In general, if the atoms that make up the ring contain heteroatoms, such rings become heterocycles, and organic compounds containing heterocycles are called heterocyclic compounds. An article called Influence of Trimethylphosphine Oxide Loading on the Measurement of Zeolite Acidity by Solid-State NMR Spectroscopy, published in 2021-05-06, which mentions a compound: 676-96-0, Name is Trimethylphosphineoxide, Molecular C3H9OP, Safety of Trimethylphosphineoxide.
The accurate characterization of the acid strength of zeolites is of great importance to understand their catalytic performance and the rational design of highly efficient zeolite catalysts. The 31P MAS NMR spectroscopy of adsorbed trimethylphosphine oxide (TMPO) technique has been widely employed to measure the acid strength of various solid acid catalysts. Here, the influence of TMPO loading on characterizing the zeolite acidity is explored by using two-dimensional (2D) hetero- and homonuclear correlation NMR experiments combined with d. functional theory calculations It is found that the TMPO loading plays a crucial role in the accurate measurement of zeolite acid strength. Saturated adsorption of TMPO mols. (P/Al = 1.0) can result in the formation of a TMPO dimer on one Bronsted acid site (BAS), which will conceal the acid strength of the specific acid site if it is merely based on 31P chem. shifts in the 1D spectrum. This is further confirmed by 2D 31P{1H} heteronuclear correlation (HETCOR) and 31P-31P double-quantum (DQ) homonuclear correlation experiments on TMPO-loaded ZSM-5 zeolites. By carefully controlling the amount of TMPO adsorption, such as low or medium TMPO loadings (i.e., P/Al = 0.2 or P/Al = 0.4), the 31P chem. shift can not only accurately reflect the BAS strength of the zeolite, but also can discriminate the Bronsted and Lewis acid sites due to well-resolved 2D 31P{1H} HETCOR NMR. The results presented herein provide a strategy to assess the acidity of zeolites more precisely by a TMPO probe mol., which is helpful for the optimization of catalytic performances of zeolite catalysts.
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Reference:
Isoxazole – Wikipedia,
Isoxazole | C3H3NO – PubChem