Malonic Acid – Definition, Formula, Significance and Properties

Malonic Acid

Malonic acid is a dicarboxylic acid belonging to the family of carboxylic acids. A dicarboxylic acid contains two carboxylic acid functional groups. Usually, a dicarboxylic acid exhibits the same chemical behavior as monocarboxylic acids. This naturally occurs in certain fruits. It is a useful organic compound with various benefits. Its IUPAC name is propanedioic acid. It should not be confused with malic or maleic acid.

Occurrence

It is an organic compound naturally found in some fruits. Fruits produced in organic farming have greater concentrations of malonic acid than those generated from conventional farming practices. It is often found in some citrus fruits and vegetables. It is a component of food items, it is present in animals, including humans.

The name of this acid is derived from the Greek word Malon. It means apple. The ionized form of malonic acid is malonate, along with its salts and esters. It occurs as a white crystal or crystalline powder in nature.

Did you Know: Several food substances contain malonic acid, including: ●      Red beetroots ●      Corns ●      Common beets ●      Scarlet beans ●      Cow’s milk Its occurrence in food items makes malonic acid a potential biomarker indicating the consumption of these foods.

History of Malonic Acid

In 1858, it was prepared for the first time by a French chemist –Victor Dessaignes. He oxidized malic acid with potassium dichromate, which is a strong oxidizing agent.

Later It was found to occur in some fruits viz citrus fruits. It can also be produced by fermenting glucose.

Significance of Malonic Acid

• It is an example of a competitive inhibitor.
• It functions in the ETS chain against succinate dehydrogenase in respiration.
• It is related to a deficiency of malonyl-CoA decarboxylase that leads to an inborn metabolism mistake.
• It serves as a potential biomarker for tracking foods that contain malonic acids.
• It finds usage in various industries.

Malonic Acid Formula

The malonic acid formula is C₃H₄O_4. It is also called propanedioic acid or dicarboxymethane, and the formula is written as CH_₂(COOH)_₂.

So, the names of C₃H₄O₄ are as follows:

• Malonic acid
• Propanedioic acid
• Carboxy Acetic acid
• Dicarboxymethane
• Methane dicarboxylic acid
• Dicarboxylate
• Dicarboxylic acid
• 1,3-Propanedioic acid
• Methane dicarbonic acid
• Propane-1,3-dioic acid

Malonic Acid Structure

The structure of malonic acid is as follows:

Malonic Acid Structure

It is diprotic. It can donate two protons per molecule.

Chemicals Closely Related to Malonic Acid ●      Difluoro Malonic acid: It is the fluorinated version of malonic acid. ●      Malonate includes esters and salts of malonic acids, such as: Disodium malonate Diethyl malonate Malonyl-CoA Dimethyl malonate

Preparation of Malonic acid

It can be prepared with chloroacetic acid (also called mono chloroacetic acid).

• Sodium carbonate gives sodium salt.
• The salt reacts with sodium cyanide.
• Nucleophilic substitution reaction gives rise to cyanoacetic acid salt.
• The nitrile group is hydrolyzed with NaOH to produce sodium malonate.
• The acidification of sodium malonate gives malonic acid.

The following diagram represents the steps mentioned above:

Industrial Preparation

Malonic acid can also be produced by hydrolyzing diethyl malonate or dimethyl malonate.

Physical Properties of Malonic acid

• Solubility: Dissolves in alcohol, pyridine, and ether.
• Molecular Wt/ Molar Mass: 104.06 g/mol
• Density: 1.619 g/cm³
• Boiling Point: Decomposes
• Melting Point: 135 to 137°C
• Nature: Acidic
• Color: White
• Stability: Usually stable under recommended conditions
• Molar heat of combustion: 864 kJ/mol
• The heat of vaporization: 92 kJ/mol
• It does not have a chiral center. So, it doesn’t exhibit optical isomerism.
• It is a hygroscopic solid that sublimes in a vacuum.

Calculation of Molecular Weight of Malonic Acid

The formula of malonic acid is C₃H₄O_4.

The atomic weight of carbon is 12.011.

The atomic weight of oxygen is 15.999.

The atomic weight of hydrogen is 1.00784.

So, its molar mass can be calculated as follows:

= (3 × 12.011) + (4 × 1.00784) + (4 × 15.999)

= 36.033 + 4. 03136 + 63.996

= 104.06 grams/ mol

Thus, the molar mass or molecular weight of malonic acid is 104.061 g/mol.

Chemical Properties of Malonic Acid

The chemical properties of malonic acid are as follows:

On Heating

When It is heated, it gives acetic acid and carbon dioxide.

Reaction with Phosphorus Pentoxide

On heating a dry mixture of malonic acid and phosphorus pentoxide, carbon suboxide is prepared.

Decomposition

It has hazardous decomposition products under fire conditions, including carbon oxides. Also, when heated, it decomposes and emits acrid smoke in addition to irritating fumes.

Organic Reactions

Malonic acid reactions are usually similar to a typical carboxylic acid. It forms amide, anhydrides, esters, and chloride derivatives on reacting with specific reactants.

Malonic anhydride serves as an intermediate in the formation of amide derivatives. Malonyl chloride is widely used for obtaining diamides or diesters. Some of the popular organic reactions involving malonic acid are as follows:

• It condenses with urea to give barbituric acid.
• Malonic acid also condenses with acetone to produce Meldrum’s acid. This acid is a versatile intermediate and helps in further transformations.

Malonate’s coenzyme A derivative— malonyl-CoA, acts as an important precursor in fatty acid biosynthesis. It is formed from acetyl CoA when it is acted upon by acetyl-CoA carboxylase. The malonate gets transferred to an acyl carrier protein for its addition to the fatty acid chain.

• Briggs–Rauscher Reaction

A popular name reaction has malonic acid as its key component. It is an example of an oscillating chemical reaction.

• Knoevenagel Condensation

The reaction is a modification of the aldol condensation reaction (the reaction between benzaldehyde and acetophenone). It involves the interaction of malonic acid or its diesters with the carbonyl group of a ketone or an aldehyde. This process is followed by a dehydration reaction.

Uses of Malonic acid

This dicarboxylic acid finds application across various industries, including automobiles, food, fragrance, and pharmaceuticals. The important uses of malonic acid are as follows:

• It is used as a precursor in polyester and other polymers.
• It is used as a flavoring agent in the fragrance industry.
• It is suitable for controlling acidity.
• It finds usage in pharmaceutical products.
• It is used in the manufacture of biodegradable containers.
• It is also a component of surgical adhesives.
• It serves as a cross-linking agent between cornstarch and potato starch to enhance its properties.
• For the preparation of barbituric salt
• In electroplating
• It is used in the production of vitamins– B1, B6, B2, and amino acids.
• It can also be used as a component in alkyd resins. This substance is widely used in several coating applications to protect objects against UV light damage, oxidation, and corrosion.
• A common application of malonic acid is as a crosslinker for low-temperature powder coatings. These are valuable for heat-sensitive substrates.
• It is on the US Department of Energy’s list of top chemicals for biomass production.
• In food and drug applications, it acts as a natural preservative additive for foods.
• Its therapeutic uses include the prevention of resorption of bone tissue in broiler chicks by adding malonic acid to feed.

Malonic Acid Health Risks

A few animal toxicity studies related to malonic acid have been done. However, they are insufficient to define serious health impacts. Some health concerns associated with malonic acid are as follows:

• It can be a strong irritant.
• It is harmful when inhaled or absorbed by the skin.
• It can lead to skin damage.
• One has to consult a doctor on persistent breathing difficulty on malonic acid exposure.
• The acid can cause harm to the mucous membranes.
• Elevated malonic acid levels are associated with elevated methylmalonic acid levels. This condition indicates metabolic disease— combined malonic and methylmalonic aciduria (CMAMMA).
• It is related to diseases such as early preeclampsia, eosinophilic esophagitis, and inborn disorder due to malonyl-CoA decarboxylase deficiency.

Points to Remember ●  It is also referred to as malonate. Malonate is the ionized version of malonic acid. ●  It belongs to a family of organic compounds called dicarboxylic acids that contain two carboxylic acid groups. ●  It is a very hydrophobic molecule. ●   It is a mild acid. ●   It exists in all living species, including humans and bacteria. ●  In humans, it participates in enzymatic reactions such as respiration. It is also involved in fatty acid biosynthesis. ● It occurs in several foods, such as corns, red beetroots, scarlet beans, cow’s milk, and common beets. ● It is also associated with several diseases like malonic and methylmalonic aciduria.

Frequently Asked Questions

1. Is malonic acid strong?

Malonic acid is a dicarboxylic acid. Its pKa1 is 2.83 and pKa2 is 5.69. The higher the pKa value, the weaker the acid. Therefore, it is a medium-strong acid.

2. What is the source of malonic acid?

It occurs naturally in some vegetables and fruits. Beetroot has high concentrations of the calcium salt of malonic acid. It also occurs in scarlet beans and corn.

3. What is malonic acid soluble in?

It is soluble in water. In an aqueous solution, this polar molecule forms an H+ ion. It also dissolves in methyl alcohol, pyridine and ether but is insoluble in hexane.