Mesylgruppe

Als Mesylgruppe (CH₃SO₂–) – auch Methansulfonylgruppe – wird der kovalent gebundene Rest der Methansulfonsäure bezeichnet. Es handelt sich dabei um die Ester der Methansulfonsäure. Der Name leitet sich von ihrer systematischen Bezeichnung Methansulfonyl ab. Die Verbindungen werden gewöhnlich als Mesylate bezeichnet und sind abzugrenzen von den Salzen der Methansulfonsäure (Mesilate). In Strukturformeln wird die Mesylgruppe manchmal mit Ms oder Mes abgekürzt. Sie ist strukturell mit der Triflylgruppe verwandt.

Herstellung

Mesylate können durch die Reaktion von Methansulfonylchlorid mit Alkoholen in Gegenwart von Basen hergestellt werden:^[1]

Eigenschaften

Die Methansulfonsäure gehört zu den starken Säuren. Das Mesylation ist folglich eine schwache Base, welche gut mesomeriestabilisiert ist:

Aus diesem Grund stellt die Mesyllatgruppe eine gute Abgangsgruppe dar, welche durch geeignete Nukleophile leicht unter Substitution abgespalten werden kann. Alkylmesylate sind gute Alkylierungsmittel. Auf Grund ihrer Fähigkeit zur Alkylierung von DNA gelten die Mesylverbindungen Methansulfonsäureallylester, Methansulfonsäureethylester und Methansulfonsäuremethylester als mögliche Cancerogene.^[2]

Verwendung

In ihrer Eigenschaft als Abgangsgruppe findet die Mesylatgruppe Anwendung in der präparativen Organischen Chemie.^[1] Durch Überführung von Alkoholen in Mesylate wird die schlechte Abgangsgruppe OH⁻ in eine gute Abgangsgruppe CH₃SO₃⁻ überführt, wodurch nucleophile Substitutionsreaktionen an dieser Position ermöglicht werden:

Diese Anwendung ist nicht besonders atomökonomisch, da stets stöchiometrische Mengen von Abfallstoffen mit vergleichsweise hoher Molekularmasse gebildet werden. Deshalb wird die Synthesemethode vorwiegend im Labormaßstab und kaum in technischen Prozessen eingesetzt.

Einzelnachweise

↑ ^a ^b H. P. Latscha, U. Kazmaier, H. A. Klein: Organische Chemie: Chemie-Basiswissen II, 6. Auflage, 2008, S. 173, Springer, Berlin, ISBN 3-540-77106-9.
↑ Eintrag zu Methansulfonsäure. In: Römpp Online. Georg Thieme Verlag, abgerufen am 29. September 2014.

Weblinks

Commons: Mesylgruppe – Sammlung von Bildern, Videos und Audiodateien

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