What is Trichloroacetic Acid?
Trichloroacetic acid is an organic compound in which three hydrogen atoms of the methyl group of acetic acid get replaced by chlorine atoms. It is a white crystalline solid. It is also known as TCA, TCAA or trichloro ethanoic acid. But its systematic IUPAC name is trichloroacetic acid. As the name suggests, it's an analogue of acetic acid. It is a strong acid which is widely used in clinical chemical and biochemistry. Specially its salts and esters are very famous for their usage in cosmetics. Its salts and esters are called trichloroacetates.
In 1839, French Chemist Jean – Baptiste Dumas discovered trichloroacetic acid. It is also called aceto - caustin. Its discovery gave a noticeable example to the theory of organic radicals and valances. This theory was based on the facts which were contrary to the beliefs of Swedish Chemist Jons Jakob Berzelius. Thus, Jean – Baptiste Dumas was the first chemist who criticized or questioned the results of the electro – chemical research of Jons Jakob Berzelius. Before the discoveries made by Dumas, results of electro – chemical research by Jons Jakob Berzelius were widely accepted at that time. It started a long debate between Jons Jakob Berzelius and Jean – Baptiste Dumas.
Formula of Trichloroacetic Acid
Structure of Trichloroacetic Acid
It is an organic covalent compound which is formed by the displacement of hydrogen atoms of acetic acid by chlorine atoms. The carbon atom which is bonded with O, OH and CCl3 group is sp2 hybridized and the carbon atom which is bonded to three chlorine atoms and COOH group is sp3 hybridized.
(Image to be added soon)
Trichloroacetic acid (CCl3COOH)
(Image to be added soon)
3D – Structure of trichloroacetic acid
Properties of Trichloroacetic Acid
Physical and chemical properties of trichloroacetic acid - Properties of trichloroacetic acid are listed below –
Its molar mass is 163.38 g/mol.
It is a white or colorless crystalline solid.
It has a sharp pungent smell.
Its density is 1.63 g.cm-3.
Its melting point is 58 ℃.
Its boiling point is 197 ℃.
It is soluble in water.
It is acidic in nature. Its pH is 1.2.
It turns blue litmus paper into red.
Its pKa value is 0.66.
It is a stable compound with a flash point over 93 ℃.
It is not reactive with water.
It is corrosive in nature like other strong acids.
Its dipole moment is 3.23 D.
It reacts with protein.
Preparation of Trichloroacetic Acid
It is produced by the reaction of chlorine gas on acetic acid in presence of a catalyst. Reaction is given below –
CH3COOH + 3Cl2 🡪 CCl3COOH + 3HCl
It can also be produced by the reaction of trichloroacetaldehyde with oxygen or by the oxidation of trichloroacetaldehyde.
Uses of Trichloroacetic Acid
Due to its stable and strong acidic nature, trichloroacetic acid is used in many fields to fulfill various purposes. Its few applications are listed below –
It is widely used in clinical chemistry in the preparation of formulations.
In biochemistry, it is used for precipitation of macromolecules. For example, it can precipitate proteins, DNA and RNA.
It is used in the chemical peels and tattoo removal.
It is used in cosmetics.
It is used on the skin for chemoablation of warts.
In diluted form it can be used on the genital warts as well.
It can be used even during pregnancy for skin infections.
Its sodium salt was used as an herbicide till the 1980s.
Effects of Trichloroacetic Acid on Health And Environment
Trichloroacetic acid is a strong acid. So, it is a corrosive compound. Its overuse on skin can cause skin damage. Its short exposure can cause serious temporary or long - lasting injuries. It can be lethal for rats when taken 5000 mg/kg. It is harmful for the environment as well.
Trichloroacetic Acid: Summary in Tabular Form
FAQs on Trichloroacetic Acid
1. What is trichloroacetic acid and what is its chemical formula?
Trichloroacetic acid, also known as TCA or trichloroethanoic acid, is a strong organic acid. It is an analogue of acetic acid where the three hydrogen atoms of the methyl group have been replaced by chlorine atoms. Its chemical formula is CCl₃COOH.
2. What are the key physical and chemical properties of trichloroacetic acid?
Trichloroacetic acid exhibits several distinct properties relevant to the CBSE syllabus. Key properties include:
- Appearance: It is a colourless or white crystalline solid.
- Odour: It has a sharp, pungent smell.
- Solubility: It is highly soluble in water, ethanol, and ether.
- Acidity: It is a very strong acid with a pKa value of approximately 0.66, making it much more acidic than acetic acid.
- Melting Point: Approximately 58°C.
- Boiling Point: Approximately 197°C.
3. Why is trichloroacetic acid (CCl₃COOH) a significantly stronger acid than acetic acid (CH₃COOH)?
Trichloroacetic acid is a much stronger acid due to the powerful -I (negative inductive) effect of the three chlorine atoms. Chlorine is highly electronegative and strongly withdraws electron density from the adjacent carbon atom. This effect is transmitted through the carbon chain to the carboxyl group, pulling electron density away from the O-H bond. This weakens the O-H bond, making it easier for the acid to donate a proton (H⁺). In contrast, the methyl group (-CH₃) in acetic acid has a +I (positive inductive) effect, which pushes electron density towards the carboxyl group, strengthening the O-H bond and making it a weaker acid.
4. How is trichloroacetic acid typically prepared?
A common method for preparing trichloroacetic acid, as studied in organic chemistry, is through the chlorination of acetic acid. This reaction requires a suitable catalyst, such as red phosphorus or sunlight. The reaction proceeds as follows:
CH₃COOH + 3Cl₂ → CCl₃COOH + 3HCl
In this reaction, the three alpha-hydrogen atoms of acetic acid are successively replaced by chlorine atoms.
5. What are the primary uses of trichloroacetic acid in biochemistry and medicine?
Trichloroacetic acid has important applications based on its chemical properties:
- In Biochemistry: It is widely used to precipitate macromolecules from a solution. It effectively causes proteins, DNA, and RNA to become insoluble, allowing for their separation and analysis.
- In Medicine & Cosmetics: Due to its corrosive nature, it is used in controlled concentrations for chemical peels, tattoo removal, and the chemoablation (chemical removal) of warts and other skin lesions.
6. How does trichloroacetic acid work for applications like chemical peels?
Trichloroacetic acid functions as a chemical cauterant. When applied to the skin, its strong acidity rapidly denatures the proteins within the skin cells, causing coagulation and destruction of the tissue in a controlled manner. This process, known as chemoablation, destroys the targeted outer layers of skin or wart tissue. The body's natural healing process then replaces the removed tissue with new, healthy cells, leading to skin resurfacing or removal of the lesion.
7. What is the hybridization of the carbon atoms in the trichloroacetic acid (CCl₃COOH) molecule?
The trichloroacetic acid molecule contains two carbon atoms with different hybridizations:
- The carbon atom of the carboxyl group (-COOH) is sp² hybridized. This is because it forms one double bond with an oxygen atom and two single bonds (one with the other oxygen and one with the -CCl₃ group).
- The carbon atom of the trichloromethyl group (-CCl₃) is sp³ hybridized, as it forms four single covalent bonds: one with the carboxyl carbon and three with the chlorine atoms.
8. Is trichloroacetic acid considered safe to handle and what precautions are necessary?
Trichloroacetic acid is a highly corrosive substance and must be handled with extreme care. Direct contact with skin or eyes can cause severe chemical burns. When working with this acid, especially in concentrated forms, it is essential to use appropriate personal protective equipment (PPE), including chemical-resistant gloves, safety goggles, and a lab coat. While it is used in medical treatments, these are performed by professionals using specific, controlled concentrations.
