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Influence of Polarity and Activation Energy in Microwave-Assisted Organic Synthesis (MAOS).

Rodríguez AM, Prieto P, de la Hoz A, Díaz-Ortiz Á, Martín DR, García JI - ChemistryOpen (2015)

Bottom Line: The aim of this work was to determine the parameters that have decisive roles in microwave-assisted reactions and to develop a model, using computational chemistry, to predict a priori the type of reactions that can be improved under microwaves.This comprises six types of reactions.The outcomes obtained in this study indicate that the most influential parameters are activation energy, enthalpy, and the polarity of all the species that participate.

View Article: PubMed Central - PubMed

Affiliation: Departamento de Química Orgánica, Universidad de Castilla-La Mancha, Facultad de Ciencias y Tecnologías Químicas 13071, Ciudad Real, Spain.

ABSTRACT
The aim of this work was to determine the parameters that have decisive roles in microwave-assisted reactions and to develop a model, using computational chemistry, to predict a priori the type of reactions that can be improved under microwaves. For this purpose, a computational study was carried out on a variety of reactions, which have been reported to be improved under microwave irradiation. This comprises six types of reactions. The outcomes obtained in this study indicate that the most influential parameters are activation energy, enthalpy, and the polarity of all the species that participate. In addition to this, in most cases, slower reacting systems observe a much greater improvement under microwave irradiation. Furthermore, for these reactions, the presence of a polar component in the reaction (solvent, reagent, susceptor, etc.) is necessary for strong coupling with the electromagnetic radiation. We also quantified that an activation energy of 20-30 kcal mol(-1) and a polarity (μ) between 7-20 D of the species involved in the process is required to obtain significant improvements under microwave irradiation.

No MeSH data available.


Nucleophilic aromatic substitution of p-halonitrobenzenes (12). Reagents and conditions: a) DMSO; conventional conditions: 190 °C, 2 min; microwave irradiation: 190 °C (300 W), 2 min. Result: acceleration rate=3.2.
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sch05: Nucleophilic aromatic substitution of p-halonitrobenzenes (12). Reagents and conditions: a) DMSO; conventional conditions: 190 °C, 2 min; microwave irradiation: 190 °C (300 W), 2 min. Result: acceleration rate=3.2.

Mentions: The second example involves a nucleophilic aromatic substitution of a fluoro substituent by a piperidine ring in a deactivated benzene scaffold (Scheme 5).25 We carried out this transformation in the polar solvent dimethyl sulfoxide (DMSO) with both classical and microwave heating. According to the experimental kinetic data obtained under microwave irradiation (k*) and by classical heating (k), the k*/k ratio for the reaction between and piperidine at 462 K is 3.2.25c


Influence of Polarity and Activation Energy in Microwave-Assisted Organic Synthesis (MAOS).

Rodríguez AM, Prieto P, de la Hoz A, Díaz-Ortiz Á, Martín DR, García JI - ChemistryOpen (2015)

Nucleophilic aromatic substitution of p-halonitrobenzenes (12). Reagents and conditions: a) DMSO; conventional conditions: 190 °C, 2 min; microwave irradiation: 190 °C (300 W), 2 min. Result: acceleration rate=3.2.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4522181&req=5

sch05: Nucleophilic aromatic substitution of p-halonitrobenzenes (12). Reagents and conditions: a) DMSO; conventional conditions: 190 °C, 2 min; microwave irradiation: 190 °C (300 W), 2 min. Result: acceleration rate=3.2.
Mentions: The second example involves a nucleophilic aromatic substitution of a fluoro substituent by a piperidine ring in a deactivated benzene scaffold (Scheme 5).25 We carried out this transformation in the polar solvent dimethyl sulfoxide (DMSO) with both classical and microwave heating. According to the experimental kinetic data obtained under microwave irradiation (k*) and by classical heating (k), the k*/k ratio for the reaction between and piperidine at 462 K is 3.2.25c

Bottom Line: The aim of this work was to determine the parameters that have decisive roles in microwave-assisted reactions and to develop a model, using computational chemistry, to predict a priori the type of reactions that can be improved under microwaves.This comprises six types of reactions.The outcomes obtained in this study indicate that the most influential parameters are activation energy, enthalpy, and the polarity of all the species that participate.

View Article: PubMed Central - PubMed

Affiliation: Departamento de Química Orgánica, Universidad de Castilla-La Mancha, Facultad de Ciencias y Tecnologías Químicas 13071, Ciudad Real, Spain.

ABSTRACT
The aim of this work was to determine the parameters that have decisive roles in microwave-assisted reactions and to develop a model, using computational chemistry, to predict a priori the type of reactions that can be improved under microwaves. For this purpose, a computational study was carried out on a variety of reactions, which have been reported to be improved under microwave irradiation. This comprises six types of reactions. The outcomes obtained in this study indicate that the most influential parameters are activation energy, enthalpy, and the polarity of all the species that participate. In addition to this, in most cases, slower reacting systems observe a much greater improvement under microwave irradiation. Furthermore, for these reactions, the presence of a polar component in the reaction (solvent, reagent, susceptor, etc.) is necessary for strong coupling with the electromagnetic radiation. We also quantified that an activation energy of 20-30 kcal mol(-1) and a polarity (μ) between 7-20 D of the species involved in the process is required to obtain significant improvements under microwave irradiation.

No MeSH data available.