Karboksylation

Karboksylation (carboxylation in English) is the chemical process of introducing a carboxyl group (-COOH) into an organic substrate. The carboxyl unit is typically delivered by carbon dioxide (CO2) or bicarbonate, and the reaction often proceeds through a carboxylate intermediate that is protonated to yield a carboxylic acid. Karboksylation can be catalyzed by enzymes in biological systems or carried out by chemical methods in the laboratory or industry.

In biology, karboksylation reactions are essential for metabolism, carbon fixation, and biosynthesis. Many enzymes called carboxylases catalyze ATP-dependent carboxylation: for example, pyruvate carboxylase converts pyruvate and CO2 into oxaloacetate; acetyl-CoA carboxylase forms malonyl-CoA; and propionyl-CoA carboxylase produces methylmalonyl-CoA. In photosynthesis, RuBisCO catalyzes the carboxylation of ribulose-1,5-bisphosphate with CO2 as part of the Calvin cycle, helping to fix atmospheric carbon into sugar phosphates.

In chemical synthesis, karboksylation provides a route to carboxylic acids from various substrates. Methods include the carboxylation of organometallic reagents with CO2, followed by acidic workup, and catalytic approaches that convert aryl or vinyl halides, alkenes, or alkynes with CO2 under suitable conditions. Classical examples include the Kolbe-Schmitt reaction, where CO2 under pressure carboxylates phenoxide to give salicylic acid derivatives. These reactions enable the use of CO2 as a one-carbon building block in organic synthesis and fine chemistry.

Overall, karboksylation is a versatile transformation operative in biology and chemistry, enabling the formation of carboxyl-containing compounds from simple carbon sources.