TY - JOUR
T1 - Reactivity of Boronic Acids toward Catechols in Aqueous Solution
AU - Suzuki, Yota
AU - Kusuyama, Daisuke
AU - Sugaya, Tomoaki
AU - Iwatsuki, Satoshi
AU - Inamo, Masahiko
AU - Takagi, Hideo D.
AU - Ishihara, Koji
N1 - Funding Information:
Financial supports were provided by JSPS KAKENHI under grant number 17K05910 and a Waseda University Grant for Special Research Projects under project number 2019C-263. We would like to thank Editage ( www.editage.jp ) for English language editing.
Publisher Copyright:
Copyright © 2020 American Chemical Society.
PY - 2020/4/17
Y1 - 2020/4/17
N2 - Fundamental information on the reactivities of boronic acids toward catechols in aqueous solution is required in all the fields dealing with boronic acid. However, comprehensive studies on reactivity are often hindered by so-called "proton ambiguity," which makes it impossible for the rate constants of boronic acid and boronate ion to be determined separately. Herein, we set up two reaction systems without proton ambiguity: (1) Alizarin Red S and (2) Tiron with several boronic acids (RB(OH)2) with different pKas and performed kinetic and equilibrium studies on the reaction systems. It was shown that the logarithms of the rate constants of RB(OH)2 and its conjugate boronate ion (RB(OH)3 -) decreased and increased linearly, respectively, with increasing pKa of RB(OH)2 for both systems. Consequently, the reactivities of RB(OH)2 and RB(OH)3 - were reversed at high RB(OH)2 pKa. It was also shown that the bulky o- substituents of phenylboronic acids retarded the backward reactions, resulting in enhancement of the formation constants of boronic acid-catechol esters.
AB - Fundamental information on the reactivities of boronic acids toward catechols in aqueous solution is required in all the fields dealing with boronic acid. However, comprehensive studies on reactivity are often hindered by so-called "proton ambiguity," which makes it impossible for the rate constants of boronic acid and boronate ion to be determined separately. Herein, we set up two reaction systems without proton ambiguity: (1) Alizarin Red S and (2) Tiron with several boronic acids (RB(OH)2) with different pKas and performed kinetic and equilibrium studies on the reaction systems. It was shown that the logarithms of the rate constants of RB(OH)2 and its conjugate boronate ion (RB(OH)3 -) decreased and increased linearly, respectively, with increasing pKa of RB(OH)2 for both systems. Consequently, the reactivities of RB(OH)2 and RB(OH)3 - were reversed at high RB(OH)2 pKa. It was also shown that the bulky o- substituents of phenylboronic acids retarded the backward reactions, resulting in enhancement of the formation constants of boronic acid-catechol esters.
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U2 - 10.1021/acs.joc.9b03326
DO - 10.1021/acs.joc.9b03326
M3 - Article
C2 - 32003994
AN - SCOPUS:85079069201
VL - 85
SP - 5255
EP - 5264
JO - Journal of Organic Chemistry
JF - Journal of Organic Chemistry
SN - 0022-3263
IS - 8
ER -