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Acetylene

physical science Maturity 11-13 Next article →

Acetylene, also known by its systematic name ethyne, is a colorless hydrocarbon gas. It is classified as the simplest alkyne, a group of organic compounds. This gas is highly valued as both a powerful fuel and a vital chemical building block. Because pure acetylene is chemically unstable, it is rarely handled in its pure state. Instead, it is usually managed as a solution within pressurized cylinders. While pure acetylene is odorless, commercial grades often have a strong smell. This scent comes from impurities like phosphine or divinyl sulfide.

Structure of acetylene with bond lengths and angles labeled
Structure of acetylene with bond lengths and angles labeled

The unique behavior of acetylene comes from its molecular structure. It consists of two carbon atoms joined by a triple bond. This triple bond makes the molecule unsaturated. The bond arrangement forces all four atoms into a straight line. Specifically, the C-C-H bond angles are exactly 180 degrees.

Structure of acetylene with bond lengths and angles labeled
Structure of acetylene with bond lengths and angles labeled

This triple bond stores a massive amount of energy. When the gas burns, it releases this energy very rapidly. This high energy content makes acetylene one of the most reactive fuels available.

To understand how it works, we can look at its bonding. In valence bond theory, each carbon atom undergoes hybridization. Specifically, the 2s orbital and one 2p orbital combine to form an sp hybrid. These sp orbitals overlap to create a strong sigma (σ) bond between the carbons. The remaining two 2p orbitals on each carbon stay unhybridized. These unhybridized orbitals overlap to form two weaker pi (π) bonds. This combination creates the characteristic triple bond. The resulting linear, symmetrical molecule belongs to the D∞h point group.

Structure of acetylene with bond lengths and angles labeled
Structure of acetylene with bond lengths and angles labeled

The history of acetylene involves several important scientific milestones. Edmund Davy discovered the gas in 1836. He found it accidentally while attempting to isolate potassium metal. He produced potassium carbide by heating potassium carbonate with carbon. When this residue reacted with water, it released the gas. In 1860, French chemist Marcellin Berthelot rediscovered it and named it acetylene. Berthelot also discovered that electricity could create the gas. He achieved this by passing hydrogen between the poles of a carbon arc.

Manufacturing methods for acetylene have changed significantly over time. The earliest industrial method used the hydrolysis of calcium carbide. This process involves reacting calcium carbide with water to release the gas. Thomas Willson developed a way to use this method on a commercial scale in 1892. Producing calcium carbide requires extreme heat, around 2000 °C, using an electric arc furnace. In the late 19th century, this was powered by hydroelectricity at Niagara Falls. Today, many countries use partial combustion of methane to produce acetylene. In 1983, approximately 400,000 tonnes were produced via this method.

BASF Nsw
BASF Nsw

Acetylene has many important industrial applications. About 20% of the gas is used for oxy-acetylene welding and cutting. When burned with oxygen, it produces a flame exceeding 3000 °C. This is the hottest common gas mixture available. It is the third-hottest natural chemical flame, following dicyanoacetylene and cyanogen. This heat allows for precise metalwork, such as brazing or tempering steel.

Carbide lamp lit
Carbide lamp lit

In the past, carbide lamps used acetylene for light in mines and lighthouses. While LEDs have replaced them, these lamps are still used in remote areas.

Carbide lamp lit
Carbide lamp lit

Beyond fuel, acetylene is a crucial feedstock for chemical synthesis. It can react with formaldehyde to produce butynediol. It also reacts with carbon monoxide to create acrylic acid. These reactions produce materials like paints, resins, and polymers. Acetylene also plays a role in advanced science. It is used in radiocarbon dating to volatilize carbon. Scientists react carbonaceous samples with lithium metal to create lithium carbide. This is then reacted with water to produce acetylene for mass spectrometry.

Reppe-chemistry-endiol-V1
Reppe-chemistry-endiol-V1

Finally, the study of polyacetylene films led to breakthroughs in organic semiconductors. This work was recognized with the Nobel Prize in Chemistry in 2000.

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File:Structure of acetylene with bond lengths and angles labeled.svg
Structure of acetylene with bond lengths...
File:Reppe-chemistry-endiol-V1.svg
Reppe-chemistry-endiol-V1.svg
File:Carbide lamp lit.jpg
Carbide lamp lit.jpg
File:Reppe-chemnistry-vinylization.png
Reppe-chemnistry-vinylization.png
File:Reppe-chemistry benzene.svg
Reppe-chemistry benzene.svg
File:Reppe-chemistry-cyclooctatetraene.svg
Reppe-chemistry-cyclooctatetraene.svg
File:BASF_Nsw.jpg
BASF_Nsw.jpg
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