Reaction scheme in the non-isothermal decomposition of (C6H5NH3)4Mo8O26 · 2 H2O

Abstract

The thermogravimatric decomposition of anilinum octamolybdate has been studied under non-isothermal conditions to elucidate the chemical reactions taking place in the first step of decomposition of the anhydrous compound.The decomposition products were analyzed by gas--liquid chromatography, gas chromatography-mass spectrometry (GC/MS), infrared spectroscopy and X-ray powder diffraction.The main decomposition product of aniline turned out to be indole, which is different from the major product in the isothermal decomposition at the same temperature, i.e. N-ethyl-aniline.A dehydrocyclization reaction is suggested as the rate-dependent process. This is probably due to the catalytic effect of the octamolybdate anion.In the study of the isothermal decomposition of anilinium octamolybdate dihydrate [1], the complex degradation of aniline was found to occur between 468 and 493 K.In the present work, we have analyzed in more detail the anilinium cation degradation process in the first decomposition step and the octamolybdate anion break<lown under non-isothermal conditions.The crystallization water is lost at 368-400 K, and the anhydrous octamolybdate anion undergoes thermal decomposition from 440 to 750 K:This process has bean studied by Kiss [2] on the ammonium salt, and it involves structural changes with Mo-O bond rupture near 550 K. Thus, extraction with ethyl acetate and quinoline has been carried out on samples from thermogravimetric decomposition under non-isothermal conditions, stopped at 573 K, in order to study the inorganic anion evolution in the first decomposition step by means of X-ray powder diffraction.The organic products extracted into ethyl acetate and quinoline have bean also analyzed, by GC/MS in the first case and I R spectroscopy in the second.