Kinetic study of thermal Z to e isomerization reactions of azobenzene and 4-dimethvlaniino-4′-nitroazobenzene in Ionic Liquids [1-R-3- methyliniidazolium bis(trifluoromethylsulfonyl)imide with R = Butyl, Pentyl, and Hexyl]

Keita Baba, Hajime Ono, Eri Itoh, Sumitaka Itoh, Kyoko Noda, Toshinori Usui, Koji Ishihara, Masahiko Inamo, Hideo D. Takagi, Tsutomu Asano

    Research output: Contribution to journalArticle

    46 Citations (Scopus)

    Abstract

    Thermal Z to E isomerization reactions of azobenzene and 4-dimethylamino-4′-nitroazobenzene were examined in three ionic liquids of general formula 1-R-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (R = butyl, pentyl. and hexyl). The first-order rate constants and activation energies for the reactions of azobenzene measured in these ionic liquids were consistent with those measured in ordinary organic solvents, which indicated that the slow isomerization through the inversion mechanism with a nonpolar transition state was little influenced by the solvent properties, such as the vis cosity and dielectric constant, of ionic liquids. On the other hand, the rate constants and the corresponding frequency factors of the Arrhenius plot were significantly reduced for the isomerization of 4-dimethylamino-4′- nitroazobenzene in ionic liquids compared with those for the isomerization in ordinary organic molecular solvents with similar dielectric properties. Although these ionic liquids are viscous, the apparent viscosity dependence of the rate constant could not be explained either by the Kramers-Grote-Hynes model or by the Agmon-Hopfield model for solution reactions. It is proposed that the positive and the negative charge centers of a highly polar rotational transition state are stabilized by the surrounding anions and cations, respectively, and that the ions must be rearranged so as to form highly ordered solvation shells around the charge centers of the reactant in the transition state. This requirement for the orderly solvation in the transition state results in unusually small frequency factors of 104-107 s -1.

    Original languageEnglish
    Pages (from-to)5328-5333
    Number of pages6
    JournalChemistry - A European Journal
    Volume12
    Issue number20
    DOIs
    Publication statusPublished - 2006 Jul 5

    Fingerprint

    Imides
    Ionic Liquids
    Azobenzene
    Isomerization
    Ionic liquids
    Kinetics
    Rate constants
    Solvation
    Arrhenius plots
    Dielectric properties
    Organic solvents
    Anions
    Cations
    Permittivity
    Negative ions
    Activation energy
    Positive ions
    Hot Temperature
    4-nitroazobenzene
    azobenzene

    Keywords

    • Azobenzenes
    • Ionic liquids
    • Isomerization
    • Kinetics

    ASJC Scopus subject areas

    • Chemistry(all)

    Cite this

    Kinetic study of thermal Z to e isomerization reactions of azobenzene and 4-dimethvlaniino-4′-nitroazobenzene in Ionic Liquids [1-R-3- methyliniidazolium bis(trifluoromethylsulfonyl)imide with R = Butyl, Pentyl, and Hexyl]. / Baba, Keita; Ono, Hajime; Itoh, Eri; Itoh, Sumitaka; Noda, Kyoko; Usui, Toshinori; Ishihara, Koji; Inamo, Masahiko; Takagi, Hideo D.; Asano, Tsutomu.

    In: Chemistry - A European Journal, Vol. 12, No. 20, 05.07.2006, p. 5328-5333.

    Research output: Contribution to journalArticle

    Baba, Keita ; Ono, Hajime ; Itoh, Eri ; Itoh, Sumitaka ; Noda, Kyoko ; Usui, Toshinori ; Ishihara, Koji ; Inamo, Masahiko ; Takagi, Hideo D. ; Asano, Tsutomu. / Kinetic study of thermal Z to e isomerization reactions of azobenzene and 4-dimethvlaniino-4′-nitroazobenzene in Ionic Liquids [1-R-3- methyliniidazolium bis(trifluoromethylsulfonyl)imide with R = Butyl, Pentyl, and Hexyl]. In: Chemistry - A European Journal. 2006 ; Vol. 12, No. 20. pp. 5328-5333.
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    abstract = "Thermal Z to E isomerization reactions of azobenzene and 4-dimethylamino-4′-nitroazobenzene were examined in three ionic liquids of general formula 1-R-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (R = butyl, pentyl. and hexyl). The first-order rate constants and activation energies for the reactions of azobenzene measured in these ionic liquids were consistent with those measured in ordinary organic solvents, which indicated that the slow isomerization through the inversion mechanism with a nonpolar transition state was little influenced by the solvent properties, such as the vis cosity and dielectric constant, of ionic liquids. On the other hand, the rate constants and the corresponding frequency factors of the Arrhenius plot were significantly reduced for the isomerization of 4-dimethylamino-4′- nitroazobenzene in ionic liquids compared with those for the isomerization in ordinary organic molecular solvents with similar dielectric properties. Although these ionic liquids are viscous, the apparent viscosity dependence of the rate constant could not be explained either by the Kramers-Grote-Hynes model or by the Agmon-Hopfield model for solution reactions. It is proposed that the positive and the negative charge centers of a highly polar rotational transition state are stabilized by the surrounding anions and cations, respectively, and that the ions must be rearranged so as to form highly ordered solvation shells around the charge centers of the reactant in the transition state. This requirement for the orderly solvation in the transition state results in unusually small frequency factors of 104-107 s -1.",
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    T1 - Kinetic study of thermal Z to e isomerization reactions of azobenzene and 4-dimethvlaniino-4′-nitroazobenzene in Ionic Liquids [1-R-3- methyliniidazolium bis(trifluoromethylsulfonyl)imide with R = Butyl, Pentyl, and Hexyl]

    AU - Baba, Keita

    AU - Ono, Hajime

    AU - Itoh, Eri

    AU - Itoh, Sumitaka

    AU - Noda, Kyoko

    AU - Usui, Toshinori

    AU - Ishihara, Koji

    AU - Inamo, Masahiko

    AU - Takagi, Hideo D.

    AU - Asano, Tsutomu

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    N2 - Thermal Z to E isomerization reactions of azobenzene and 4-dimethylamino-4′-nitroazobenzene were examined in three ionic liquids of general formula 1-R-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (R = butyl, pentyl. and hexyl). The first-order rate constants and activation energies for the reactions of azobenzene measured in these ionic liquids were consistent with those measured in ordinary organic solvents, which indicated that the slow isomerization through the inversion mechanism with a nonpolar transition state was little influenced by the solvent properties, such as the vis cosity and dielectric constant, of ionic liquids. On the other hand, the rate constants and the corresponding frequency factors of the Arrhenius plot were significantly reduced for the isomerization of 4-dimethylamino-4′- nitroazobenzene in ionic liquids compared with those for the isomerization in ordinary organic molecular solvents with similar dielectric properties. Although these ionic liquids are viscous, the apparent viscosity dependence of the rate constant could not be explained either by the Kramers-Grote-Hynes model or by the Agmon-Hopfield model for solution reactions. It is proposed that the positive and the negative charge centers of a highly polar rotational transition state are stabilized by the surrounding anions and cations, respectively, and that the ions must be rearranged so as to form highly ordered solvation shells around the charge centers of the reactant in the transition state. This requirement for the orderly solvation in the transition state results in unusually small frequency factors of 104-107 s -1.

    AB - Thermal Z to E isomerization reactions of azobenzene and 4-dimethylamino-4′-nitroazobenzene were examined in three ionic liquids of general formula 1-R-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (R = butyl, pentyl. and hexyl). The first-order rate constants and activation energies for the reactions of azobenzene measured in these ionic liquids were consistent with those measured in ordinary organic solvents, which indicated that the slow isomerization through the inversion mechanism with a nonpolar transition state was little influenced by the solvent properties, such as the vis cosity and dielectric constant, of ionic liquids. On the other hand, the rate constants and the corresponding frequency factors of the Arrhenius plot were significantly reduced for the isomerization of 4-dimethylamino-4′- nitroazobenzene in ionic liquids compared with those for the isomerization in ordinary organic molecular solvents with similar dielectric properties. Although these ionic liquids are viscous, the apparent viscosity dependence of the rate constant could not be explained either by the Kramers-Grote-Hynes model or by the Agmon-Hopfield model for solution reactions. It is proposed that the positive and the negative charge centers of a highly polar rotational transition state are stabilized by the surrounding anions and cations, respectively, and that the ions must be rearranged so as to form highly ordered solvation shells around the charge centers of the reactant in the transition state. This requirement for the orderly solvation in the transition state results in unusually small frequency factors of 104-107 s -1.

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