Organic electrochemistry

The electrosynthesis is concerned with the synthesis of organic compounds on electrochemical redox reactions . Its origin can be seen with the Kolbe electrolysis in 1849. In addition, the field of organic electrochemistry includes methods of electroanalysis , if organic compounds are recorded with them.

Basics

Cathodic reduction or anodic oxidations carried on leichtesten of molecules with pi-electron systems , such as alkenes , aromatics, or heteroatom - double bonds like C = N, C = O or C = S. Through the uptake or release of electrons at the electrodes , neutral molecules form reactive intermediate stages, radical anions or radical cations or ions, uncharged radicals , which can react accordingly. A high selectivity of the subsequent reaction is important for achieving a certain reaction product. The preferred reaction path depends on the current density , which is set by a potential difference characteristic of the redox process, the concentration of the reactants and the solvent . So is z. B. to avoid that the radicals formed as intermediates react with the solvent, if this is not desired.

An example of an anodic conversion is the dimerization of aromatics:

${\displaystyle \mathrm {2\ Ar-H\longrightarrow Ar-Ar+2\ H^{+}+2\ e^{-}} }$

An example of the cathodic conversion is the dimerization of acrylonitrile to adiponitrile :

${\displaystyle \mathrm {2\ CH_{2}=CH-CN+2\ e^{-}+2\ H_{2}O\longrightarrow NC-CH_{2}-CH_{2}-CH_{2}-CH_{2}-CN+2\ OH^{-}} }$

There are also indirect electrochemical conversions, in which the chemical oxidizing agents or reducing agents used are regenerated electrochemically. For example, when anthracene is oxidized to anthraquinone with potassium dichromate, the chromium (III) ions (Cr ³⁺ ) formed can be anodically oxidized again to dichromate ions (Cr ₂ O ₇ ²⁻ ) and thus returned to the process.

Industrial applications

Examples are the production of

• Adiponitrile as acrylonitrile ,
• Sebacic acid or its ester via Kolbe electrolysis from succinic acid or its ester,
• Hydroquinone from benzene via 1,4-benzoquinone ,
• Benzaldehyde from toluene ,
• 4-aminophenol from nitrobenzene ,
• Piperidine from pyridine ,
• 2,5-dimethoxydihydrofuran from furan ,
• Glyoxylic acid from oxalic acid ,
• organic fluorine compounds via electrofluorination .

literature

• Hartmut Wendt: Organic Electrochemistry, Chemistry in Our Time , 19th year 1985, No. 5, pp 145-155, ISSN  0009-2851
• WD Luz, E. Zirngiebl: The future of electrochemistry , chemistry in our time , 23rd year 1989, No. 5, pp 151-160, ISSN  0009-2851
• Fritz Beck: Electroorganic Chemistry: Basics and Applications , Verlag Chemie, Weinheim 1974, ISBN 3-527-25488-9 .