Tetrabutylammonium peroxydisulfate ((n-Bu4N)(2)S2O8 : (TBA)(2)S2O8), which has been prepared from tetrabutylammonium hydrogen sulfate and potassium persulfate, shows high solubility in organic solvents, such as methylene chloride, chloroform, acetonitrile, and acetone, in contrast to the poor solubility of known metal peroxydisulfates.(1)) (TBA)(2)S2O8 has become a useful source of the tetrabutylammonium sulfate radical, which is relatively stable in organic solvents. Oxidation of allylic and benzylic alcohols to aldehydes, tetrahydrofuranylation(1,2)) and tetrahydropyranylation(2,3)) of alcohols, beta-masked formylation and acetylation of electron-deficient olefins,(4)) conversion of N,N-dimethylhydrazones to carbonyl compounds,(5)) regioselective iodination of aromatic compounds,(6)) alpha-iodination of alpha,beta-unsaturated ketones,(7)) deprotection of p-methoxybenzyl ethers,(8)) deprotection of 4,4'-dimethoxytrityl groups of deoxynucleosides,(9)) and epoxidation of alpha,beta-unsaturated ketones or aldehydes have been achieved by using (TBA)(2)S2O8.(10)).