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

*この研究の対応する著者

研究成果: Article査読

17 被引用数 (Scopus)

抄録

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.

本文言語English
ページ(範囲)760-768
ページ数9
ジャーナルJournal of Physical Organic Chemistry
25
9
DOI
出版ステータスPublished - 2012 9月

ASJC Scopus subject areas

  • 物理化学および理論化学
  • 有機化学

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