What is Malonic Acid Definition Formula Reactions and Uses in Organic 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 Properties and Chemistry
1. What is malonic acid?
Malonic acid is a dicarboxylic acid with the molecular formula C3H4O4 and the structure HOOC–CH2–COOH. It contains two carboxyl (–COOH) groups attached to the same carbon chain, making it an important compound in organic chemistry. It is also called propanedioic acid under IUPAC nomenclature.
2. What is the structural formula of malonic acid?
The structural formula of malonic acid is HOOC–CH2–COOH. It consists of:
- A central methylene group (–CH2–)
- Two terminal carboxylic acid groups (–COOH)
This arrangement makes malonic acid a simple example of a 1,3-dicarboxylic acid.
3. Why is malonic acid considered a dicarboxylic acid?
Malonic acid is considered a dicarboxylic acid because it contains two carboxyl (–COOH) functional groups in one molecule. Each –COOH group can donate one proton (H+), so malonic acid is a diprotic acid. This allows it to form two different salts and undergo two stages of ionization in aqueous solution.
4. What happens when malonic acid is heated?
When malonic acid is heated, it undergoes decarboxylation to form acetic acid and carbon dioxide.
The balanced reaction is:
HOOC–CH2–COOH(s) → CH3COOH(l) + CO2(g)
This reaction occurs easily because the two carboxyl groups are separated by only one carbon atom, which stabilizes the transition state.
5. What is the pKa of malonic acid?
Malonic acid has two dissociation constants with pKa1 ≈ 2.83 and pKa2 ≈ 5.69. These values correspond to the stepwise ionization:
- First ionization: H2C3H2O4 ⇌ HC3H2O4- + H+
- Second ionization: HC3H2O4- ⇌ C3H2O42- + H+
The first proton is released more easily than the second due to increasing negative charge.
6. How is malonic acid prepared in the laboratory?
Malonic acid is commonly prepared by hydrolysis of diethyl malonate followed by acidification.
- Step 1: Hydrolysis of diethyl malonate in aqueous base
- Step 2: Acidification to yield malonic acid
Simplified reaction (acidic hydrolysis):
(C2H5OOC)CH2COOC2H5 + 2H2O → HOOC–CH2–COOH + 2C2H5OH
7. What is the malonic ester synthesis?
The malonic ester synthesis is a method used to prepare substituted acetic acids from diethyl malonate. It involves:
- Deprotonation of diethyl malonate with a strong base (e.g., sodium ethoxide)
- Alkylation with an alkyl halide (R–X)
- Hydrolysis and decarboxylation to form a substituted acetic acid
This reaction is important in organic synthesis for forming carbon–carbon bonds.
8. What are the uses of malonic acid?
Malonic acid is used in organic synthesis, pharmaceuticals, and polymer production. Major uses include:
- Preparation of barbiturates and other pharmaceuticals
- Intermediate in the malonic ester synthesis
- Production of specialty polymers and resins
- Biochemical studies of metabolic pathways
It is also used as a building block for various carboxylic acid derivatives.
9. What is the difference between malonic acid and succinic acid?
The main difference between malonic acid and succinic acid is the number of carbon atoms in the chain.
- Malonic acid: C3H4O4, structure HOOC–CH2–COOH (3 carbons)
- Succinic acid: C4H6O4, structure HOOC–CH2–CH2–COOH (4 carbons)
Succinic acid has one additional –CH2– group, which affects acidity and thermal behavior.
10. Is malonic acid stronger than acetic acid?
Yes, malonic acid is stronger than acetic acid because its first pKa (≈2.83) is lower than that of acetic acid (≈4.76). The increased acidity is due to:
- The presence of a second electron-withdrawing –COOH group
- Greater stabilization of the conjugate base by inductive effects
This makes malonic acid significantly more acidic in aqueous solution than acetic acid.
