Active methylene compounds



  • Active methylene compounds are organic compounds that contain a methylene group (CH2) that is adjacent to a carbonyl group (C=O) and is capable of undergoing various chemical reactions.
  • The carbon atom in the methylene group is considered "active" because it is more acidic and more reactive than a typical methylene group due to the presence of the neighboring carbonyl group.
  • Examples of active methylene compounds include malonic ester, acetoacetic ester, and ethyl cyanoacetate.
  • Malonic ester is a diester of malonic acid, and has the formula CH2(CO2Et)2. It contains two active methylene groups, and is commonly used as a starting material for various organic syntheses. The carbanion of malonic ester is stabilized by resonance, making it a useful nucleophile in various reactions.
  • Acetoacetic ester (also known as ethyl acetoacetate) is another important active methylene compound. It has the formula CH3COCH2CO2Et, and contains one active methylene group. Acetoacetic ester is used as a starting material for various syntheses, including the acetoacetic ester synthesis, which is a method for preparing methyl ketones.
  • Ethyl cyanoacetate is another example of an active methylene compound. It has the formula CH3C(CN)CO2Et, and contains one active methylene group and one cyano group. Ethyl cyanoacetate is commonly used in organic syntheses as a source of the cyano group, which can be easily converted into various other functional groups.

Ethyl acetoacetate

Ethyl acetoacetate is an organic compound that is the ethyl ester of acetoacetate. The chemical formula of this compound is C6H10O3 or CH3COOCH2COOC2H5. This compound is present as a colourless liquid with a fruity fragrance that is used as a food flavouring. It is also used as a chemical intermediate for the production of various types of chemical compounds. This compound is also used industrially in the production of synthetic dyes and drugs.

Ethyl acetoacetate is industry produced compound. The ethyl acetoacetate structure is produced using the treatment of ethanol with diketene. The production of this compound in the laboratory is a very well-known procedure. This is done by using the process of Claisen condensation of ethyl acetate. 

The reaction produces one molecule of ethyl acetoacetate and one molecule of ethanol from the condensation of two molecules of ethyl acetate. 

The structure of Ethyl acetoacetate is as follows

Keto enol tautomerism  of Ethyl acetoacetate

Aldehydes, ketones and other carbonyl compounds exhibit this special type of tautomerism. This type of tautomerism has been observed in EAA. It involves migration of proton from a-carbon to carbonyl oxygen by the following mechanism.

The tautomer containing carbonyl group (>C=O) is designated as keto form, and the other one containing hydroxyl group (-OH) attached to a doubly bonded carbon is referred as enol form. This kind of tautomerism is termed as keto-enol tautomerism.

 Claisen Ester Condensation

The Claisen condensation is a carbon–carbon bond forming reaction that occurs between two esters or one ester and another carbonyl compound in the presence of a strong base, resulting in a β-keto ester or a β-diketone.