title: Mechanism for microwave heating of 1-(4'-cyanophenyl)-4-propylcyclohexane characterized by in situ microwave irradiation NMR spectroscopy.
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. (1)H 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.
authors.affiliation: Graduate School of Engineering, Yokohama National University, 79-5 Tokiwadai, Hodogaya-ku, Yokohama 240-8501, Japan.
authors.forename: Yugo
authors.initials: Y
authors.lastname: Tasei
authors.affiliation: Department of Chemistry, School of Science, Kitasato University, 1-15-1 Kitasato, Minami-ku, Sagamihara 252-0373, Japan.
authors.forename: Takuya
authors.initials: T
authors.lastname: Yamakami
authors.affiliation: Graduate School of Engineering, Yokohama National University, 79-5 Tokiwadai, Hodogaya-ku, Yokohama 240-8501, Japan.
authors.forename: Izuru
authors.initials: I
authors.lastname: Kawamura
authors.affiliation: Probe Laboratory Inc., 1-7-17, Kawasaki, Hamura, Tokyo 205-0021, Japan.
authors.forename: Teruaki
authors.initials: T
authors.lastname: Fujito
authors.affiliation: Department of Chemistry, School of Science, Kitasato University, 1-15-1 Kitasato, Minami-ku, Sagamihara 252-0373, Japan.
authors.forename: Kiminori
authors.initials: K
authors.lastname: Ushida
authors.affiliation: Faculty of Engineering, Chubu University, 200 Matsumoto-cho, Kasugai 457-8501, Japan.
authors.forename: Motoyasu
authors.initials: M
authors.lastname: Sato
authors.affiliation: Graduate School of Engineering, Yokohama National University, 79-5 Tokiwadai, Hodogaya-ku, Yokohama 240-8501, Japan. Electronic address: naito@ynu.ac.jp.
authors.forename: Akira
authors.initials: A
authors.lastname: Naito
mesh_terms: D003510:Cyclohexanes / Q000528:radiation effects*; D006358:Hot Temperature; D050866:Liquid Crystals; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D008872:Microwaves; D009570:Nitriles / Q000528:radiation effects*; D013696:Temperature
chemical_list: C000606449:1-(4'-cyanophenyl)-4-propylcyclohexane; D003510:Cyclohexanes; D009570:Nitriles
keywords: High temperature heating; Isotropic phase; Liquid crystalline phase; Microwave heating; Microwave irradiation NMR spectroscopy; Non-equilibrium local heating