Higher oxidation state organoselenides as catalysts for the activation of hydrogen peroxide
Goodman, Margaret A
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Organoselenides in higher oxidation states are effective catalysts for the activation of hydrogen peroxide. Arylseleninic acids were found to be catalysts for the oxidation of bromide with hydrogen peroxide in a two-phase mixture of ether and pH-6 phosphate buffer. Benzeneseleninic acid and 4-methoxyphenylseleninic acid were more efficient catalysts than 3,5-bis(trifluoromethyl)phenylseleninic acid, 4-nitrophenylseleninic acid, 4-dimethylaminophenylseleninic acid, and 2,4,6-trimethylphenylseleninic acid. Aryl benzyl selenoxides are also catalysts for the bromination of organic substrates in two-phase systems of CH 2 Cl 2 and pH-6 phosphate buffer containing 2 M NaBr and 2.6 M H202. The catalysts are effective at 2.5 mol % relative to the organic substrates. In the bromination of 4-pentenoic acid, catalysts with electron-donating groups (EDG) provide increased reactivity relative to electron-withdrawing group (EWG) substituted catalysts. Benzyl 2-(dimethylaminomethyl)phenyl selenoxide was the most effective catalyst and was used in the preparative bromination of 4-pentenoic acid, 2,2-diphenyl-4-pentenoic acid, 1,3,5-trimethoxybenzene, N,N -dimethylaniline, and N -phenylmorpholine. Initial studies have shown that aryl benzyl selenoxides are additionally effective catalysts for the epoxidation of organic substrates. In the epoxidation of cis-cyclooctene, electron-withdrawing substituents in the selenoxides demonstrate a faster rate of reaction compared to their electron-donating group counterparts. Benzyl 3,5-bistrifluoromethylphenyl selenoxide was the most effective catalyst studied. Aryl benzyl selenoxides are efficient catalysts for epoxidation of alkenes and for Baeyer-Villiger oxidation of various carbonyl-containing compounds using H 2 O 2 . Of the selenoxides examined here, selenoxide 63 is kinetically the most active catalyst. Rates of Baeyer-Villiger oxidation and epoxidation of the substrates studied with the selenoxide catalysts were similar. Attempts at asymmetric induction with C 2 symmetric selenoxides proved ineffective. Preliminary data indicates that chalcogen containing xerogels may be viable marine antifouling and fouling-release agents. The chalcogens catalyze formation of a hypo-halous barrier with the halide salts and hydrogen peroxide present in ocean water. This barrier aids in the prevention of settlement and removal of bioorganisms. It was determined that xerogels with some hydrophilic silanes are necessary for halide and hydrogen peroxide permeation. Catalysts with two active sites are more effective than catalysts with one active site. Further work is needed to determine the optimal xerogel composition and the most efficient chalcogen catalyst.