Manganese-Catalyzed Epoxidations of Alkenes in Bicarbonate Solutions
Benjamin S. Lane, Matthew Vogt, Victoria J. DeRose and Kevin Burgess*
*Department of Chemistry, Texas A & M University, P.O. Box 30012, College
Station, Texas 77842-3012, Email: burgess
tamu.edu
B. S. Lane, M. Vogt, V. J. DeRosa, K. Burgess, J. Am. Chem. Soc., 2002, 124, 11946-11954.
DOI: 10.1021/ja025956j
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Abstract
An epoxidation of alkenes using hydrogen peroxide as the terminal oxidant is promoted by catalytic amounts (1.0-0.1 mol %) of manganese(2+) salts, and must be performed using at least catalytic amounts of bicarbonate buffer. Various aryl-substituted, cyclic, and trialkyl-substituted alkenes were epoxidized under these conditions using 10 equiv of hydrogen peroxide, but monoalkyl-alkenes were not. Additives such as sodium acetate and salicylic acid enhanced the rate of the desired epoxidation reaction by 2-3 times. Possible mechanisms for the reaction are discussed.
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Details
This study presents a manganese-catalyzed method for the epoxidation of alkenes using hydrogen peroxide as the oxidant and bicarbonate buffer as a crucial component. The method, refined through parallel screening, employs catalytic amounts of manganese(2+) salts, with MnSO4 identified as the most effective catalyst. The reaction forms peroxymonocarbonate, which is essential for the epoxidation process. The study also explores the role of various additives to enhance reaction efficiency, identifying sodium acetate and salicylic acid as effective in tBuOH and DMF solvents, respectively. These additives improve the reaction rate and yield, especially for less reactive alkenes, and reduce the required amount of hydrogen peroxide. The mechanism likely involves manganese-peroxycarbonate complexes, with Mn(4+) species playing a key role. The method is environmentally friendly, cost-effective, and suitable for large-scale applications, offering high selectivity and stability for acid-sensitive epoxides. The study underscores the importance of bicarbonate buffer and the potential of manganese catalysts in green chemistry.
Key Words
Epoxidation, Manganese Compounds, Hydrogen Peroxide
ID: J48-Y2002-1290
