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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.


General scheme for ring-closing metathesis of diallyl derivatives. Reagents and conditions: a) Ru catalyst, BMIM; conventional conditions: 33 °C, 2 min, 4 % (16 a), 45 % (16 b); microwave irradiation: 33 °C (110 W), 2 min, 85 % (16 a), 91 % (16 b). Result: acceleration.
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sch07: General scheme for ring-closing metathesis of diallyl derivatives. Reagents and conditions: a) Ru catalyst, BMIM; conventional conditions: 33 °C, 2 min, 4 % (16 a), 45 % (16 b); microwave irradiation: 33 °C (110 W), 2 min, 85 % (16 a), 91 % (16 b). Result: acceleration.

Mentions: The third example concerns a ring-closing metathesis (RCM) reaction. Kiddle and co-workers26 reported the RCM of diallyl derivatives using ruthenium-based catalysts (Scheme 7). The reaction can be rapidly conducted in either an ionic liquid, such as 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF4]), or in a microwave-transparent solvent (MTS) such as dichloromethane. In both cases, the reaction was successfully improved under microwave irradiation. The best results were obtained using ionic liquids, although a dramatic decrease in reaction time was not observed when using dichloromethane as the solvent. It is important to note that the reaction temperature did not exceed 33 °C.


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)

General scheme for ring-closing metathesis of diallyl derivatives. Reagents and conditions: a) Ru catalyst, BMIM; conventional conditions: 33 °C, 2 min, 4 % (16 a), 45 % (16 b); microwave irradiation: 33 °C (110 W), 2 min, 85 % (16 a), 91 % (16 b). Result: acceleration.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

sch07: General scheme for ring-closing metathesis of diallyl derivatives. Reagents and conditions: a) Ru catalyst, BMIM; conventional conditions: 33 °C, 2 min, 4 % (16 a), 45 % (16 b); microwave irradiation: 33 °C (110 W), 2 min, 85 % (16 a), 91 % (16 b). Result: acceleration.
Mentions: The third example concerns a ring-closing metathesis (RCM) reaction. Kiddle and co-workers26 reported the RCM of diallyl derivatives using ruthenium-based catalysts (Scheme 7). The reaction can be rapidly conducted in either an ionic liquid, such as 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF4]), or in a microwave-transparent solvent (MTS) such as dichloromethane. In both cases, the reaction was successfully improved under microwave irradiation. The best results were obtained using ionic liquids, although a dramatic decrease in reaction time was not observed when using dichloromethane as the solvent. It is important to note that the reaction temperature did not exceed 33 °C.

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.