Mechanism for microwave heating of 1-(4'-cyanophenyl)-4-propylcyclohexane characterized by in situ microwave irradiation NMR spectroscopy

Yugo Tasei, Takuya Yamakami, Izuru Kawamura, Teruaki Fujito, Kiminori Ushida, Motoyasu Sato, Akira Naito

Abstract

Abstract Microwave heating is widely used to accelerate organic reactions and enhance the activity of enzymes. However, the detailed molecular mechanism for the effect of microwave on chemical reactions is not yet fully understood. To investigate the effects of microwave heating on organic compounds, we have developed an in situ microwave irradiation NMR spectroscopy. 1H NMR spectra of 1-(4′-cyanophenyl)-4-propylcyclohexane (PCH3) in the liquid crystalline and isotropic phases were observed under microwave irradiation. When the temperature was regulated at slightly higher than the phase transition temperature (Tc = 45 C) under a gas flow temperature control system, liquid crystalline phase mostly changed to the isotropic phase. Under microwave irradiation and with the gas flow temperature maintained at 20 C, which is 25 C below the Tc, the isotropic phase appeared stationary as an approximately 2% fraction in the liquid crystalline phase. The temperature of the liquid crystalline state was estimated to be 38 C according to the line width, which is at least 7 C lower than the Tc. The temperature of this isotropic phase should be higher than 45 C, which is considered to be a non-equilibrium local heating state induced by microwave irradiation. Microwaves at a power of 195 W were irradiated to the isotropic phase of PCH3 at 50 C and after 2 min, the temperature reached 220 C. The temperature of PCH3 under microwave irradiation was estimated by measurement of the chemical shift changes of individual protons in the molecule. These results demonstrate that microwave heating generates very high temperature within a short time using an in situ microwave irradiation NMR spectrometer.

Original languageEnglish
Article number5602
Pages (from-to)27-34
Number of pages8
JournalJournal of Magnetic Resonance
Volume254
DOIs
StatePublished - 2015
Externally publishedYes

Fingerprint

Microwave irradiation
Temperature
Microwave heating
Crystalline materials
Liquids
Nuclear magnetic resonance spectroscopy
Flow of gases
Microwaves
Nuclear magnetic resonance
Chemical shift
Organic compounds
Flow control
Temperature control
Linewidth
Superconducting transition temperature
Spectrometers
Chemical reactions
Protons
Enzymes
Phase transitions

Keywords

  • High temperature heating
  • Isotropic phase
  • Liquid crystalline phase
  • Microwave heating
  • Microwave irradiation NMR spectroscopy
  • Non-equilibrium local heating

ASJC Scopus subject areas

  • Nuclear and High Energy Physics
  • Biochemistry
  • Biophysics
  • Condensed Matter Physics

Cite this

Mechanism for microwave heating of 1-(4'-cyanophenyl)-4-propylcyclohexane characterized by in situ microwave irradiation NMR spectroscopy. / Tasei, Yugo; Yamakami, Takuya; Kawamura, Izuru; Fujito, Teruaki; Ushida, Kiminori; Sato, Motoyasu; Naito, Akira.

In: Journal of Magnetic Resonance, Vol. 254, 5602, 2015, p. 27-34.

Research output: Contribution to journalArticle

Tasei, Yugo; Yamakami, Takuya; Kawamura, Izuru; Fujito, Teruaki; Ushida, Kiminori; Sato, Motoyasu; Naito, Akira / Mechanism for microwave heating of 1-(4'-cyanophenyl)-4-propylcyclohexane characterized by in situ microwave irradiation NMR spectroscopy.

In: Journal of Magnetic Resonance, Vol. 254, 5602, 2015, p. 27-34.

Research output: Contribution to journalArticle

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keywords = "High temperature heating, Isotropic phase, Liquid crystalline phase, Microwave heating, Microwave irradiation NMR spectroscopy, Non-equilibrium local heating",
author = "Yugo Tasei and Takuya Yamakami and Izuru Kawamura and Teruaki Fujito and Kiminori Ushida and Motoyasu Sato and Akira Naito",
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T1 - Mechanism for microwave heating of 1-(4'-cyanophenyl)-4-propylcyclohexane characterized by in situ microwave irradiation NMR spectroscopy

AU - Tasei,Yugo

AU - Yamakami,Takuya

AU - Kawamura,Izuru

AU - Fujito,Teruaki

AU - Ushida,Kiminori

AU - Sato,Motoyasu

AU - Naito,Akira

PY - 2015

Y1 - 2015

N2 - Abstract Microwave heating is widely used to accelerate organic reactions and enhance the activity of enzymes. However, the detailed molecular mechanism for the effect of microwave on chemical reactions is not yet fully understood. To investigate the effects of microwave heating on organic compounds, we have developed an in situ microwave irradiation NMR spectroscopy. 1H NMR spectra of 1-(4′-cyanophenyl)-4-propylcyclohexane (PCH3) in the liquid crystalline and isotropic phases were observed under microwave irradiation. When the temperature was regulated at slightly higher than the phase transition temperature (Tc = 45 C) under a gas flow temperature control system, liquid crystalline phase mostly changed to the isotropic phase. Under microwave irradiation and with the gas flow temperature maintained at 20 C, which is 25 C below the Tc, the isotropic phase appeared stationary as an approximately 2% fraction in the liquid crystalline phase. The temperature of the liquid crystalline state was estimated to be 38 C according to the line width, which is at least 7 C lower than the Tc. The temperature of this isotropic phase should be higher than 45 C, which is considered to be a non-equilibrium local heating state induced by microwave irradiation. Microwaves at a power of 195 W were irradiated to the isotropic phase of PCH3 at 50 C and after 2 min, the temperature reached 220 C. The temperature of PCH3 under microwave irradiation was estimated by measurement of the chemical shift changes of individual protons in the molecule. These results demonstrate that microwave heating generates very high temperature within a short time using an in situ microwave irradiation NMR spectrometer.

AB - Abstract Microwave heating is widely used to accelerate organic reactions and enhance the activity of enzymes. However, the detailed molecular mechanism for the effect of microwave on chemical reactions is not yet fully understood. To investigate the effects of microwave heating on organic compounds, we have developed an in situ microwave irradiation NMR spectroscopy. 1H NMR spectra of 1-(4′-cyanophenyl)-4-propylcyclohexane (PCH3) in the liquid crystalline and isotropic phases were observed under microwave irradiation. When the temperature was regulated at slightly higher than the phase transition temperature (Tc = 45 C) under a gas flow temperature control system, liquid crystalline phase mostly changed to the isotropic phase. Under microwave irradiation and with the gas flow temperature maintained at 20 C, which is 25 C below the Tc, the isotropic phase appeared stationary as an approximately 2% fraction in the liquid crystalline phase. The temperature of the liquid crystalline state was estimated to be 38 C according to the line width, which is at least 7 C lower than the Tc. The temperature of this isotropic phase should be higher than 45 C, which is considered to be a non-equilibrium local heating state induced by microwave irradiation. Microwaves at a power of 195 W were irradiated to the isotropic phase of PCH3 at 50 C and after 2 min, the temperature reached 220 C. The temperature of PCH3 under microwave irradiation was estimated by measurement of the chemical shift changes of individual protons in the molecule. These results demonstrate that microwave heating generates very high temperature within a short time using an in situ microwave irradiation NMR spectrometer.

KW - High temperature heating

KW - Isotropic phase

KW - Liquid crystalline phase

KW - Microwave heating

KW - Microwave irradiation NMR spectroscopy

KW - Non-equilibrium local heating

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