Organic mercury compounds

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The organic mercury compound dimethylmercury contains a covalent bond between the carbon atoms and mercury.

Organic mercury compounds (also known as organic mercury compounds or organic mercury compounds ) are organometallic chemical compounds that contain at least one covalent bond between mercury (II) and organic residues. They have the general formulas R 1 -Hg-X or R 1 -Hg-R 2 , where R 1 and R 2 are alkyl or aryl groups and X represents an anionic binding partner. The covalent C-Hg bond is stable to air and moisture under normal conditions, but is light-sensitive ( photolabile ). When exposed to light, the C-Hg bond is cleaved homolytically with the formation of radicals. Recombination of the radicals creates the compound R 1 -R 1 from the compound R 1 -Hg-X . Examples of R 1 aryl groups: Biphenyl formation from two phenyl radicals and benzidine formation from two aniline radicals.

The toxicity of organic mercury compounds poses a risk in principle, but can be beneficial if used in a controlled manner. Use is very limited. For example, thiomersal is used as an antiseptic in accordance with the Cosmetics Ordinance in very low concentrations to preserve make-up and make-up removal products for the eyes.

synthesis

Organic mercury compounds can be synthesized in a number of ways . In terms of their chemical reactivity, they are similar to organic palladium compounds . The polarity of the bond between carbon and mercury changes with the nature of the organic residue.

Mercury of aromatics

Mercury (II) acetate, a mercuration reagent

Electron- rich aromatic hydrocarbons are directly mercured when treated with mercury (II) acetate . The acetate group remaining on the mercury atom can be displaced by chloride. An example is the synthesis of o -chloromercuriphenol:

C 6 H 5 OH + Hg (O 2 CCH 3 ) 2 → C 6 H 4 (OH) -2-HgO 2 CCH 3 + CH 3 CO 2 H
C 6 H 4 (OH) -2-HgO 2 CCH 3 + NaCl → C 6 H 4 (OH) -2-HgCl + NaO 2 CCH 3

The first such reaction, including a mercuration of benzene , was reported by Otto Dimroth between 1898 and 1902.

Addition to Alkenes (Oxymercuration)

The Hg 2+ cation binds to alkenes and induces the addition of hydroxide (in the presence of alcohols, alkoxide ). The oxymercuration generally gives very good yields under very mild conditions. This reaction is called the Hofmann-Sand reaction .
For example, treatment of 1-methylcyclohexene with mercury (II) acetate in aqueous tetrahydrofuran gives an α-mercury ester:

Oxymercuration reaction scheme

The α-mercury ester can be converted as follows:

CH 3 OCH 2 CH (HgO 2 CCH 3 ) CO 2 CH 3 + Br 2 → CH 3 OCH 2 CHBrCO 2 CH 3 + BrHgO 2 CCH 3
  • Amines or other nucleophiles can also be attached analogously . So instead of water z. B. attack the alcohol of a side chain intramolecularly and form a cyclic ether .

Reaction of Hg (II) compounds with carbanions

A general synthetic route to organic mercury compounds is via alkylation of Hg (II) salts with Grignard reagents or organolithium compounds .

Diethyl mercury results from the reaction of mercury chloride with two equivalents of ethyl magnesium bromide , a conversion that is typically carried out in diethyl ether . The resulting (CH 3 CH 2 ) 2 Hg is a high density liquid (2.466 g / cm 3 ) that boils at 57 ° C at 16 torr. The compound is only slightly soluble in ethanol , but readily soluble in ether.

Similarly, diphenylmercury ((C 6 H 5 ) 2 Hg, melting point 121-123 ° C) can be produced by reacting mercury chloride and phenyl magnesium bromide . A similar preparation uses phenyl sodium in the presence of mercury (II) salts.

Other methods

Hg (II) compounds can be alkylated by treatment with diazonium salts in the presence of elemental copper . In this way, 2-chloromercuric naphthalene was produced.

use

The following organic mercury compounds have (or have had) an application:

  • 4-chloromercuri-benzoic acid

  • Merbromin

  • Mersalyl

  • Thimerosal

Synthesis reagents

Due to the easily controllable conditions under which the cleavage of the C-Hg bond occurs, organic mercury compounds are versatile synthetic reagents.

Dichlorocarbon donor

Phenylmercury can with sodium trichloroacetate -Quecksilber be converted to phenyl (trichloromethyl). This compound releases dichlorocarbene when heated :

C 6 H 5 HgCl + CCl 3 COONa → C 6 H 5 HgCCl 3 + CO 2 + NaCl.
C 6 H 5 HgCCl 3 → C 6 H 5 HgCl + CCl 2 .

Phenyl donor

Diphenylmercury can serve as a source of the phenyl radical (C 6 H 5 · ) in certain syntheses . Treatment with aluminum gives aluminum triphenyl :

3 Ph 2 Hg + 2 Al → 2 Ph 3 Al + 3 Hg

Transmetalation

As mentioned, organic mercury compounds react with halogens to form the corresponding organic halide. Organic mercury compounds are usually used in transmetallation reactions with lanthanides and alkaline earth metals .

The cross-coupling of organic mercury compounds with organic halides is catalyzed by palladium, which provides a method for the formation of CC bonds. As a rule, the reaction proceeds with low selectivity, but this can be increased in the presence of halides. The use of Hg (II) reagents has been demonstrated in the carbonylation of lactones under palladium-catalyzed conditions (CC bond and cis-ester formation).

Bactericides, fungicides, insecticides, antiseptics, preservatives

The use of organic mercury compounds as bactericides , fungicides, insecticides, antiseptics or preservatives is based on their toxicity. Their application is limited.

Incorrect use and accumulation of the toxic heavy metal mercury ensured that since 1982 organic mercury compounds may no longer be used for dressing seeds in Germany .

In Germany, thiomersal is permitted as an antiseptic in accordance with the Cosmetics Ordinance in concentrations of up to 0.007% (calculated as mercury) to preserve make-up and make-up removal products for the eyes.

The mercury-containing dye merbromin was sold in Germany until 2003 in the form of a two percent aqueous solution as an antiseptic (trade name Mercurochrome ).

Diuretics such as mersalyl used to be common but have been replaced by thiazides and loop diuretics , which are safer and work longer.

Binding to thiols

Affinity chromatography

Thiols (R-SH), also known as mercaptans ( Latin: mercurium captāns 'mercury trapping' due to their tendency to bind to mercury with a high affinity), as well as thiolates (RS - ) and thioketones (R 2 C = S), soft nucleophiles, form a stable coordination complex with mercury (II), a soft electrophile.

This effect can be used to isolate thiolated compounds - for example 2-thiouridine- containing RNA or cysteine- containing proteins - from a mixture or a biological preparation by affinity chromatography with covalently bound to carrier material (for example agarose , Sepharose , glass beads, etc.) Performs organic mercury compounds.

Titration

4-chloro-mercuribenzoic acid can be used to titrate SH groups.

Selective inhibition

In biochemical and biological research, organic mercury compounds are used as more or less selective inhibitors because of their strong binding to cysteine ​​groups in proteins. The selectivity in the inhibition is based on the organic part of the compound.

An example of this is the marking and identification of the transmembrane phosphate transporter of the mitochondrial membrane. Even at very low concentrations ( nM range), Mersalyl inhibits the transport of phosphate into the mitochondria. Since Mersalyl is membrane- impermeable due to the anionic organic part, the inhibition takes place “from the outside”, from the cytoplasmic side. This inhibition is reversible by adding thiol reagents (cysteine, mercaptoethanol etc.) . The selective marking takes place in the following steps:

  • Phosphate transport in mitochondria is inhibited with very small amounts of Mersaly, i. H. the Transporter-SH group is "protected" with Mersalyl.
  • An excess of the membrane-permeable SH reagent N -ethylmaleimide (NEM) is added, whereby all “free” SH groups are covalently and irreversibly blocked.
  • The excess of NEM is neutralized with cysteine; at the same time the “protective” Mersalyl is removed.
  • Mitochondrons are separated from the reaction mixture (NEM, cysteine ​​and Mersalyl) by centrifugation .
  • The phosphate transporter SH group that is now available can be selectively labeled with radioactive or spin-labeled NEM.

Selective activation

An example of the activation of an enzyme is the protease procollagenase from fibroblasts of the human skin, which can be activated by four different organic mercury compounds, 4-chloro-mercuribenzoic acid, mersalyl, 4-aminophenylmercuric acetate and phenylmercuric chloride.

literature

Web links

See also

Individual evidence

  1. ↑ Lexicon of Chemistry: Organic Mercury Compounds ; Retrieved April 6, 2017.
  2. ↑ Development and application of a novel analytical method for the determination of organic mercury compounds in sediments with the help of a coupled SFC-AFS system. University of Hamburg e-Dissertation, 1998, accessed on August 10, 2015 .
  3. ↑ Naarmann, Herbert; Naegele, Dieter: Polymers obtainable by oxidative polymerisation. June 19, 1987, accessed August 1, 2015 .
  4. ↑ H. Hintermann: Organomercurials. Their Formation and Pathways in the Environment  (= Metal Ions in Life Sciences), Volume 7. RSC publishing, Cambridge 2010, ISBN 978-1-84755-177-1 , pp. 365-401.
  5. ↑ M. Aschner, N. Onishchenko and S. Ceccatelli: Toxicology of Alkylmercury Compounds  (= Metal Ions in Life Sciences), Volume 7. RSC publishing, Cambridge 2010, ISBN 978-1-84755-177-1 , p. 403– 434.
  6. ^ Russell N. Grimes: Metal Interactions with Boron Clusters . Springer Science & Business Media, November 11, 2013, ISBN 978-1-4899-2154-3 , p. 209.
  7. ↑ Whitmore FC, Hanson ER: o-Chloromercuriphenol In: Organic Syntheses . 4, 1925, p. 13, doi : 10.15227 / orgsyn.004.0013 ; Coll. Vol. 1, 1941, p. 161 ( PDF ).
  8. ↑ Otto Dimroth : Direct introduction of mercury into aromatic compounds . In: Reports of the German Chemical Society . 31, No. 2, 1898, pp. 2154-2156. doi : 10.1002 / cber.189803102162 .
  9. ↑ Otto Dimroth : About the action of mercury oxide salts on aromatic compounds . In: Reports of the German Chemical Society . 32, No. 1, 1899, pp. 758-765. doi : 10.1002 / cber.189903201116 .
  10. ↑ Otto Dimroth : About the mercuration of aromatic compounds . In: Reports of the German Chemical Society . 35, No. 2, 1902, pp. 2032-2045. doi : 10.1002 / cber.190203502154 .
  11. ↑ Beyer-Walter, Textbook of Organic Chemistry , 23rd edition, S. Hirzel Verlag 1998, ISBN 3-7776-0808-4 .
  12. ↑ KA Hofmann and J. Sand: About the behavior of mercuric salts against olefins . In: Reports of the German Chemical Society . 33, No. 1, 1900, pp. 1340-1353. doi : 10.1002 / cber.190003301231 .
  13. ^ FA Carey, RJ Sundberg, Organic Chemistry , Wiley-VCH Verlag, 2004, ISBN 3-527-29217-9 .
  14. ^ Siegfried Hauptmann : Organic Chemistry , 2nd revised edition, VEB Deutscher Verlag für Grundstoffindindustrie, Leipzig, 1985, p. 547, ISBN 3-342-00280-8 .
  15. ↑ WA Herrmann (Ed.): Synthetic Methods of Organometallic and Inorganic Chemistry Volume 5, Copper, Silver, Gold, Zinc, Cadmium, and Mercury , ISBN 3-13-103061-5 .
  16. ↑ Calvery, HO: Diphenylmercury In: Organic Syntheses . 4, 1941, pp. 54-55, doi : 10.15227 / orgsyn.009.0054 ; Coll. Vol. 1, 1941, p. 228 ( PDF ).
  17. ↑ TO Nesmajanow: β-Naphthylmercuric Chloride In: Organic Syntheses . 12, 1932, p. 54, doi : 10.15227 / orgsyn.012.0054 ; Coll. Vol. 2, 1943, p. 432 ( PDF ).
  18. ↑ TJ Logan: Phenyl (trichloromethyl) mercury In: Organic Syntheses . 46, 1966, p. 98, doi : 10.15227 / orgsyn.046.0098 ; Coll. Vol. 5, 1973, p. 969 ( PDF ).
  19. ^ TA Neely, William W. Schwarz and Herbert W. Vaughan: Triphenylaluminium In: Organic Syntheses . 45, 1965, p. 107, doi : 10.15227 / orgsyn.045.0107 ; Coll. Vol. 5, 1973, p. 1116 ( PDF ).
  20. ↑ Pavel Kočovský: Reactivity control in palladium-catalyzed reactions: a personal account , J. Organometallic Chemistry 687 (2003), pp. 256-268. doi: 10.1016 / j.jorganchem.2003.07.008 .
  21. ↑ Michael Binnewies, Maik Finze, Manfred Jäckel, Peer Schmidt, Helge Willner and Geoff Rayner-Canham: General and Inorganic Chemistry . Springer-Verlag, December 2, 2016, ISBN 978-3-662-45067-3 , p. 836.
  22. ↑ Saskia Dombrowski: Reports on Food Safety 2009: National reporting to the EU - National Residue Control Plan (NRKP) and Import Residue Control Plan (ERKP) - Report on the official feed control 2009 . Springer-Verlag, June 22, 2011, ISBN 978-3-0348-0128-7 , p. 43.
  23. ↑ Appendix 6 to Section 3 of the Cosmetics Ordinance .
  24. ↑ Merbromin in the mirror of expert opinions. In: Pharmaceutical newspaper. Edition 39/2003.
  25. ↑ New formulation form: Mercury for use on the skin ( PDF ).
  26. ^ Oxford American Dictionaries ( Mac OS X Leopard ).
  27. ^ Dictionary.com: mercaptan
  28. ↑ Jonathan Clayden, Nick Greeves, and Stuart Warren: Organic Chemistry . OUP Oxford, March 15, 2012, ISBN 978-0-19-927029-3 , p. 658.
  29. ↑ Masao Ono and Masaya Kawakami: Separation of Newly-Synthesized RNA by Organomercurial Agarose Affinity Chromatography . In: J. Biochem. . 81, No. 5, 1977, pp. 1247-1252. PMID 19428 .
  30. ^ E. Quagliariello and F. Palmieri, Structure and Function of Membrane Proteins: Proceedings of the International Symposium on Structure and Function of Membrane Proteins Held in Selva Di Fasano (Italy), May 23-26, 1983 . Elsevier, May 21, 2014, ISBN 978-1-4831-6290-4 , pp. 43-52.
  31. ↑ GP Stricklin, JJ Jeffrey, WT Roswit and AZ Eisen: Human skin fibroblast procollagenase: mechanisms of activation by organomercurials and trypsin , Biochemistry (1983), Vol. 22 (1), pp. 61-68. PMID 6299336 .