Thermochemical and Theoretical Studies of Dimethylpyridine-2,6-dicarboxylate and Pyridine-2,3-, Pyridine-2,5-, and Pyridine-2,6-dicarboxylic Acids

Abstract

The standard (p°) 0.1 MPa) molar enthalpies of formation for gaseous pyridine-2,5-dicarboxylic acid, pyridine-2,6-dicarboxylic acid, and dimethylpyridine-2,6-dicarboxylate were derived from the standard molar enthalpies of combustion, in oxygen, at T ) 298.15 K, measured by static bomb combustion calorimetry, and the standard molar enthalpies of sublimation, at 298.15 K, measured by Calvet microcalorimetry: pyridine-2,5-dicarboxylic acid, -(580.6 ( 5.0) kJ‚mol -1 ; pyridine-2,6-dicarboxylic acid, -(608.0 ( 6.1) kJ‚mol -1 ; dimethylpyridine-2,6-dicarboxylate, -(562.4 ( 4.2) kJ‚mol -1 . The enthalpy of formation for crystalline pyridine-2,3-dicarboxylic acid was also derived from combustion calorimetry measurements as -(733.1 ( 2.0) kJ‚mol -1 . In addition, theoretical calculations using the density functional theory and the B3LYP/6-311G** hybrid exchange-correlation energy functional have been performed for these molecules in order to obtain the most stable geometries and to access their relative stabilities. The good correlation obtained between experimental and theoretical results allowed the estimation of the enthalpy of sublimation for pyridine-2,3-dicarboxylic acid.

Thermodynamic Properties of Three Pyridine Carboxylic Acid Methyl Ester Isomers

“…Recently, Roux et al 35 reported an enthalpic increment of (18.0 ( 4.6) kJ‚mol -1 for the methylation of benzoic acid, which is in good agreement with the increment for the dimethylation of pyridine-2,6-dicarboxylic acid. 12 The present results point to a similar increment for the methylation of 4-pyridine carboxylic acid and to a higher increment for the methylation of 2-pyridine carboxylic acid. This should reflect the effect of the intramolecular hydrogen bond in 2-pyridine carboxylic acid described by Shahawy et al 36 on the basis of theoretical SCF-CI calculations.…”

“…In this context, systematic experimental and theoretical thermochemical studies on heterocyclic molecules derived from pyridine have been done in our Thermochemistry Laboratory for more than a decade in order to evaluate the energetic effects of different substituents on the pyridinic ring. [1][2][3][4][5][6][7][8][9][10][11][12][13][14] The main goal of the present work is to determine the gaseous enthalpies of formation of methyl picolinate (2-PyCOOCH 3 ), methyl nicotinate (3-PyCOOCH 3 ), and methyl isonicotinate (4-PyCOOCH 3 ), represented in Figure 1, together with the measurement of other relevant properties to the thermodynamic characterization of those isomers.…”

Interplay of thermochemistry and Structural Chemistry, the journal (volume 21, 2010) and the discipline

“…What are the relative stabilities of the isomeric diacetylpyridines? Is it the same order as recently found for the related pyridinedicarboxylic acids [84] wherein COOH replaces COCH 3 ?…”

Interplay of thermochemistry and Structural Chemistry, the journal (volume 19, 2008) and the discipline

“…The structure of this zinc(II) complex revealed the peculiarity of having the ethylenediamine ligand acting in a very unusual way as a bridge. The enthalpy of formation of dipicolinic acid has been recently determined as well as its 2,3-and 2,5-isomers [110].…”

“…We wonder what is the case for the isomeric pyridine-3,4-dicarboxylate chelate derivative? Comparison between the 2,3-and 3,4-diacids has surprisingly been lacking: for example, the enthalpy of formation of only the former has been measured [110].…”