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Thermal Effect in the Microwave-assisted Aminolysis of Benzoates and Amines

[ Vol. 7 , Issue. 1 ]

Author(s):

Dongqiang Yang and Jiaxi Xu*   Pages 74 - 82 ( 9 )

Abstract:


Background: Microwave selective heating thermal effect is obvious in unimolecular organic reactions. However, it is unclear whether it exists in bimolecular organic reactions under strictly controlled reaction temperature conditions.

Objective: To determine whether microwave selective heating effect exists in the microwave-assisted bimolecular reactions.

Methods: Hammett linear relationships in “one-pot” aminolyses of mixed 4-nitrophenyl substituted benzoates with benzylamine and 4-nitrophenyl benzoate with mixed substituted anilines were selected as molecular level probes to explore the thermal effect in the microwave-assisted bimolecular reactions.

Results: In less polar solvent, there is an obvious “hot spots” effect. “One-pot” aminolyses of mixed 4-nitrophenyl substituted benzoates with benzylamine and 4-nitrophenyl benzoate with mixed substituted anilines were performed in less polar solvent toluene under oil-bath and microwave heating conditions. Generally, slopes of Hammett plots or effect of substituents on reaction rates decrease along with temperature increases under oil-bath heating conditions. Under microwave irradiation conditions, slopes of Hammett plots or effect of substituents on reaction rates decrease in comparison with those under oil-bath heating conditions at the same setting temperature, revealing that higher temperature regions (“hot spots”) still exist in intermolecular organic reactions.

Conclusion: Microwave selective heating thermal effect still exists in bimolecular organic reactions under strictly controlled reaction temperature conditions, revealing that higher temperature regions (“hot spots”) do exist in intermolecular organic reactions.

Keywords:

Selective heating, microwave irradiation, microwave effect, hammett equation, hot spot, benzoates.

Affiliation:

State Key Laboratory of Chemical Resource Engineering, Department of Organic Chemistry, College of Chemistry, Beijing University of Chemical Technology, Beijing 100029, State Key Laboratory of Chemical Resource Engineering, Department of Organic Chemistry, College of Chemistry, Beijing University of Chemical Technology, Beijing 100029



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