Citric Acid Formula: Structure, Properties, Uses

Citric acid occurs in citrus fruits that include lemons, oranges, pomelo, etc. Citric acid is a weak organic acid with having a chemical formula \({{\rm{C}}_6}{{\rm{H}}_8}{{\rm{O}}_7}\). IUPAC name of citric acid is \(2\)-hydroxypropane-\(1,2,3\)-tricarboxylic acid. The sour taste of citrus fruits such as lemon and orange is due to the presence of citric acid by \(8\%\) of its total dry weight. Citric acid is completely soluble in water due to its polarity.

Though we know that citric acid is present in nature, there are various ways by which citric acid can be synthesized to meet industrial demands. One of the most widespread methods is the fermentation of fungi such as Aspergillus niger or Candida species from various sources of carbohydrates, such as molasses and starch. Citric acid is very beneficial to our health as it acts as an antioxidant. Thus, it is used in many beverages, medicines, skincare products, as well as disinfectants. In this article, let’s learn everything about citric acid chemical formula and its uses.

Citric Acid Formula and Structure

Citric acid was first isolated by the chemist Carl Wilhelm Scheele in \(1784\) by crystallizing it from lemon juice. Citric acid is an organic compound with having a chemical formula \({{\rm{C}}_6}{{\rm{H}}_8}{{\rm{O}}_7}\). It can be defined as a tricarboxylic acid, i.e., propane-\(1,2,3\)-tricarboxylic acid with a hydroxy substituent at position \({\rm{C – 2}}\). Citric acid is also known as a tribasic acid.

Citric acid acts as an important intermediate in the citric acid cycle, an important biochemical metabolism in all aerobic organisms. Citric acid does not have any chiral carbon; hence it is an optically inactive compound.

Physical Properties of Citric Acid

The physical properties of Citric acid are explained below:

Chemical Formula	\({{\rm{C}}_6}{{\rm{H}}_8}{{\rm{O}}_7}\)
Extended Formula	\({\rm{HOC}}\left( {{\rm{C}}{{\rm{O}}_2}{\rm{H}}} \right){\left( {{\rm{C}}{{\rm{H}}_2}{\rm{C}}{{\rm{O}}_2}{\rm{H}}} \right)_2}\)
Molar Mass / Molecular Weight	\(192.124{\mkern 1mu} \,{\rm{gmo}}{{\rm{l}}^{ – 1}}\)
Density	\(1.665\,{\mkern 1mu} {\rm{gc}}{{\rm{m}}^{ – 3}}\)
Boiling Point	\(310\,^\circ {\rm{C}}\)
Melting Point	\(153\,^\circ {\rm{C}}\)
Solubility	Soluble in water, alcohol, ether, acetone.

Citric Acid Synthesis

The demand for citric acid is far more than its availability in citrus fruits. So, it needs to be produced in the industry. Citric acid can be prepared from natural substances as well as synthetically by following various chemical procedures. Let’s discuss them in brief:

1. By Submerged Fermentation

A very simple process can produce citric acid, i.e., fermentation of a mould called Aspergillus niger mould found in some fruits and vegetables as ‘Black mould’. This mould is fed with carbohydrates such as glucose, sucrose, or molasses, submerged and fermented at \(30\,^\circ {\rm{C}}\) for around \(8\) days. This leads to the formation of citric acid as a supernatant that is filtered and separated from the residue left as fungal biomass.

2. Chemical Synthesis of Citric Acid from Glycerol

Through a series of steps, glycerol gets converted to citric acid that gives a good yield about \(70\% \left( {\frac{{\rm{w}}}{{\rm{w}}}} \right)\). Firstly, glycerol is treated with \({\rm{HCl}}\) followed by oxidation to form \(1,3\) Dichloro-propanone. \({\rm{HCN}}\) is then added through a Nucleophilic addition reaction; the compound formed undergoes nitrile hydrolysis to form a Di-cyano derivative. After nitrile hydrolysis and nucleophilic substitution in the presence of an excess of \({\rm{KCN}}\), and acid hydrolysis in the last step, citric acid is formed. A complete series of chemical reactions given below can be helpful to explain their entire procedure in detail:

Uses of Citric Acid

Citric acid is mostly used in foods and beverages such as soft drinks, juices, etc. It gives them a tangy, citrus taste. Thus, it is widely used as a flavouring agent.
It acts as food preservatives because its acidic pH inhibits the growth of many bacteria on food, thus preventing them from getting spoiled. In frozen foods, citric acid is lowering the pH making oxidative enzymes inactive.
Citric acid is used in soaps and detergents to soften their basic pH.
It is also used in many cosmetic products as a preservative to maintain acid-base pH balance.
In pharmaceuticals, citric acid is also used as an acidulant to control pH and acts as an anticoagulant by chelating calcium in the blood.
In diseases like osteoporosis, lemon peels, as a source of citric acid, are used to improve bone health as they contain a high amount of calcium and vitamin C, which assist in the maintenance of bones.

Side Effects of Citric Acid

Overexposure to citric acid can erode tooth enamel, which may lead to tooth decay. Mostly, this does not happen due to an overdose of citrus fruits. But, over intake of beverages containing citric acid can lead to such conditions.
Sometimes, if many citrus fruits are taken, it may cause acidity in the stomach and stomach ache.
Serious side effects of citric acid include numbness or tingly feeling, muscle twitching or cramps, rapid weight gain or swelling in the body, fast or slow heart rate, sudden mood changes, diarrhoea, convulsions, etc.

Summary

The chemical formula of citric acid is \({{\rm{C}}_6}{{\rm{H}}_8}{{\rm{O}}_7}\) and its IUPAC name is \(2\)-hydroxypropane – \(1,2,3\)-tricarboxylic acid. Due to the presence of three carboxylic acid groups, it is a weak tribasic acid. It exists as an optically inactive compound. Citric acid is found naturally in citrus fruits that include lemons, oranges, pomelo, etc. It is widely used in the food industry as it acts as an acidifier, a flavouring, and a chelating agent that make them useful food preservatives.

Citric acid is a non-toxic compound as it is biodegradable. Thus, it can be thoroughly used in pharmaceutical industries to make medicines. Citric acid is produced by fermentation of Aspergillus niger in large quantities in bioreactors. Citric acid is soluble in water due to the presence of three carboxylic acid groups. Citric acid can be chemically synthesized from glycerol through a series of reaction steps. This process gives a good yield of citric acid.

Though citric acid has immense benefits, it also has few side effects, including tooth decay, nausea, vomiting, etc.

In biochemistry, it acts as an intermediate in the citric acid cycle, which is a metabolic process in aerobic organisms to produce a high amount of energy that is derived from the breakdown of carbon compounds in the body. Thus, it can be concluded that citric acid is a very important organic acid used in a wide range of applications.

FAQs on Citric Acid Formula

Q.1. Is citric acid, basic or acidic?
Ans: Citric acid is an acidic compound. It turns blue litmus paper to red. It is a weak tribasic acid.

Q.2. Does the body absorb citric acid?
Ans: The guts absorb citric acid after oral administration. It enhances the bioavailability of minerals and helps the body to absorb them efficiently.

Q.3. Can you drink water after drinking citric acid?
Ans: Yes, we can drink water after drinking citric acid as it is completely soluble in water. In fact, water, along with citric acid, acts as a detoxifying agent for our body. It flushes out all toxins.

Q.4. Does citric acid make you poop?
Ans: Citric acid is a natural laxative that helps in detoxifying the body, along with the digestive tract. Peels of citrus fruits are rich in the soluble fibre pectin, accelerating colonic transit time and minimizing constipation. In addition to this, citrus fruits contain a flavanol called naringenin, which may also help to cure constipation.

Q.5. How bad is citric acid for you?
Ans: Though citric acid is of immense importance for our health, overexposure to citric acid may lead to tooth decay, acidity in the stomach and stomach ache. Feelings like numbness, muscle twitching or cramps, rapid weight gain or swelling in the body, fast or slow heart rate, sudden mood changes, diarrhoea, convulsions are other associated side effects caused due to overdose of citric acid.