Infrared spectra in the frequency region 1300-1760cm-' are reported for 41 substituted sodium benzoates and 10 substituted sodium salicylates in deuterium oxide solution, and for 9 substituted salicylic acids in chloroforn~ and carbon tetrachloride solutions. Carboxylate stretching frequencies of benzoates and salicylates correlate poorly with substituent constants, but the asymmetric frequencies of benzoates and salicylates correlate well with each other, and the asymmetric frequencies of benzoates correlate well with the asymmetric frequencies of the corresponding nitrobenzenes. It is suggested that, among substituted aromatic compounds, group vibrations which couple with the ring vibrations may correlate well with similar vibrations of other groups, but not with coupled vibrations of different symmetry, uncoupled vibrations, or substituent constants. Chelation in chloroform solutions of salicylic acid dimers can be detected by its influence on substituent effects, but infrared spectra provide no good evidence for chelation in aqueous sodium salicylates.

The decarboxylation of pyrrole-2-carboxylic acid in aqueous buffers at 50" and ionic strength 1.0 has been found to be first order with respect to substrate at a fixed pH. As the p H is decreased, the rate constant increases slightly in the p H range 3-1, then rises rapidly from p H 1 to 10 M HCI. The '3C-carboxyl kinetic isotope effect is 2.8% in 4 M HCIO, and negligible at p H -3. These observations can be accounted for by a mechanism, previously proposed for the decarboxylation of anthranilic acid, in which the species undergoing decarboxylation is the carboxylate ion protonated at the 2-position of the pyrrole ring. This intermediate can be formed both by ring-protonation of the carboxylate anion and by ionization of the ring-protonated acid. At low acidities ring-protonation is rate determining, but at higher acidities the rate of protonation exceeds that of decarboxylation.I1 a t t t trouve, qu'a p H donnt dans des solutions tampons aqueuses a 50 "C et une force ionique de 1.0, la dtcarboxylation de I'acide pyrrole-2 carboxylique est du premier ordre en substrat. Quand le p H est diminut, la constante de vitesse augmente ltgerement entre p H 3 et 1 puis augmente rapidement du p H 1 a HCI 10 M . L'effet isotopique cinttique du carboxyle est de 2.8 % dans HCIO, 4 M e t ntgligeable a p H -3. I1 est possible de rationaliser ces observations a I'aide d'un mecanisme, propose prtctdemment pour la decarboxylation de l'acide anthranilique, dans lequel l'espece qui subit la dtcarboxylation est I'ion carboxylate protone a la position 2 du noyau du pyrrole. Cet intermediaire peut Ctre form6 soit par la protonation du noyau portant I'anion carboxylate soit par ionisation de l'acide proton6 sur le noyau. A basses aciditts, la protonation du cycle est I'etape determinante mais a des aciditts plus Clevees la vitesse de protonation est plus grande que la decarboxylation.

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