Pranjal Protim Dutta
B.Sc 4th sem
Stability of keto form
Keto-enol tautomerism in EAA
The class of compounds containing a methylene
(>CH₂) group directly bonded to two electron
withdrawing groups are called active methylene
compounds. Ethyl acetoacetate(EAA) and diethyl
malonate falls in this class. Now we shall discuss
about preparation, properties and uses of EAA. The
structure of EAA is:
CH₃ C CH₂ C OC₂H₅
Let us discuss the mechanism of this reaction
Ethyl acetoacetate is a colourless, pleasant smelling liquid
with b.p 180.4°C and density 1.0282. It is sparingly
soluble in water but freely soluble in organic solvents.
As the methylene hydrogen is acidic in nature, hence it
can be easily replaced by some other groups. Hence
from ethyl acetoacetate we can synthesize large number
Now why the methylene hydrogen is acidic in
1. Acidity of methylene hydrogen
It is attributed to two factors:
• Inductive effect
Aldehydes, ketones and some other compounds undergo
this special type of tautomerism. It involves the
migration of a proton from ἀ-carbon to the carbonyl
Due to the greater strength of π-bond of C=O group as
compared to that of C=C group, the keto form is more
stable then enol form. In simple aldehydes and ketones
the amount of enol form is negligible (<1%). However
the percentage of enol form increases in case of 1,3-
dicarbonyl compounds. It is because of the formation of
Ethyl acetoacetate exist as a tautomeric mixture of keto
and enol form.
Facts in favor of keto form:
• EAA forms a bisulphite compound with sodium
• EAA forms a cyanohydrin with hydrogen cyanide.
• EAA forms an oxime with hydroxylamine and
phenylhydrazone with phenylhydrazine.
• On reduction with sodium amalgum or by using LiAlH₄
in pyridine, EAA gives ß-hydroxybutyric ester
containing a secondary alcohol group.
• When EAA is hydrolysed with dil.NaOH solution in cold
followed by acidification, it forms acetoacetic acid. This
on heating yields acetone thereby showing that
acetoacetic acid is a ß-ketoacid and ethyl acetoacetate is
Facts in favor of enol form:
• EAA reacts with sodium metal to form sodium derivative
and hydrogen gas is evolved. This indicates the presence
of –OH group.
• EAA forms an acetyl derivative with acetyl chloride
which shows the presence of –OH group.
• When EAA is treated with alcoholic bromine solution,
the brown color of the later is discharged. This indicates
the presence of C=C bond.
• EAA forms a reddish violet color when treated with
FeCl₃. This indicates the presence of C=C-OH structural
unit as in phenol.
EAA is used for the synthesis of various compounds such
• Mono and dicarboxyllic acid.
• α,ß-unsaturated acids.
• Ketones .
• 4-Methyl uracil
From the above discussion we can conclude that:
• Ethyl acetoacetate is the ethyl ester of acetoacetic
• It is used for the synthesis of large number of
• It is also as flavouring for food.