RT Journal Article
T1 Equilibrium constants and protonation site for N-methylbenzenesulfonamides
A1 Moreira, José A.
A1 Costa, Ana M. Rosa da
A1 García Río, Luis
A1 Pessêgo, Márcia Isabel Duarte
K1 Linear free-energy relationships
K1 N-methylbenzenesulfonamides
K1 Protonation equilibrium
AB The protonation equilibria of four substituted N-methylbenzenesulfonamides, X-MBS: X = 4-MeO (3a), 4-Me (3b), 4-Cl (3c) and 4-NO2 (3d), in aqueous sulfuric acid were studied at 25 °C by UV–vis spectroscopy. As expected, the values for the acidity constants are highly dependent on the electron-donor character of the substituent (the pKBH+ values are −3.5 ± 0.2, −4.2 ± 0.2, −5.2 ± 0.3 and −6.0 ± 0.3 for 3a, 3b, 3c and 3d, respectively). The solvation parameter m* is always higher than 0.5 and points to a decrease in the importance of solvation on the cation stabilization as the electron-donor character of the substituent increases. Hammett plots of the equilibrium constants showed a better correlation with the σ+ substituent parameter than with σ, which indicates that the initial protonation site is the oxygen atom of the sulfonyl group
PB Beilstein Institute
SN 1860-5397
YR 2011
FD 2011
LK http://hdl.handle.net/10347/22450
UL http://hdl.handle.net/10347/22450
LA eng
NO Moreira, J. A.; Rosa da Costa, A. M.; García-Río, L.; Pessêgo, M. Beilstein J. Org. Chem. 2011, 7, 1732–1738. doi:10.3762/bjoc.7.203
NO This work was funded by Fundação para a Ciência e Tecnologia – Portugal (POCI/QUI/57077/2004) and CIQA, Centre for Research in Chemistry of Algarve. M. Pessêgo acknowledges FCT for PhD Grant SFRH/BD/60911/2009.
DS Minerva
RD 24 abr 2026