CHEMISTRY OF THE CALCINATION OF 15-CROWN-5 AND 18-CROWN-6 ETHERS OCCLUDED IN FAUJASITE POLYTYPE ZEOLITES

The decomposition of sodium 18-crown-6 and 15-crown-5 ether complexes, occluded in FAU and EMT zeolite cages, under oxidative and inert atmo spheres, has been studied using thermoanalysis (TG-DTA), IR and mass s pectroscopy. At ca. 373 K, the Na-crown ether complex is hydrolysed yi elding a bridging hydroxy group in the zeolite framework and a neutral [Na-crown ether](OH-)-O-+ species. This bridging hydroxy group, with a stretching vibration frequency of 3608 cm(-1), is generated at an un usually low temperature. This heterolytic splitting of water molecules is most pronounced for sodium 18-crown-6 complexes occluded in EMT ze olites. Based on in situ IR spectra of adsorbed degradation products a nd MS analysis of desorbing products, the decomposition chemistry of t he crown ether complexes is established. In an oxidative atmosphere, t he crown ethers degrade to aldehydes via an alkenic intermediate, and oxidize further to acetic acid and finally to carbon oxides. In an ine rt atmosphere, acetaldehyde is formed, desorbing at elevated temperatu res.