Key Reactions & Applications of Malonic Acid in Chemistry
Malonic Acid IUPAC Name
Malonic acid is a dicarboxylic acid with structural formula CH2(COOH)2 and chemical formula C3H4O4. The name malonic acid originated from the word ‘Malon’ which is Greek for ‘apple’. The IUPAC name of malonic acid is Propanedioic acid. Methane Dicarboxylic acid is another name for malonic acid. The ester and salts of malonic acid are called malonates. The dicarboxylic acid has organic reactions similar to the monocarboxylic acid where amide, ester, anhydride, and chloride derivatives are formed. Lastly, the malonic ester malonate as a coenzyme A derivative malonyl CoA that is as important a precursor as Acetyl CoA in the biosynthesis of fatty acids.
Synthesis of Malonic Acid
The synthesis of malonic acid usually begins with chloroacetic acid. It is also synthesized by cyanoacetic acid or by acid saponification reaction of malonates. From monochloroacetic acid, it is produced by sodium or potassium cyanide.
The sodium carbonate primarily breaks down to give sodium salt which reacts with sodium cyanide to give sodium salt of cyanoacetic acid by the process of nucleophilic substitution.
Further, via hydrolyzation, the nitrile group binds with sodium malonate, whose acidification results in the production of malonic acid.
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Malonic Acid Structural Formula
The structural formula of malonic acid can be given as
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The malonic acid Lewis structure has been found by the X-ray crystallography method. The malonic acid structure CH2(COOH)2 has two carboxylic acids. The salts and esters of malonic acid (malonates) have structures similar to malonic acid.
Properties of Malonic Acid
Malonic acid molecular weight: 104.061 g.mol-1
The density of malonic acid is 1.619 g/cm3.
It appears as a crystalline powder that is white or colourless.
At the boiling point above 140oC the compound decomposes. The melting point is 135-137o C.
If heated to decomposition under fire it emits carbon oxide fumes and acrid irritating smoke.
Acidity pKa = 2.85 at 25oC. pKa1 = 2.83, pKa2 = 5.69
The molar heat of combustion is 864 kJ/mol. The heat of vaporization is 92 kJ/mol.
It is soluble in water. Solubility 763 g/L.
It has a white crystal or crystalline powder structure. The compound is naturally occurring and can be found in many vegetables, fruits. The dicarboxylic acid compound was first prepared by Victor Dessaignes by the oxidation reaction of malic acid.
Malonic Acid Uses
Malonic acid acts as a precursor for conversion to 1,3-propanediol, which is a compound used in polyesters and polymers with the huge market size.
Malonic acid is used for the preparation of cinnamic acid, a compound used for the formation of cin metacin which is an anti-inflammatory. The malonates are used in syntheses of B1 and B6, barbiturates, and several other valuable compounds.
It is used in cosmetics as a buffering and as a flavouring agent in food.
Malonic acid is used as a component of alkyd resins, used in coating applications to protect from UV rays, oxidation, and corrosion.
Malonic acid is a building block to many valuable compounds in food and drug applications, pharmaceutical, electronics industry, fragrances, specialty polymer, specialty solvents, and many more.
Health Hazards of Malonic Acid
Upon exposure, Malonic acid can cause a range of symptoms in the eyes, skin, and respiratory tract. It can irritate eyes, skin. The compound if inhaled can irritate the respiratory tract. It may also cause serious eye damage or eye irritation. Hence, if exposed eyes should be washed with normal water or with a saline solution. If redness or irritation is observed in the affected skin, the area should be immediately washed with water. The contaminated clothes should be removed.
If ingested it may cause gastrointestinal irritation such as nausea, vomiting, etc. The mouth should be immediately rinsed with water several times and further medical help should be taken.
It is a strong irritant that can affect both skin and mucous membranes.
If heated the compound releases toxic fumes of carbon dioxide and monoxide and gases that may irritate the respiratory tract if inhaled.
FAQs on Malonic Acid: Structure, Synthesis, and Properties
1. What is malonic acid and what is its chemical formula?
Malonic acid is an organic compound classified as a dicarboxylic acid. Its structure features two carboxyl groups (-COOH) attached to a central methylene group (-CH₂-). It appears as a white crystalline solid. The chemical formula for malonic acid is C₃H₄O₄.
2. What is the IUPAC name for malonic acid?
The official IUPAC (International Union of Pure and Applied Chemistry) name for malonic acid is propanedioic acid. The name is derived from its structure: a three-carbon chain ('prop') with two carboxylic acid functional groups ('dioic acid').
3. What are the primary uses and applications of malonic acid?
Malonic acid and its esters are important precursors in organic synthesis. Some of its key applications include:
- The synthesis of specialty chemicals, particularly flavouring agents and fragrances.
- The production of various pharmaceuticals, such as barbiturates, non-steroidal anti-inflammatory drugs (NSAIDs), and sedatives.
- Its use in manufacturing certain types of polyesters and polymers.
- Acting as a key component in reactions like the Knoevenagel condensation to form more complex molecules.
4. What happens when malonic acid is heated?
When malonic acid is heated to a temperature just above its melting point (approximately 135 °C), it undergoes a characteristic reaction called decarboxylation. In this process, the molecule loses one of its carboxyl groups as carbon dioxide (CO₂), resulting in the formation of acetic acid (CH₃COOH).
5. How does malonic acid's structure allow it to act as a competitive inhibitor?
Malonic acid is a classic example of a competitive inhibitor for the enzyme succinate dehydrogenase, which is part of the Krebs cycle. Its inhibitory action is due to its structural similarity to the enzyme's natural substrate, succinate. Both are dicarboxylate ions, but malonic acid has one methylene bridge (-CH₂-) while succinate has two (-CH₂-CH₂-). Malonate binds to the enzyme's active site but cannot be dehydrogenated, thereby blocking succinate from binding and halting the metabolic pathway at that step.
6. Why are the hydrogen atoms on the central carbon of malonic acid particularly acidic?
The hydrogen atoms of the central methylene (-CH₂-) group in malonic acid are unusually acidic. This heightened acidity is because the two adjacent electron-withdrawing carboxyl groups effectively stabilize the carbanion that forms when a proton is removed. The negative charge on this carbanion is delocalized through resonance onto the oxygen atoms of both carboxyl groups, spreading the charge and making the conjugate base very stable. This acidity is crucial for its role in synthesis reactions.
7. How does malonic acid differ from other dicarboxylic acids like oxalic acid and succinic acid?
Malonic, oxalic, and succinic acids are all dicarboxylic acids but differ in the number of carbon atoms separating their two carboxyl groups, which affects their properties:
- Oxalic acid (ethanedioic acid): Has zero separating carbons (HOOC-COOH). It is the strongest of the three.
- Malonic acid (propanedioic acid): Has one separating carbon atom (HOOC-CH₂-COOH). It is known for undergoing easy decarboxylation.
- Succinic acid (butanedioic acid): Has two separating carbon atoms (HOOC-CH₂-CH₂-COOH). It is a stable intermediate in the Krebs cycle.
8. What is the importance of the Knoevenagel condensation reaction involving malonic acid?
The Knoevenagel condensation is a fundamental carbon-carbon bond-forming reaction in organic chemistry. It involves the reaction of an active hydrogen compound, such as malonic acid, with the carbonyl group of an aldehyde or ketone. This reaction is important because it is a reliable method for synthesising α,β-unsaturated carboxylic acids and their derivatives, which are valuable building blocks for more complex organic molecules.
