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11.
Comparative thermolysis of β-and α-pinenes in supercritical ethanol: the reaction characterization and enantiomeric ratios of products 总被引:2,自引:0,他引:2
A. M. Chibiryaev A. Yermakova I. V. Kozhevnikov O. I. Sal’nikova V. I. Anikeev 《Russian Chemical Bulletin》2007,56(6):1234-1238
The thermolysis of β-pinene and the co-thermolysis of an equimolar mixture of β-and α-pinenes in supercritical ethanol were
carried out. The reaction of β-pinene affords β-myrcene as the major product (>70%). Considerable differences in the temperature
dependence of the reaction rate were revealed for the transformations of β-pinene into β-myrcene and of α-pinene into limonene.
The pre-exponential factors and the activation energies were calculated. The enantiomeric ratios of the thermolysis products
of β-and α-pinenes and limonene were estimated. The starting monoterpenes do not undergo racemization during thermolysis.
The thermolysis of enantiomerically pure α-pinene affords racemic (±)-limonene, whereas (−)-β-pinene gives (−)-limonene. The
enantiomeric ratio in the latter remains equal to the enantiomeric purity of the starting β-pinene.
Dedicated to the memory of Academician N. N. Vorozhtsov on the 100th anniversary of his birth.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1188–1192, June, 2007. 相似文献
12.
The influence of water on the isomerization of α-pinene in a supercritical aqueous-alcoholic solvent
A. Ermakova A. M. Chibiryaev P. E. Mikenin O. I. Sal’nikova V. I. Anikeev 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2008,82(1):62-67
The influence of water as a cosolvent and catalyst of the isomerization of α-pinene in a supercritical aqueous-alcoholic (ethanol) solvent was studied experimentally. At T = 657 K and p = 230 atm, an increase in the concentration of water in the reaction mixture was found to increase the rate of the reaction and its selectivity with respect to the desired product, limonene. Water exhibited the properties of an acid catalyst because of its ionization. Mathematical experimental data processing was performed to evaluate and separate the contributions of the radical and ionic paths to the total rate of the reactions that occurred during the thermal isomerization of α-pinene. 相似文献
13.
A. M. Chibiryaev A. Ermakova I. V. Kozhevnikov 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2011,85(8):1347-1357
Revision of the experimental data on α-pinene thermal isomerization attained in supercritical ethanol allowed us to expand
the reaction scheme, which includes now six main products and eleven reversible reactions. The equilibrium constants of every
reaction (K
T, j
and K
Φ, j) were calculated to allow for reversibility of reactions. The thermochemical data of the pure compounds required to calculate
constants K
T, j
and K
Φ, j
(standard enthalpy and entropy of formation Δf
H° (298.15 K), Δf
S° (298.15 K), heat capacity C
p
(T), critical parameters T
cr and p
cr, boiling point T
b, and the acentric factor ω) were preliminary estimated using the empirical Joback and Benson methods. A kinetic model based
on the new expanded scheme of reversible reactions was successfully identified and its kinetic parameters k
j
(600 K) and E
j
were determined. Detailed examination of the new kinetic model allowed us to refine the generally accepted mechanism of α-pinene
thermal isomerization and to distinguish additional features of the multistep process. 相似文献