scholarly journals Thermodynamic properties of L-menthol in crystalline and gaseous states

Author(s):  
A. V. Blokhin ◽  
Ya. N. Yurkshtovich

Objectives. Menthol causes a cooling sensation and reduces the nerve activity when it is applied locally, ingested, or inhaled. This feature explains its extensive use as both an aromatizer and a flavoring agent in food manufacturing, tobacco industry, cosmetics production, as well as a mild anesthetic and antiseptic in dentistry. This work aimed to perform a comprehensive thermodynamic study of L-menthol in both crystalline and gaseous states.Methods. To determine the combustion energy of L-menthol in the crystalline state, combustion bomb calorimetry was used. The temperature dependence of L-menthol’s heat capacity in the range of 5–370 K and the melting (fusion) parameters were determined using adiabatic calorimetry. Quantum chemical calculations were performed on a standalone virtual machine in the Google Cloud Platform using an eight-core Intel Xeon Scalable Processor (Skylake) with a 2.0 GHz (up to 2.7 GHz at peak load) clock frequency and 8 GB RAM.Results. The energy and enthalpy of L-menthol combustion in the crystalline state were determined, and the standard enthalpy of L-menthol formation in the gaseous state was calculated using the standard enthalpy of sublimation. The standard thermodynamic functions (reduced enthalpy, entropy, and reduced Gibbs energy) of L-menthol in both crystalline and liquid states were obtained based on the smoothed values of heat capacity and melting parameters. The group of isodesmic reactions for the ab initio calculation of the enthalpy of formation for gaseous L-menthol was substantiated. Electronic energy and frequencies of normal modes of the molecules involved in these reactions were calculated using the Gaussian 4 composite quantum chemical method. Further, the sublimation enthalpy of L-menthol was calculated using the extended Politzer equation according to the electrostatic potential model.Conclusions. The first comprehensive thermodynamic study of L-menthol in various states of aggregation was performed, and the values calculated using semiempirical methods were consistent with the experimental values within error limits, which confirms the reliability of the results.

1971 ◽  
Vol 49 (24) ◽  
pp. 4096-4109 ◽  
Author(s):  
Saul Goldman ◽  
G. C. B. Cave

Values of ΔG0, ΔH0, and ΔS0 at 25 °C were obtained by distribution studies and by calorimetry, for the dimerization and trimerization of tetra-n-butylammonium picrate (1) in anhydrous benzene, chlorobenzene, and o-dichlorobenzene. The standard enthalpy of sublimation of 1 was calculated. The values of ΔG0 for the ionization, dimerization, and trimerization of 1 were linear functions of the reciprocal of the dielectric constant of the solvent. The intercepts and slopes of these graphs are interpreted; partial desolvation of the ions, and of the monomers on association is invoked. A simple potential function is used with the data, in order to deduce suitable models of the dimer and the trimer of 1.


2017 ◽  
Vol 55 (8) ◽  
pp. 1683-1697 ◽  
Author(s):  
G. V. Belov ◽  
N. M. Aristova ◽  
I. V. Morozov ◽  
M. A. Sineva
Keyword(s):  

2008 ◽  
Vol 62 (6) ◽  
Author(s):  
Xinliang Yu ◽  
Bing Yi ◽  
Wenhao Yu ◽  
Xueye Wang

AbstractIn this study, the DFT/B3LYP level of theory with the 6-31G (d) basis set was used to calculate a set of quantum chemical descriptors for structure units of vinyl polymers. These descriptors were used to predict the molar heat capacity of “liquid” at constant pressure (C P1(298 K)) and the molar Lorentz and Lorenz polarization (P LL). Two more physically meaningful quantitative structure-property relationship (QSPR) models obtained from the training sets applying multiple linear stepwise regression (MLR) analysis were evaluated externally using the test sets. Correlation coefficients between the predicted and the experimental values were: 0.998 for C P1(298 K) and 0.979 for P LL. The results indicate that the QSPR models constructed using quantum chemical descriptors can be applied to predict the properties of polymers confirming the role of quantum chemical descriptors in the QSPRs studies of polymers.


1973 ◽  
Vol 26 (5) ◽  
pp. 1005 ◽  
Author(s):  
PD Bolton ◽  
J Ellis ◽  
KA Fleming ◽  
IR Lantzke

Thermodynamic acidity constants have been measured over the temperature range 5-50� for aqueous solutions of sodium 4?-dimethylaminoazobenzene- 4-sulphonate (methyl orange) and sodium 4?-dimethylaminoazobenzene-2- sulphonate (ortho-methyl orange). From these data values of the standard enthalpy, entropy, and heat capacity changes have been calculated for these compounds. These results are discussed in conjunction with previous spectrophotometric and other data with reference to the nature of the equilibrium systems involved in these protonation reactions. It is concluded that existing evidence does not allow an unequivocal assignment of the sites of protonation of these and related molecules.


1990 ◽  
Vol 45 (11-12) ◽  
pp. 1328-1334 ◽  
Author(s):  
Walter M. F. Fabian

AbstractThe reliability of three popular semiempirical quantum chemical methods (AM1, PM3, MNDO) for the treatment of tautomeric equilibria is tested in a series of five-membered nitrogen heterocycles. The known flaw of MNDO to overestimate the stability of compounds with two or more adjacent pyridine-like lone pairs is also present in AM1 and to a somewhat lesser extent in PM3. Tautomeric species differing in the number of adjacent pyridine-like lone pairs, thus, cannot be adequately treated by these semiempirical methods. Both AM1 as well as PM3, however, represent major improvements over MNDO in the case of lactam-lactim tautomerism. The stability of N-oxides as compared to N-hydroxy tautomers seems to be overestimated by the PM3 method. All three semiempirical methods yield quite reliable ionization potentials and dipole moments.


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