Lactamium based ionic liquids are described. They comprise at least one of: the reaction product of a lactam compound having a formula (IV) wherein n is 1, 2 or 4 to 8, and a Brøsted acid HX; or a Brøsted acid HX, where X is a halide, and a metal halide; where the reaction product is p-toluenesulfonate, halide, or the halometallate; or the reaction product of a lactam compound having a formula (V) wherein the ring has at least C—C one double bond, and n is 1 to 8, and a Brøsted acid HX; or a Brøsted acid HX, where X is a halide, and a metal halide; or the reaction product of a lactam compound having a formula (VI) wherein n is 1 to 8, m is 1 to 8, and the rings can be saturated or unsaturated; and a Brøsted acid HX; or a Brøsted acid HX, where X is a halide, and a metal halide.