Alkylation of lead (II) salts to tetraalkyllead in aqueous solution

Abstract

It was recently reported by Ahmad et al.¹ that lead (II) salts react with alkyl iodides in aqueous solution to produce tetraalkyllead compounds. They stated this reaction would have serious environmental consequences for water quality and for the well-being of aquatic biota. The experiments were carried out in a small (250 ml) flask nearly filled with an aqueous lead (II) acetate solution (210 ml) and sealed with an aluminium foil wrapped stopper. We have now repeated the experiment and report that tetramethyllead (TML) is not formed by direct reaction of lead (II) salts with methyl iodide in an aqueous system, but comes from a secondary reaction of metallic lead with methyl iodide^2,3. Apparently, Ahmad et al.¹ inadvertently contacted the aluminium foil-wrapped stopper with a small quantity of lead (II) acetate solution to produce finely divided metallic lead which reacted with methyl iodide to produce TML. The reduction of lead (II) salts to metallic lead in both acid and alkaline solutions by aluminium and other metals has been reported previously⁴. When the reactions described by Ahmad et al.¹ were carried out in the absence and presence of aluminium, TML formed in those tests in which lead (II) acetate solution contacted aluminium but not when aluminium was absent. Our results indicate that methylation of lead (II) acetate does not occur in the environment to form tetraalkyllead compounds which would be deleterious to water quality.