Ethylaluminium sesquichloride
Encyclopedia
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
polymerization
s. Other applications include use in alkylation
reactions and as a catalyst component in linear oligomerization 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.
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.
A magnesium-aluminium alloy can provide the reduction function simultaneously with reaction between aluminium and the alkyl halide:
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.
3Cl3 + 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.
Triethylaluminium
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 ...
and as a catalyst component in Ziegler-Natta type systems for olefin and diene
Diene
In organic chemistry a diene or diolefin is a hydrocarbon that contains two carbon double bonds.Conjugated dienes are functional groups, with a general formula of CnH2n-2. Dienes and alkynes are functional isomers...
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...
s. Other applications include use in alkylation
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 . Alkylating agents are widely used in chemistry because the alkyl group is probably the most common group encountered in...
reactions and as a catalyst component in linear oligomerization 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.
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.
Conversion to trialkylaluminium compoundss
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 + Mg2Cl
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):3Cl3 + 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.