Selective photooxidation of small alkenes by O2 with red light in zeolite Y

Article abstract of DOI:10.1021/ja00084a024

Upon loading of 2,3-dimethyl-2-butene (DMB) and O₂ into zeolite NaY, photochemistry was observed at wavelengths as long as 760 nm. Similarly, photoexcitation of trans- or cis-2-butene and O₂ 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-l-butene (>90%) and acetone in the case of DMB + O₂. trans- or cis-2-butene + O₂ gave exclusively 3-hydroperoxy-1-butene. The constitutes the first synthesis of this hydroperoxide by direct photolysis of 2-butene-O₂ pairs. Laser reaction excitation spectra in the 500-700-nm region revealed a continuous absorption for both the DMB-O₂ and the 2-butene-O₂ systems. It is attributed to a charge-transfer transition. Comparison with corresponding absorption spectra in conventional media shows that the excited alkene-O₂ charge-transfer states are stabilized by electrostatic interactions with the zeolite NaY environment by 12 000cm^-1. Substantially 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 cis-or trans-2-butene in room temperature NaY under complete stereochemical retention.