Halogenations of aromatic compounds using tetrabutylammonium peroxydisulfate

Abstract

Tetrabutylammonium peroxydisulfate has been prepared from tetrabutyl-ammonium hydrogen sulfate and potassium persulfate and shows strong oxidizing abilities. This new peroxide shows high solubility in various organic solvents in contrast to the poor solubililty of known metal peroxydisulfate such as potassium persulfate and sodium persulfate. Tetrabutylammonium peroxydisulfate is a useful source of tetrabutylammonium sulfate radical. Iodination of electron rich aromatic compounds has been achieved with tetrabutylammonium peroxydisulfate and iodine under the mild conditions in good yield. The iodination occurred at para position of electron donating group regioselectively. α, β -Unsaturated carbonyl compounds were successfully iodinated at α -position. 5-position of pyrimidine nucleosides were also iodinated under the same condition in excellent yields. Electron rich aromatic compounds were easily brominated with tetrabutyl-ammonium peroxydisulfate and bromine. Bromination occurred at para position of electron donating group. α, β -Unsaturated carbonyl compounds were also brominated under the same conditions. Bromination occurred α-position of cyclic enones. Highly activated aromatic compounds were selectively monobrominated with tetrabutylammonium peroxydisulfate and lithium bromide. Only monobromination occurred and bromination position is selectively para position of electron donating group. Without employing harmful bromine, this method can be used for safe, practical and selective bromination of highly activated aromatic compounds. Chlorination of activated aromatic compounds was achieved with tetrabutylammonium peroxydisulfate and hydrogen chloride solution. Chlorination occurred at para position of electron donating group. This method does not employ chlorine gas but uses cheap hydrogen chloride solution as a chlorine source, the procedure for chlorination of aromatic compounds was safe and practical. Instead of hydrogen chloride solution, lithium chlor...