Title:Thermal Effect in the Microwave-assisted Aminolysis of Benzoates and Amines
VOLUME: 7 ISSUE: 1
Author(s):Dongqiang Yang and Jiaxi Xu*
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
Keywords:Selective heating, microwave irradiation, microwave effect, hammett equation, hot spot, benzoates.
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.