Hydrogenation Of Isoprene Research Articles

FvCr2(CO)4L2(Fv = Fulvalene; L = PMe2Ph, PMe3), Metal−Metal-Bonded Compounds Which Undergo Spontaneous Thermal Homolysis to Their Biradical Isomers. Relevant Chemistry of the Compounds FvCr2(CO)4L2X2(X = H, Cl, Br, I)

Two new (fulvalene)dichromium carbonyl dihydrides, FvCr2(CO)4L2H2 (L = PMe2Ph (2b), PMe3 (2c)) were prepared by phosphine substitution of FvCr2(CO)6H2 (2a) and studied by variable-temperature 1H, 13C{1H}, and 31P{1H} NMR. Compound 2b assumes a 77:23 and 2c an 85:15 cis/trans isomeric ratio at −50 °C, while low-temperature NMR spectra of 2b present evidence for the meso and dl forms of the cis,cis isomer. Hydride hydrogen atom abstraction from 2b and 2c by Ph3C•, as well as hydrogenation of isoprene and 1,3,5-hexatriene by 2b and 2c, result in the formation of FvCr2(CO)4L2 (L = PMe2Ph (6a), PMe3 (6b)). Variable-temperature IR and 1H, 13C{1H}, and 31P{1H} NMR studies demonstrate that both 6a and 6b maintain facile equilibria between the trans isomers of the chromium−chromium-bonded species and the novel biradical species L(CO)2Cr(μ-Fv)Cr(CO)2L at room temperature in solution. Room-temperature reactions of 6a with alkyl halides reflect the radical character of this compound, halogen atom abstractions leading...

Catalytic hydrogenation in the liquid phase. Part 1. Hydrogenation of isoprene catalysed by palladium, palladium-gold and palladium-silver catalysts

The hydrogenation of isoprene (2-methyl-1,3-butadiene) proceeds at 273 K in EtOH solvent in the presence of Pd catalysts to give the three possible methylbutene isomers with high selectivity (≥ 98%): their proportions, which remain constant until all the isoprene has reacted, are approximately 2-methyl-2-butene, 50%; 3-methyl-1-butene and 2-methyl-1-butene, each 25%. However especially with Pd CaCo 3 , Pd BaSO 4 and Pd C the proportion of the 2-methyl-2-butene is significantly less than 50% and those of the others correspondingly greater; with PdAu SiO 2 made by reduction with N 2H 4, the proportion of 2-methyl-2-butene decreases with increasing concentration of the Group 11 element. Monoalkene selectivities are described by a simple reaction model based on two isomeric half-hydrogenated π-allylic radicals; the terminal carbon atoms of the delocalised π-bond carry charges which depend on the number of CH 3-substituents, and the relative chances of adding an H atom at each position, which determine product composition, are affected by the charge on the H atom. Increasing Au or Ag concentration is the bimetallic series increases its negative charge.

ChemInform Abstract: Selective Hydrogenation of Isoprene on Eggshell and Uniform Palladium Profile Catalysts.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Selective hydrogenation of isoprene on eggshell and uniform palladium profile catalysts

The effects of palladium concentration profile on the selective hydrogenation of isoprene (IP) were investigated by comparing the catalytic performance of well-controlled eggshell and uniform profile catalysts. The catalytic performance test, combined with other complementary characterization techniques, provides the information for fundamental understanding of the relationship between catalyst preparation and performance. Experimental results indicate that the catalyst with an eggshell palladium profile has a higher partial hydrogenation selectivity and less coke formation. The results also indicate that the better activity maintenance for the eggshell catalyst is due to the lower tendency for coke formation from conjugated dienes polymerization. As a result, the eggshell catalyst is much more active, selective and stable than the uniform profile catalyst. In this study, the catalytic reactions were carried out at reaction conditions similar to those of a commercial run: 44°C and 30 atm. The palladium concentration profiles and particle sizes were determined by EPMA (electron probe microanalysis) and TEM (transmission electron microscopy) respectively. The coke deposited on the catalysts was characterized by DSC (differential scanning calorimetry) and the likely coke precursors were identified by GC/MS (gas chromatography/mass spectrometer) spectroscopy.

An improved method for the diimide hydrogenation of butadiene and isoprene containing polymers

AbstractThe hydrogenation of unsaturated polymers with diimide generated in‐situ by thermolysis of p‐toluenesulfonyl hydrazide (TSH) is a commonly used method for preparing laboratory scale quantities of saturated diene based polymers. The by‐products from TSH, particularly p‐toluenesulfinic acid, can attack at olefinic sites, adding p‐tolylsulfone functionality and degrading polymer molecular weight. The addition of tri‐n‐propyl amine has been found to eliminate these side reactions in butadiene containing polymers and copolymers, enabling the preparation of polymers devoid of backbone unsaturation. No detectable sulfur‐containing impurities were indicated by IR, NMR, or elemental analysis, and no chain degradation was observed via GPC analysis of the hydrogenated polymers. cis‐Polybutadiene and butadiene containing random and block copolymers with styrene were hydrogenated cleanly using this technique. A ratio of 2 mol TSH and 2 mol amine/mol of olefin was necessary to assure > 99% hydrogenation, and a w/v ratio of 2 parts butadiene/100 parts o‐xylene gave the most efficient hydrogenation. Polymers prepared from isoprene were only partially hydrogenated when treated with TSH in the presence of tri‐n‐propyl amine, and gave evidence of slight degradation of the polymer structure.

Alumina-supported bimetallics of palladium alloyed with germanium, tin, lead, or antimony from organometallic precursors II. gas-phase hydrogenation of 2-methyl-1-buten-3-yne (valylene) and 2-methyl-1,3-butadiene (isoprene)

A series of PdGe, PdSb, PdSn, and PdPb/α-Al 2O 3 catalysts, prepared by the controlled surface reaction (CSR) technique from organometallic precursors have been tested in the gas-phase hydrogenation of 2-methyl-1-buten-3-yne (valylene) and 2-methyl-1,3-butadiene (isoprene). On catalysts reduced at 573 K, the turnover frequencies for valylene (TON V) and isoprene (TON I) hydrogenation were not modified by addition to the 0.09 wt% Pd/α-Al 2O 3 base catalyst of Ge, Sb, Sn, or Pb, up to 0.1 wt% (at 293 K: TON V = 20 s −1 and TON I = 33 s −1). Pd/α-Al 2O 3 reduced at 773 K was severely sintered ( d TEM increased from 2.8 run to 12.4 nm) and TON V and TON I at 293 K increased to 190 and 283 s −1, respectively, as a result of an apparent crystal size effect: the reactants adsorb more strongly on the smaller Pd particles. Upon alloying with Ge, Sb, Sn, or Pb and a subsequent reduction at 773 K, a modest decrease of both TON V (by a factor of 2) and TON I (by a factor of 2–5) was observed. At high conversion, both the selectivity to isoprene (S I) in valylene hydrogenation, and to olefins ( S O ) in isoprene hydrogenation on Pd/α-Al 2O 3 were improved upon alloying with Sb, Sn, or Pb (Ge had no effect). In addition, the isomerization of 2-methyl-1-butene and 3-methyl-1-butene (double bond migration reaction) during isoprene hydrogenation was partially suppressed on PdSn and PdPb/α-Al 2O 3. The improvement in selectivities was interpreted in terms of a change in the relative adsorption strength of the reactants and intermediate products over the new bimetallic sites.

Vapor-phase synthesis of isoprene from formaldehyde and isobutylene over CuSO4−MOx/SiO2 catalysts

Vapor-phase synthesis of isoprene from formaldehyde and isobutylene over CuSO4−MOx/SiO2 catalysts has been studied. The results show that CuSO4−MOx/SiO2 catalysts exhibit a good catalytic activity; especially when the metal oxides have appropriate basicity, is isoprene yield greatly enhanced. The results of product analysis indicate that there are side-reactions during isoprene production, which are isoprene hydrogenation, polymerization of isobutylene, copolymerization of isobutylene and isoprene, and reaction of C5 aldehyde and ketone formed during isoprene production. In addition, catalytic behavior of the catalysts and probable mechanism of side-reactions are discussed.

Preparation and characterization of copper-thorium oxide catalysts. 2. ESR study of copper(II) ion pairs and correlation with the selective hydrogenation of isoprene

Preparation and characterization of copper-thorium oxide catalysts. 2. ESR study of copper(II) ion pairs and correlation with the selective hydrogenation of isoprene

Hydrogenation of isoprene on Pt(111)

The hydrogenation of isoprene (2-methyl-1,3-butadiene) was investigated on Pt(111) under quasi-atmospheric pressure and over a temperature range of 200 K. The surface was characterized by LEED and AES. Special attention has been given to the rate-determining adsorbed species; their relative abundances on the surface, governed by temperature and pressure parameters, showed evidence for their competitive influence on kinetics. However, only temperature affected product selectivity. As for sulfur poisoning, adsorption site blocking and hence mobility inhibition for adsorbed molecules can explain the shape of the deactivation curves.

Site structure sensitivity of diene hydrogenation and isomerization reactions on MOS 2/ γ-Al 2O 3 catalysts

The hydrogenation and isomerization of two diene molecules, cis-1,3-pentadiene and 2-methyl1,3-butadiene (isoprene), have been performed at 50°C on a 13.8 wt% MoO 3/ γ-Al 2O 3 sulfided hydrotreating catalyst. The alumina support was not active for hydrogenation and its activity for isomerization was found poisoned by the presence of the MoS 2 phase. The observed diene hydrogenation and isomerization activities are therefore attributed to the sulfide phase. Both the activity and the product distribution have been found strongly dependent on the sulfur content of the ( 1 010) edge plane of the MoS 2 slabs. In that edge plane all the Mo ions are similar. Therefore the active sites responsible for the various catalytic functions must be distinguished on the basis of the environment of the Mo ions. More precisely hydrogenation has been found sensitive to Mo ions tricoordinatively unsaturated (cus) and isomerization to 2-cus and 4-cus Mo ions. However, as each vacancy or sulfur ion is shared by two Mo ions in the ( 1 010) edge plane, a full description of the sites leads us to consider an “elementary ensemble” of two Mo ions and their six associated sulfur ions and/or vacancies. The active sites responsible for the different catalytic functions observed correspond primarily to different configurations of sulfur ions and vacancies in the “elementary ensemble” or, in other words, to different site structures. It is shown that due to its strongly preferred 3–4 hydrogenation, the reaction scheme of isoprene hydrogenation is simple enough to correspond to a catalytic function for each product. It is then shown that different site structures could be assigned to each of these functions and that simple statistical calculations can satisfactorily explain the experimental product distribution. The selectivity and activity of the catalyst for the diene hydrogenation and isomerization reactions studied are therefore dependent on the structure of the sites present in the ( 1 010) edge plane of the MoS 2 slabs.

ChemInform Abstract: Hydrogenation and Isomerization of Alkadienes on Powdered MoSxHy

Abstract Hydrogenation of 2-methyl-1,3-butadiene (isoprene) in the absence of gaseous hydrogen is used to reveal and titrate reactive hydrogen species occluded in powdered MoS 2 previously reduced under H 2 . Highly coordinatively unsaturated (cus) Mo ions are generated on MoS 2 by reduction treatment at various temperatures between 373 and 973 K. After each reduction treatment, the catalyst stoichiometry is measured, so that the values x and y in MoS x H y can be established. Different compositions where x is between 1.67 and 2.01 and y is between 0.002 and 0.12 have been investigated. To probe the unsaturated Mo ions, hydrogenation of isoprene and isomerization of cis -1,3-pentadiene are performed at 373 K under 1 atm pressure of hydrogen. Similarly to the case of supported MoS 2 on γ-Al 2 O 3 catalyst, which has already been investigated, a correlation is proposed between the alkadiene transformation activities and the coordinatively unsaturated (1010) edge Mo ions, viz., hydrogenation and 3 cus ions, isomerization and 2 and 4 cus ions.

Hydrogenation and isomerization of alkadienes on powdered MoS xH y

Hydrogenation of 2-methyl-1,3-butadiene (isoprene) in the absence of gaseous hydrogen is used to reveal and titrate reactive hydrogen species occluded in powdered MoS 2 previously reduced under H 2. Highly coordinatively unsaturated (cus) Mo ions are generated on MoS 2 by reduction treatment at various temperatures between 373 and 973 K. After each reduction treatment, the catalyst stoichiometry is measured, so that the values x and y in MoS xH y can be established. Different compositions where x is between 1.67 and 2.01 and y is between 0.002 and 0.12 have been investigated. To probe the unsaturated Mo ions, hydrogenation of isoprene and isomerization of cis-1,3-pentadiene are performed at 373 K under 1 atm pressure of hydrogen. Similarly to the case of supported MoS 2 on γ-Al 2O 3 catalyst, which has already been investigated, a correlation is proposed between the alkadiene transformation activities and the coordinatively unsaturated (1010) edge Mo ions, viz., hydrogenation and 3 cus ions, isomerization and 2 and 4 cus ions.

Catalytic behaviour of interlayer-supported palladium(II) complexes on lithium hectorite

Aminated lithium hectorites, HT-A1 (-OSiMe 2CH 2OCH 2CH 2NH 2) and HT-A2 (-OCH 2CH 2NH 2), were prepared by chemical modification of the OH group in lithium hectorite (LHT). Interlayer-supported Pd II complexes on LHT, Pd/HT-A1 and Pd/HT-A2 were synthesized by the reaction of [Pd(OAc) 2] 3 with HT-Al and HT-A2, respectively. XRD studies showed that the basal spacings ( d 001) of LHT and Pd/HT-A1 swollen with solvents varied with the dipole moment of the solvent. Catalytic activities and selectivities of Pd/HT-A1 for the hydrogenation of mono-olefins and dienes were investigated in the liquid-solid heterogeneous system. The hydrogenation rate decreased in the order 1-pentene > 2-methyl-1-butene > cyclo-octene. The selectivity for partial hydrogenation depended on the type of diene: conjugated dienes > unconjugated dienes. The selectivity for the partial hydrogenation of isoprene by Pd/HT-A1 was independent of the solvent, while that of the homogeneous catalyst [Pd(OAc) 2] 3 increased with increasing dipole moment of the solvent.

Alumina-supported bimetallics of palladium alloyed with germanium, tin, lead, or antimony from organometallic precursors: I. Preparation and characterization

Bimetallic PdSn, PdSb, PdPb, and PdGe on alumina catalysts with a low metal content have been prepared using either chloride or Organometallic precursors. For the catalysts obtained from chloride precursors no interaction was observed between the two metals, and the catalysts behaved like pure Pd Al 2O 3 . In contrast, the reactions of (C 4H 9) 4Sn, (C 4H 9) 4Pb, (C 4H 9) 4Ge, or (C 4H 9) 3Sb in n-heptane solution with reduced Pd Al 2O 3 catalyst yielded a supported alloy. The interaction between metallic palladium and the organic modifier is highly selective and leads to the formation of a well-tailored bimetallic catalyst. When these final solids are reduced at 573 or 773 K, the second metal locates preferentially at the outer layer of the bimetallic aggregates. After reduction at 773 K large metallic aggregates are obtained (particle size ≅ 15 nm), and the formation of β-palladium hydride, which can be formed with pure palladium catalysts, is suppressed by the addition of a small amount of the second metal. The specific activity of the palladium surface atoms for isoprene hydrogenation is then lowered, and the selectivity increased.

ChemInform Abstract: The Active Site for Isoprene Hydrogenation on MoS2/γ‐Al2O3 Catalysts.

ChemInform Abstract: The Active Site for Isoprene Hydrogenation on MoS2/γ‐Al2O3 Catalysts.

Interaction of molecules with molybdenum disulphide catalysts: An experimental and molecular graphics study. Isoprene

The interaction of isoprene with molybdenum disulphide has been studied by computer-assisted modelling of the binding of the molecule at active sites. Possible structures of intermediate-active-site complexes were evaluated by the method of molecular mechanics. For isoprene hydrogenation the preferred catalytic sites, according to energy minimisation calculations, proved to be corner molybdenum atoms having threefold unsaturation. This conclusion agrees with deductions from experimental studies of isoprene hydrogenation. The modelling studies are valuable for revealing the steric relationships between active sites and substrate molecules, for calculating the most likely structures, and for revealing non-bonded interactions.

Kinetic study of pyrolysis gasoline hydrogenation over supported palladium catalyst

The hydrogenation of pyrolysis gasoline was carried out over a supported palladium catalyst. Some of the operation variables which showed the effects on catalyst reduction and pyrolysis gasoline hydrogenation were discussed. The reduction conditions were studied by TPR technique and verified by the hydrogenation reaction. The supported palladium oxide could be reduced to palladium completely in less than one hour at 100°C and 4.5 atm of H 2. The sintering of palladium became significant when the reduction temperature was above 300°C. The reaction temperature which gave the maximum pseudo rate constant of hydrogenation increased with increaing pressure. The kinetics of hydrogenation of model compounds, isoprene and styrene, were also studied in a semibatch basket reactor. The increase in hydrogen pressure not only enhances the rate of hydrogenation but also depresses the polymerization of dienes. It can be concluded that the reaction temperature and pressure should be compromised in order to obtain the optimum operation for hydrogenation of diene to monoolefin.

On the catalytic amidocarbonylation of substituted allylic alcohols

Substituted allylic alcohols (3-methyl-2-buten-1-ol and 2-methyl-3-buten-2-ol) were isomerized and amidocarbonylated. In addition to the expected product, N-acetylleucine, arising from their rearrangement to 3-methylbutanal and subsequent amidocarbonylation (22% yield), we isolated two additional products (28% yield). These were shown by spectroscopic methods and by syntheses, via amidocarbonylations of the respective aldehydes, to be 2-acetamido-5-methylhexanoic acid and 2-acetamido-4-methylhexanoic acid. Their formation is postulated to be the sequential result of (i) dehydration first to form isoprene, (ii) hydroformylation and hydrogenation of isoprene to give 3-methyl-1-pentanal and 4-methyl-1-pentanal, and (iii) aldehyde amidocarbonylation. Treatment of isoprene itself under the same conditions also gave these latter two acetylamino acids.

Selective hydrogenation of dienes on copper-chromite catalysts III reaction mechanism and nature of the occluded hydrogen species

We reported previously that the selective hydrogenation of dienes on copper chromite involves the association of a cuprous ion in an octahedral environment and an occluded hydrogen species as the catalytic sites. In this work, the reaction mechanism of isoprene hydrogenation is studied using deuterium as a tracer atom. The deuterium location, as well as the selectivities observed in the hydrogenation of 1,3-pentadienes are consistent with the formation of allylic carbanions. Moreover, these results suggest that a hydridic nature of at least a part of the occluded hydrogen is required. According to Siegel's model, a general reaction scheme is proposed and similarities between the properties of the copper chromite and the cuprous ion in homogeneous catalysts are reported.

Mechanisms of the formation of isomers of isoamylenes in selective hydrogenation of isoprene on a palladium-lead catalyst

1. The isomeric composition of isoamylenes formed during hydrogenation of isoprene on a Pd-Pb catalyst is not significantly dependent on the conditions of the reaction and differs from the equilibrium composition. The rate of formation of each isomer is described by an equation similar to the general kinetic equation for hydrogenation of isoprene into isoamylenes. 2. In the presence of isoprene, the isoamylenes formed are not retained by the surface of the catalyst, and their isomerization and subsequent hydrogenation thus does not take place. 3. A scheme in stages is proposed which explains the mechanisms of selective hydrogen ation of isoprene and isotopic exchange observed. Kinetic equations which coincide with the experimental equations can be obtained based on this scheme.