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Equilibrium constants and protonation site for N-methylbenzenesulfonamides
The protonation equilibria of four substituted N-methylbenzenesulfonamides, X-MBS: X = 4-MeO (3a), 4-Me (3b), 4-Cl (3c) and 4-NO(2) (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-dono...
Autores principales: | , , , |
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Formato: | Online Artículo Texto |
Lenguaje: | English |
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Beilstein-Institut
2011
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Materias: | |
Acceso en línea: | https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3252878/ https://www.ncbi.nlm.nih.gov/pubmed/22238552 http://dx.doi.org/10.3762/bjoc.7.203 |
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author | Moreira, José A Rosa da Costa, Ana M García-Río, Luis Pessêgo, Márcia |
author_facet | Moreira, José A Rosa da Costa, Ana M García-Río, Luis Pessêgo, Márcia |
author_sort | Moreira, José A |
collection | PubMed |
description | The protonation equilibria of four substituted N-methylbenzenesulfonamides, X-MBS: X = 4-MeO (3a), 4-Me (3b), 4-Cl (3c) and 4-NO(2) (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 pK(BH+) 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. |
format | Online Article Text |
id | pubmed-3252878 |
institution | National Center for Biotechnology Information |
language | English |
publishDate | 2011 |
publisher | Beilstein-Institut |
record_format | MEDLINE/PubMed |
spelling | pubmed-32528782012-01-11 Equilibrium constants and protonation site for N-methylbenzenesulfonamides Moreira, José A Rosa da Costa, Ana M García-Río, Luis Pessêgo, Márcia Beilstein J Org Chem Full Research Paper The protonation equilibria of four substituted N-methylbenzenesulfonamides, X-MBS: X = 4-MeO (3a), 4-Me (3b), 4-Cl (3c) and 4-NO(2) (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 pK(BH+) 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. Beilstein-Institut 2011-12-27 /pmc/articles/PMC3252878/ /pubmed/22238552 http://dx.doi.org/10.3762/bjoc.7.203 Text en Copyright © 2011, Moreira et al. https://creativecommons.org/licenses/by/2.0https://www.beilstein-journals.org/bjoc/termsThis is an Open Access article under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. The license is subject to the Beilstein Journal of Organic Chemistry terms and conditions: (https://www.beilstein-journals.org/bjoc/terms) |
spellingShingle | Full Research Paper Moreira, José A Rosa da Costa, Ana M García-Río, Luis Pessêgo, Márcia Equilibrium constants and protonation site for N-methylbenzenesulfonamides |
title | Equilibrium constants and protonation site for N-methylbenzenesulfonamides |
title_full | Equilibrium constants and protonation site for N-methylbenzenesulfonamides |
title_fullStr | Equilibrium constants and protonation site for N-methylbenzenesulfonamides |
title_full_unstemmed | Equilibrium constants and protonation site for N-methylbenzenesulfonamides |
title_short | Equilibrium constants and protonation site for N-methylbenzenesulfonamides |
title_sort | equilibrium constants and protonation site for n-methylbenzenesulfonamides |
topic | Full Research Paper |
url | https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3252878/ https://www.ncbi.nlm.nih.gov/pubmed/22238552 http://dx.doi.org/10.3762/bjoc.7.203 |
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