Ethylaluminium sesquichloride, also called EASC, is an industrially important
organoaluminium compound
Organoaluminium chemistry is the study of compounds containing bonds between carbon and aluminium. It is one of the major themes within organometallic chemistry. Illustrative organoaluminium compounds are the dimer trimethylaluminium, the monomer ...
used primarily as a precursor to
triethylaluminium
Triethylaluminium is one of the simplest examples of an organoaluminium compound. Despite its name it has the formula Al2( C2H5)6 (abbreviated as Al2Et6 or TEA), as it exists as a dimer. This colorless liquid is pyrophoric. It is an industrially ...
and as a catalyst component in
Ziegler–Natta type systems for
olefin and
diene
In organic chemistry a diene ( ) (diolefin ( ) or alkadiene) is a covalent compound that contains two double bonds, usually among carbon atoms. They thus contain two alk''ene'' units, with the standard prefix ''di'' of systematic nomenclature. ...
polymerization
In polymer chemistry, polymerization (American English), or polymerisation (British English), is a process of reacting monomer molecules together in a chemical reaction to form polymer chains or three-dimensional networks. There are many fo ...
s. Other applications include use in
alkylation
Alkylation is the transfer of an alkyl group from one molecule to another. The alkyl group may be transferred as an alkyl carbocation, a free radical, a carbanion, or a carbene (or their equivalents). Alkylating agents are reagents for effecti ...
reactions and as a catalyst component in linear
oligomerization
In chemistry and biochemistry, an oligomer () is a molecule that consists of a few repeating units which could be derived, actually or conceptually, from smaller molecules, monomers.Quote: ''Oligomer molecule: A molecule of intermediate relativ ...
and cyclization of unsaturated hydrocarbons. EASC is a colourless liquid, spontaneously combustible in air and reacts violently when in contact with water and many other compounds.
[Aluminum alkyls. Albemarle Corporation]
2010
Production
Methyl, ethyl, and other alkyl or aralkyl halides that are not dehydrohalogenated readily can react with aluminium metal in an exothermic process to form organoaluminium sesquihalides in high yields. An important example is the reaction of ethyl chloride with aluminium to form ethylaluminium sesquichloride.
:3 C
2H
5Cl + 2 Al → (C
2H
5)
3Al
2Cl
3
The reaction is carried out with aluminium in the form of turnings, shavings, granules, or powder. Oxygen and moisture must be rigorously excluded. The reaction can be initiated with a small amount of mercury or iodine. It also can be started by treating the aluminium with an alkylaluminium halide.
The products are equilibrium mixtures of the codimer (R
2AlX • RAlX
2) and homodimers
R2AlX)2 and (RAlX2)2 in which the two aluminium atoms of each component are halogen-bridged.
When byproduct reactions take place to a significant extent, the excess Al – Cl content in the R
3Al
2Cl
3 product can be decreased by addition of the calculated amount of triethylaluminium. Overall, however, it is critical to control reaction conditions as slight excursions can result in catastrophic events.
Reactions
Conversion to trialkylaluminium compounds
The alkylaluminium sesquihalides convert to dialkylaluminium halide or trialkylaluminium materials upon treatment with active metals, such as sodium or magnesium. For example,
diethylaluminium chloride
Diethylaluminium chloride, abbreviated DEAC, is an organoaluminium compound. Although usually given the chemical formula (C2H5)2AlCl, it exists as a dimer, C2H5)2AlClsub>2 It is a precursor to Ziegler-Natta catalysts employed for the production ...
or triethylaluminium can be produced from ethylaluminium sesquichloride by sodium reduction:
:2 (C
2H
5)
3Al
2Cl
3 + 3 Na → 3 (C
2H
5)
2AlCl + Al + 3 NaCl
:3 (C
2H
5)
2AlCl + 3 Na → 2 (C
2H
5)
3Al + Al + 3 NaCl
A magnesium-aluminium alloy can provide the reduction function simultaneously with reaction between aluminium and the alkyl halide:
:4 C
2H
5Cl + Al
2Mg → 2 (C
2H
5)
2AlCl + MgCl
2
The sesquichloride reduction process is currently the most economical route available for production of trimethylaluminium. Trialkylaluminium products made by this process generally contain trace levels of residual chloride but do not contain aluminium hydrides other low-level components found in the aluminium-hydrogen-olefin processes.
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]
Reaction of acids with trialkylaluminiums to produce alkylaluminium chlorides
Diethylaluminium chloride (DEAC), ethylaluminium sesquichloride (EASC), and ethylaluminium dichloride (EADC) can all be prepared by the reaction of triethylaluminium with HCl (where n = 1,1.5 or 2):
:(C2H5)3Al3 + n HCl → (C2H5)3−nAlCln + n C2H6
The products and their derivatives are used as components of catalysts for the production of polyolefins and some elastomers
An elastomer is a polymer with viscoelasticity (i.e. both viscosity and elasticity) and with weak intermolecular forces, generally low Young's modulus and high failure strain compared with other materials. The term, a portmanteau of ''elastic p ...
.[
]
References
{{Aluminium compounds
Organoaluminium compounds