Yoko Kono, K. Ishihara, A. Nagasawa
Sep 30, 1997
Citations
0
Influential Citations
13
Citations
Journal
Inorganica Chimica Acta
Abstract
Abstract Methylboronic acid–methylboronate interchange has been studied kinetically by the band shape analysis of 11 B NMR signals. The system was analyzed as two-site exchange CH 3 B(OH) 2 ⇌CH 3 B(OH) 3 − for a self-buffered aqueous solution in pH 9.5–11.4 at 24–55°C. The exchange rate was expressed as: rate=( k ex [CH 3 B(OH) 3 − ]+ k X2 )[CH 3 B(OH) 2 ]=( k ex [CH 3 B(OH) 2 ]+ k Y2 )[CH 3 B(OH) 3 − ]. The second-order rate constant, k ex (dm 3 mol −1 s −1 ) (24.2°C)=7.03×10 5 , is independent of pH, and the kinetic parameters obtained at I =0.10 M are Δ H ≠ (kJ mol −1 )=17.5±1.9 and Δ S ≠ (J mol −1 K −1 )=−74.3±6.2. A dimeric transition state is suggested for the path similarly to the interchange between boric acid and borate. The first-order rate constants k X2 and k Y2 depend on the hydroxide ion concentration indicating alternative routes for the interchange.