1184-59-4Relevant articles and documents
Low-Temperature Decomposition of Alkyl Iodides on Ni(100) Surfaces: Evidence for the Formation of Alkyl Free Radicals
Zaera, Francisco,Tjandra, Sariwan
, p. 3044 - 3049 (1994)
Previous studies have shown that alkyl iodides dissociate on metal substrates around 200 K to produce iodine atoms alkyl moieties on the surface; here we report a new low-temperature decomposition pathway for those compounds on Ni(100) that leads to the formation of a close to 1:1 alkane-alkene mixture below 150 K.This latter reactions is proposed to occur via a mechanism where alkyl iodide dissociation results in the direct formation of free radicals.A combination of thermal desorption experiments with isotope labeling and hydrogen coadsorption was used to establish the importance of the nickel surface in the overall process and to rule out either surface disproportionation or gas-phase reactions as the source of the low-temperature products.Evidence was also obtained for a possible rearrangement of the adsorbed alkyl iodide molecules from a fat geometry into an upright configuration at high coverages, a change that would explain the ease with which the radicals formed after C-I bond scission are released into the gas phase instead of being left on the surface as adsorbed alkyl surface moieties.A comparison with other systems is also presented.
Metal ions do not play a direct role in the formation of carbon-carbon triple bonds during reduction of trihaloalkyls by CrII or V II
Levy, Ophir,Bino, Avi
supporting information, p. 15944 - 15947 (2013/02/23)
Carbyne radicals: Reactions of trihaloalkyl compounds with Cr2+ or V2+ in aqueous solutions yield alkynes and other products. Stepwise halogen abstractions from the trihaloalkyls form alkyl carbyne triradicals in solution. These radicals undergo coupling reactions, producing triply bonded alkyne molecules (see scheme). This process is not metal-assisted and does not occur in the coordination sphere of the metal ions.
Deuterium kinetic isotope effects on the thermal isomerizations of deuteriocyclopropane to deuterium-labeled propenes
Baldwin, John E.,Singer, Stephanie R.
, p. 1510 - 1515 (2007/10/03)
The gas-phase thermal isomerizations of deuteriocyclopropane to the four possible monodeuterium-labeled propenes have been followed at 435°C. The observed distribution of products provides estimates of two deuterium kinetic isotope effects, the secondary ksh/ks D for the carbon-carbon bond cleavage leading to trimethylene diradical reactive intermediates and the primary kp h/kpD ratio for a [1,2] shift of a hydrogen or deuterium leading from the diradical to a labeled propene. The values determined are ksD/ksD = 1.09 ± 0.03 and kpH/kpD = 1.55 ± 0.06. The experimental ksD/ksD value found agrees well with some, but not all, earlier calculated values and conjectures.
Novel Support Effects on the Mechanism of Propene-Deuterium Addition and Exchange Reactions over Dispersed ZrO2
Naito, Shuichi,Tanimoto, Mitsutoshi
, p. 306 - 313 (2007/10/03)
The effect on the rate and mechanisms of propene-deuterium reactions of dispersing ZrO2 on various supports such as silica, alumina, and titanium dioxide has been studied by microwave spectroscopic analysis of monodeuteropropene as well as by kinetic investigation.By dispersal of ZrO2 on these supports, the rate of the C3H6-D2 reactions is increased considerably compared to that over unsupported ZrO2, with the decrease of activation energy.Hydrogen exchange in propene proceeds simultaneously with addition via the associative mechanism through n-propyl and s-propyl intermediates.Through XPS analysis of ZrO2/SiO2, it was found that a monolayer of ZrO2 is formed over the silica support.The monolayer catalyst exhibits catalytic behavior quite different from that of unsupported ZrO2.On the other hand, alumina surfaces modified by ZrO2 layers may be the main active sites in the case of ZrO2/Al2O3.The marked enhancement of the reaction rate in the lower loading region of ZrO2/TiO2 may be explained by the strong interaction of atomically dispersed zirconium ions with active centers on TiO2
Effects of Surface Defects and Coadsorbed Iodine on the Chemistry of Alkyl Groups on Copper Surfaces: Evidence for a Cage Effect
Jenks, Cynthia J.,Paul, Anumita,Smoliar, Laura A.,Bent, Brian E.
, p. 572 - 578 (2007/10/02)
The effects of defect sites and coadsorbed iodine atoms on the chemistry of alkyl groups with two to four carbon atoms on copper surfaces have been studied by temparature-programmed reaction (TPR).The primary reaction pathway for the adsorbed alkyl group both in the presence and absence of defects and iodine atoms is β-hydride elimination.Because desorption is not (under most conditions) the rate-determining step in the evolution of the product from the surface, the rate of the surface β-hydride elimination reaction could be monitored by TPR.Neither surface defects nor low coverages of coadsorbed iodine significantly affect the β-elimination rate.For high coverages of iodine, however, the rate of β-elimination by 5-10percent of the adsorbed alkyl groups is decreased by over five orders of magnitude (Trxn = 385 K versus 230 K).The reaction kinetics together with observations from low-energy electron diffraction studies suggest that the dramatic inhibition of the β-elimination rate for high iodine coverages is due to cages of immobile iodine atoms that surround the alkyl groups and prohibit hydrogen transfer to the surface.
Mechanism of Propene-Deuterium Addition and Exchange Reaction over Silica-Supported ZrO2
Naito, Shuichi,Tanimoto, Mitsutoshi
, p. 3205 - 3211 (2007/10/02)
The mechanism of propene-deuterium reaction over unsupported and silica-supported ZrO2 catalysts was studied with kinetic investigation as well as microwave spectroscopic analysis of monodeuteriopropene. Unsupported ZrO2 exhibited the identical catalytic behavior for C3H6-D2 reaction with other oxide catalysts previously reported: Only propane-d2 was selectively formed in the addition process, with no hydrogen exchange in propene. By supporting on silica, the rate of C3H6-D2 reaction increased considerably, with the decrease of activation energy. Hydrogen exchange in propene proceeded simultaneously with addition via associative mechanism through propyl and isopropyl intermediates. Small particles of ZrO2 were proposed as active sites of this characteristic catalytic behavior.
Marked Size Effect of Zinc Oxide Particles Supported on Silica in Propene-Deuterium Addition and Exchange Reactions
Naito, Shuichi,Tanimoto, Mistutoshi,Soma, Mitsuyuki
, p. 1443 - 1445 (2007/10/02)
Small particles of ZnO trapped between silica particles exhibit a marked size effect on the reaction rates as well as on the reaction intermediates of the propene-deuterium addition and exchange reactions.
Remarkable Dispersion Effect of TiO2 Catalyst on Silica Support in Propene - Deuterium Addition and Exchange Reaction
Naito, Shuichi,Tanimoto, Mitsutoshi
, p. 2145 - 2148 (2007/10/02)
Investigation on the effect of dispersing small particles of TiO2 over silica upon the rate and mechanism of propene-deuterium reaction revealed that lower loading catalysts (1-8 wtpercent) exhibit markedly different catalytic behavior from that over unloaded TiO2.
Synergetic Ligand Effect in the Hydrogen Exchange Reaction of Propene over Pd-Cu and Pt-Cu Alloy Catalysts
Naito, Shuichi,Tanimoto, Mitsutoshi
, p. 411 - 414 (2007/10/02)
Marked changes of reation intermediates on alloying were disclosed by the microwave spectroscopic analysis of the monodeuteriopropene formed during C3H6-C3D6 exchange reaction over Pd-Cu and Pt-Cu alloy catalysts.
Mechanism of Deuterium Addition and Exchange of Propene over Silica-supported Gold and Silver Catalysts
Naito, Shuichi,Tanimoto, Mitsutoshi
, p. 4115 - 4124 (2007/10/02)
The mechanism of the C3H6-D2 reaction over silica-supported Au and Ag catalysts has been studied by applying microwave spectroscopy as well as kinetic measurements.A large kinetic isotope effect was observed for the rate of propane formation between the C3H6-H2 andC3H6D2 reactions, indicating that the hydrogen dissociation is the rate-determining step.Both deuterium addition and exchange processes proceeded via an associative mechanism involving n-propyl as well as s-propyl species, although the methyl hydrogen of propene was less active for exchange through this process.In addition, intramolecular 1,3- and 2,3-hydrogen-shift processes were observed for the first time; they proceeded only in the presence of gaseous hydrogen and caused the exchange of the methyl hydrogen of propene.The characteristic features of supported Group IB metals in this reaction are compared with those of Group VIII metals, and the possible structures of reaction intermediates are discussed in detail.
