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

Author(s): Dongqiang Yang, Jiaxi Xu*

Journal Name: Current Microwave Chemistry

Volume 7 , Issue 1 , 2020

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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.

[1]
Hayes, B.L. Microwave Synthesis: Chemistry at the Speed of Light; CEM Publishing: Matthews, NC, USA, 2002.
[2]
Kappe, C.O.; Stadler, A. Microwaves in Organic and Medicinal Chemistry; Wiley-VCH: Weinheim, 2005.
[http://dx.doi.org/10.1002/3527606556]
[3]
Oliver Kappe, C. Microwave dielectric heating in synthetic organic chemistry. Chem. Soc. Rev., 2008, 37(6), 1127-1139.
[http://dx.doi.org/10.1039/b803001b] [PMID: 18497926]
[4]
Xu, J.X. Microwave irradiation and selectivities in organic reactions. Huaxue Jinzhan, 2007, 19, 700-712.
[5]
Hu, L.; Wang, Y.; Li, B.; Du, D-M.; Xu, J. Diastereoselectivity in the staudinger reaction: A useful probe for investigation of nonthermal microwave effects. Tetrahedron, 2007, 63, 9387-9392.
[http://dx.doi.org/10.1016/j.tet.2007.06.112]
[6]
Perreux, L.; Loupy, A. A tentative rationalization of microwave effects in organic synthesis according to the reaction medium, and mechanistic considerations. Tetrahedron, 2001, 57, 9199-9223.
[http://dx.doi.org/10.1016/S0040-4020(01)00905-X]
[7]
de la Hoz, A.; Díaz-Ortiz, A.; Moreno, A. Microwaves in organic synthesis. Thermal and non-thermal microwave effects. Chem. Soc. Rev., 2005, 34(2), 164-178.
[http://dx.doi.org/10.1039/B411438H] [PMID: 15672180]
[8]
Dudley, G.B.; Richert, R.; Stiegman, A.E. On the existence of and mechanism for microwave-specific reaction rate enhancement. Chem. Sci. (Camb.), 2015, 6(4), 2144-2152.
[http://dx.doi.org/10.1039/C4SC03372H] [PMID: 29308138]
[9]
Kappe, C.O.; Pieber, B.; Dallinger, D. Microwave effects in organic synthesis: myth or reality? Angew. Chem. Int. Ed. Engl., 2013, 52(4), 1088-1094.
[http://dx.doi.org/10.1002/anie.201204103] [PMID: 23225754]
[10]
Chen, P-K.; Rosana, M.R.; Dudley, G.B.; Stiegman, A.E. Parameters affecting the microwave-specific acceleration of a chemical reaction. J. Org. Chem., 2014, 79(16), 7425-7436.
[http://dx.doi.org/10.1021/jo5011526] [PMID: 25050921]
[11]
Li, X.H.; Xu, J.X. Determination on temperature gradient of different polar reactants in reaction mixture under microwave irradiation with molecular probe. Tetrahedron, 2016, 35, 5515-5520.
[http://dx.doi.org/10.1016/j.tet.2016.07.041]
[12]
Yang, D.Q.; Xu, J.X. Influence of the product polarity on temperature profiles in the microwave-assisted Claisen rearrangement. Curr. Microw. Chem., 2018, 5, 120-127.
[http://dx.doi.org/10.2174/2213335605666180425144619]
[13]
Camelia Gabriel, S.G.; Edward, H. Grant, Ben S. J. Halsteadb and D. Michael P.; Mingos. Dielectric parameters relevant to microwave dielectric heating. Chem. Soc. Rev., 1998, 27, 213-223.
[http://dx.doi.org/10.1039/a827213z]
[14]
Leadbeater, N.E.; Smith, R.J. In situ Raman spectroscopy as a probe for the effect of power on microwave-promoted Suzuki coupling reactions. Org. Biomol. Chem., 2007, 5(17), 2770-2774.
[http://dx.doi.org/10.1039/b707692d] [PMID: 17700844]
[15]
Leadbeater, N.E.; Stencel, L.M.; Wood, E.C. Probing the effects of microwave irradiation on enzyme-catalysed organic transformations: the case of lipase-catalysed transesterification reactions. Org. Biomol. Chem., 2007, 5(7), 1052-1055.
[http://dx.doi.org/10.1039/b617544a] [PMID: 17377658]
[16]
Schmink, J.R.; Holcomb, J.L.; Leadbeater, N.E. Use of Raman spectroscopy as an in situ tool to obtain kinetic data for organic transformations. Chemistry, 2008, 14(32), 9943-9950.
[http://dx.doi.org/10.1002/chem.200801158] [PMID: 18830985]
[17]
Schmink, J.R.; Leadbeater, N.E. Probing “microwave effects” using Raman spectroscopy. Org. Biomol. Chem., 2009, 7(18), 3842-3846.
[http://dx.doi.org/10.1039/b910591c] [PMID: 19707691]
[18]
Kappe, C.O. How to measure reaction temperature in microwave-heated transformations. Chem. Soc. Rev., 2013, 42(12), 4977-4990.
[http://dx.doi.org/10.1039/c3cs00010a] [PMID: 23443140]
[19]
Li, X.H.; Xu, J.X. Identification of microwave selective heating effort in an intermolecular reaction with Hammett linear relationship as a molecular level probe. Curr. Microw. Chem., 2017, 4, 339-346.
[20]
Yau, H.M.; Croft, A.K.; Harper, J.B. ‘One-pot’ Hammett plots: a general method for the rapid acquisition of relative rate data. Chem. Commun. (Camb.), 2012, 48(71), 8937-8939.
[http://dx.doi.org/10.1039/c2cc34074g] [PMID: 22847368]
[21]
Herrero, M.A.; Kremsner, J.M.; Kappe, C.O. Nonthermal microwave effects revisited: on the importance of internal temperature monitoring and agitation in microwave chemistry. J. Org. Chem., 2008, 73(1), 36-47.
[http://dx.doi.org/10.1021/jo7022697] [PMID: 18062704]
[22]
Hammett, L.P. Some relations between reaction rates and equilibrium constants. Chem. Rev., 1934, 17, 125-136.
[http://dx.doi.org/10.1021/cr60056a010]
[23]
Hammett, L.P. The effect of structure upon the reactions of organic compounds. Benzene derivatives. J. Am. Chem. Soc., 1937, 59, 96-103.
[http://dx.doi.org/10.1021/ja01280a022]
[24]
Hammett, L.P. Linear free energy relationships in rate and equilibrium phenomena. Trans. Faraday Soc., 1938, 34, 156-165.
[http://dx.doi.org/10.1039/tf9383400156]
[25]
Hansch, C.; Leo, A.; Taft, R.W. A survey of hammett substituent constants and resonance and field parameters. Chem. Rev., 1991, 91, 165-195.
[http://dx.doi.org/10.1021/cr00002a004]
[26]
Li, X.H.; Xu, J.X. Effects of the microwave power on the microwave-assisted esterification. Curr. Microw. Chem., 2017, 4, 339-346.
[http://dx.doi.org/10.2174/2213335603666160906151018]


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VOLUME: 7
ISSUE: 1
Year: 2020
Page: [74 - 82]
Pages: 9
DOI: 10.2174/2213335607666200115164318
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