Acetylene

Acetylene

Overview
Acetylene is the chemical compound
Chemical compound
A chemical compound is a pure chemical substance consisting of two or more different chemical elements that can be separated into simpler substances by chemical reactions. Chemical compounds have a unique and defined chemical structure; they consist of a fixed ratio of atoms that are held together...

 with the formula C2H2. It is a hydrocarbon
Hydrocarbon
In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons from which one hydrogen atom has been removed are functional groups, called hydrocarbyls....

 and the simplest alkyne
Alkyne
Alkynes are hydrocarbons that have a triple bond between two carbon atoms, with the formula CnH2n-2. Alkynes are traditionally known as acetylenes, although the name acetylene also refers specifically to C2H2, known formally as ethyne using IUPAC nomenclature...

. This colorless gas is widely used as a fuel and a chemical building block. It is unstable in pure form and thus is usually handled as a solution.

As an alkyne, acetylene is unsaturated
Saturation (chemistry)
In chemistry, saturation has six different meanings, all based on reaching a maximum capacity...

 because its two carbon atoms are bonded
Chemical bond
A chemical bond is an attraction between atoms that allows the formation of chemical substances that contain two or more atoms. The bond is caused by the electromagnetic force attraction between opposite charges, either between electrons and nuclei, or as the result of a dipole attraction...

 together in a triple bond
Triple bond
A triple bond in chemistry is a chemical bond between two chemical elements involving six bonding electrons instead of the usual two in a covalent single bond. The most common triple bond, that between two carbon atoms, can be found in alkynes. Other functional groups containing a triple bond are...

. The carbon-carbon triple bond places all four atoms in the same straight line, with CCH bond angles of 180°.
Discussion
Ask a question about 'Acetylene'
Start a new discussion about 'Acetylene'
Answer questions from other users
Full Discussion Forum
 
Unanswered Questions
Encyclopedia
Acetylene is the chemical compound
Chemical compound
A chemical compound is a pure chemical substance consisting of two or more different chemical elements that can be separated into simpler substances by chemical reactions. Chemical compounds have a unique and defined chemical structure; they consist of a fixed ratio of atoms that are held together...

 with the formula C2H2. It is a hydrocarbon
Hydrocarbon
In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons from which one hydrogen atom has been removed are functional groups, called hydrocarbyls....

 and the simplest alkyne
Alkyne
Alkynes are hydrocarbons that have a triple bond between two carbon atoms, with the formula CnH2n-2. Alkynes are traditionally known as acetylenes, although the name acetylene also refers specifically to C2H2, known formally as ethyne using IUPAC nomenclature...

. This colorless gas is widely used as a fuel and a chemical building block. It is unstable in pure form and thus is usually handled as a solution.

As an alkyne, acetylene is unsaturated
Saturation (chemistry)
In chemistry, saturation has six different meanings, all based on reaching a maximum capacity...

 because its two carbon atoms are bonded
Chemical bond
A chemical bond is an attraction between atoms that allows the formation of chemical substances that contain two or more atoms. The bond is caused by the electromagnetic force attraction between opposite charges, either between electrons and nuclei, or as the result of a dipole attraction...

 together in a triple bond
Triple bond
A triple bond in chemistry is a chemical bond between two chemical elements involving six bonding electrons instead of the usual two in a covalent single bond. The most common triple bond, that between two carbon atoms, can be found in alkynes. Other functional groups containing a triple bond are...

. The carbon-carbon triple bond places all four atoms in the same straight line, with CCH bond angles of 180°. Since acetylene is a linear symmetrical molecule, it possesses the D∞h point group
Point group
In geometry, a point group is a group of geometric symmetries that keep at least one point fixed. Point groups can exist in a Euclidean space with any dimension, and every point group in dimension d is a subgroup of the orthogonal group O...

.

Discovery


Acetylene was discovered in 1836 by Edmund Davy
Edmund Davy
Edmund Davy FRS was a professor of Chemistry at the Royal Cork Institution from 1813 and professor of chemistry at the Royal Dublin Society from 1826. He discovered acetylene, as it was later named by Marcellin Berthelot...

 who identified it as a "new carburet of hydrogen". It was rediscovered in 1860 by French chemist Marcellin Berthelot
Marcellin Berthelot
Marcelin Pierre Eugène Berthelot was a French chemist and politician noted for the Thomsen-Berthelot principle of thermochemistry. He synthesized many organic compounds from inorganic substances and disproved the theory of vitalism. He is considered as one of the greatest chemists of all time.He...

, who coined the name "acetylene". Berthelot was able to prepare this gas by passing vapours of organic compounds (methanol, ethanol, etc.) through a red-hot tube and collecting the effluent
Effluent
Effluent is an outflowing of water or gas from a natural body of water, or from a human-made structure.Effluent is defined by the United States Environmental Protection Agency as “wastewater - treated or untreated - that flows out of a treatment plant, sewer, or industrial outfall. Generally refers...

. He also found acetylene was formed by sparking electricity through mixed cyanogen
Cyanogen
Cyanogen is the chemical compound with the formula 2. It is a colorless, toxic gas with a pungent odor.The molecule is a pseudohalogen. Cyanogen molecules consist of two CN groups — analogous to diatomic halogen molecules, such as Cl2, but far less oxidizing...

 and hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...

 gases. Berthelot later obtained acetylene directly by passing hydrogen between the poles of a carbon arc
Arc lamp
"Arc lamp" or "arc light" is the general term for a class of lamps that produce light by an electric arc . The lamp consists of two electrodes, first made from carbon but typically made today of tungsten, which are separated by a gas...

.

Preparation


Today acetylene is mainly manufactured by the partial combustion
Combustion
Combustion or burning is the sequence of exothermic chemical reactions between a fuel and an oxidant accompanied by the production of heat and conversion of chemical species. The release of heat can result in the production of light in the form of either glowing or a flame...

 of methane
Methane
Methane is a chemical compound with the chemical formula . It is the simplest alkane, the principal component of natural gas, and probably the most abundant organic compound on earth. The relative abundance of methane makes it an attractive fuel...

 or appears as a side product in the ethylene
Ethylene
Ethylene is a gaseous organic compound with the formula . It is the simplest alkene . Because it contains a carbon-carbon double bond, ethylene is classified as an unsaturated hydrocarbon. Ethylene is widely used in industry and is also a plant hormone...

 stream from cracking
Cracking (chemistry)
In petroleum geology and chemistry, cracking is the process whereby complex organic molecules such as kerogens or heavy hydrocarbons are broken down into simpler molecules such as light hydrocarbons, by the breaking of carbon-carbon bonds in the precursors. The rate of cracking and the end products...

 of hydrocarbon
Hydrocarbon
In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons from which one hydrogen atom has been removed are functional groups, called hydrocarbyls....

s. Approximately 400,000 tonnes are produced this way annually. Its presence in ethylene is usually undesirable because of its explosive character and its ability to poison Ziegler-Natta catalyst
Ziegler-Natta catalyst
A Ziegler–Natta catalyst is a catalyst used in the synthesis of polymers of 1-alkenes . Three types of Ziegler–Natta catalysts are currently employed:* Solid and supported catalysts based on titanium compounds...

s. It is selectively hydrogenated into ethylene
Ethylene
Ethylene is a gaseous organic compound with the formula . It is the simplest alkene . Because it contains a carbon-carbon double bond, ethylene is classified as an unsaturated hydrocarbon. Ethylene is widely used in industry and is also a plant hormone...

, usually using Pd-Ag catalysts.

Until the 1950s, when oil supplanted coal as the chief source of carbon, acetylene (and the aromatic fraction from coal tar
Coal tar
Coal tar is a brown or black liquid of extremely high viscosity, which smells of naphthalene and aromatic hydrocarbons. Coal tar is among the by-products when coal iscarbonized to make coke or gasified to make coal gas...

) was the main source of organic chemicals in the chemical industry. It was prepared by the hydrolysis
Hydrolysis
Hydrolysis is a chemical reaction during which molecules of water are split into hydrogen cations and hydroxide anions in the process of a chemical mechanism. It is the type of reaction that is used to break down certain polymers, especially those made by condensation polymerization...

 of calcium carbide
Calcium carbide
thumb|right|Calcium carbide.Calcium carbide is a chemical compound with the chemical formula of CaC2. The pure material is colorless, however pieces of technical grade calcium carbide are grey or brown and consist of only 80-85% of CaC2 . Because of presence of PH3, NH3, and H2S it has a...

, a reaction discovered by Friedrich Wöhler
Friedrich Wöhler
Friedrich Wöhler was a German chemist, best known for his synthesis of urea, but also the first to isolate several chemical elements.-Biography:He was born in Eschersheim, which belonged to aau...

 in 1862 and still familiar to students:
CaC2 + 2H2O → Ca(OH)2 + C2H2


Calcium carbide production requires extremely high temperatures, ~2000 °C, necessitating the use of an electric arc furnace
Electric arc furnace
An electric arc furnace is a furnace that heats charged material by means of an electric arc.Arc furnaces range in size from small units of approximately one ton capacity up to about 400 ton units used for secondary steelmaking...

. In the US, this process was an important part of the late-19th century revolution in chemistry enabled by the massive hydroelectric power project at Niagara Falls
Niagara Falls
The Niagara Falls, located on the Niagara River draining Lake Erie into Lake Ontario, is the collective name for the Horseshoe Falls and the adjacent American Falls along with the comparatively small Bridal Veil Falls, which combined form the highest flow rate of any waterfalls in the world and has...

.

Bonding



In terms of valence bond theory
Valence bond theory
In chemistry, valence bond theory is one of two basic theories, along with molecular orbital theory, that were developed to use the methods of quantum mechanics to explain chemical bonding. It focuses on how the atomic orbitals of the dissociated atoms combine to give individual chemical bonds...

, in each carbon atom the 2s orbital
Atomic orbital
An atomic orbital is a mathematical function that describes the wave-like behavior of either one electron or a pair of electrons in an atom. This function can be used to calculate the probability of finding any electron of an atom in any specific region around the atom's nucleus...

 hybridizes
Orbital hybridisation
In chemistry, hybridisation is the concept of mixing atomic orbitals to form new hybrid orbitals suitable for the qualitative description of atomic bonding properties. Hybridised orbitals are very useful in the explanation of the shape of molecular orbitals for molecules. It is an integral part...

 with one 2p orbital thus forming an sp hybrid. The other two 2p orbitals remain unhybridized. The two ends of the two sp hybrid orbital overlap
Orbital overlap
Orbital overlap was an idea first introduced by Linus Pauling to explain the molecular bond angles observed through experimentation and is the basis for the concept of orbital hybridisation. s orbitals are spherical and have no directionality while p orbitals are oriented 90° to one another...

 to form a strong σ valence bond
Sigma bond
In chemistry, sigma bonds are the strongest type of covalent chemical bond. They are formed by head-on overlapping between atomic orbitals. Sigma bonding is most clearly defined for diatomic molecules using the language and tools of symmetry groups. In this formal approach, a σ-bond is...

 between the carbons, while on each of the other two ends hydrogen atoms attach also by σ bonds. The two unchanged 2p orbitals form a pair of weaker π valence bonds
Pi bond
In chemistry, pi bonds are covalent chemical bonds where two lobes of one involved atomic orbital overlap two lobes of the other involved atomic orbital...

.

Reactions



One new application is the conversion of acetylene to ethylene for use in making a variety of polyethylene
Polyethylene
Polyethylene or polythene is the most widely used plastic, with an annual production of approximately 80 million metric tons...

 plastics. An important reaction of acetylene is its combustion, the basis of the acetylene welding technologies. Otherwise, its major applications involve its conversion to acrylic acid derivatives.

Compared to most hydrocarbon
Hydrocarbon
In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons from which one hydrogen atom has been removed are functional groups, called hydrocarbyls....

s, acetylene is relatively acidic, though it is still much less acidic than water or ethanol
Ethanol
Ethanol, also called ethyl alcohol, pure alcohol, grain alcohol, or drinking alcohol, is a volatile, flammable, colorless liquid. It is a psychoactive drug and one of the oldest recreational drugs. Best known as the type of alcohol found in alcoholic beverages, it is also used in thermometers, as a...

. Thus it reacts with strong bases to form acetylide salts. For example, acetylene reacts with sodium amide
Sodium amide
Sodium amide, commonly called sodamide, is the chemical compound with the formula NaNH2. This solid, which is dangerously reactive toward water, is white when pure, but commercial samples are typically gray due to the presence of small quantities of metallic iron from the manufacturing process...

 in liquid ammonia
Ammonia
Ammonia is a compound of nitrogen and hydrogen with the formula . It is a colourless gas with a characteristic pungent odour. Ammonia contributes significantly to the nutritional needs of terrestrial organisms by serving as a precursor to food and fertilizers. Ammonia, either directly or...

 to form sodium acetylide, and with butyllithium in cold THF
Tetrahydrofuran
Tetrahydrofuran is a colorless, water-miscible organic liquid with low viscosity at standard temperature and pressure. This heterocyclic compound has the chemical formula 4O. As one of the most polar ethers with a wide liquid range, it is a useful solvent. Its main use, however, is as a precursor...

 to give lithium acetylide.

Acetylene (systematic name: ethyne) is the chemical compound
Chemical compound
A chemical compound is a pure chemical substance consisting of two or more different chemical elements that can be separated into simpler substances by chemical reactions. Chemical compounds have a unique and defined chemical structure; they consist of a fixed ratio of atoms that are held together...

 with the formula C2H2. It is a hydrocarbon
Hydrocarbon
In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons from which one hydrogen atom has been removed are functional groups, called hydrocarbyls....

 and the simplest alkyne
Alkyne
Alkynes are hydrocarbons that have a triple bond between two carbon atoms, with the formula CnH2n-2. Alkynes are traditionally known as acetylenes, although the name acetylene also refers specifically to C2H2, known formally as ethyne using IUPAC nomenclature...

. This colorless gas is widely used as a fuel and a chemical building block. It is unstable in pure form and thus is usually handled as a solution.

As an alkyne, acetylene is unsaturated
Saturation (chemistry)
In chemistry, saturation has six different meanings, all based on reaching a maximum capacity...

 because its two carbon atoms are bonded
Chemical bond
A chemical bond is an attraction between atoms that allows the formation of chemical substances that contain two or more atoms. The bond is caused by the electromagnetic force attraction between opposite charges, either between electrons and nuclei, or as the result of a dipole attraction...

 together in a triple bond
Triple bond
A triple bond in chemistry is a chemical bond between two chemical elements involving six bonding electrons instead of the usual two in a covalent single bond. The most common triple bond, that between two carbon atoms, can be found in alkynes. Other functional groups containing a triple bond are...

. The carbon-carbon triple bond places all four atoms in the same straight line, with CCH bond angles of 180°. Since acetylene is a linear symmetrical molecule, it possesses the D∞h point group
Point group
In geometry, a point group is a group of geometric symmetries that keep at least one point fixed. Point groups can exist in a Euclidean space with any dimension, and every point group in dimension d is a subgroup of the orthogonal group O...

.

Discovery


Acetylene was discovered in 1836 by Edmund Davy
Edmund Davy
Edmund Davy FRS was a professor of Chemistry at the Royal Cork Institution from 1813 and professor of chemistry at the Royal Dublin Society from 1826. He discovered acetylene, as it was later named by Marcellin Berthelot...

 who identified it as a "new carburet of hydrogen". It was rediscovered in 1860 by French chemist Marcellin Berthelot
Marcellin Berthelot
Marcelin Pierre Eugène Berthelot was a French chemist and politician noted for the Thomsen-Berthelot principle of thermochemistry. He synthesized many organic compounds from inorganic substances and disproved the theory of vitalism. He is considered as one of the greatest chemists of all time.He...

, who coined the name "acetylene". Berthelot was able to prepare this gas by passing vapours of organic compounds (methanol, ethanol, etc.) through a red-hot tube and collecting the effluent
Effluent
Effluent is an outflowing of water or gas from a natural body of water, or from a human-made structure.Effluent is defined by the United States Environmental Protection Agency as “wastewater - treated or untreated - that flows out of a treatment plant, sewer, or industrial outfall. Generally refers...

. He also found acetylene was formed by sparking electricity through mixed cyanogen
Cyanogen
Cyanogen is the chemical compound with the formula 2. It is a colorless, toxic gas with a pungent odor.The molecule is a pseudohalogen. Cyanogen molecules consist of two CN groups — analogous to diatomic halogen molecules, such as Cl2, but far less oxidizing...

 and hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...

 gases. Berthelot later obtained acetylene directly by passing hydrogen between the poles of a carbon arc
Arc lamp
"Arc lamp" or "arc light" is the general term for a class of lamps that produce light by an electric arc . The lamp consists of two electrodes, first made from carbon but typically made today of tungsten, which are separated by a gas...

.

Preparation


Today acetylene is mainly manufactured by the partial combustion
Combustion
Combustion or burning is the sequence of exothermic chemical reactions between a fuel and an oxidant accompanied by the production of heat and conversion of chemical species. The release of heat can result in the production of light in the form of either glowing or a flame...

 of methane
Methane
Methane is a chemical compound with the chemical formula . It is the simplest alkane, the principal component of natural gas, and probably the most abundant organic compound on earth. The relative abundance of methane makes it an attractive fuel...

 or appears as a side product in the ethylene
Ethylene
Ethylene is a gaseous organic compound with the formula . It is the simplest alkene . Because it contains a carbon-carbon double bond, ethylene is classified as an unsaturated hydrocarbon. Ethylene is widely used in industry and is also a plant hormone...

 stream from cracking
Cracking (chemistry)
In petroleum geology and chemistry, cracking is the process whereby complex organic molecules such as kerogens or heavy hydrocarbons are broken down into simpler molecules such as light hydrocarbons, by the breaking of carbon-carbon bonds in the precursors. The rate of cracking and the end products...

 of hydrocarbon
Hydrocarbon
In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons from which one hydrogen atom has been removed are functional groups, called hydrocarbyls....

s. Approximately 400,000 tonnes are produced this way annually. Its presence in ethylene is usually undesirable because of its explosive character and its ability to poison Ziegler-Natta catalyst
Ziegler-Natta catalyst
A Ziegler–Natta catalyst is a catalyst used in the synthesis of polymers of 1-alkenes . Three types of Ziegler–Natta catalysts are currently employed:* Solid and supported catalysts based on titanium compounds...

s. It is selectively hydrogenated into ethylene
Ethylene
Ethylene is a gaseous organic compound with the formula . It is the simplest alkene . Because it contains a carbon-carbon double bond, ethylene is classified as an unsaturated hydrocarbon. Ethylene is widely used in industry and is also a plant hormone...

, usually using Pd-Ag catalysts.

Until the 1950s, when oil supplanted coal as the chief source of carbon, acetylene (and the aromatic fraction from coal tar
Coal tar
Coal tar is a brown or black liquid of extremely high viscosity, which smells of naphthalene and aromatic hydrocarbons. Coal tar is among the by-products when coal iscarbonized to make coke or gasified to make coal gas...

) was the main source of organic chemicals in the chemical industry. It was prepared by the hydrolysis
Hydrolysis
Hydrolysis is a chemical reaction during which molecules of water are split into hydrogen cations and hydroxide anions in the process of a chemical mechanism. It is the type of reaction that is used to break down certain polymers, especially those made by condensation polymerization...

 of calcium carbide
Calcium carbide
thumb|right|Calcium carbide.Calcium carbide is a chemical compound with the chemical formula of CaC2. The pure material is colorless, however pieces of technical grade calcium carbide are grey or brown and consist of only 80-85% of CaC2 . Because of presence of PH3, NH3, and H2S it has a...

, a reaction discovered by Friedrich Wöhler
Friedrich Wöhler
Friedrich Wöhler was a German chemist, best known for his synthesis of urea, but also the first to isolate several chemical elements.-Biography:He was born in Eschersheim, which belonged to aau...

 in 1862 and still familiar to students:
CaC2 + 2H2O → Ca(OH)2 + C2H2


Calcium carbide production requires extremely high temperatures, ~2000 °C, necessitating the use of an electric arc furnace
Electric arc furnace
An electric arc furnace is a furnace that heats charged material by means of an electric arc.Arc furnaces range in size from small units of approximately one ton capacity up to about 400 ton units used for secondary steelmaking...

. In the US, this process was an important part of the late-19th century revolution in chemistry enabled by the massive hydroelectric power project at Niagara Falls
Niagara Falls
The Niagara Falls, located on the Niagara River draining Lake Erie into Lake Ontario, is the collective name for the Horseshoe Falls and the adjacent American Falls along with the comparatively small Bridal Veil Falls, which combined form the highest flow rate of any waterfalls in the world and has...

.

Bonding



In terms of valence bond theory
Valence bond theory
In chemistry, valence bond theory is one of two basic theories, along with molecular orbital theory, that were developed to use the methods of quantum mechanics to explain chemical bonding. It focuses on how the atomic orbitals of the dissociated atoms combine to give individual chemical bonds...

, in each carbon atom the 2s orbital
Atomic orbital
An atomic orbital is a mathematical function that describes the wave-like behavior of either one electron or a pair of electrons in an atom. This function can be used to calculate the probability of finding any electron of an atom in any specific region around the atom's nucleus...

 hybridizes
Orbital hybridisation
In chemistry, hybridisation is the concept of mixing atomic orbitals to form new hybrid orbitals suitable for the qualitative description of atomic bonding properties. Hybridised orbitals are very useful in the explanation of the shape of molecular orbitals for molecules. It is an integral part...

 with one 2p orbital thus forming an sp hybrid. The other two 2p orbitals remain unhybridized. The two ends of the two sp hybrid orbital overlap
Orbital overlap
Orbital overlap was an idea first introduced by Linus Pauling to explain the molecular bond angles observed through experimentation and is the basis for the concept of orbital hybridisation. s orbitals are spherical and have no directionality while p orbitals are oriented 90° to one another...

 to form a strong σ valence bond
Sigma bond
In chemistry, sigma bonds are the strongest type of covalent chemical bond. They are formed by head-on overlapping between atomic orbitals. Sigma bonding is most clearly defined for diatomic molecules using the language and tools of symmetry groups. In this formal approach, a σ-bond is...

 between the carbons, while on each of the other two ends hydrogen atoms attach also by σ bonds. The two unchanged 2p orbitals form a pair of weaker π valence bonds
Pi bond
In chemistry, pi bonds are covalent chemical bonds where two lobes of one involved atomic orbital overlap two lobes of the other involved atomic orbital...

.

Reactions



One new application is the conversion of acetylene to ethylene for use in making a variety of polyethylene
Polyethylene
Polyethylene or polythene is the most widely used plastic, with an annual production of approximately 80 million metric tons...

 plastics. An important reaction of acetylene is its combustion, the basis of the acetylene welding technologies. Otherwise, its major applications involve its conversion to acrylic acid derivatives.

Compared to most hydrocarbon
Hydrocarbon
In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons from which one hydrogen atom has been removed are functional groups, called hydrocarbyls....

s, acetylene is relatively acidic, though it is still much less acidic than water or ethanol
Ethanol
Ethanol, also called ethyl alcohol, pure alcohol, grain alcohol, or drinking alcohol, is a volatile, flammable, colorless liquid. It is a psychoactive drug and one of the oldest recreational drugs. Best known as the type of alcohol found in alcoholic beverages, it is also used in thermometers, as a...

. Thus it reacts with strong bases to form acetylide salts. For example, acetylene reacts with sodium amide
Sodium amide
Sodium amide, commonly called sodamide, is the chemical compound with the formula NaNH2. This solid, which is dangerously reactive toward water, is white when pure, but commercial samples are typically gray due to the presence of small quantities of metallic iron from the manufacturing process...

 in liquid ammonia
Ammonia
Ammonia is a compound of nitrogen and hydrogen with the formula . It is a colourless gas with a characteristic pungent odour. Ammonia contributes significantly to the nutritional needs of terrestrial organisms by serving as a precursor to food and fertilizers. Ammonia, either directly or...

 to form sodium acetylide, and with butyllithium in cold THF
Tetrahydrofuran
Tetrahydrofuran is a colorless, water-miscible organic liquid with low viscosity at standard temperature and pressure. This heterocyclic compound has the chemical formula 4O. As one of the most polar ethers with a wide liquid range, it is a useful solvent. Its main use, however, is as a precursor...

 to give lithium acetylide.

Acetylene (systematic name: ethyne) is the chemical compound
Chemical compound
A chemical compound is a pure chemical substance consisting of two or more different chemical elements that can be separated into simpler substances by chemical reactions. Chemical compounds have a unique and defined chemical structure; they consist of a fixed ratio of atoms that are held together...

 with the formula C2H2. It is a hydrocarbon
Hydrocarbon
In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons from which one hydrogen atom has been removed are functional groups, called hydrocarbyls....

 and the simplest alkyne
Alkyne
Alkynes are hydrocarbons that have a triple bond between two carbon atoms, with the formula CnH2n-2. Alkynes are traditionally known as acetylenes, although the name acetylene also refers specifically to C2H2, known formally as ethyne using IUPAC nomenclature...

. This colorless gas is widely used as a fuel and a chemical building block. It is unstable in pure form and thus is usually handled as a solution.

As an alkyne, acetylene is unsaturated
Saturation (chemistry)
In chemistry, saturation has six different meanings, all based on reaching a maximum capacity...

 because its two carbon atoms are bonded
Chemical bond
A chemical bond is an attraction between atoms that allows the formation of chemical substances that contain two or more atoms. The bond is caused by the electromagnetic force attraction between opposite charges, either between electrons and nuclei, or as the result of a dipole attraction...

 together in a triple bond
Triple bond
A triple bond in chemistry is a chemical bond between two chemical elements involving six bonding electrons instead of the usual two in a covalent single bond. The most common triple bond, that between two carbon atoms, can be found in alkynes. Other functional groups containing a triple bond are...

. The carbon-carbon triple bond places all four atoms in the same straight line, with CCH bond angles of 180°. Since acetylene is a linear symmetrical molecule, it possesses the D∞h point group
Point group
In geometry, a point group is a group of geometric symmetries that keep at least one point fixed. Point groups can exist in a Euclidean space with any dimension, and every point group in dimension d is a subgroup of the orthogonal group O...

.

Discovery


Acetylene was discovered in 1836 by Edmund Davy
Edmund Davy
Edmund Davy FRS was a professor of Chemistry at the Royal Cork Institution from 1813 and professor of chemistry at the Royal Dublin Society from 1826. He discovered acetylene, as it was later named by Marcellin Berthelot...

 who identified it as a "new carburet of hydrogen". It was rediscovered in 1860 by French chemist Marcellin Berthelot
Marcellin Berthelot
Marcelin Pierre Eugène Berthelot was a French chemist and politician noted for the Thomsen-Berthelot principle of thermochemistry. He synthesized many organic compounds from inorganic substances and disproved the theory of vitalism. He is considered as one of the greatest chemists of all time.He...

, who coined the name "acetylene". Berthelot was able to prepare this gas by passing vapours of organic compounds (methanol, ethanol, etc.) through a red-hot tube and collecting the effluent
Effluent
Effluent is an outflowing of water or gas from a natural body of water, or from a human-made structure.Effluent is defined by the United States Environmental Protection Agency as “wastewater - treated or untreated - that flows out of a treatment plant, sewer, or industrial outfall. Generally refers...

. He also found acetylene was formed by sparking electricity through mixed cyanogen
Cyanogen
Cyanogen is the chemical compound with the formula 2. It is a colorless, toxic gas with a pungent odor.The molecule is a pseudohalogen. Cyanogen molecules consist of two CN groups — analogous to diatomic halogen molecules, such as Cl2, but far less oxidizing...

 and hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...

 gases. Berthelot later obtained acetylene directly by passing hydrogen between the poles of a carbon arc
Arc lamp
"Arc lamp" or "arc light" is the general term for a class of lamps that produce light by an electric arc . The lamp consists of two electrodes, first made from carbon but typically made today of tungsten, which are separated by a gas...

.

Preparation


Today acetylene is mainly manufactured by the partial combustion
Combustion
Combustion or burning is the sequence of exothermic chemical reactions between a fuel and an oxidant accompanied by the production of heat and conversion of chemical species. The release of heat can result in the production of light in the form of either glowing or a flame...

 of methane
Methane
Methane is a chemical compound with the chemical formula . It is the simplest alkane, the principal component of natural gas, and probably the most abundant organic compound on earth. The relative abundance of methane makes it an attractive fuel...

 or appears as a side product in the ethylene
Ethylene
Ethylene is a gaseous organic compound with the formula . It is the simplest alkene . Because it contains a carbon-carbon double bond, ethylene is classified as an unsaturated hydrocarbon. Ethylene is widely used in industry and is also a plant hormone...

 stream from cracking
Cracking (chemistry)
In petroleum geology and chemistry, cracking is the process whereby complex organic molecules such as kerogens or heavy hydrocarbons are broken down into simpler molecules such as light hydrocarbons, by the breaking of carbon-carbon bonds in the precursors. The rate of cracking and the end products...

 of hydrocarbon
Hydrocarbon
In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons from which one hydrogen atom has been removed are functional groups, called hydrocarbyls....

s. Approximately 400,000 tonnes are produced this way annually. Its presence in ethylene is usually undesirable because of its explosive character and its ability to poison Ziegler-Natta catalyst
Ziegler-Natta catalyst
A Ziegler–Natta catalyst is a catalyst used in the synthesis of polymers of 1-alkenes . Three types of Ziegler–Natta catalysts are currently employed:* Solid and supported catalysts based on titanium compounds...

s. It is selectively hydrogenated into ethylene
Ethylene
Ethylene is a gaseous organic compound with the formula . It is the simplest alkene . Because it contains a carbon-carbon double bond, ethylene is classified as an unsaturated hydrocarbon. Ethylene is widely used in industry and is also a plant hormone...

, usually using Pd-Ag catalysts.

Until the 1950s, when oil supplanted coal as the chief source of carbon, acetylene (and the aromatic fraction from coal tar
Coal tar
Coal tar is a brown or black liquid of extremely high viscosity, which smells of naphthalene and aromatic hydrocarbons. Coal tar is among the by-products when coal iscarbonized to make coke or gasified to make coal gas...

) was the main source of organic chemicals in the chemical industry. It was prepared by the hydrolysis
Hydrolysis
Hydrolysis is a chemical reaction during which molecules of water are split into hydrogen cations and hydroxide anions in the process of a chemical mechanism. It is the type of reaction that is used to break down certain polymers, especially those made by condensation polymerization...

 of calcium carbide
Calcium carbide
thumb|right|Calcium carbide.Calcium carbide is a chemical compound with the chemical formula of CaC2. The pure material is colorless, however pieces of technical grade calcium carbide are grey or brown and consist of only 80-85% of CaC2 . Because of presence of PH3, NH3, and H2S it has a...

, a reaction discovered by Friedrich Wöhler
Friedrich Wöhler
Friedrich Wöhler was a German chemist, best known for his synthesis of urea, but also the first to isolate several chemical elements.-Biography:He was born in Eschersheim, which belonged to aau...

 in 1862 and still familiar to students:
CaC2 + 2H2O → Ca(OH)2 + C2H2


Calcium carbide production requires extremely high temperatures, ~2000 °C, necessitating the use of an electric arc furnace
Electric arc furnace
An electric arc furnace is a furnace that heats charged material by means of an electric arc.Arc furnaces range in size from small units of approximately one ton capacity up to about 400 ton units used for secondary steelmaking...

. In the US, this process was an important part of the late-19th century revolution in chemistry enabled by the massive hydroelectric power project at Niagara Falls
Niagara Falls
The Niagara Falls, located on the Niagara River draining Lake Erie into Lake Ontario, is the collective name for the Horseshoe Falls and the adjacent American Falls along with the comparatively small Bridal Veil Falls, which combined form the highest flow rate of any waterfalls in the world and has...

.

Bonding



In terms of valence bond theory
Valence bond theory
In chemistry, valence bond theory is one of two basic theories, along with molecular orbital theory, that were developed to use the methods of quantum mechanics to explain chemical bonding. It focuses on how the atomic orbitals of the dissociated atoms combine to give individual chemical bonds...

, in each carbon atom the 2s orbital
Atomic orbital
An atomic orbital is a mathematical function that describes the wave-like behavior of either one electron or a pair of electrons in an atom. This function can be used to calculate the probability of finding any electron of an atom in any specific region around the atom's nucleus...

 hybridizes
Orbital hybridisation
In chemistry, hybridisation is the concept of mixing atomic orbitals to form new hybrid orbitals suitable for the qualitative description of atomic bonding properties. Hybridised orbitals are very useful in the explanation of the shape of molecular orbitals for molecules. It is an integral part...

 with one 2p orbital thus forming an sp hybrid. The other two 2p orbitals remain unhybridized. The two ends of the two sp hybrid orbital overlap
Orbital overlap
Orbital overlap was an idea first introduced by Linus Pauling to explain the molecular bond angles observed through experimentation and is the basis for the concept of orbital hybridisation. s orbitals are spherical and have no directionality while p orbitals are oriented 90° to one another...

 to form a strong σ valence bond
Sigma bond
In chemistry, sigma bonds are the strongest type of covalent chemical bond. They are formed by head-on overlapping between atomic orbitals. Sigma bonding is most clearly defined for diatomic molecules using the language and tools of symmetry groups. In this formal approach, a σ-bond is...

 between the carbons, while on each of the other two ends hydrogen atoms attach also by σ bonds. The two unchanged 2p orbitals form a pair of weaker π valence bonds
Pi bond
In chemistry, pi bonds are covalent chemical bonds where two lobes of one involved atomic orbital overlap two lobes of the other involved atomic orbital...

.

Reactions



One new application is the conversion of acetylene to ethylene for use in making a variety of polyethylene
Polyethylene
Polyethylene or polythene is the most widely used plastic, with an annual production of approximately 80 million metric tons...

 plastics. An important reaction of acetylene is its combustion, the basis of the acetylene welding technologies. Otherwise, its major applications involve its conversion to acrylic acid derivatives.

Compared to most hydrocarbon
Hydrocarbon
In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons from which one hydrogen atom has been removed are functional groups, called hydrocarbyls....

s, acetylene is relatively acidic, though it is still much less acidic than water or ethanol
Ethanol
Ethanol, also called ethyl alcohol, pure alcohol, grain alcohol, or drinking alcohol, is a volatile, flammable, colorless liquid. It is a psychoactive drug and one of the oldest recreational drugs. Best known as the type of alcohol found in alcoholic beverages, it is also used in thermometers, as a...

. Thus it reacts with strong bases to form acetylide salts. For example, acetylene reacts with sodium amide
Sodium amide
Sodium amide, commonly called sodamide, is the chemical compound with the formula NaNH2. This solid, which is dangerously reactive toward water, is white when pure, but commercial samples are typically gray due to the presence of small quantities of metallic iron from the manufacturing process...

 in liquid ammonia
Ammonia
Ammonia is a compound of nitrogen and hydrogen with the formula . It is a colourless gas with a characteristic pungent odour. Ammonia contributes significantly to the nutritional needs of terrestrial organisms by serving as a precursor to food and fertilizers. Ammonia, either directly or...

 to form sodium acetylide, and with butyllithium in cold THF
Tetrahydrofuran
Tetrahydrofuran is a colorless, water-miscible organic liquid with low viscosity at standard temperature and pressure. This heterocyclic compound has the chemical formula 4O. As one of the most polar ethers with a wide liquid range, it is a useful solvent. Its main use, however, is as a precursor...

 to give lithium acetylide.


Acetylides of heavy metals are easily formed by reaction of acetylene with the metal ions. Several, e.g., silver acetylide
Silver acetylide
Silver acetylide is an inorganic chemical compound with the formula Ag2C2, a metal acetylide. The name is derived from the way it is synthesized, and emphasizes that the compound can be regarded as a salt of the weak acid, acetylene. Since acetylene is called "ethyne" in the modern IUPAC...

 and copper acetylide, are powerful and very dangerous explosives. Copper acetylide is also formed by reacting acetylene with metallic copper or its alloys; these materials are therefore unsuitable for installations for handling acetylene.

Reppe chemistry


Walter Reppe
Walter Reppe
Walter Julius Reppe was a German chemist. He is notable for his contributions to the chemistry of acetylene.-Education and career:...

 discovered that in the presence of metal catalysts, acetylene can react to give a wide range of industrially significant chemicals.
  • With alcohol
    Alcohol
    In chemistry, an alcohol is an organic compound in which the hydroxy functional group is bound to a carbon atom. In particular, this carbon center should be saturated, having single bonds to three other atoms....

    s, hydrogen cyanide, hydrogen chloride
    Hydrogen chloride
    The compound hydrogen chloride has the formula HCl. At room temperature, it is a colorless gas, which forms white fumes of hydrochloric acid upon contact with atmospheric humidity. Hydrogen chloride gas and hydrochloric acid are important in technology and industry...

    , or carboxylic acid
    Carboxylic acid
    Carboxylic acids are organic acids characterized by the presence of at least one carboxyl group. The general formula of a carboxylic acid is R-COOH, where R is some monovalent functional group...

    s to give vinyl
    Vinyl
    A vinyl compound is any organic compound that contains a vinyl group ,which are derivatives of ethene, CH2=CH2, with one hydrogen atom replaced with some other group...

     compounds:

  • With aldehydes to give ethynyl diols.
1,4-Butynediol
1,4-Butynediol
1,4-Butynediol is an organic compound that is an alkyne and a diol. This yellow crystalline solid is soluble in water and ethanol.-Synthesis:1,4-Butynediol can be produced in the Reppe synthesis, where formaldehyde and acetylene are the reactants:...

 is produced industrially in this way from formaldehyde
Formaldehyde
Formaldehyde is an organic compound with the formula CH2O. It is the simplest aldehyde, hence its systematic name methanal.Formaldehyde is a colorless gas with a characteristic pungent odor. It is an important precursor to many other chemical compounds, especially for polymers...

 and acetylene.

  • With carbon monoxide
    Carbon monoxide
    Carbon monoxide , also called carbonous oxide, is a colorless, odorless, and tasteless gas that is slightly lighter than air. It is highly toxic to humans and animals in higher quantities, although it is also produced in normal animal metabolism in low quantities, and is thought to have some normal...

     to give acrylic acid
    Acrylic acid
    Acrylic acid is an organic compound with the formula CH2=CHCO2H. It is the simplest unsaturated carboxylic acid, consisting of a vinyl group connected directly to a carboxylic acid terminus. This colorless liquid has a characteristic acrid or tart smell. It is miscible with water, alcohols,...

    , or acrylic esters, which can be used to produce acrylic glass
    Acrylic glass
    Poly is a transparent thermoplastic, often used as a light or shatter-resistant alternative to glass. It is sometimes called acrylic glass. Chemically, it is the synthetic polymer of methyl methacrylate...

    .

  • Cyclicization to give benzene
    Benzene
    Benzene is an organic chemical compound. It is composed of 6 carbon atoms in a ring, with 1 hydrogen atom attached to each carbon atom, with the molecular formula C6H6....

     and cyclooctatetraene
    Cyclooctatetraene
    1,3,5,7-Cyclooctatetraene is an unsaturated derivative of cyclooctane, with the formula C8H8. It is also known as [8]annulene. This polyunsaturated hydrocarbon is a colorless to light yellow flammable liquid at room temperature...

    :

Welding


Approximately 20 percent of acetylene is consumed for oxyacetylene gas welding and cutting
Oxy-fuel welding and cutting
Oxy-fuel welding and oxy-fuel cutting are processes that use fuel gases and oxygen to weld and cut metals, respectively. French engineers Edmond Fouché and Charles Picard became the first to develop oxygen-acetylene welding in 1903...

 due to the high temperature of the flame; combustion of acetylene with oxygen produces a flame of over 3600 K (3300 °C, 6000 °F), releasing 11.8 kJ/g. Oxyacetylene is the hottest burning common fuel gas. Acetylene is the third hottest natural chemical flame after cyanogen
Cyanogen
Cyanogen is the chemical compound with the formula 2. It is a colorless, toxic gas with a pungent odor.The molecule is a pseudohalogen. Cyanogen molecules consist of two CN groups — analogous to diatomic halogen molecules, such as Cl2, but far less oxidizing...

 at 4798 K (4525 °C, 8180 °F) and dicyanoacetylene's 5260 K (4990 °C, 9010 °F). Oxy-acetylene welding
Oxy-fuel welding and cutting
Oxy-fuel welding and oxy-fuel cutting are processes that use fuel gases and oxygen to weld and cut metals, respectively. French engineers Edmond Fouché and Charles Picard became the first to develop oxygen-acetylene welding in 1903...

 was a very popular welding process in previous decades; however, the development and advantages of arc-based welding processes
Arc welding
Arc welding is a type of welding that uses a welding power supply to create an electric arc between an electrode and the base material to melt the metals at the welding point. They can use either direct or alternating current, and consumable or non-consumable electrodes...

 have made oxy-fuel welding nearly extinct for many applications. Acetylene usage for welding has dropped significantly. On the other hand, oxy-acetylene welding equipment is quite versatile – not only because the torch is preferred for some sorts of iron or steel welding (as in certain artistic applications), but also because it lends itself easily to brazing, braze-welding, metal heating (for annealing or tempering, bending or forming), the loosening of corroded nuts and bolts, and other applications. Bell Canada
Bell Canada
Bell Canada is a major Canadian telecommunications company. Including its subsidiaries such as Bell Aliant, Northwestel, Télébec, and NorthernTel, it is the incumbent local exchange carrier for telephone and DSL Internet services in most of Canada east of Manitoba and in the northern territories,...

 cable repair technicians still use portable acetylene fueled torch kits as a soldering
Soldering
Soldering is a process in which two or more metal items are joined together by melting and flowing a filler metal into the joint, the filler metal having a lower melting point than the workpiece...

 tool for sealing lead sleeve splices in manholes and in some aerial locations. Oxyacetylene welding may also be used in areas where electricity is not readily accessible. As well, oxy-fuel cutting is still very popular and oxy-acetylene cutting is utilized in nearly every metal fabrication shop. For use in welding and cutting, the working pressures must be controlled by a regulator, since above 15 psi acetylene will decompose explosively.

Niche applications


In 1881, the Russian chemist Mikhail Kucherov described the hydration
Hydration reaction
In organic chemistry, a hydration reaction is a chemical reaction in which a hydroxyl group and a hydrogen cation are added to the two carbon atoms bonded together in the carbon-carbon double bond which makes up an alkene functional group. The reaction usually runs in a strong acidic, aqueous...

 of acetylene to acetaldehyde
Acetaldehyde
Acetaldehyde is an organic chemical compound with the formula CH3CHO or MeCHO. It is one of the most important aldehydes, occurring widely in nature and being produced on a large scale industrially. Acetaldehyde occurs naturally in coffee, bread, and ripe fruit, and is produced by plants as part...

 using catalysts such as mercury(II) bromide
Mercury(II) bromide
Mercury bromide or mercuric bromide is the chemical compound composed of mercury and bromine with the formula HgBr2. This white crystalline solid is a laboratory reagent...

. Before the advent of the Wacker process
Wacker process
The Wacker process or the Hoechst-Wacker process originally referred to the oxidation of ethylene to acetaldehyde by oxygen in water in the presence of a tetrachloropalladate catalyst...

, this reaction was conducted on an industrial scale.

The polymerization
Polymerization
In polymer chemistry, polymerization is a process of reacting monomer molecules together in a chemical reaction to form three-dimensional networks or polymer chains...

 of acetylene with Ziegler-Natta catalyst
Ziegler-Natta catalyst
A Ziegler–Natta catalyst is a catalyst used in the synthesis of polymers of 1-alkenes . Three types of Ziegler–Natta catalysts are currently employed:* Solid and supported catalysts based on titanium compounds...

s produces polyacetylene
Polyacetylene
Polyacetylene is an organic polymer with the repeat unit n. The high electrical conductivity discovered for these polymers beginning in the 1960's accelerated interest in the use of organic compounds in microelectronics...

 films. Polyacetylene, a chain of CH centres with alternating single and double bonds, was the one of first discovered organic semiconductor
Organic semiconductor
An organic semiconductor is an organic material with semiconductor properties. Single molecules, short chain and organic polymers can be semiconductive. Semiconducting small molecules include the polycyclic aromatic compounds pentacene, anthracene, and rubrene...

s. Its reaction with iodine
Iodine
Iodine is a chemical element with the symbol I and atomic number 53. The name is pronounced , , or . The name is from the , meaning violet or purple, due to the color of elemental iodine vapor....

 produces a highly electrically conducting material. Although such materials are not useful, these discoveries led to the developments of organic semiconductor
Organic semiconductor
An organic semiconductor is an organic material with semiconductor properties. Single molecules, short chain and organic polymers can be semiconductive. Semiconducting small molecules include the polycyclic aromatic compounds pentacene, anthracene, and rubrene...

s, as recognized by the Nobel Prize in Chemistry
Nobel Prize in Chemistry
The Nobel Prize in Chemistry is awarded annually by the Royal Swedish Academy of Sciences to scientists in the various fields of chemistry. It is one of the five Nobel Prizes established by the will of Alfred Nobel in 1895, awarded for outstanding contributions in chemistry, physics, literature,...

 in 2000 to Alan J. Heeger
Alan J. Heeger
Alan Jay Heeger is an American physicist, academic and Nobel Prize laureate in chemistry.Heeger was born in Sioux City, Iowa to a Jewish family. He earned a B.S. in physics and mathematics from the University of Nebraska-Lincoln in 1957, and a Ph.D in physics from the University of California,...

, Alan G MacDiarmid, and Hideki Shirakawa
Hideki Shirakawa
Hideki Shirakawa is a Japanese chemist and winner of the 2000 Nobel Prize in Chemistry for his discovery of conductive polymers together with physics professor Alan J. Heeger and chemistry professor Alan G...

.

In the early 20th Century acetylene was widely used for illumination, including street lighting in some towns. Most early automobiles used carbide lamp
Carbide lamp
Carbide lamps, properly known as acetylene gas lamps, are simple lamps that produce and burn acetylene which is created by the reaction of calcium carbide with water....

s before the adoption of electric headlights.

Acetylene is sometimes used for carburization
Carburization
Carburizing, spelled carburising in the UK, is a heat treatment process in which iron or steel is heated in the presence of another material which liberates carbon as it decomposes. Depending on the amount of time and temperature, the affected area can vary in carbon content...

 (that is, hardening) of steel
Steel
Steel is an alloy that consists mostly of iron and has a carbon content between 0.2% and 2.1% by weight, depending on the grade. Carbon is the most common alloying material for iron, but various other alloying elements are used, such as manganese, chromium, vanadium, and tungsten...

 when the object is too large to fit into a furnace.

Acetylene is used to volatilize carbon in radiocarbon dating
Radiocarbon dating
Radiocarbon dating is a radiometric dating method that uses the naturally occurring radioisotope carbon-14 to estimate the age of carbon-bearing materials up to about 58,000 to 62,000 years. Raw, i.e. uncalibrated, radiocarbon ages are usually reported in radiocarbon years "Before Present" ,...

. The carbonaceous material in an archeological sample is reacted with lithium
Lithium
Lithium is a soft, silver-white metal that belongs to the alkali metal group of chemical elements. It is represented by the symbol Li, and it has the atomic number 3. Under standard conditions it is the lightest metal and the least dense solid element. Like all alkali metals, lithium is highly...

 metal in a small specialized research furnace to form lithium carbide
Lithium carbide
Lithium carbide, Li2C2, often known as dilithium acetylide, is a chemical compound of lithium and carbon, an acetylide. It is an intermediate compound produced during radiocarbon dating procedures...

 (also known as lithium acetylide). The carbide can then be reacted with water, as usual, to form acetylene gas to be fed into mass spectrometer to sort out the isotopic ratio of carbon 14 to carbon 12.

Natural occurrence


Acetylene is a moderately common chemical in the universe, often associated with the atmospheres of gas giant
Gas giant
A gas giant is a large planet that is not primarily composed of rock or other solid matter. There are four gas giants in the Solar System: Jupiter, Saturn, Uranus, and Neptune...

s. One curious discovery of acetylene is on Enceladus
Enceladus (moon)
Enceladus is the sixth-largest of the moons of Saturn. It was discovered in 1789 by William Herschel. Until the two Voyager spacecraft passed near it in the early 1980s very little was known about this small moon besides the identification of water ice on its surface...

, a moon of Saturn
Saturn
Saturn is the sixth planet from the Sun and the second largest planet in the Solar System, after Jupiter. Saturn is named after the Roman god Saturn, equated to the Greek Cronus , the Babylonian Ninurta and the Hindu Shani. Saturn's astronomical symbol represents the Roman god's sickle.Saturn,...

. Natural acetylene is believed to form from either catalytic decomposition of long chain hydrocarbons at temperatures of 1,770 K and above. Since such temperatures are highly unlikely on such a small distant body, this discovery is potentially suggestive of catalytic reactions within that moon, making it a promising site to search for prebiotic chemistry.

Safety and handling


Acetylene is not especially toxic but when generated from calcium carbide it can contain toxic impurities such as traces of phosphine
Phosphine
Phosphine is the compound with the chemical formula PH3. It is a colorless, flammable, toxic gas. Pure phosphine is odourless, but technical grade samples have a highly unpleasant odor like garlic or rotting fish, due to the presence of substituted phosphine and diphosphine...

 and arsine
Arsine
Arsine is the chemical compound with the formula AsH3. This flammable, pyrophoric, and highly toxic gas is one of the simplest compounds of arsenic...

. It is also highly flammable (hence its use in welding). Its singular hazard is associated with its intrinsic instability, especially when it is pressurized. Samples of concentrated or pure acetylene can easily react in an addition-type reaction to form a number of products, typically benzene and/or vinylacetylene. This reaction is exothermic. Consequently, acetylene can explode with extreme violence if the pressure of the gas exceeds about 200 kPa (29 psi) as a gas or when in liquid or solid form. It is therefore shipped and stored dissolved in acetone
Acetone
Acetone is the organic compound with the formula 2CO, a colorless, mobile, flammable liquid, the simplest example of the ketones.Acetone is miscible with water and serves as an important solvent in its own right, typically as the solvent of choice for cleaning purposes in the laboratory...

 or dimethylformamide
Dimethylformamide
Dimethylformamide is an organic compound with the formula 2NCH. Commonly abbreviated as DMF , this colourless liquid is miscible with water and the majority of organic liquids. DMF is a common solvent for chemical reactions...

 (DMF), contained in a metal cylinder with a porous filling (Agamassan
Agamassan
Agamassan is a porous substrate used to safely absorb acetylene and thus allow the transport, storage and commercial exploitation of the otherwise unstable gas. It was developed and patented by the Swedish Nobel Laureate and industrialist Gustaf Dalén...

), which renders it safe to transport and use, given proper handling.

External links