693-86-7Relevant articles and documents
Cross-Linked "poisonous" Polymer: Thermochemically Stable Catalyst Support for Tuning Chemoselectivity
Yun, Seongho,Lee, Songhyun,Yook, Sunwoo,Patel, Hasmukh A.,Yavuz, Cafer T.,Choi, Minkee
, p. 2435 - 2442 (2016/04/26)
Designed catalyst poisons can be deliberately added in various reactions for tuning chemoselectivity. In general, the poisons are "transient" selectivity modifiers that are readily leached out during reactions and thus should be continuously fed to maintain the selectivity. In this work, we supported Pd catalysts on a thermochemically stable cross-linked polymer containing diphenyl sulfide linkages, which can simultaneously act as a catalyst support and a "permanent" selectivity modifier. The entire surfaces of the Pd clusters were ligated (or poisoned) by sulfide groups of the polymer support. The sulfide groups capping the Pd surface behaved like a "molecular gate" that enabled exceptionally discriminative adsorption of alkynes over alkenes. H2/D2 isotope exchange revealed that the capped Pd surface alone is inactive for H2 (or D2) dissociation, but in the presence of coflowing acetylene (alkyne), it becomes active for H2 dissociation as well as acetylene hydrogenation. The results indicated that acetylene adsorbs on the Pd surface and enables cooperative adsorption of H2. In contrast, ethylene (alkene) did not facilitate H2-D2 exchange, and hydrogenation of ethylene was not observed. The results indicated that alkynes can induce decapping of the sulfide groups from the Pd surface, while alkenes with weaker adsorption strength cannot. The discriminative adsorption of alkynes over alkenes led to highly chemoselective hydrogenation of various alkynes to alkenes with minimal overhydrogenation and the conversion of side functional groups. The catalytic functions can be retained over a long reaction period due to the high thermochemical stability of the polymer.
Deuterium-Hydrogen Exchange and Scrambling Reactions in the Pyrolysis of Labeled Cyclopentene. A Radical Mechanism
Kosnik, Kenneth G.,Benson, Sidney W.
, p. 2790 - 2795 (2007/10/02)
Inter- and intraradical mechanism that promote deuterium-hydrogen scrambling in labeled cyclopentene-d1 are investigated at 800 K and 1200 K.Rate constants are estimated for each step and for possible competing side reactions.The fast radical bimolecular exchange at 800 K and unimolecaular scrambling at 1200 K of labeled cyclopentene are shown to be faster than the Woodward-Hoffman allowed 1,4 concerted molecular elimination of hydrogen.The low-energy estimate of 8.0 kcal/mol by Lewis of the difference between the allowed 1,4 and disallowed 1,2 channels can thus be explained.No conclusions can be drawn concerning the 1,2 channel.The estimated rates of radical reactions are in agreement with experiments on the addition of D2 to cyclopentadiene at 300 deg C which shows only cis, 3-5 addition and with pyrolysis experiments at 500 +/- 20 deg C which show about 5percent contribution of a higher than first-order radical reaction.The mechanism of this radical decomposition is given and its steps are explicitly evaluated.
