Lactic Acid Formula: We frequently make curd from milk in our daily lives. Milk, as we all know, contains “Lactose.” The curd is formed when lactose is converted to lactic acid by bacteria. Curd becomes sour due to the presence of only lactic acid, as acids are sour. Lactic acid is an organic acid with having the chemical formula \({{\rm{C}}_{\rm{3}}}{{\rm{H}}_{\rm{6}}}{{\rm{O}}_{\rm{3}}}.\) It is commonly known as milk acid. The functional group present in this compound is carboxylic acid. The chemical name of lactic acid is \(2\)-Hydroxypropanoic acid or \({\rm{\alpha }}\)-Hydroxypropanoic acid.

Lactic acid was first noticed and described in sour milk by a Swedish German pharmaceutical chemist, Carl Wilhelm Scheele, in \(1780.\) Lactic acid is produced in the biological system during fermentation from by an enzyme – lactate dehydrogenase. It is used in making dairy products such as yogurt, cheese, food preservatives, and chemicals. Thus, we can say that lactic acid is a very important chemical compound for many biological systems. Let’s learn everything about the lactic acid chemical formula and its properties in detail on this page.

What is Lactic Acid?

Lactic acid is an organic acid. It is the main constituent of milk. Hence, also known as milk acid. It contains “carboxylic acid” as a functional group. Lactic acid is a chemical byproduct of anaerobic respiration (which cells produce energy without oxygen).

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In the biological system, there are two types of bacteria: good bacteria and bad bacteria. A good bacteria named “Lactobacillus” convert lactose in milk to lactic acid and turn it into yogurt. Lactic acid is also present in our gut, blood, deposited by muscle and red blood cells.

Lactic Acid Chemical Formula and Structure

The chemical formula of Lactic Acid is \({{\rm{C}}_{\rm{3}}}{{\rm{H}}_{\rm{6}}}{{\rm{O}}_{\rm{3}}}{\rm{.}}\) Its IUPAC name is \(2\)-Hydroxypropanoic acid. It contains three carbon atoms, a hydroxyl group, and carboxylic acid as a functional group.

In the structure of lactic acid, we can see that a single carbon atom contains four different groups, they are: \({\rm{ – C}}{{\rm{H}}_{\rm{3}}}{\rm{, – H, – OH,}}\) and \({\rm{ – COOH}}{\rm{.}}\) Thus, it can be inferred that this carbon is optically active, i.e., it is a chiral carbon. Lactic acid is an optically active compound. It has two optical isomers, L-Lactic acid, and D-Lactic acid. L-Lactic acid is most common in living organisms. It is also known as \({\rm{\alpha }}\) -Hydroxypropanoic acid because \({\rm{ – OH}}\) group is present at \({\rm{\alpha }}\) position adjacent to \({\rm{ – COOH}}\) group. Lactic acid plays a significant part in various biochemical processes, for example, ‘ anaerobic respiration.

Physical Properties of Lactic Acid

Chemical Formula of Lactic Acid	\({{\rm{C}}_{\rm{3}}}{{\rm{H}}_{\rm{6}}}{{\rm{O}}_{\rm{3}}}\)
Extended Formula of Lactic Acid	\({\rm{C}}{{\rm{H}}_{\rm{3}}}{\rm{CH}}\left( {{\rm{OH}}} \right){\rm{C}}{{\rm{O}}_{\rm{2}}}{\rm{H}}\)
Molar Mass/Molecular Weight	\({\rm{90}}{\rm{.08\;gmo}}{{\rm{l}}^{{\rm{ – 1}}}}\)
Boiling Point	\({\rm{122}}\,^\circ {\rm{C}}\)
Melting Point	\({\rm{16}}.{\rm{8}}\,^\circ {\rm{C}}\)
pKa	\(3.86\)
Colour	White in solid-state. Colourless in the liquid state
Solubility	Soluble in water

Lactic Acid in Chemistry

Lactic acid has intramolecular hydrogen bonding because of adjacent carboxyl and hydroxyl groups. It deprotonates in its aqueous solution to form its conjugate base, lactate.

Lactic acid can be synthesized chemically or naturally by fermentation of carbohydrates by Lactobacillus bacteria.

Chemical Synthesis of Lactic Acid

From \({\rm{\alpha }}\) -Chloro Propanoic Acid \({\rm{\alpha }}\)-Chloro propanoic acid reacts with silver hydroxide \(\left( {{\rm{AgOH}}} \right)\) to form -Hydroxypropanoic acid, i.e., lactic acid and silver chloride.

From Acetaldehyde Lactic acid is prepared from acetaldehyde by following simple two-step synthesis; firstly, it involves nucleophilic addition of \({\rm{HCN}}\) to the carbonyl group of acetaldehyde and secondly, aqueous hydrolysis of the nitrile takes place to yield the carboxylic acid product, i.e., lactic acid.

Some Important Chemical Reactions of Lactic Acid

Reaction with Sodium bicarbonate

Lactic acid reacts with Sodium bicarbonate \(\left( {{\rm{NaHC}}{{\rm{O}}_{\rm{3}}}} \right)\) to give salt (sodium lactate), water, and release carbon dioxide gas. This reaction can be used to test the presence of the carboxylic acid group in lactic acid.

Reaction with Ethanol

Lactic acid reacts with ethanol \(\left( {{{\rm{C}}_{\rm{2}}}{{\rm{H}}_{\rm{5}}}{\rm{OH}}} \right)\) In the presence of sulphuric acid, to form ethyl lactate and a water molecule. It resembles an esterification reaction where acid and alcohol react to form an ester.

Reaction with Ammonia

Lactic acid, when heated with ammonia, reacts to form an important compound ‘Lactamide.’

Importance of Lactic Acid in Human Body

Lactic acid is formed when the body breaks down carbohydrates to generate energy in limited or low levels of oxygen. In the human body, lactic acid is primarily produced in muscle cells and red blood cells during intense exercise. When the rate of demand for energy in the body is high:

1. Glucose is broken down and oxidized to pyruvate.
2. Lactate is then produced from the pyruvate faster than the body can process it, causing lactate concentrations to rise in the body.
3. As pyruvate is reduced to lactate while NADH (Nicotinamide Adenine Dinucleotide (NAD) \(+\) Hydrogen) is oxidized to \({\rm{NA}}{{\rm{D}}^{\rm{ + }}}{\rm{,}}\) the production of lactate is beneficial for \({\rm{NA}}{{\rm{D}}^{\rm{ + }}}.\)
4. This \({\rm{NA}}{{\rm{D}}^{\rm{ + }}}\) is used up in the oxidation of glyceraldehyde-\(3\)-phosphate during the production of pyruvate from glucose, and this process ensures that energy production is maintained throughout the exercise.

Uses of Lactic Acid

1. Lactic acid is used for skincare products as they help remove dull spots, hyperpigmentation, and other factors to treat uneven skin tone and complexion.
2. It is used in the food industry as preservatives and pharmaceuticals also. Lots of medicines containing “Probiotics” are composed of Lactobacillus bacteria that help us fight against various diseases.

3. Lactic acid plays an essential role in making dairy products such as yogurt, cheese, etc., as it helps in the coagulation of milk protein. The presence of lactic acid or lactate in milk is due to the fermentation of lactose caused mainly by lactic acid bacteria.

4. Poly Lactic Acid (PLA) is one of the most commercially successful bio-plastics due to its capacity to be easily processed and mechanical properties. Its monomer is lactic acid, which is derived from carbohydrates through fermentation. PLA can easily degrade into lactic acid, so it is used as medical implants in the form of plates, pins, anchors, screws, rods, mesh, etc.
5. Silage is fodder made from green foliage crops preserved by the addition of lactic acid, achieved through fermentation. It can be fed to cattle, sheep, and other ruminants that are easily digestible and nutritious for animals. Many strains of Lactic Acid Bacteria (LAB) are used to produce Silage.

Summary

In a nutshell, Lactic acid is an organic acid with having the chemical formula \({{\rm{C}}_{\rm{3}}}{{\rm{H}}_{\rm{6}}}{{\rm{O}}_{\rm{3}}}{\rm{.}}\) Its IUPAC name is \(2\)-Hydroxypropanoic acid as it contains three carbon atoms, a hydroxyl group, and a carboxylic acid. Lactic acid is an optically active compound as a single carbon atom contains four different groups, they are: \({\rm{ – C}}{{\rm{H}}_{\rm{3}}}{\rm{, – H, – OH,}}\) and \({\rm{ – COOH}}{\rm{.}}\)

It has two optical isomers, \({\rm{L}}\) -Lactic acid and \({\rm{D}}\) -Lactic acid. \({\rm{L}}\) -Lactic acid is mostly found in living things. Lactic acid is produced by Lactobacillus bacteria. These microorganisms are highly beneficial for human health and are present in abundant quantities in dairy products. Lactic acid plays an essential role in various biochemical processes, for example, anaerobic respiration.

It is produced in the body during intense physical activities when oxygen concentration gets lowered in the body. After doing lots of physical activities, we often feel tired, fatigue or even muscle cramps in our body. The reason behind this is the accumulation of lactic acid in muscles. But lactate (a conjugate base of lactic acid) is very helpful to the human body as it makes bodywork well by providing an uninterrupted energy supply even in a shortage of oxygen. Thus, we can say that lactate synthesis is a “necessary evil.”

FAQs on Lactic Acid Formula

1. What is Lactic Acid Formula
Ans: Lactic acid is an organic acid with having the chemical formula \({{\rm{C}}_{\rm{3}}}{{\rm{H}}_{\rm{6}}}{{\rm{O}}_{\rm{3}}}{\rm{.}}\) Its IUPAC name is \(2\)-Hydroxypropanoic acid.

2. What is lactic acid made from?
Ans: Lactic acid is made from the fermentation of molasses and other carbohydrates like corn, beet sugar, cane sugar, and tapioca.

3. What reacts with lactic acid?
Ans: After doing lots of physical activities, we often feel tired, fatigue, or even muscle cramps in our bodies. The reason behind this is the accumulation of lactic acid in muscles. This lactic acid production takes place at a low level of oxygen. But it reacts with extra oxygen that we inhale, breaking it into carbon dioxide and water. This can be noticed by disappearing cramps as the lactic acid breaks down.

4. What is the colour of lactic acid?
Ans: Lactic acid is white in solid-state and colourless in the liquid solution.

5. Is lactic acid a solid, liquid, or gas at room temperature?
Ans: Lactic acid exists as a water-soluble liquid at room temperature but, it getsze into a white solid at a lower temperature, i.e., around \({\rm{18}}.{\rm{6}}\,^\circ {\rm{C}}.\)

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