Abstract: The ionic liquid for desulfurization of light fuels is 1-methyl-3-pentyl 1H-imidazolium periodate, having the structural formula: The compound is prepared by mixing 1-methyl-3-pentyl 1H-imidazolium tetrafluoroborate with sodium periodate in dichloromethane and water, stirring the mixture for 24 hours, and extracting the compound from the product with dichloromethane. The ionic liquid may be used for the desulfurization of light fuels by bringing the ionic liquid into contact with the crude light petroleum oil at a temperature of about 50° C. with stirring for a period of time sufficient to oxidize the sulfur containing impurities to water soluble sulfones, washing the mixture with water to remove the ionic liquids and water soluble sulfones, and drying the desulfurized light fuel product.