Comparative kinetic study on the reaction fon N-n-butyl-2,6-dinitroaniline with NaOh by microwave and conventional heating

FABRIZIO POLITANO; ELBA I. BUJÁN

Carlos Paz

Congreso; 13th Latin American Conference on Physical Organic Chemistry; 2015

With the emergence of microwave irradiation as a heating source at the end of the last century, started the use of microwave ovens in organic chemical laboratories too. Many reports about the use of microwave irradiation in order to accelerate chemical transformations have been published since then. An important discussion about these results is if the observed effects can be explained by purely thermal/kinetic phenomena (thermal microwave effects) or by a specific or nonthermal microwave effect.1 The design of experiments that allow to arrive to conclusive results is fundamental. Many reported results in this field were not conclusive about the existence of some ?nonthermal microwave effects? because they have committed some inaccuracies on the measurement of some variables such as temperature or agitation.2In this work we have performed a comparative kinetic study in order to investigate if some specific microwave effect acts on a particular reaction. The reaction of N-n-butyl-2,6-dinitroaniline (1) with NaOH in 10% 1,4-dioxane/water and 1 M ionic strength was studied under both conventional and microwave heating at 50°C, in an interval of NaOH concentration between 0.1 and 1 M. The reaction forms two products: 2,6-dinitrophenol (2) and 7-nitro-2-n-propyl-1H-benzimidazole 3-oxide (3). The observed rates constant, as well as the molar fractions and pseudo-first order rate constants for the formation of products were calculated.We have not noticed differences between the molar fractions and rate constants calculated for the two forms of heating. We conclude that there is no specific microwave effect on this reaction, or an improvement with use of microwave irradiation. These results are consistent with recent reports.3(1) Perreux, L.; Loupy, A. In Microwaves in Organic Synthesis, Third Edition; de la Hoz, A.; Loupy, A., Eds.; Wiley-VCH Verlag GmbH & Co. KGaA, 2012; pp. 127?207.(2) Herrero, M.; Kremsner, J. M.; Kappe, C. O. J. Org. Chem. 2008, 73, 36?47.(3) Kappe, C. O.; Pieber, B.; Dallinger, D. Angew. Chem. Int. Ed. Engl. 2013, 52, 1088?1094.