Spectroscopic study in the UV-Vis, near and mid IR of cationic species formed by interaction of thiophene, dithiophene and terthiophene with the zeolite H-Y

Abstract

The vibrational (in the mid-IR and near-IR) and the UV-Vis spectra of products formed upon interaction of thiophene with H-Y, show the initial formation of neutral hydrogen bonded adducts. In the presence of thiophene excess, protonation slowly occurs with formation of C₄H₅S⁺ followed by oligomerization leading to C₈H₇S₂ ⁺, C₁₂H₉S₃ ⁺ and more complex species. This conclusion is fully confirmed by the study of the direct interaction of H-Y with dithiophene and terthiophene, where protonated C₈H₇S₂ ⁺ and C₁₂H₉S₃ ⁺ are produced in the initial interaction stages. The ascertained occurrence of intramolecular and intermolecular hydrogen transfer points towards a network of complex reactions leading to the final formation of some families of similar isomers. Some of the protonated (oligomeric) species interact via strong hydrogen bonds with the unreacted Brønsted groups of H-Y. The positively charged species can easily react with NH₃ with the formation of NH₄ ⁺ and neutral species. At room temperature the process is partially reversible.