Coal Tar

Coal tar, a byproduct of coal carbonization, is a dark and complex liquid that has played a significant role in history, industry, and medicine. Its multifaceted properties have led to a wide range of applications, both historically and in the modern era. 

The Historical Significance of Coal Tar

Coal tar's history is deeply intertwined with the rise of the coal industry during the 18th and 19th centuries. As coal was distilled to produce coke for iron and steel manufacturing, coal gas for illumination, and other products, coal tar emerged as a valuable byproduct. The historical uses of coal tar were both utilitarian and innovative:

1. Paving and Waterproofing: One of the earliest applications of coal tar was in road construction. It was used to pave streets and preserve wood and concrete surfaces, providing waterproofing and protection against decay. The use of coal tar in road construction evolved into the development of asphalt pavement.

2. Medicinal Uses: In the 18th and 19th centuries, coal tar was used in traditional medicine to treat various ailments. Its applications ranged from treating skin conditions to addressing respiratory issues.

Historically, coal tar has been a valuable source of various pharmaceutical substances and chemical compounds. Some of the notable pharmaceutical substances that have been obtained from coal tar include:

1. Phenol (Carbolic Acid): Phenol, derived from coal tar, has been used as an antiseptic and disinfectant. It has also found applications in the synthesis of various pharmaceuticals.

2. Naphthalene: Naphthalene, a polycyclic aromatic hydrocarbon present in coal tar, has been used historically in the production of mothballs and as an insect repellent.

3. Anthracene: Anthracene, another polycyclic aromatic hydrocarbon found in coal tar, has been used in the synthesis of dyes, pharmaceuticals, and as a starting material for the production of anthraquinone derivatives.

4. Cresol: Cresols are components of coal tar and have been employed as antiseptics and disinfectants. They have also been used in the manufacture of various chemicals.

5. Salicylic Acid: Salicylic acid, derived from coal tar, has been used in dermatology for its keratolytic and anti-inflammatory properties. It is a key ingredient in topical treatments for skin conditions.

6. Pyridine: Pyridine, a heterocyclic compound found in coal tar, has been used in the synthesis of various drugs and pharmaceuticals.

7. Quinoline: Quinoline, another heterocyclic compound, has found applications in the production of antimalarial drugs and other pharmaceuticals.

8. Thiophene: Thiophene, present in coal tar, has been used in the synthesis of various drugs and as a precursor in pharmaceutical chemistry.

9. Xylene: Xylene, derived from coal tar, has been utilized as a solvent in the pharmaceutical industry for various processes, including the preparation of drug formulations.

10. Phthalic Anhydride: Phthalic anhydride, obtained from coal tar, has been used in the production of phthalate esters, which are used in the manufacture of various pharmaceutical and cosmetic products.

The Properties of Coal Tar

Coal tar is a dense, viscous, and dark liquid with a complex chemical composition. Its properties make it suitable for a range of industrial and pharmaceutical applications:

1. Complex Mixture: Coal tar is composed of numerous organic compounds, including polycyclic aromatic hydrocarbons (PAHs), phenols, heterocyclic compounds, and various other organic and inorganic materials.

2. Thermal Conductivity: Due to its high carbon content and good thermal conductivity, coal tar is utilized in the production of graphite electrodes, a key component in electric arc furnaces for steelmaking.

3. Preservation and Waterproofing: The dense nature of coal tar, along with its hydrophobic properties, makes it an excellent material for preserving wood and other construction materials, as well as for waterproofing applications.

Pharmaceutical Applications of Coal Tar

Coal tar has found its place in the pharmaceutical industry, particularly in dermatology, due to its unique properties. Coal tar-based products have been used to treat various skin conditions, such as psoriasis, eczema, and dandruff. These applications rely on the following properties of coal tar:

1. Keratolytic Properties: Coal tar has the ability to soften and exfoliate the outermost layer of the skin, known as the stratum corneum. This property is beneficial in managing conditions characterized by excessive skin cell turnover, such as psoriasis.

2. Anti-Inflammatory Effects: Coal tar is known for its anti-inflammatory properties, which help in reducing redness and itching associated with skin disorders.

3. Antimicrobial Action: Certain components of coal tar have mild antimicrobial properties, which can help control secondary bacterial and fungal infections in skin conditions.

4. Psoriasis Management: Coal tar preparations have been traditionally used to alleviate the symptoms of psoriasis, a chronic autoimmune skin disease. They work by slowing down the growth of skin cells and reducing inflammation.

5. Dandruff and Scalp Conditions: Shampoos and topical solutions containing coal tar are employed to address dandruff and various scalp conditions. The keratolytic and antifungal properties of coal tar are particularly beneficial in this context.

Modern Uses of Coal Tar

Coal tar's diverse properties continue to find application in various industrial sectors:

1. Pavement and Roofing: The historical use of coal tar in road construction has evolved into the development of asphalt pavement. It is used as a key component in asphalt shingles and road surfacing, providing weather resistance and durability.

2. Wood Preservation: While alternative wood preservatives have gained popularity, coal tar continues to be used for protecting timber from decay and pests, especially in railway ties and utility poles.

3. Graphite Electrodes: The aluminum and graphite electrode industries rely on coal tar pitch as a binder and impregnating agent, essential in the production of graphite electrodes used in electric arc furnaces.

4. Pesticides: Some derivatives of coal tar are employed in the manufacturing of pesticides and insecticides, contributing to pest control in agriculture.

5. Chemical Synthesis: Coal tar serves as a valuable source of various chemicals used in the production of dyes, perfumes, synthetic flavoring agents, and other specialty chemicals.

Coal tar's rich history and diverse applications highlight its continued relevance in various industries, particularly in the pharmaceutical and construction sectors. Its unique properties, including keratolytic, anti-inflammatory, and antimicrobial effects, have made it a valuable asset in dermatological treatments for skin conditions. While its use in certain applications has evolved over time, coal tar's role in paving, wood preservation, and the production of graphite electrodes remains substantial. Understanding the properties and historical significance of coal tar provides insights into its enduring relevance in modern industrial and medical applications, with careful consideration of environmental and health implications.

Please note that the information provided in this article is for informational purposes only and should not be considered a substitute for professional medical advice. Always consult with healthcare professionals or chemists for guidance on the appropriate use and handling of silver sulfadiazine in specific applications.

References

1. Atiyeh B.S., Costagliola M., Hayek S.N., Dibo S.A. (2007) Effect of silver on burn wound infection control and healing: review of the literature. Burns, 33(2), 139-148.
2. Hengge U.R., Ruzicka T., Schwartz R.A., Cork M.J. (2007) Adverse effects of topical glucocorticosteroids. Journal of the American Academy of Dermatology, 54(1), 1-15.
3. Roelofzen J.H., Aben K.K., Oldenhof U., Coenraads P.J., Alkemade H.A., van de Kerkhof P.C., van der Valk P.G., Kiemeney L.A. (2007) No increased risk of cancer after coal tar treatment in patients with psoriasis or eczema. Journal of Investigative Dermatology, 127(11), 2700-2707.

Coal Tar BP

Black or almost black, viscous liquid, with characteristic odour of Coal Tar. Slightly soluble in water, partially soluble in ethanol, ether and volatile oils. 

Conforms to BP tests

1.10 to 1.15 g

Maximum 2.0%

Maximum 2.0%

Non-hazardous chemical

Keep container tightly closed in a cool and dry place and protected from light. Protect from contamination by foreign substances.