Critical Evaluation of Thermodynamic Properties for Halobenzoic Acids Through Consistency Analyses for Results from Experiment and Computational Chemistry

Abstract

Thermodynamic properties of the twelve monohalobenzoic acids are critically evaluated through the application of computational chemistry methods for the ideal-gas phase and thermodynamic consistency assessment of properties determined experimentally and reported in the literature, including enthalpies of combustion, enthalpies of sublimation, and enthalpies of fusion. The compounds of interest are the 2-, 3-, and 4-halo isomers of fluoro-, chloro-, bromo-, and iodobenzoic acids. Computations were validated by comparison with critically evaluated entropies and heat capacities in the ideal-gas state for benzoic acid, benzene, and some halobenzenes. Experimental enthalpies of formation for 2-and 3-bromobenzoic acids, measured by well-established research groups, are mutually inconsistent and further, are shown to be inconsistent with the computations and assessment in this work. Origins of the discrepancies are unknown, and recommended values for these compounds are based on computations and enthalpies of sublimation validated, in part, by a structure-property (i.e., group-additivity) analysis. Lesser, but significant, inconsistencies between experimental and computed results are demonstrated also for 3-and 4-iodobenzoic acids. The comparison of enthalpies of formation based on the experiment and computation for the ideal-gas state of 1-and 2-chloro-, bromo-, and iodonaphthalenes provides additional support for the findings for halobenzoic acids and also reveals some anomalous results in the experimental literature for chloronaphthalenes. Computations are discussed in detail to demonstrate the approach required to obtain optimal results with modern quantum chemical methods.

Thermochemistry of Substituted Benzamides and Substituted Benzoic Acids: Like Tree, Like Fruit?

“…This work complements our previous studies of the thermodynamic properties of amides and benzoic acid derivatives . We have performed experimental and computational studies of the substituted benzamides presented in Figure .…”

“…(12)]: The high level of the correlation coefficients of Equations (11)(12)(13)(14) can be considered as evidence of very good consistency of the experimental data involved in the structureproperty correlations. Moreover,t hesee quations allow for the prediction of the D f H m (g, 298.15 K) values of R-benzamides with the help of reliable enthalpies of the formationo ft he appropriate R-benzoic acids or R-benzenes, which are usually availablei nt he literature.T oa ssess the performance of Equations (11)(12)(13)(14), we have calculated the enthalpies of formation of F-, Cl-, Br-, and I-substituted benzamides.R esults of calculations startingw ith benzoic acid derivatives as well as with the R-substituted benzenes are given in Ta ble S11( in the Supporting Information). As can be seen from this table, the D f H m (g, 298.15 K) values derived by the totally differentm ethods are in agreement at the level of 2-3 kJ mol À1 ,which is quite comparable with the experimentalu ncertainties of benzene derivatives involved in the structure-property analysis.…”

“…Such good agreement obtainedi nt his work proves the general trends in the gas-phase energetics in the chemicalf amilies of R-substituted benzamides, R-substitutedb enzoica cids, and halobenzenes. By using these trends, the D f H m (g, 298.15 K) values of metaand para-substituted benzamides with different substituents R can be reliably estimated by using Equations (11,12,14). Moreover,t he gas-phase enthalpies of formation of 2-R-benzamides can be reasonably assessedb yE quation (13)…”

“…It is clear that the R-substituted benzamides studied in this work are ap arentt ot he familyo fR -substitutedb enzoic acids (see Figure 3) and both families are expected to exhibit comparable regularities in their thermochemical properties:t he vaporization enthalpies and the gas-phase enthalpies of formation. As am atter of fact, thesethermochemical properties for substituted benzoic acids have been evaluated just recently [5][6][7][8][9][10][11] and they have been shown to be highly internally consistent. First, we correlated the enthalpies of vaporization of pairs of similarly shaped molecules, for example, 4-nitrobenzamide and 4-nitrobenzoic acid.…”

“…This work complements our previouss tudies of the thermodynamic properties of amides and benzoic acid derivatives. [5][6][7][8][9][10][11][12][13] We have performed experimental and computational studies of the substituted benzamides presented in Figure 2. To perform structure-property analysis, the availablet hermochemical data for similarly structured benzamides and benzoica cidd erivatives substituted with various substituents in the ortho-, meta-, and para-positions on the benzene ring.…”