Abstract
AbstractDifferent benzylic compounds were efficiently oxidized to the corresponding ketones with aqueous 70% tert-butyl hydroperoxide (TBHP) and the catalytic system composed of CuCl2.2H2O and 2,2’-biquinoline-4,4’-dicarboxylic acid dipotassium salt (BQC). The catalytic system CuCl2/BQC/TBHP allows obtaining high yields at room temperature under organic solvent-free conditions. The interest of this system lies in its cost effectiveness and its benign nature towards the environment. Benzylic tertbutylperoxy ethers and benzylic alcohols were observed and suggested as the reaction intermediates. Analysis of organic products by atomic absorption did not show any contamination with copper metal. In terms of efficiency, CuCl2/BQC system is comparable or superior to the most of the catalytic systems described in the literature and which are based on toxic organic solvent.
Highlights
Ketones are one of the most important classes of organic compounds
We developed different catalytic transformations in water including the hydration of nitriles to the corresponding amides catalyzed by [Rh(COD)Cl]2/P(m-C6H4SO3Na)3 (TPPTS) [35], the transfer hydrogenation of aldehydes and ketones with isopropanol catalyzed by water-soluble rhodium complexes [36], Oppenauer-type oxidation of alcohols [37,38], and reductive amination of aldehydes [39]
Copper chloride dihydrate, 2,2’-biquinoline-4,4’-dicarboxylic acid dipotassium salt (BQC), tetrabutylammonium chloride (TBAC), sodium carbonate, and aqueous 70% tert-butyl hydroperoxide were purchased from Aldrich Chemical Co. and used without further purification
Summary
Ketones are one of the most important classes of organic compounds. They are used as solvents and precursors to a variety of polymers and biologically active compounds such as pharmaceuticals, flavors, agrochemicals, and fragrances. Despite the economic and environmental benefits of copper-based catalysts compare to the other transition metals that are either toxic or very expensive, their use for benzylic oxidations is not abundant [29,30]. With all these metals, the vast majority of catalytic processes are, performed in costly and toxic organic solvents. Despite the evident ecological and economical advantages of aqueous phase catalysis, to the best of our knowledge there are no reports concerning selective oxidation of alkylarenes to benzylic ketones in water at room temperature and based on copper catalysts. In this paper we are pleased to report our results regarding this unprecedented, general, and highly efficient organic solvent-free catalytic oxidation of alkylarenes (Scheme 1)
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