Higher reactivity of 3-pyridinium boronic acid compared with 3-pyridinium boronate ion toward 4-isopropyltropolone in acidic aqueous solution

Fundamental reaction analyses for an effective organoboron-based chemosensor

Satoshi Iwatsuki, Yuki Kanamitsu, Hidetaka Ohara, Eisuke Watanabe, Koji Ishihara

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    15 Citations (Scopus)

    Abstract

    The pK as of 3-pyridylboronic acid and its derivatives were determined spectrophotometrically. Most of them had two pK as assignable to the boron center and pyridine moiety. The pK a assignment performed by 11B nuclear magnetic resonance spectroscopy revealed that both boron centers in 3-pyridylboronic acid [3-PyB(OH) 2] and the N-methylated derivative [3-(N-Me)Py +B(OH) 2] have strong acidities (pK a = 4.4 for both). It was found that introduction of a substituent to pyridine-C atom in 3-pyridylboronic acid drastically increased the acidity of the pyridinium moiety, but decreased the acidity of the boron center, whereas the introduction to pyridine-N atom had no influence on the acidity of the boron center. Kinetic studies on the complexation reactions of 3-pyridinium boronic acid [3-HPy +B(OH) 2] with 4-isopropyltropolone (Hipt) carried out in strongly acidic aqueous solution indicated that the positive charge on the boronic acid influenced little on its reactivity; 3-HPy +B(OH) 2 reacts with Hipt and protonated H 2ipt +, and its reactivity was in line with those of a series of boronic acids. Kinetics in weakly acidic aqueous solution revealed that 3-HPy +B(OH) 2 reacts with Hipt faster than its conjugate boronate [3-HPy +B(OH) 3 -], which is consistent with our recent results. The reactivity of 3-(N-Me)Py +B(OH) 2 towards Hipt was also examined kinetically; the reactivities of 3-(N-Me)Py +B(OH) 2 and 3-(N-Me)Py +B(OH) 3 - are almost the same as those of their original 3-HPy +B(OH) 2 and 3-HPy +B(OH) 3 -, respectively.

    Original languageEnglish
    Pages (from-to)760-768
    Number of pages9
    JournalJournal of Physical Organic Chemistry
    Volume25
    Issue number9
    DOIs
    Publication statusPublished - 2012 Sep

    Fingerprint

    Boronic Acids
    Boron
    Acidity
    reactivity
    Ions
    aqueous solutions
    acidity
    acids
    boron
    Acids
    pyridines
    ions
    Derivatives
    Atoms
    Kinetics
    Complexation
    Nuclear magnetic resonance spectroscopy
    magnetic resonance spectroscopy
    kinetics
    atoms

    Keywords

    • acid dissociation
    • boronate ion
    • boronic acid
    • kinetics
    • mechanism

    ASJC Scopus subject areas

    • Organic Chemistry
    • Physical and Theoretical Chemistry

    Cite this

    @article{17e0aafb3d2743fe9726d3168fc0c7a5,
    title = "Higher reactivity of 3-pyridinium boronic acid compared with 3-pyridinium boronate ion toward 4-isopropyltropolone in acidic aqueous solution: Fundamental reaction analyses for an effective organoboron-based chemosensor",
    abstract = "The pK as of 3-pyridylboronic acid and its derivatives were determined spectrophotometrically. Most of them had two pK as assignable to the boron center and pyridine moiety. The pK a assignment performed by 11B nuclear magnetic resonance spectroscopy revealed that both boron centers in 3-pyridylboronic acid [3-PyB(OH) 2] and the N-methylated derivative [3-(N-Me)Py +B(OH) 2] have strong acidities (pK a = 4.4 for both). It was found that introduction of a substituent to pyridine-C atom in 3-pyridylboronic acid drastically increased the acidity of the pyridinium moiety, but decreased the acidity of the boron center, whereas the introduction to pyridine-N atom had no influence on the acidity of the boron center. Kinetic studies on the complexation reactions of 3-pyridinium boronic acid [3-HPy +B(OH) 2] with 4-isopropyltropolone (Hipt) carried out in strongly acidic aqueous solution indicated that the positive charge on the boronic acid influenced little on its reactivity; 3-HPy +B(OH) 2 reacts with Hipt and protonated H 2ipt +, and its reactivity was in line with those of a series of boronic acids. Kinetics in weakly acidic aqueous solution revealed that 3-HPy +B(OH) 2 reacts with Hipt faster than its conjugate boronate [3-HPy +B(OH) 3 -], which is consistent with our recent results. The reactivity of 3-(N-Me)Py +B(OH) 2 towards Hipt was also examined kinetically; the reactivities of 3-(N-Me)Py +B(OH) 2 and 3-(N-Me)Py +B(OH) 3 - are almost the same as those of their original 3-HPy +B(OH) 2 and 3-HPy +B(OH) 3 -, respectively.",
    keywords = "acid dissociation, boronate ion, boronic acid, kinetics, mechanism",
    author = "Satoshi Iwatsuki and Yuki Kanamitsu and Hidetaka Ohara and Eisuke Watanabe and Koji Ishihara",
    year = "2012",
    month = "9",
    doi = "10.1002/poc.2915",
    language = "English",
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    pages = "760--768",
    journal = "Journal of Physical Organic Chemistry",
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    publisher = "John Wiley and Sons Ltd",
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    TY - JOUR

    T1 - Higher reactivity of 3-pyridinium boronic acid compared with 3-pyridinium boronate ion toward 4-isopropyltropolone in acidic aqueous solution

    T2 - Fundamental reaction analyses for an effective organoboron-based chemosensor

    AU - Iwatsuki, Satoshi

    AU - Kanamitsu, Yuki

    AU - Ohara, Hidetaka

    AU - Watanabe, Eisuke

    AU - Ishihara, Koji

    PY - 2012/9

    Y1 - 2012/9

    N2 - The pK as of 3-pyridylboronic acid and its derivatives were determined spectrophotometrically. Most of them had two pK as assignable to the boron center and pyridine moiety. The pK a assignment performed by 11B nuclear magnetic resonance spectroscopy revealed that both boron centers in 3-pyridylboronic acid [3-PyB(OH) 2] and the N-methylated derivative [3-(N-Me)Py +B(OH) 2] have strong acidities (pK a = 4.4 for both). It was found that introduction of a substituent to pyridine-C atom in 3-pyridylboronic acid drastically increased the acidity of the pyridinium moiety, but decreased the acidity of the boron center, whereas the introduction to pyridine-N atom had no influence on the acidity of the boron center. Kinetic studies on the complexation reactions of 3-pyridinium boronic acid [3-HPy +B(OH) 2] with 4-isopropyltropolone (Hipt) carried out in strongly acidic aqueous solution indicated that the positive charge on the boronic acid influenced little on its reactivity; 3-HPy +B(OH) 2 reacts with Hipt and protonated H 2ipt +, and its reactivity was in line with those of a series of boronic acids. Kinetics in weakly acidic aqueous solution revealed that 3-HPy +B(OH) 2 reacts with Hipt faster than its conjugate boronate [3-HPy +B(OH) 3 -], which is consistent with our recent results. The reactivity of 3-(N-Me)Py +B(OH) 2 towards Hipt was also examined kinetically; the reactivities of 3-(N-Me)Py +B(OH) 2 and 3-(N-Me)Py +B(OH) 3 - are almost the same as those of their original 3-HPy +B(OH) 2 and 3-HPy +B(OH) 3 -, respectively.

    AB - The pK as of 3-pyridylboronic acid and its derivatives were determined spectrophotometrically. Most of them had two pK as assignable to the boron center and pyridine moiety. The pK a assignment performed by 11B nuclear magnetic resonance spectroscopy revealed that both boron centers in 3-pyridylboronic acid [3-PyB(OH) 2] and the N-methylated derivative [3-(N-Me)Py +B(OH) 2] have strong acidities (pK a = 4.4 for both). It was found that introduction of a substituent to pyridine-C atom in 3-pyridylboronic acid drastically increased the acidity of the pyridinium moiety, but decreased the acidity of the boron center, whereas the introduction to pyridine-N atom had no influence on the acidity of the boron center. Kinetic studies on the complexation reactions of 3-pyridinium boronic acid [3-HPy +B(OH) 2] with 4-isopropyltropolone (Hipt) carried out in strongly acidic aqueous solution indicated that the positive charge on the boronic acid influenced little on its reactivity; 3-HPy +B(OH) 2 reacts with Hipt and protonated H 2ipt +, and its reactivity was in line with those of a series of boronic acids. Kinetics in weakly acidic aqueous solution revealed that 3-HPy +B(OH) 2 reacts with Hipt faster than its conjugate boronate [3-HPy +B(OH) 3 -], which is consistent with our recent results. The reactivity of 3-(N-Me)Py +B(OH) 2 towards Hipt was also examined kinetically; the reactivities of 3-(N-Me)Py +B(OH) 2 and 3-(N-Me)Py +B(OH) 3 - are almost the same as those of their original 3-HPy +B(OH) 2 and 3-HPy +B(OH) 3 -, respectively.

    KW - acid dissociation

    KW - boronate ion

    KW - boronic acid

    KW - kinetics

    KW - mechanism

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    U2 - 10.1002/poc.2915

    DO - 10.1002/poc.2915

    M3 - Article

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    EP - 768

    JO - Journal of Physical Organic Chemistry

    JF - Journal of Physical Organic Chemistry

    SN - 0894-3230

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    ER -