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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.


Intramolecular hetero Diels–Alder cycloaddition of alkenyl-tethered 2(1H)-pyrazinones (10). Reagents and conditions: a) 1,2-dichloroethane, [BMIM][PF6]; conventional conditions: 132 °C, 1–2 d, 54%; microwave irradiation: 170 °C (300 W), 10 min, 67–77 %. Box: structure of [BMIM][PF6]. Result: acceleration.
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sch04: Intramolecular hetero Diels–Alder cycloaddition of alkenyl-tethered 2(1H)-pyrazinones (10). Reagents and conditions: a) 1,2-dichloroethane, [BMIM][PF6]; conventional conditions: 132 °C, 1–2 d, 54%; microwave irradiation: 170 °C (300 W), 10 min, 67–77 %. Box: structure of [BMIM][PF6]. Result: acceleration.

Mentions: This group contains a series of reactions that were previously studied theoretically in our research group.16f,16h Type III reactions are exothermic (ΔH<0 kcal mol−1) and have high activation energies (Ea=20–30 kcal mol−1). The first reaction studied was the intramolecular hetero-Diels–Alder cycloaddition of alkenyl-tethered 2(1H)-pyrazinones 10 a–b (Scheme 4). The reaction mixture was irradiated in a single-mode microwave cavity using a preselected maximum temperature of 190 °C (300 W maximum power) in a sealed vessel, with dichloroethane as the solvent and 0.035 mmol of 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF6]). The reaction took place within 10 min and gave good yields (67–77 %). Under these conditions, the complete conversion of 10 took place in about 8–10 min, which represents a considerable decrease in the reaction time as compared with the 1–2 days required under conventional reflux conditions in chlorobenzene (131 °C).24


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)

Intramolecular hetero Diels–Alder cycloaddition of alkenyl-tethered 2(1H)-pyrazinones (10). Reagents and conditions: a) 1,2-dichloroethane, [BMIM][PF6]; conventional conditions: 132 °C, 1–2 d, 54%; microwave irradiation: 170 °C (300 W), 10 min, 67–77 %. Box: structure of [BMIM][PF6]. Result: acceleration.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

sch04: Intramolecular hetero Diels–Alder cycloaddition of alkenyl-tethered 2(1H)-pyrazinones (10). Reagents and conditions: a) 1,2-dichloroethane, [BMIM][PF6]; conventional conditions: 132 °C, 1–2 d, 54%; microwave irradiation: 170 °C (300 W), 10 min, 67–77 %. Box: structure of [BMIM][PF6]. Result: acceleration.
Mentions: This group contains a series of reactions that were previously studied theoretically in our research group.16f,16h Type III reactions are exothermic (ΔH<0 kcal mol−1) and have high activation energies (Ea=20–30 kcal mol−1). The first reaction studied was the intramolecular hetero-Diels–Alder cycloaddition of alkenyl-tethered 2(1H)-pyrazinones 10 a–b (Scheme 4). The reaction mixture was irradiated in a single-mode microwave cavity using a preselected maximum temperature of 190 °C (300 W maximum power) in a sealed vessel, with dichloroethane as the solvent and 0.035 mmol of 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF6]). The reaction took place within 10 min and gave good yields (67–77 %). Under these conditions, the complete conversion of 10 took place in about 8–10 min, which represents a considerable decrease in the reaction time as compared with the 1–2 days required under conventional reflux conditions in chlorobenzene (131 °C).24

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.