Decarboxylation

Decarboxylation is a chemical process in which a carboxyl group is removed and carbon dioxide is released (CO2). Decarboxylation is usually defined as a process between carboxylic acids that removes a carbon atom from a carbon chain. Carboxylation, or the adding of CO2 to a molecule, is the opposite reaction, which is the initial chemical step in photosynthesis. Decarboxylases, or carboxy-lyases in the more technical word, are enzymes that catalyse decarboxylations.

The word “decarboxylation” generally refers to the substitution of a hydrogen atom for a carboxyl group (-COOH):

RH + CO2 = RCO2H

One of the earliest known chemical processes is decarboxylation. Pyrolysis and destructive distillation are thought to be accompanied by this process. Metal salts, particularly copper compounds, improve the process by acting as intermediaries for metal carboxylate complexes. Decarboxylation of aryl carboxylates yields the corresponding aryl anion, which can subsequently be subjected to cross coupling reactions. distillation decarboxylation is frequently sluggish. As a result, normal fatty acids do not readily decarboxylate.

Decarboxylation and CO2

Decarboxylation processes happen quickly in enzymes, but they happen much more slowly in solution, if they happen at all. We would anticipate the high energy of the carbanion to induce the transition state for C–C bond cleavage to be high in energy where the reaction generates a carbanion and CO2. Because the energy of the carbanion is a thermodynamic characteristic, it is evident that an enzyme cannot affect it. Enzymes, on the other hand, overcome the barrier to carbanion formation. We had believed that CO2 is well behaved and forms without its own obstacles while thinking about decarboxylation. However, we looked at reactions in solution of chemicals that looked like enzymic intermediates and discovered that several of them were sensitive to unanticipated catalysis.

CO2 is a particularly reactive electrophile, as we discovered. Because the carbanion may rapidly add to CO2 in conflict with their separation and solvation, separation of the products may be the principal obstacle impeding the forward process in decarboxylation reactions when CO2 develops in the same step as a carbanion. The carbanion’s basicity may also be exaggerated since we presume that if decarboxylation is sluggish, it’s because the carbanion has a lot of energy. CO2 appears to be able to leave without reversion more quickly in reactions where the carbanion is protonated internally. We used kinetic analysis of catalytic processes, carbon kinetic isotope effects, and the production of pre decarboxylation intermediates to test these theories.

In another situation, we discovered that decarboxylation is catalysed by a general base, with a strong carbon kinetic isotope effect. In the rate-determining step, this necessitates both a proton transfer from an intermediate and the breakdown of a C–C bond. This would happen if the method included an unexpected initial addition of water to the carboxyl, followed by a cleavage step that produced bicarbonate. Some enzyme-catalyzed reactions appear to yield intermediates that are produced by the first addition of water or a nucleophile to the carboxyl or nascent CO2. Catalysts help separate the species on either side of the C–C bond, which might alleviate the problem by employing catalytic principles found in many enzymes that enhance hydrolytic processes, such as links in catalysis through activity evolution

Decarboxylation of Sodium Formate

The sodium salt of formic acid, HCOOH, is sodium format or HCOONa. It generally takes the form of a deluxe white powder. The breakdown process happens when sodium formate is heated. Sodium oxalate is generated as a result of this reaction, and hydrogen is liberated.

Physical properties of Sodium Formate

• The molecular weight of sodium formate is 68 g/mol

• 1.92 g/cm³ is the density

• Sodium formate has a melting point of 253° C

• The smell of sodium formate is similar to that of formic acid

• The refractive index of sodium formate is 1.371

Chemical Properties of Sodium Formate

• Sodium Formate is a salt containing both a strong base (NaOH) and a mild acid (H2O) (HCOOH).

• As a buffer, formic acid and sodium formate can be employed.

Point to remember

• Decarboxylation is the process of releasing carbon dioxide

• Thermal decarboxylation is easy for esters or carboxylic acids having a carbonyl group at the 3- (or b-) position

• The carboxylic acid or carboxylate anion is the reactive species

• As a result, the ester must first be hydrolyzed to obtain the acid 

• The decarboxylation process then continues via a cyclic transition state, yielding an enol intermediate that tautomerizes to the carbonyl

Conclusion

Decarboxylation is the process of removing carbon dioxide from a carboxylic acid’s carboxyl group.

When we decarboxylate the sodium salt of a carboxylic acid with soda lime, we get an alkane (a 3:1 mixture of caustic soda NaOH and quicklime CaO).

CH3COONa + NaOHm−−−→ CH4 + Na2CO3