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Mechanistic Insight into the Heterogeneous Hydrogenation of Furan Derivatives with the use of Parahydrogen
Author(s) -
Salnikov Oleg G.,
Kovtunova Larisa M.,
Skovpin Ivan V.,
Bukhtiyarov Valerii I.,
Kovtunov Kirill V.,
Koptyug Igor V.
Publication year - 2018
Publication title -
chemcatchem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.497
H-Index - 106
eISSN - 1867-3899
pISSN - 1867-3880
DOI - 10.1002/cctc.201701653
Subject(s) - chemistry , furan , spin isomers of hydrogen , catalysis , tetrahydrofuran , photochemistry , molecule , dehydrogenation , hydrogen , isomerization , hydrogenolysis , medicinal chemistry , organic chemistry , solvent
Parahydrogen‐induced polarization (PHIP) was shown to be a useful and unique technique to study the mechanisms of catalytic reactions involving hydrogen. In this paper, PHIP was utilized for mechanistic investigation of the gas‐phase hydrogenation of furan, 2,3‐dihydrofuran, and 2,5‐dihydrofuran over titania‐supported Rh, Pd, and Pt catalysts. In the hydrogenation of all three substrates over the Rh/TiO 2 catalyst, the PHIP technique revealed the possibility of pairwise addition of two H atoms from the same H 2 molecule with the formation of tetrahydrofuran molecules while retaining spin correlation between the added protons. In the hydrogenation of 2,3‐dihydrofuran over the Rh/TiO 2 catalyst, PHIP effects were detected not only for tetrahydrofuran but also for the reactant (2,3‐dihydrofuran) at positions 2 and 3 of the heterocyclic ring. Such unexpected results are direct evidence for the pairwise replacement of the hydrogen atoms in 2,3‐dihydorfuran. A probable mechanism for this pairwise replacement includes sequential steps of addition and elimination of hydrogen atoms. In contrast, if the hydrogenation of 2,5‐dihydrofuran was performed over Rh/TiO 2 , PHIP effects were detected for all protons of 2,3‐dihydrofuran, implying that 2,3‐dihydrofuran could be formed from 2,5‐dihydrofuran not only through isomerization of the C=C bond but also through dehydrogenation of 2,5‐dihydrofuran to furan with subsequent semihydrogenation.