie all other organic acid decarbox~lations in which an "isotope effect" has been searched for thus far, the decarboxylation of anthranilic acid cloes not show an "isotope effect". From the experimental facts available, it appears that the mechanism of the decarboxylatioli is best explained as billlolecular electrophilic substitution, with the attack of a proton being the rate determining step. While other possibilities are not entirely excluded, a proton attack on t h e a carbon of the zwitterion is the detailed mechanism suggested as being most probable.

Effect of changing pH upon the kinetic 13C-isotope effect in the decarboxylation of 4-methoxyanthranilic acid

“…[4] are of the same form with respect described (3), except that the carbon dioxide produccd to [Hfl; as [H'] illcreases, the first fraction in the reaction was swept from the reaction vessel by a increases (or decreases) inoilotonically froin strcam of nitrogen gas and collecled in a liquid nitrogen kAK2 to kHAK,, and the second increases (or trap. It was then transferred to a high-vacuum line, decreases) froln lcg~l(lc~ -; k-,) to k+/(k+ sublimed 10 times from liquid nitrogen, and its volume, temperature, and pressure were measured.…”

Rates of Decarboxylation of Substituted Anthranilic Acids in Nitrobenzene Solution

“…Previous investigations of anthranilic acid decarboxylation have shown that the reaction is first order in boiling aqueous solution but catalyzed by mineral acids (1,2). The aqueous-acid-catalyzed reactioil xvas coilsidered to involve attack by a proton fro111 the mineral acid on carbon 1 of the aromatic ring ( 2 ) and therefore to belong to the class of SE2 aromatic displacenle~lt reactions (3).…”

“…In the melt the reaction has been reported to be first order (2,4) but this is not very i~lfornlative since the con~position of the reaction mixture changes during the decarbosylation fro111 pure anthranilic acid to pure aniline. Since aniline could serve as proton donor it might take over the role of a second ~nolecule of anthranilic acid in an inter~nolecular reaction.…”

“…The rate is increased by electron-releasing substituents and decreased by deuterium in the functional groups. The relative rates are interpreted b y means of the Hainnlett equation and its extensions and it is concluded that the rate-determining step involves attack b y proton froin one anthranilic acid ~nolecule 011 carbon 1 of a second n~olecule.Previous investigations of anthranilic acid decarboxylation have shown that the reaction is first order in boiling aqueous solution but catalyzed by mineral acids (1,2). The aqueous-acid-catalyzed reactioil xvas coilsidered to involve attack by a proton fro111 the mineral acid on carbon 1 of the aromatic ring ( 2 ) and therefore to belong to the class of SE2 aromatic displacenle~lt reactions (3).…”

“…The aqueous-acid-catalyzed reactioil xvas coilsidered to involve attack by a proton fro111 the mineral acid on carbon 1 of the aromatic ring ( 2 ) and therefore to belong to the class of SE2 aromatic displacenle~lt reactions (3). Decarboxylatioil in the melt, however, must involve shift of a protoil to the ring from one of the functional groups of ailthranilic acid itself.…”