Ethylaluminium sesquichloride, also called EASC, is an industrially important organoaluminium compound 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 In organic chemistry, an alkene is a hydrocarbon containing a carbon–carbon double bond. Alkene is often used as synonym of olefin, that is, any hydrocarbon containing one or more double bonds.H. Stephen Stoker (2015): General, Organic, a ...

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 f ...

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 effectin ...

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 relat ...

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 C₂H₅Cl + 2 Al → (C₂H₅)₃Al₂Cl₃ 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 (R₂AlX • RAlX₂) 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 R₃Al₂Cl₃ 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 or triethylaluminium can be produced from ethylaluminium sesquichloride by sodium reduction: :2 (C₂H₅)₃Al₂Cl₃ + 3 Na → 3 (C₂H₅)₂AlCl + Al + 3 NaCl :3 (C₂H₅)₂AlCl + 3 Na → 2 (C₂H₅)₃Al + Al + 3 NaCl A magnesium-aluminium alloy can provide the reduction function simultaneously with reaction between aluminium and the alkyl halide: :4 C₂H₅Cl + Al₂Mg → 2 (C₂H₅)₂AlCl + MgCl₂ 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.

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−nAlCl_n + n C₂H₆ The products and their derivatives are used as components of catalysts for the production of polyolefins and some elastomers.

References

{{Aluminium compounds Organoaluminium compounds