Coal tar
What is Coal tar???
Coal tar is derived from coal. It is a byproduct of the production of coke, a solid fuel that contains mostly carbon, and coal gas. Coal tar is used primarily for the production of refined chemicals and coal-tar products, such as creosote and coal-tar pitch. Certain preparations of coal tar have long been used to treat various skin conditions, such as eczema, psoriasis, and dandruff.
the principal liquid product resulting from the carbonization of coal, i.e., the heating of coal in the absence of air, at temperatures ranging from about 900 to 1,200 °C (1,650 to 2,200 °F). Many commercially important compounds are derived from coal tar.
Low-temperature tars result when coal, peat, lignite, or wood are carbonized at temperatures not exceeding 700 °C (1,300 °F). Tar acids, phenolic compounds that react with caustic soda to form water-soluble salts, are extracted from coal tar after it has been distilled.
Tar bases are the alkaline constituents of distillate oils, remaining after tar acids have been removed. One of the bases that is recovered is pyridine, a colourless nitrogenous liquid that has a pungent odour and produces derivatives that are of pharmaceutical value. Pitch is the material remaining after the removal of pyridine and other distillates; it is useful in the aluminum industry for the manufacture of electrodes.
Coal tar content
Coal tar used in this invention, especially the use of coal tar containing 44-75% cyclic compounds, the present invention is used in asphalt-containing polycyclic compounds> 30-60%, coal tar and coal tar pitch of accounting and 10- 100%. Coal tar and asphalt dissolved in a solvent, coal tar and asphalt content in the solvent is 8-90%, especially 10-30%. Coal tar is a bitumen derived from crude coal tar, water gas tar, oil gas tar or from the combination of such tars with their constituents. Coal tar is a black and like gilsonite, viscous, naphthalene-like odor, amorphous residue mainly from the distillation of coal.
Composition of coal tar
The majority of its composition is poly nuclear aromatic compounds such an aromatic hydrocarbon, naphthalene, phenolic, anthracitic, quinolone compound with the trace of insoluble materials. Different grades have different float tests and softening points. Although this invention is not constrained to, the preferred coal tars have a float test at 122 degrees F., seconds: ranging from about 75 to about 230 seconds and more preferably from about 180 to 220 seconds and conform in general to specification outlined by RT-10 (Road tar-10) RT-11 and RT-12 in ASTM D490.
Coal tar Treatment
Coal tar is obtained by the destructive distillation of bituminous coal at very high temperatures. It is believed that over 10,000 different compounds make up coal tar but only 400 or so have been identified. The main groups of compounds making up crude coal tar are 48% hydrocarbons, 42% carbon and 10% water.
In its natural form is a thick, nearly black, viscous liquid with a characteristic smell. It is most often obtained in solution form (0.1 to 20%) and mixed with other ingredients, such as salicylic acid and sulphur, to make lotions, creams, ointments, and shampoos. It has been used for decades to help treat the scaling, itching, and inflammation of psoriasis, eczema, and other skin disorders.
Uses of coal tar
The use of coal tar is declining as newer compounds effective against the different forms of psoriasis are replacing it. However, it still has the advantages of being low cost and causing less systemic toxicity as compared with more modern therapies.
Coal tar therapy has been used for more than a century in dermatology. It is a topical (applied to the skin) treatment mostly used for acute (short-term) scalp psoriasis. It has anti-inflammatory and anti-scaling properties that are useful in treating chronic plaque psoriasis. Crude coal (coal tar BP, a standard formulation) is the most effective form, typically in a concentration of 1% to 10% in a soft paraffin base, although few people with psoriasis can tolerate the smell and mess.
Cleaner extracts of coal tar included in brand-name products are more practicable for home use, but they are less effective and improvement takes longer.
Contact of coal tar products with normal skin is not usually harmful and they can be used for widespread small lesions; however, irritation, contact allergy, and sterile folliculitis (pusfilled spots at the base of the hair) can occur. The milder tar extracts can be used on the face and skin folds. Tar baths and tar shampoos are also helpful and some of these products can be purchased over the counter without a prescription.
Coal tar has also been used in combination with ultraviolet B light in hospitals. It was formulated by American dermatologist William Goeckerman in 1925 and is known as the Goeckerman method. Some hospital day-units still use tar products in the bath prior to treatment.
Coal tar is still used to treat a variety of skin disorders, particularly conditions where the skin is flaky and scaly.
- Scalp psoriasis
- Palmoplantar pustulosis
- Plaque psoriasis
- Atopic dermatitis
Exactly how coal-tar works to treat these conditions is not completely understood. It appears to have antimicrobial, antipruritic (reduce itching) and keratoplastic (normalise keratin growth in the skin and reduce scaling) effects.
How to use coal tar
may be compounded with other ingredients to make creams, ointments, paints, pastes, gels, soaps, solutions and shampoos. Follow closely the instructions on the label on how to use your coal-tar preparation. Listed below are some general tips for using products.
- Apply it at bedtime if possible to avoid daytime inconvenience of the smell and staining
- Leave on skin for at least 2 hours unless otherwise directed by your doctor
- If treating the scalp, apply with a downward stroke in the same direction as hair growth
- Cover or wrap with bandages to help the preparation stay in place and prevent staining. Do not use plastic wrap as this may cause irritation and infection
- Do not apply to infected, blistered, raw or oozing areas of the skin
- After applying, protect the treated area from direct sunlight and do not use a sunlamp unless otherwise directed by your doctor.
Undesirable Effects
Most patients tolerate coal-tar preparations well. It may initially cause mild stinging or skin irritation as your body gets used to the medicine. However, if this continues to stop using the preparation and see your doctor.
When used on the scalp, it may temporarily discolour bleached, tinted, light blond or gray hair. Also, stains skin and clothing. The stain on the skin will wear off after you have stopped using the preparation.
may cause photosensitivity, hence the need to stay out of direct sunlight when using these preparations. In some instances your doctor may use the Goeckerman regimen, which is a combination of coal-tar with UVB phototherapy. This has been found to be particularly successful for treating psoriasis.
There is some controversy over the carcinogenic. In animal studies, it has been shown to increase the chance of skin cancer. However, in human studies, an increase in the incidence of cancers has not been found after 75 years of documented use.
What is coal-tar pitch?
Coal-tar pitch is a thick black liquid that remains after the distillation of coal-tar. It is used as a base for coatings and paint, in roofing and paving, and as a binder in asphalt products. Both coal-tar and coal-tar pitch contain many chemical compounds, including carcinogens such as benzene.
