Oxidação biomimetica de cicloexano por peroxido de hidrogenio catalisada por sais de cobre (II)

AUTOR(ES)
DATA DE PUBLICAÇÃO

1991

RESUMO

Cyclohexane was oxidized by the GoChAgg system (pyridine, copper (II) salt, H2O2 under ambient conditions. The only reaction product was cyclohexanone. Efficiency and turnover number were studied as a function of the following reaction parameters; temperature; amount of catalyst, substrate and oxidant; presence of acetic acid; effect of counter-ion associated to the metal and presence of water in the reaction mixture. The best results were obtained by using 15 mmol of hydrogen peroxide, 20 mmol of cyclohexane, 28 mL of pyridine and 1,0 mmol of copper chloride, between 20°C e 40°C, in the absence of acetic acid. Under these conditions, the system produced 2,4 mmol of cyclohexanone with 100% selectivity and 32% efficiency in only 30 min. Accumulation of the reaction products by the addition of hydrogen peroxide every 30 min produced a 0.22 M solution of oxidized products in 120 min. However, a decrease in the selectivity, with the formation of 15% cyclohexanol, was observed. After 6 accumulations, both the efficiency and the turnover number reached a plateau, and other accumulation were not possible due to phase separation. By using tert-butyl hydroperoxide as an oxidant, the system produces mainly cicylohexene. The olefin formation takes place as soon as the reaction starts, cyclohexanone and cyclohexanol being produced only after the first hour. After 4 h reaction time, 3.63 mmol cyclohexene (67%), 2.00 mmol cyclohexanone (34%) and 0.17 mmol cyclohexanol (3%) are obtained, with 78% effiency (based on the oxidant). In the accumulation reactions, a 0.5 M solution of the products (cylohexene + cyclohexanone + cyclohexanol) was obtained in 16 h, or 4 accumulations. The formation of chlorinated products, such as 2-chlorocyclohexanone, shows that other nucleophiles may be incorporated in the hydrocarbon. The results above allow the proposition of a reaction mechanism.

ASSUNTO(S)

oxidação hidrocarbonetos catalisadores

ACESSO AO ARTIGO

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