The chloroaluminate ionic liquid (CAIL) of the (CH3)(3)NHCl-nAlCl(3) composition was studied by physico-chemical methods and catalytic activity measurements in heptane isomerization reaction. The data were also obtained on HCl solubility in CAIL depending on pressure and AlCl3 distribution between CAIL and heptanes depending on concentration. Based on obtained results CAIL is a homogeneous catalytic system containing an active component (HCl), co-catalyst (AlCl3) strengthening its catalytic activity, and solvent-so-called "neutral" ionic liquid. The CAIL main deactivation causes were studied including HCl loss and formation of acid soluble oil (ASO) poisoning the catalyst. The difference between CAIL and superacid catalysts poisoning by ASO was discussed. (c) 2006 Elsevier B.V. All rights reserved.