Carboxylation

Carboxylation as is known in the chemical reaction for introducing a carboxyl group into an organic compound, carboxylic acid produced.

  • 3.1 carboxylation of Acetyleniden
  • 3.2 carboxylation of phenolates
  • 3.3 carboxylation of alkyl magnesium halides
  • 3.4 carboxylation by phosgene
  • 3.5 Biochemical carboxylations

Reaction mechanism

The carboxylation reaction mechanism extends from here mostly as a nucleophilic addition across a carbon-heteroatom (CX ) multiple bond, in this case, a carbon- oxygen double bond (see: carbonyl group). At the other viewpoint but - on the side of the second reactant - the reaction can be also assigned to the electrophilic substitutions (see examples).

Reactants

Carboxylierungsreagenz

The carboxylation can be conducted with carbon dioxide as the reactant is not only, but also with metal complexes, such as nickel tetracarbonyl, or phosgene ( here with subsequent hydrolysis ). All these reactants in common is the presence of a " positivised " ( electron-deficient ) carbon atom, which is engaged by the nucleophile.

Nucleophile

As the nucleophile are electron-rich compounds such as anions (e.g., Acetylenide and phenates ) or compounds having a charge imbalance ( dipoles, such as alkylmagnesium halides ( Grignard compounds) or polarized aromatics ).

Examples

Carboxylation of Acetyleniden

Acetylenide react with carbon dioxide in the form of dry ice to alkynoic:

Carboxylation of phenolates

The preparation of 2 - hydroxybenzoic acids is carried out by carboxylation of phenates with carbon dioxide ( the Kolbe-Schmitt reaction):

Viewed from the side of the phenol occurs electrophilic substitution of a hydrogen for the carboxy group on the aromatic ring.

Carboxylation of alkyl magnesium halides

Carboxylic acids are formed by carboxylation of alkyl magnesium halides ( Grignard reagents ) at room temperature:

Carboxylation by phosgene

In the presence of a Lewis acid as catalyst, aromatics may be carboxylated by means of phosgene:

This reaction is based on the mechanism of an electrophilic substitution. The resulting carboxylic acid chloride is still to be subsequently hydrolyzed to the carboxylic acid and hydrogen chloride.

Biochemical carboxylations

The transmission of the carboxyl groups is important in biochemical systems and by enzymes called carboxylases (carboxy - transferases ) gives:

Chemistry Phenols Biotin Carbonylation Decarboxylation
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