Trichloroacetic acid Structure, properties, synthesis, uses, effects

The trichloroacetic acid is a solid organic compound whose chemical formula is C_twoHCl₃OR_two or CCl₃-COOH. It is also known as trichloroethanoic acid and as TCA. It is a monocarboxylic acid in which the hydrogens of the second carbon atom have been replaced by chlorine. Its crystals are colorless to white.

TCA is very soluble in water, generating very acidic solutions. It can precipitate proteins from an aqueous solution. Prolonged contact with trichloroacetic acid can cause skin burns.. 

However, this has been used to advantage to treat skin disorders, as it is used in dilute solution and in a very well controlled manner. ACT is also often used in the so-called peeling chemical for skin rejuvenation.

On the other hand, because it is an organochlorine compound that is found in the environment in small proportions, it has been held responsible as a possible cause of damage to forests..

Despite its content of the element chlorine, there are no data to confirm whether or not trichloroacetic acid is carcinogenic..

Article index

• 1 Structure
• 2 Nomenclature
• 3 Properties
  • 3.1 Physical state
  • 3.2 Molecular weight
  • 3.3 Melting point
  • 3.4 Boiling point
  • 3.5 Density
  • 3.6 Solubility
  • 3.7 pH
  • 3.8 Dissociation constant
  • 3.9 Chemical properties
• 4 Synthesis
• 5 Use in protein analysis
• 6 Therapeutic uses
• 7 Use in dermatological treatments
  • 7.1 For skin disorders
  • 7.2 For cosmetic treatments
• 8 Effect of TCA contamination
• 9 References

Structure

Trichloroacetic acid is a monocarboxylic acid, that is, it contains a single -COOH group. Its skeleton contains only 2 carbon atoms. It is similar to acetic acid CH₃-COOH but instead of the methyl group -CH₃, owns a -CCl group₃, that is, its formula is CCl₃-COOH.

Nomenclature

- Trichloroacetic acid

- Trichloroethanoic acid

- 2,2,2-trichloroacetic acid

- TCA TriChloroacetic Acid)

Properties

Physical state

Colorless to white crystalline solid. Its crystals are rhombohedral

Molecular weight

163.38 g / mol

Melting point

57.5 ºC

Boiling point

195.5 ºC

Density

1.6 g / cm³

Solubility

Very good solubility in water: 120 g / 100 mL at 25 ºC.

Soluble in ethanol CH₃CH_twoOH and in diethyl ether CH₃CH_twoOCH_twoCH₃. Slightly soluble in CCl carbon tetrachloride₄.

pH

The pH of an aqueous solution with 0.1 mol / L is 1.2.

Dissociation constant

pK_to = 0.51 (means it is a stronger acid than acetic acid)

Chemical properties

Trichloroacetic acid is a hygroscopic solid, it absorbs moisture from the air forming a viscous liquid. Has a pungent or pungent odor.

When it dissolves in water, the release of heat occurs. It is corrosive towards metals such as iron, zinc and aluminum, and towards biological tissues. It is extremely corrosive to human skin on prolonged contact.

It has the property of precipitating proteins in solution.

When heated with alkalis to decomposition it emits toxic fumes of chloroform CH₃Cl, hydrochloric acid HCl, carbon dioxide CO_two and carbon monoxide CO.

In the sources consulted there is no consensus on whether or not it is carcinogenic.

Synthesis

It is prepared at an industrial level by chlorination of acetic acid CH₃-COOH, with chlorine Cl_two in the presence or not of catalysts.

Use in protein analysis

Trichloroacetic acid is widely used for the determination of proteins, such as albumin. It is a very effective agent for its precipitation, especially from dilute protein solutions..

Precipitation occurs in a specific and quantitative way, which allows them to be separated from other non-protein substances, such as polysaccharides, cations bound to proteins and salts, and allows to denature proteases (enzymes that allow protein breakdown).

According to the literature consulted, not much is known about the precipitation mechanism. It has been suggested that the dominant form could be that of hydrophobic aggregation, since there is an interval, around 15% of trifluoroacetic acid, in which optimal precipitation occurs..

Therapeutic uses

Diluted TCA solutions have been used successfully in the treatment of acute external otitis (ear pain in the area before the eardrum or external auditory canal).

TCA deactivates inflammatory cells by changing their properties, drying the inflamed region, reducing edema and quickly relieving pain. It is also very well tolerated by patients, both children and adults..

Additionally, it restores the acidic state of the area, inhibiting the proliferation of bacteria and fungi in the acute phase of the disease. Its mechanism of action prevents the recurrence and progression of the disease to the chronic phase.

Use in dermatological treatments

For skin disorders

It has been used in the treatment of actinic keratosis, which is a skin disease characterized by a scaly area that forms in areas of the skin chronically exposed to UV radiation for years, such as the face, leather scalp or forearms.

A small percentage of this disease leads to skin cancer, hence the importance of treating it early. 

It is also used for rosacea, seborrheic dermatitis, acne, xanthelasmas (small benign bumps of fat), warts, moles, and hyperpigmentation.

The procedure is called chemi-exfoliation or peeling Chemical and tricholoacetic acid is preferred over other chemical compounds for its safety, effectiveness, and systemic non-toxicity.

TCA chemically destroys the epidermis and upper dermis of the treated area. The new epidermis migrates from the skin attachments under the destroyed tissue, after which the overlying cortex is shed within a few days.

Dermal regeneration is evident in 2 to 3 weeks. Histological changes in the skin are homogenization of collagen architecture and an increase in elastic tissue in the dermis..

These changes are permanent. In addition, abnormal cells are removed and replaced by normal epidermal cells..

For cosmetic treatments

Burning or exfoliation peeling with trichloroacetic acid is also used in the cosmetic treatment of aged, wrinkled skin, freckles, acne scars and tattoos.

It can produce a relatively deep skin burn without producing systemic toxicity. Treatments should always be performed by trained and experienced personnel.

The variables to take into account for the success of the technique are the adequate concentration of the acid according to the type and thickness of the skin, the application technique, the effectiveness of the previous skin preparation, density and activity of the sebaceous glands and application of keratolytic agents before treatment.

Each patient must be evaluated to select the appropriate concentration and avoid disastrous results.

Effect of TCA contamination

Trichloroacetic acid is a chemical compound found in the air, rain, vegetation, and soil. For this reason it has been implicated as responsible for adverse effects on some forests and jungles..

There is uncertainty as to the sources of TCA in the environment. Although there is consensus that it can come from the oxidation of chlorinated solvents present in the atmosphere, the concentrations of TCA found in precipitation are much higher than what would be expected if it were from such solvents..

TCA can also be produced in and degraded in soil. Plants can take TCA from both the air and the soil and be transported from the leaves to the roots and vice versa. It is estimated that it is metabolized in the foliage.

In tests carried out by some researchers on seedlings of a type of pine treated with levels of trichloroacetic acid similar to those found in the air in some areas of Europe, the USA and Canada, it was found that there are no visible damage to plants or changes in the growth of these due to eating disorders.

Only some decrease in protein content was found in TCA-treated plants, possibly due to the property of trichloroacetic acid to precipitate proteins..

References

1. Novák, P. and Havlícek, V. (2016). Protein Extraction and Precipitation. In Proteomic Profiling and Analytical Chemistry (Second Edition). Recovered from sciencedirect.com.
2. U.S. National Library of Medicine. (2019). Trichloroacetic acid. Recovered from: pubchem.ncbi.nlm.nih.gov
3. Cape, N.J. et al. (2003). Long-Term Exposure of Sitka Spruce Seedlings to Trichloroacetic Acid. Environ. Sci. Technol. 2003, 37, 2953-2957. Recovered from pubs.acs.org.
4. Brodland, D.G. et al. (1988). Trichloroacetic Acid Chemexfoliation (Chemical Peel) for Extensive Premalignant Actinic Damage of the Face and Scalp. Mayo Clin Proc 63: 887-896, 1988. Retrieved from ncbi.nlm.nih.gov.
5. Collins, P.S. (1989). Trichloroacetic Acid Peels Revisited. Dermatol. Surg. Oncol. 1989; 15: 933-940. Recovered from onlinelibrary.wiley.com.
6. Kantas, I. et al. (2007). The use of trichloroacetic acid in the treatment of acute external otitis. Eur Arch Otorhinolaryngol (2007) 264: 9-14. Recovered from ncbi.clm.nih.gov.