Kinetic and Spectroscopic Characterisation of Highly Reactive Methanesulfonates. Leaving Group Effects for Solvolyses and Comments on Geminal Electronic Effects Influencing S\(_N\)1 Reactivity
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- Highly reactive methanesulfonates (mesylates, ROMs) have been prepared from 1-phenylethanol. cyclohex-2-en-1-ol, diphenylmethanol and p-methoxybenzyl alcohol by treatment with methanesulfonyl chloride and triethylamine in dichloro- or trichloro-methane at - 20 to 0 °C. The mesylates. characterised in solution by \(^1\)H and \(^{13}\)C NMR at -20 °C, were obtained in satisfactory purity (ca. 95%) in cold solutions but they decomposed by reaction with chloride, triethylamine or the parent alcohol. Rate constants for solvolyses in aqueous acetoneHighly reactive methanesulfonates (mesylates, ROMs) have been prepared from 1-phenylethanol. cyclohex-2-en-1-ol, diphenylmethanol and p-methoxybenzyl alcohol by treatment with methanesulfonyl chloride and triethylamine in dichloro- or trichloro-methane at - 20 to 0 °C. The mesylates. characterised in solution by \(^1\)H and \(^{13}\)C NMR at -20 °C, were obtained in satisfactory purity (ca. 95%) in cold solutions but they decomposed by reaction with chloride, triethylamine or the parent alcohol. Rate constants for solvolyses in aqueous acetone and aqueous ethanol have been determined by a fast response conductimetric method. Product selectivities for solvolyses of pmethoxybenzyl mesylate in aqueous ethanol and methanol at 0 °C have been determined by HPLC. From additional new or Iiterature kinetic data for solvolyses of corresponding bromides. chlorides and p-nitrobenzoates (OPNB). Br/CI. OMs/Br and OMs/OPNB rate ratios were calculated; the results are consistent with electronic effects stabilising the carbocationic transition states and increasing OMs/Br rate ratios for these SN 1 solvolyses; none of the evidence supports a geminal electronic effect on Br/CI rate ratios (e.g. caused by stabilisation of the initial state in pmethoxybenzyl chloride). Steric effects on ester /halide rate ratios for solvolyses of tertiary substrates are confirmed. Relative rates over a 10\(^{16}\) range for ester and halide leaving groups are evaluated for solvolyses of 1-phenylethyl substrates in 80% ethanol-water. updating previous work by Noyce et al. (1972).…
Autor(en): | T. W. Bentley, Manfred Christl, R. Kemmer, G. Llewellyn, J. E. Oakley |
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URN: | urn:nbn:de:bvb:20-opus-58748 |
Dokumentart: | Artikel / Aufsatz in einer Zeitschrift |
Institute der Universität: | Fakultät für Chemie und Pharmazie / Institut für Organische Chemie |
Sprache der Veröffentlichung: | Englisch |
Erscheinungsjahr: | 1994 |
Originalveröffentlichung / Quelle: | In: Journal of the Chemical Society / Perkin transactions / 2 (1994) 2531-2538. |
Allgemeine fachliche Zuordnung (DDC-Klassifikation): | 5 Naturwissenschaften und Mathematik / 54 Chemie / 540 Chemie und zugeordnete Wissenschaften |
Normierte Schlagworte (GND): | Organische Chemie |
Datum der Freischaltung: | 29.09.2011 |
Lizenz (Deutsch): | Deutsches Urheberrecht |