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Current Microwave Chemistry

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ISSN (Print): 2213-3356
ISSN (Online): 2213-3364

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General Research Article

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

Author(s): Dongqiang Yang and Jiaxi Xu*

Volume 7, Issue 1, 2020

Page: [74 - 82] Pages: 9

DOI: 10.2174/2213335607666200115164318

Price: $65

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.

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