In addition to what has been posted already, these were found:
Carbon-13 and oxygen-18 isotope effects in the decarboxylation of nicotinic acid of natural isotopic composition.
Zielinski, M.; Zielinska, A.; Papiernik-Zielinska, H.; McKenzie, J. A.; Bernasconi, S.; Paul, H. Isotope Laboratory (Laboratory Nuclear Chemistry), Faculty Chemistry, Jagiellonian University, Krakow, Pol.
Journal of Radioanalytical and Nuclear Chemistry (1998), 230(1-2), 71-74.
Abstract
13C and 18O isotope effects in the decarboxylation of nicotinic acid (I) of natural isotopic compn. above and below its melting temp. were studied and compared with the primary (PKIE) and secondary kinetic isotope effects (SKIE) of 13C and 18O, resp., in the decarboxylation of other heterocyclic acids. The temp. dependence of the 18O SKIE is neg. in the total 221-255° temp. interval investigated initially. The 13C KIE measured above the m.p. of I (235-270°) are located in the range 1.007-1.009. Below the m.p. of I, the 13C KIE are larger and reveal the neg. temp. dependence (13C KIE decreases with the reaction temp. from 1.013 at 230° to 1.0114 at 221°). A discussion of the above isotopic results is presented.
Effect of alkali additions on decarboxylation of nicotinic and isocinchomeronic acids in an aqueous medium.
Suvorov, B. V.; Serazetdinova, V. A.; Lebedeva, O. B. Inst. Khim. Nauk, Alma-Ata, USSR.
Izvestiya Akademii Nauk Kazakhskoi SSR, Seriya Khimicheskaya (1985), (3), 53-7.
Abstract
The decarboxylation of the title acids at 200-300° was retarded by NH3 and esp. by KOH.
And this one is quite close, it could have some other references or information.
Decarboxylation of some 2-substituted pyridinecarboxylic acids.
Moser, Russell J.; Brown, Ellis V. Dep. Chem., Univ. Kentucky, Lexington, Ky., USA.
J. Org. Chem. (1972), 37(24), 3941-2.
Abstract
The rates of decarboxylation of 2-chloro- and 2-nitro-x-pyridinecarboxylic acids (x = 3,4,5) and 2-bromo-, 2-amino-, and 2-acetamido-3-pyridinecarboxylic acids as well as 3-pyridinecarboxylic acid were studied in 3-nitrotoluene. Only 3-pyridinecarboxylic acids with electron withdrawing groups at the 2-position decarboxylated below 227°. It is possible to decarboxylate 3-pyridinecarboxylic acids, at lower temps., by placing an electron withdrawing group ortho to the carboxyl group.