Sulfate ionic liquids promoted FeCl3-catalyzed dehydration of propargyl alcohols

•Sulfate ionic liquids exhibited high catalytic activity at 1 mol % of catalyst amount.•Sulfate anions promoted the formation of desired conjugated enyne and inhibited the formation of by-product naphthofuran derivative.•Deuterium kinetic isotope studies revealed that the formation of conjugated enyne 2a and by-product naphthofuran derivative 2b followed the E2 elimination and SN2 mechanism, respectively.