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Creosote

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Creosote is a broad category of carbonaceous chemicals used primarily as preservatives or antiseptics. These substances are created through the distillation of various tars or the pyrolysis of plant-derived materials like wood or fossil fuels. Because they can prevent decay and kill microorganisms, they are vital for protecting materials from the environment.

Piling
Piling

In modern industry, the term is most often associated with protecting wood from rot and insects. This makes creosote essential for infrastructure like railroad ties and utility poles.

There are several ways to produce different types of creosote based on the source material. Coal-tar creosote is derived from the carbonization of bituminous coal. Wood-tar creosote comes from the distillation of wood, often beechwood. Other varieties include oil-tar creosote from petroleum or oil shale, and peat-tar creosote from peat. There is also water-gas-tar creosote, which comes from the tar produced by water gas.

Derivation of coal-tar creosote
Derivation of coal-tar creosote

Each type has a unique chemical makeup based on its origin.

In the modern industrial world, coal-tar creosote is the standard for wood preservation. The United States Environmental Protection Agency (EPA) defines it as a pesticide used to protect wood. To meet American Wood Protection Association (AWPA) standards, it must be a pure coal tar product. It is used to treat foundation pilings, marine pilings, lumber, posts, railroad ties, timbers, and utility poles.

RailroadTiesBeforeAfterCreosoteSantaFeRRAlbuquerqueNM
RailroadTiesBeforeAfterCreosoteSantaFeRRAlbuquerqueNM

This specific type of creosote relies on the presence of naphthalenes and anthracenes to be effective.

Applying this preservative requires a very specific mechanical process. According to the EPA and AWPA, the manufacturing process must be a pressure process. This means the liquid is forced deep into the wood fibers under high pressure. This is done under the supervision of a licensed applicator certified by State Departments of Agriculture. Regulations strictly prohibit using creosote through brush-on, spray, or other non-pressure methods. This ensures the chemical is deeply embedded to provide long-lasting protection.

The history of creosote involves many important scientific discoveries. Carl Reichenbach discovered wood-tar creosote in 1832 through the dry distillation of beechwood. He noticed that dipping meat in a dilute solution prevented putrefaction and added a smoky flavor. In 1834, Friedrich Ferdinand Runge discovered carbolic acid, also known as phenol, in coal tar. For many years, chemists mistakenly believed that creosote and carbolic acid were identical substances. It was not until the 1840s that researchers like Eugen Freiherr von Gorup-Besanez proved they were chemically different.

John Smibert - Bishop George Berkeley - Google Art Project
John Smibert - Bishop George Berkeley - Google Art Project

Chemically, wood-tar and coal-tar creosotes are quite distinct. Wood-tar creosote is a greasy liquid that can be colorless or yellowish. It contains high levels of methyl ethers of phenol, such as guaiacol and creosol. These methyl ethers make the substance less caustic and poisonous than simple phenols. This characteristic allowed it to be used historically in medical applications like ointments or even as an anesthetic. In contrast, coal-tar creosote is much stronger and more toxic.

Derivation of wood-tar creosote
Derivation of wood-tar creosote

While they share some phenol derivatives, their active components differ significantly.

You can actually experience the effects of creosote in your daily life through food. The stable scent and flavor of smoked meat are caused by the principal chemicals in creosote. Specifically, guaiacol is responsible for the smoky taste, while syringol provides the smoky aroma.

Derivation of wood-tar creosote
Derivation of wood-tar creosote

Even in your home, you might see related substances in chimney flues. When coal or wood burns under variable conditions, it produces soot and tarry smoke. These materials are natural examples of the complex chemical changes that occur during combustion.

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🖼️ Images & Media (11)
File:RailroadTiesBeforeAfterCreosoteSantaFeRRAlbuquerqueNM.jpg
RailroadTiesBeforeAfterCreosoteSantaFeRRAl...
File:Derivation of wood-tar creosote.svg
Derivation of wood-tar creosote.svg
File:John Smibert - Bishop George Berkeley - Google Art Project.jpg
John Smibert - Bishop George Berkeley -...
File:Derivation of coal-tar creosote.svg
Derivation of coal-tar creosote.svg
File:Wood Pavers (36011657806).jpg
Wood Pavers (36011657806).jpg
File:Derivation of water-gas-tar creosote.svg
Derivation of water-gas-tar creosote.svg
File:Piling.jpg
Piling.jpg
File:M-cresol reaction with methanol.png
M-cresol reaction with methanol.png
File:Phenol reaction with methanol.png
Phenol reaction with methanol.png
File:P-cresol degradation to benzoate.png
P-cresol degradation to benzoate.png
File:Phenol reaction with iron and peroxide.png
Phenol reaction with iron and peroxide.png
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