| Malonic acid
(also called Propanedioic Acid ) is a white crystalline C-3 dicarboxylic acid;
melting at 135 -136 C; readily soluble in water, alcohol and ether; solution in
water is medium-strong acidic. It can be derived by oxidizing malic acid or by
the hydrolysis of cyanacetic acid. Malonic acid itself is rather unstable and
has few applications. It's diethyl ester (diethyl malonate) is more important
commercially. Diethyl malonate, a colourless, fragrant liquid boiling at 199 C,
is prepared by the reaction of monochloroacetatic acid with methanol, carbon
monoxide or by the reaction cyanoacetic acid (the half nitriled-malonic acid)
with ethyl alcohol. Malonic acid and its esters contain active methylene groups
which have relatively acidic alpha-protons due to H atoms adjacent to two
carbonyl groups. The reactivity of its methylene group provide the sequence of
reactions of alkylation, hydrolysis of the esters and decarboxylation resulting
in substituted ketones. The methylene groups in 1,3-dicarboxylic acid utilize
the synthesis of barbiturates; a hydrogen atom is removed by sodium ethoxide,
and the derivative reacts with an alkyl halide to form a diethyl alkylmalonate.
The diethyl dialkylmalonates are converted to barbiturates by reaction with
urea. Malonic acid and its esters are characterized by the large number of
condensation products. They are important intermediates in syntheses of vitamins
B1 and B6, barbiturates, non-steroidal anti-inflammatory agents, other numerous
pharmaceuticals, agrochemicals and flavors & fragrances
compounds.
Meldrum's acid
is chemically 2,2-Dimethyl-m-dioxane-4,6-dione or Isopropylidene malonate.
This product is a condensation product of malonic acid.
This compound is an oxygen analogue of barbituric acid.
Like
malonic acid, Meldrum's acid has reactive hydrogen atom on the carbon alpha to
both carbonyl groups. Meldrum's acid undergoes Knoevenagel condensation reaction
as a reactant to forms condensed products. Knoevenagel condensation is a nucleophilic addition of a
reactive
hydrogen atom at 1,3-diketone compounds to a carbonyl
group, followed by an dehydration reaction. 1,3-Diketone compounds (beta-ketones)
include malonic
acid, diethyl malonate,
Meldrum's acid,
barbituric
acid, and acetoacetic acid derivatives.
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