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.

Other applications include use in alkylation reactions and as a catalyst component in linear oligomerization and cyclization of unsaturated hydrocarbons.

[1] Methyl, ethyl, and other alkyl or aralkyl halides that are not dehydrohalogenated readily can react with aluminium in an exothermic process to form organoaluminium sesquihalides in high yields.

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.

[2] The alkylaluminium sesquihalides convert to dialkylaluminium halide or trialkylaluminium materials upon treatment with active metals, such as sodium or magnesium.