Marco Ricci

Direct synthesis of phenols by iron-catalyzed biphasic oxidation of aromatic hydrocarbons with hydrogen peroxide

The hydroxylation of a series of aromatic hydrocarbons with hydrogen peroxide, catalyzed by iron complexes with pyrazine-3-carboxylic acid N-oxide, was investigated, operating in a biphasic reaction medium. n nThe new catalyst showed a high selectivity to the corresponding phenols, minimizing the over-oxidation reactions to polyoxygenated derivatives and tars which, along with dimers formation, are the major limitations of the classical Fenton’s reagent for a practical synthetic application. n nIn the case of alkylbenzenes, the competitive side chain oxidation at the benzylic positions also occurred. Electron rich substrates, such as anisole, were oxidized with very poor selectivity. n nThe reactions were carried out in a biphasic system that allows a convenient recovery and recycling of the catalyst by phase separation techniques. The catalyst showed a complete retention of activity after six consecutive reaction cycles. n nThe new catalyst appears as a promising tool for the direct synthesis of phenols, in alternative to the conventional multi-step methods.

Ligand effect on the iron-catalysed biphasic oxidation of aromatic hydrocarbons by hydrogen peroxide

Abstract The hydroxylation of benzene and toluene with hydrogen peroxide, catalysed by iron complexes with nitrogen ligands in a biphasic reaction medium, was investigated. After testing a series of pyridine and pyrazinecarboxylic acid derivatives, it was found that the ligand markedly affects the catalyst efficiency and the selectivity based on the oxidant. In the case of toluene, the ligand has a tuning effect on the catalyst activity, driving the oxidation preferentially to the ring or to the methyl group. The complex with pyrazine-3-carboxylic acid N -oxide was selected as the most efficient catalyst and appears to be a promising tool for the direct synthesis of phenols. The mechanism of the aromatic hydroxylation is also discussed, in comparison with the conventional Fenton’s reagent.

New efficient catalysts for the aerobic oxidation of ethers

Some nickel, copper, and silver salts or complexes are efficient catalysts for the oxidation of benzylic ethers with oxygen in 1,2-dimethoxyethane. Salts of the weakly coordinating anion trifluoroacetate are particularly efficient, approaching (and, in some cases, improving) the yields obtained with cobalt(II) chloride, the best catalyst so far reported.