Diethylaluminium chloride
Introduction '''Diethylaluminium chloride''', abbreviated DEAC, is an organoaluminium compound. Although often given the chemical formula (C2H5)2AlCl, it exists as a dimer, (C2H5)2AlCl2 It is a precursor to Ziegler-Natta catalysts employed for the production of polyolefins. The compound is also a Lewis acid, useful in organic synthesis. The compound is a colorless waxy solid, but is usually handled as a solution in hydrocarbon solvents. It is highly reactive, even pyrophoric.
Structure and bonding Compounds of the empirical formula AlR2Cl (R = alkyl, aryl) usually exist as dimers with the formula (R2Al)2(μ-Cl)2.The bridging ligands (indicated by "μ-") are halides, not the organic substituents. The aluminium adopts a tetrahedral geometry. Each Al(III) center follows the octet rule. In contrast, triethylaluminium and trimethylaluminium feature bridging alkyl groups and these compounds violate the octet rule.
Production Diethylaluminium chloride can be produced from ethylaluminium sesquichloride, (C2H5)3Al2Cl3, by reduction with sodium::2 (C2H5)3Al2Cl3 + 3 Na → 3 (C2H5)2AlCl + Al + 3 NaClIt is also obtained from the reaction of triethylaluminium with hydrochloric acid::(C2H5)3Al + HCl → (C2H5)2AlCl + C2H6Reproportionation reactions can also be used::2 (C2H5)3Al + AlCl3 → 3 (C2H5)2AlCl:(C2H5)3Al2Cl3 + (C2H5)3Al → 3 (C2H5)2AlCl
Uses Diethylaluminium chloride and other organoaluminium compounds are used in combination with transition metal compounds as Ziegler–Natta catalysts for the polymerization of various alkenes.As a Lewis acid, diethylaluminium chloride also has uses in organic synthesis. For example, it is used to catalyze the Diels–Alder and ene reactions. Alternatively, it can react as a nucleophile or a proton scavenger.
Safety Diethylaluminium chloride is not only flammable but pyrophoric.
References * Hu, Y. J.; Jiang, H. L.; Wang, H. H., "Preparation of highly branched polyethylene with acenaphthenediimine nickel chloride/diethylaluminum chloride catalyst". ''Chinese Journal of Polymer Science'' 2006, 24 (5), 483–488. * Yao, Y. M.; Qi, G. Z.; Shen, Q.; Hu, J. Y.; Lin, Y. H., "Reactivity and structural characterization of divalent samarium aryloxide with diethylaluminum chloride". ''Chinese Science Bulletin'' 2003, 48 (20), 2164–2167.
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