Oxymercuration

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The oxymercuration (also: Hofmann Sand reaction ) is a method to alkenes with high selectivity to alcohols according to the Markownikoff Rule to transfer. In oxymercuration, water is attached to an alkene with the aid of mercury (II) acetate . This hydration is similar to the addition of hydrohalic acids to alkenes and belongs to the electrophilic addition type of reaction .

execution

The alkene is reacted with water and mercury acetate. Tetrahydrofuran , which can dissolve all components, is usually used as the solvent . The resulting mercury alcohol is reduced to alcohol with sodium borohydride and sodium hydroxide solution .

Oxymercuration reaction scheme

The oxymercuration generally gives very good yields under very mild conditions. Analogously, also alcohols , amines or other nucleophiles accumulate. So instead of water z. B. attack the alcohol of a side chain intramolecularly and form a cyclic ether .

mechanism

Mercury (II) acetate partially dissociates in water to form H 3 C − COO - , H 3 C − COOHg + and Hg 2+ . The H 3 C − COOHg + ion attaches itself to the double bond of the alkene and forms a mercurinium ion. Alcohol (R = alkyl, aryl) or water (R = H) is added to this, resulting in a mercury ether (R = alkyl, aryl) or mercury alcohol (R = H):

Oxymercuration reaction mechanism

The H 3 C − COOHg + residue on the ether (or alcohol, if R is a hydrogen atom) can be split off with sodium borohydride and sodium hydroxide solution. This creates acetate ions , mercury and the desired ether (R = alkyl, aryl) or alcohol (R = H):

Demerkurierung

criticism

Oxymercuration is unsuitable for industrial applications because of the low atom economy of the reaction and the toxic properties of organic mercury compounds . Therefore the application of the reaction is limited to the laboratory scale. An alternative is offered by epoxidations , which also take place on an industrial scale with catalysis in sufficient yields.

Individual evidence

  1. ↑ Beyer-Walter, Textbook of Organic Chemistry , 23rd Edition, S. Hirzel Verlag 1998 ISBN 3-7776-0808-4 .
  2. ^ A b F. A. Carey, RJ Sundberg, Organic Chemistry , Wiley-VCH Verlag, 2004, ISBN 3-527-29217-9 .
  3. ^ Zerong Wang: Comprehensive Organic Name Reactions and Reagents . John Wiley & Sons, New Jersey 2009, ISBN 978-0-471-70450-8 , pp. 1473-1476 .
  4. ^ A b Siegfried Hauptmann : Organic Chemistry , 2nd Edition, VEB Deutscher Verlag für Grundstoffindustrie, Leipzig, 1985, p. 548, ISBN 3-342-00280-8 .
  5. ↑ Entry on Hofmann-Sand reaction. In: Römpp Online . Georg Thieme Verlag, accessed on June 15, 2014.