Irradiation of a cyclohexane and O 2 -loaded zeolite NaY with green or blue light resulted in oxidation of the alkane to cyclohexyl hydroperoxide and cyclohexanone (plus water) as the sole products. The hydroperoxide was found to rearrange thermally to cyclohexanone without side reaction. Complete selectivity in terms of the final oxidation product cyclohexanone persists even at high (>40%) conversion of cyclohexane. The chemistry was monitored by in-situ FT-infrared spectroscopy and the visible reactant absorption by diffuse reflectance spectroscopy. The absorption is attributed to the cyclohexane‚O 2 charge-transfer transition, which is shifted from the UV into the visible by the very high electrostatic field of the zeolite matrix cage. At elevated temperature, cyclohexane is thermally oxidized by O 2 to the same products.
Upon loading of 2,3-dimethyl-2-butene (DMB) and 02 into zeolite NaY, photochemistry was observed at wavelengths as long as 760 nm. Similarly, photoexcitation of transor cis-2-butene and 02 in this zeolite resulted in chemical reaction at a threshold wavelength of 600 nm. Reactions were initiated either with filtered tungsten-source light or the emission of a CW dye laser and typically conducted at -50 °C. Products identified by FT-infrared spectroscopy were 2,3-dimethyl-3-hydroperoxy-1 -butene (>90%) and acetone in the case of DMB + 02. transor cj's-2-butene + 02 gave exclusively 3-hydroperoxy-1 -butene. This constitutes the first synthesis of this hydroperoxide by direct photolysis of 2-buteneO2 pairs. Laser reaction excitation spectra in the 500-700-nm region revealed a continuous absorption for both the DMB-02 and the 2-butene-02 systems. It is attributed to a charge-transfer transition.Comparison with corresponding absorption spectra in conventional media shows that the excited alkene-02 chargetransfer states are stabilized by electrostatic interactions with the zeolite NaY environment by 12 000 cm*1. Substantially less stabilization was observed in high-silica faujasite. Thermal decomposition of the hydroperoxide photoproducts upon warm-up from -50 °C to room temperature was monitored by infrared spectroscopy. It was found that 3-hydroperoxy-1 -butene thermally epoxidizes the excess cisor trans-2-butene in room temperature NaY under complete stereochemical retention.
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