The skeletal isomerization of n-pentane in the presence of a trimethylamine hydrochloride-aluminum chloride ionic liquid has been studied at 20A degrees C. It has been found that the catalytic activity of the ionic liquid in n-pentane isomerization increases with an increase in the trimethylamine hydrochloride: aluminum chloride molar ratio. The optimum ratio of the catalyst complex components at the highest yields of the desired isoparaffins attained has been determined. The catalytic activity of the ionic liquid increased when a copper salt was added. The maximum total yield of isoparaffins is achieved with copper(II) chloride as an activating additive for the ionic liquid, whereas the maximum yield of isopentane is attained when copper(II) sulfate is introduced.