Triethylaluminium
Encyclopedia
Triethylaluminium is an organoaluminium compound. This volatile, colorless liquid is highly pyrophoric, igniting immediately upon exposure to air. It is normally stored in stainless steel containers either as a pure liquid or as a solution in hydrocarbon
solvents such as hexane
, heptane
, or toluene
. TEA is mainly used as a co-catalyst in the industrial production of polyethylene
and for the production of medium chain alcohol
s.
, CH2CH3. One pair of ethyl
groups are bridging
and four are terminal ligand
s. The two bridging carbon centres are five-coordinate. The bonding is reminiscent of that of diborane
, involving 3-centred, 2-electron bonds. As in trimethylaluminium
, triethylaluminium is structurally fluctional resulting rapid interchange of the terminal and bridging ethyl groups. At higher temperatures, the dimer cracks
into monomeric AlEt3.
Because of this efficient synthesis, triethylaluminium is one of the most available organoaluminium compounds.
TEA can also be generated from ethylaluminium sesquichloride
(Al2Cl3Et3), which arises by treating aluminium powder with chloroethane
. Reduction of ethylaluminium sesquichloride with an alkali metal such as sodium gives TEA:
For this reaction, even weak acids can be employed such as terminal acetylene
s and alcohols.
The linkage between the pair of aluminium centres is relatively weak and can be cleaved by bases (L) to give adduct
s with the formula AlEt3L:
s, which are converted to detergent
s. The first step involves the oligomerization of ethylene, which gives a mixture of "trialkylaluminium" compounds (simplified here as octyl groups):
Subsequently, these tralkyl compounds are oxidized to aluminium alkoxide
s, which are then hydrolysed:
:
. Its easy ignition makes it particularly desirable as a rocket engine
ignitor
. It also can be used as a rocket fuel, but has not been for any production vehicle. The SpaceX
Falcon 9
heavy-lift
rocket
uses a triethylaluminium-triethylborane
mixture as a first-stage ignitor.
Triethylaluminium thickened with polyisobutylene is used as an incendiary weapon, as a pyrophoric alternative to napalm
, e.g. in the M74
rockets for the M202A1 launchers. In this application it is known as TPA, for thickened pyrotechnic agent or thickened pyrophoric agent. The usual amount of the thickener is 6%. The amount of thickener can be decreased to 1% if other diluents are added. For example, n-hexane, can be used with increased safety by rendering the compound non-pyrophoric until the diluent evaporates, at which point a combined fireball results from both the TEA and the hexane vapors.
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....
solvents such as hexane
Hexane
Hexane is a hydrocarbon with the chemical formula C6H14; that is, an alkane with six carbon atoms.The term may refer to any of four other structural isomers with that formula, or to a mixture of them. In the IUPAC nomenclature, however, hexane is the unbranched isomer ; the other four structures...
, heptane
Heptane
n-Heptane is the straight-chain alkane with the chemical formula H3C5CH3 or C7H16. When used as a test fuel component in anti-knock test engines, a 100% heptane fuel is the zero point of the octane rating scale...
, or toluene
Toluene
Toluene, formerly known as toluol, is a clear, water-insoluble liquid with the typical smell of paint thinners. It is a mono-substituted benzene derivative, i.e., one in which a single hydrogen atom from the benzene molecule has been replaced by a univalent group, in this case CH3.It is an aromatic...
. TEA is mainly used as a co-catalyst in the industrial production of polyethylene
Polyethylene
Polyethylene or polythene is the most widely used plastic, with an annual production of approximately 80 million metric tons...
and for the production of medium chain 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.
Structure and bonding
Although called triethylaluminium, the compound has a dimeric structure with the formula Al2Et6, where Et is ethylEthyl
Ethyl may refer to:* Ethyl group, a functional group in organic chemistry* Ethyl Corporation, a fuel additive company* Ethanol, also known as ethyl alcohol* Cold Ethyl, a rock band founded by Nicke Andersson...
, CH2CH3. One pair of ethyl
Ethyl
Ethyl may refer to:* Ethyl group, a functional group in organic chemistry* Ethyl Corporation, a fuel additive company* Ethanol, also known as ethyl alcohol* Cold Ethyl, a rock band founded by Nicke Andersson...
groups are bridging
Bridging ligand
A bridging ligand is a ligand that connects two or more atoms, usually metal ions. The ligand may be atomic or polyatomic. Virtually all complex organic compounds can serve as bridging ligands, so the term is usually restricted to small ligands such as pseudohalides or to ligands that are...
and four are terminal ligand
Ligand
In coordination chemistry, a ligand is an ion or molecule that binds to a central metal atom to form a coordination complex. The bonding between metal and ligand generally involves formal donation of one or more of the ligand's electron pairs. The nature of metal-ligand bonding can range from...
s. The two bridging carbon centres are five-coordinate. The bonding is reminiscent of that of diborane
Diborane
Diborane is the chemical compound consisting of boron and hydrogen with the formula B2H6. It is a colorless gas at room temperature with a repulsively sweet odor. Diborane mixes well with air, easily forming explosive mixtures. Diborane will ignite spontaneously in moist air at room temperature...
, involving 3-centred, 2-electron bonds. As in trimethylaluminium
Trimethylaluminium
Trimethylaluminium is the chemical compound with the formula Al26, abbreviated as Al2Me6, 2 or the abbreviation TMA. This pyrophoric, colorless liquid is an industrially important organoaluminium compound...
, triethylaluminium is structurally fluctional resulting rapid interchange of the terminal and bridging ethyl groups. At higher temperatures, the dimer cracks
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...
into monomeric AlEt3.
Synthesis and reactions
TEA can be formed via several routes. The discovery of an efficient route was significant technologically. The multistep process can be summarized in the following reaction:- 2 Al + 3 H2 + 6 C2H4 → Al2Et6
Because of this efficient synthesis, triethylaluminium is one of the most available organoaluminium compounds.
TEA can also be generated from ethylaluminium sesquichloride
Ethylaluminium sesquichloride
Ethylaluminium sesquichloride, also called EASC, is an industrially important organoaluminium compound used primarily as a precursor to triethylaluminium and as a catalyst component in Ziegler-Natta type systems for olefin and diene polymerizations...
(Al2Cl3Et3), which arises by treating aluminium powder with chloroethane
Chloroethane
Chloroethane or monochloroethane, commonly known by its old name ethyl chloride, is a chemical compound with chemical formula , once widely used in producing tetraethyllead, a gasoline additive...
. Reduction of ethylaluminium sesquichloride with an alkali metal such as sodium gives TEA:
- 3 Al2Cl3Et3 + 9 Na → 2 Al2Et6 + 2 Al + 9 NaCl
Reactivity
The Al-C bond is polarized such that triethylaluminium is easily protonated, releasing ethane:- Al2Et6 + 6 HX → 2 Al2X6 + 6 EtH
For this reaction, even weak acids can be employed such as terminal acetylene
Acetylene
Acetylene is the chemical compound with the formula C2H2. It is a hydrocarbon and the simplest alkyne. 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 because...
s and alcohols.
The linkage between the pair of aluminium centres is relatively weak and can be cleaved by bases (L) to give adduct
Adduct
An adduct is a product of a direct addition of two or more distinct molecules, resulting in a single reaction product containing all atoms of all components. The resultant is considered a distinct molecular species...
s with the formula AlEt3L:
- Al2Et6 + 2 L → 2 LAlEt3
Applications
TEA is used industrially as an intermediate in the production of fatty alcoholFatty alcohol
Fatty alcohols are aliphatic alcohols consisting of a chain of 8 to 22 carbon atoms. Fatty alcohols usually have even number of carbon atoms and a single alcohol group attached to the terminal carbon. Some are unsaturated and some are branched...
s, which are converted to detergent
Detergent
A detergent is a surfactant or a mixture of surfactants with "cleaning properties in dilute solutions." In common usage, "detergent" refers to alkylbenzenesulfonates, a family of compounds that are similar to soap but are less affected by hard water...
s. The first step involves the oligomerization of ethylene, which gives a mixture of "trialkylaluminium" compounds (simplified here as octyl groups):
- Al2(C2H5)6 + 18 C2H4 → Al2(C8H17)6
Subsequently, these tralkyl compounds are oxidized to aluminium alkoxide
Alkoxide
An alkoxide is the conjugate base of an alcohol and therefore consists of an organic group bonded to a negatively charged oxygen atom. They can be written as RO−, where R is the organic substituent. Alkoxides are strong bases and, when R is not bulky, good nucleophiles and good ligands...
s, which are then hydrolysed:
- Al2(C8H17)6 + 3/2 O2 → Al2(OC8H17)6
- Al2(OC8H17)6 + 3/2 H2O → 6 C8H17OH + 2 "Al(OH)3"
Reagent in organic and organometallic chemistry
TEA has niches uses as a precursor to other organoaluminium compounds, such as diethylaluminium cyanideDiethylaluminium cyanide
Diethylaluminum cyanide is the organoaluminum compound with formula n. This compound is usually handled as a solution in toluene. This compound is a reagent for the hydrocyanation of α,β-unsaturated ketones. - Synthesis :...
:
- 0.5 Al2Et6 + HCN → 1/n [Et2AlCN]n + C2H6
Pyrophoric agent
TEA ignites on contact with air and will ignite and/or decompose on contact with water, and with any other oxidizer. TEA is one of the few substances pyrophoric enough to ignite on contact with cryogenic liquid oxygenLiquid oxygen
Liquid oxygen — abbreviated LOx, LOX or Lox in the aerospace, submarine and gas industries — is one of the physical forms of elemental oxygen.-Physical properties:...
. Its easy ignition makes it particularly desirable as a rocket engine
Rocket engine
A rocket engine, or simply "rocket", is a jet engineRocket Propulsion Elements; 7th edition- chapter 1 that uses only propellant mass for forming its high speed propulsive jet. Rocket engines are reaction engines and obtain thrust in accordance with Newton's third law...
ignitor
Pyrotechnic initiator
A pyrotechnic initiator is a device containing a pyrotechnic composition used primarily to ignite other, more difficult-to-ignite materials, e.g. thermites, gas generators, and solid-fuel rockets...
. It also can be used as a rocket fuel, but has not been for any production vehicle. The SpaceX
SpaceX
Space Exploration Technologies Corporation, or more popularly and informally known as SpaceX, is an American space transport company that operates out of Hawthorne, California...
Falcon 9
Falcon 9
Falcon 9 is a rocket-powered spaceflight launch system designed and manufactured by SpaceX. Both stages of its two-stage-to-orbit vehicle use liquid oxygen and rocket-grade kerosene propellants...
heavy-lift
Comparison of heavy lift launch systems
This page exposes the full list of orbital launch systems. For the short simple list of launchers families, see Comparison of orbital launchers families....
rocket
Rocket
A rocket is a missile, spacecraft, aircraft or other vehicle which obtains thrust from a rocket engine. In all rockets, the exhaust is formed entirely from propellants carried within the rocket before use. Rocket engines work by action and reaction...
uses a triethylaluminium-triethylborane
Triethylborane
Triethylborane , also called triethylborine and triethylboron, is an organoborane , a near-colorless to yellowish transparent liquid with pungent ether-like odor. Its chemical formula can be written as C6H15B, or 3B, or 3B, or Et3B.Triethylborane is strongly pyrophoric, igniting spontaneously in...
mixture as a first-stage ignitor.
Triethylaluminium thickened with polyisobutylene is used as an incendiary weapon, as a pyrophoric alternative to napalm
Napalm
Napalm is a thickening/gelling agent generally mixed with gasoline or a similar fuel for use in an incendiary device, primarily as an anti-personnel weapon...
, e.g. in the M74
M74
M74 or M-74 may refer to:* M74 motorway, a motorway in Scotland* Messier 74, a spiral galaxy in the constellation Pisces* M74 rocket, an incendiary rocket for a shoulder-fired M202A1 FLASH launcher...
rockets for the M202A1 launchers. In this application it is known as TPA, for thickened pyrotechnic agent or thickened pyrophoric agent. The usual amount of the thickener is 6%. The amount of thickener can be decreased to 1% if other diluents are added. For example, n-hexane, can be used with increased safety by rendering the compound non-pyrophoric until the diluent evaporates, at which point a combined fireball results from both the TEA and the hexane vapors.
See also
- TriethylboraneTriethylboraneTriethylborane , also called triethylborine and triethylboron, is an organoborane , a near-colorless to yellowish transparent liquid with pungent ether-like odor. Its chemical formula can be written as C6H15B, or 3B, or 3B, or Et3B.Triethylborane is strongly pyrophoric, igniting spontaneously in...
, used as an ignitor in the Pratt & Whitney J58Pratt & Whitney J58The Pratt & Whitney J58 was a jet engine used on the Lockheed A-12, and subsequently on the YF-12 and SR-71 Blackbird aircraft. The J58 was a variable cycle engine which functioned as both a turbojet and a fan-assisted ramjet. The J58 was a single-spool turbojet engine with an afterburner...
turbojet/ramjetRamjetA ramjet, sometimes referred to as a stovepipe jet, or an athodyd, is a form of airbreathing jet engine using the engine's forward motion to compress incoming air, without a rotary compressor. Ramjets cannot produce thrust at zero airspeed and thus cannot move an aircraft from a standstill...
engines. - TrimethylaluminiumTrimethylaluminiumTrimethylaluminium is the chemical compound with the formula Al26, abbreviated as Al2Me6, 2 or the abbreviation TMA. This pyrophoric, colorless liquid is an industrially important organoaluminium compound...