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Chemical Reaction in Binary Mixtures near the Critical Region: Thermal Decomposition of 2,2′‐Azobis(isobutyronitrile) in CO 2 /Ethanol
Author(s) -
Li Hongping,
Han Buxing,
Liu Jun,
Gao Liang,
Hou Zhenshan,
Jiang Tao,
Liu Zhimin,
Zhang Xiaogang,
He Jun
Publication year - 2002
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/1521-3765(20021216)8:24<5593::aid-chem5593>3.0.co;2-b
Subject(s) - solvent , chemistry , critical point (mathematics) , solvent effects , thermodynamics , thermal decomposition , organic chemistry , mathematical analysis , physics , mathematics
The effects of pressure and of the composition of the CO 2 /ethanol mixed solvent in the critical region on the kinetics of the decomposition of 2,2′‐azobis(isobutyronitrile) (AIBN) were studied at 333.15 K. The rate constants ( k d ) in the mixed solvent far from the critical point and in liquid n ‐hexane and ethanol were also determined for comparison. It was found that k d is very sensitive to pressure in the mixed solvent near the critical point. However, in the mixed solvent outside the critical region k d is nearly independent of pressure. Interestingly, k d in the mixed solvent in the critical region can be higher than that in ethanol at the same temperature, suggesting that no significant enhancement in the reaction rate by a small pressure change in the critical region of the mixed solvent can be achieved by changing the composition of the liquid solvent in the traditional way. Transition‐state theory can predict k d in the mixed solvent far from the critical point and in the liquid solvents well. However, it cannot predict k d in the mixed solvent in the critical region. The special intermolecular interaction between the solvent and the reaction species may contribute to this interesting phenomenon. This work also shows that if pure CO 2 or ethanol are used as solvents, the reaction cannot be carried out in the critical region of the solvents at the desired temperature, while it can be conducted in the critical region of the mixed solvent of suitable composition, where the solvent is highly compressible.