On the analysis of calorimetric data in the study of dimerization of carboxylic acids in nonpolar solvents

Abstract

PAWEL G~R A L S K Iand STEFANIA TANIEWSKA-OSINSKA. Can. J . Chem. 61. 2209Chem. 61. (1983.The calorimetric dilution method was analyzed for the accuracy with which thc equilibrium constant (K,,) and clirnerization enthalpy (AH,,) can be detcrrnined. The calculations wcrc carried out using the ideal monomer-dimer model. It was found that the error in determining the functions dcscribing dimerization increases strongly with rising K,, values but is independent of AH,, values. Doubt is expressed whether dimerization and trimerization can be studied simultaneously by the calorimetric method. A suggestion is made to use spectroscopy and calorimetry jointly rather than separately to determine Kc, and AH,, values rapidly and conveniently, producing. in many cases, more accurate results. On a Cvalui la prCcision de la mCthode de dilution calorimCtrique dans la determination de la constante d'tquilibre (K,') et dc I'enthalpie de dimCrisation (AH,,). On a effectuC les calculs en utilisant un [nodele monomkre-dimere idCal. En dCterminant les fonctions qui dCcrivent la dimirisation on trouvd que I'erreur augnlente cle faqon mArquCe lorsque la valcur de K, , augmente mais elle ne dkpend pas de AH,,. On doute que I'on puisse Ctudicr simultandmcnt la dimkrisation et la trimirisation par la nlithode calorimCtrique. On propose d'utiliscr la spectroscopic conjointenlent avec la calorinlitrie et non sCparCment pour dCterminer rapidcrnent de faqon convcnablc Ics valeurs de K,, et de AHd. On obtient dans plusieurs cas des rCsultats plus prCcis.[Traduit par le journal]

Density Functional Theory Study of the Oligomerization of Carboxylic Acids

“…For all carboxylic acids we found that the formation of trimers according to reaction 3CA → (CA) 3 is thermodynamically spontaneous in chloroform and carbon tetrachloride. The stability of (CA) 3 species in solution support experimental data of acetic acid -carbon tetrachloride 50 and benzoic acid -benzene benzoic 52 In conclusion, this work proposes the application of a computational approach for the determination of the structure and stability in solution of molecular clusters. We conducted all calculations using an accurate, but computationally demanding, hybrid density functional method (M06-2X).…”

“…The energetics of trimerization reaction in Table 5 as trimers were required to account for osmometric data. 52 We have verified the stability of benzoic acid trimers in benzene by computing the energetics of the benzoic acid -benzene system, and the resulting Boltzmann average free energy of trimerization reaction 3(BA) → (BA) 3 is negative (-1.94 kcal mol -1 ). On the other hand, recent density functional theory…”

“…ide 50 and benzoic acid−benzene 52 systems, which suggested that trimers are present in appreciable concentrations in apolar aprotic solvents.…”

Hydrogen bonding. Part 1.—Equilibrium constants and enthalpies of complexation for monomeric carboxylic acids with N-methylpyrrolidinone in 1,1,1-trichloroethane

“…(2) A number of methods has been used to obtain values for eqn (2), and there have been a few investigations in which calorimetric methods have been used to obtain AH:, given a known value of 1yd. 19 Since a calorimetric method is nearly always needed to obtain AH:, we found it convenient to use the same method to obtain both K: and AH: and we now outline the procedure. We suppose, first of all, that only monomers and dimers are present.…”

“…spectroscopy, monitoring the absorption band of the base in a titration-type experiment. If only the equilibria eqn (1) (A = RO) and eqn (19) (A = RO) are considered, then again KY is larger than K:g, with qs/q z 0.5 on the molar scale. Thus if the complexation of dimeric species takes place via eqn (19), the dimeric alcohols are slightly weaker than the monomeric alcohols, whereas the dimeric carboxylic acids are much weaker than the monomeric carboxylic acids.…”