Thermodynamic properties of simple alkenes

Employing low temperature thermal measurements, heat capacities (C_s) in the crystal and liquid states, and phase transition data, T_m and ΔH_m, the condensed phase thermodynamic properties, (G_s -H°₀)/T, H_s -H°₀, S_s and C_s, in the temperature range 0–360 K were evaluated for the following eleven alkenes: ethylene, propylene, 1-butene, cis-2-butene, trans-2-butene, 1-pentene, cis-2-pentene, trans-2-pentene, 2-methyl-1-butene, 3-methyl-1-butene and 2-methyl-2-butene. The sources of experimental data, methods of evaluation, and the calculated results are described in detail.     

The thermal reaction of 2-pentene around 500°C at low extent of reaction

The thermal reaction of 2-pentene (cis or trans) has been performed in a static system over the temperature range of 470°–535°C at low extent of reaction and for initial pressures of 20–100 torr. The main products of decomposition are methane and 1,3-butadiene. Other minor primary products have been monitored: trans-2-pentene, trans- and cis-2-butenes, ethane, 1,3-pentadienes, 3-methyl-1-butene, propylene, 1-butene, hydrogen, ethylene, and 1-pentene. The initial orders of formation, 0.8–1.1 for most of the products and 1.5–1.8 for 1-pentene, increase with temperature. The formation of the products and the influence of temperature on their orders can be essentially explained by a free radical chain mechanism. But cis–trans or trans–cis isomerization and hydrogen elimination from cis-2-pentene certainly involve both molecular and free radical processes. The formation of 1-pentene mainly occurs from the abstraction of the hydrogen atom of 2-pentene by resonance stabilized free radicals (C₅H₉.).     

Reactions of unsymmetrically substituted allyl radicals with methyl radicals

The Hg(6³P₁) photosensitized decompositions of 3-methyl-1-butene, 2-methyl-2-butene, 3,3-dimethyl-1-butene, and 2,3-dimethyl-1-butene have been used to generate 1-methylallyl, 1,2-dimethylallyl, 1,1-dimethylallyl, and 1,1,2-trimethylallyl radicals in the gas phase at 24 ± 1°C. From a study of the relative yields of the CH₃ combination products, the relative reactivities of the reaction centers in each of these unsymmetrically substituted ambident radicals have been determined. The more substituted centers are found to be the less reactive, and this is ascribed primarily to greater steric interaction at these centers during reaction. Measurement of the ratio of trans- to cis-2-pentene formed from the 1-methylallyl radical, combined with published values for this ratio at higher temperatures, enabled the differences in entropy and heat of formation of the trans- and cis-forms of this radical to be calculated as 0.62 ± 0.85 J mol^?1 K^?1 and - 0.63 ± 0.25 kJ mol^?1, respectively, at 298K. Approximate values of the disproportionation/combination ratios for reaction of CH₃ with 1,1-dimethylallyl and 1-methylallyl have been estimated and used to compute rate constants for the recombinations of tert-butyl and isopropyl radicals that are in agreement with recently published data.     

Quantum chemical model of dehydration of 2-butanol catalyzed by zeolite X

The CNDO/2 method was used for quantum chemical calculations of the 2-butanol interaction with zeolite X modelled by the cluster Si₃AlO₁₂H₉. Two-site adsorption on a pair consisting of an acidic and a basic catalytic site promotes dehydration of the alcohol. The activation energy of trans-2-butene formation was estimated to be much higher than those of cis-2-butene and 1-butene formation, in agreement with experimental findings.     

Theoretical study of the complex reaction of O(3P) with cis-2-butene

The complex triplet potential energy surface for the reaction of the triplet oxygen atom O(³P) with cis-2-butene is investigated at the CBS-QB3 level of theory. The different possible isomerization and dissociation pathways, including both O-additions and H-abstractions, are thoroughly studied. Our calculations show that as found for the trans-2-butene reaction, in the high-pressure limit, the major product is CH₃CHC(O)H + CH₃ (P1), whereas in the low-pressure limit the most thermodynamically stable product forms CH₃CO + CH₃CH₂ (P4). The experimental negative activation energy reported for the addition step is very well reproduced at the CBS-QB3 level of theory. Various thermodynamic and kinetic values of interest for these reactions are predicted for the first time. A discussion on the negative activation energy for the addition step of the trans- and cis-2-butene reactions with O(³P) focussing on the addition reactant complexes is presented.     

1-(Triphenylmethyl)allyl potassium :conformational preference and [1,2]-rearrangement

Upon treatment with the superbasic 1 : 1 mixture of butyllithium and potassium tert-butoxide cis- and trans-1,1,1-triphenyl-2-butene as well as 4,4,4-triphenyl-1-butene undergo a hydrogen/metal exchange to afford 1-(triphenylmethyl)allyl potassium [4,4,4-triphenyl-2-butenyl potassium] which can exist in two stereoisomeric forms. Torsional equilibration leads to an endo/exo-ratio of approximately 50 : 50. Novel endo-stabilizing interactions are discussed to rationalize this result. At temperatures around or above 0°C a phenyl 1,2-migration, though no 1,4-migration takes place.     

Niederdruck-Oligomerisation von Mono-Olefinen mit löslichen Nickel/Aluminium-Bimetallkatalysatoren Teil III. Reaktionskinetische Untersuchungen über die Dimerisation und Trimerisation des Áthylens

The kinetics of the di- and trimerization of ethylen in organic solvents under the influence of a homogeneous catalyst containing π-tetramethylcyclobutadiene-nickeldichloride and a prereacted mixture of ethylaluminiumdichloride and tri-n-butylphosphine are reported. The primary reaction product is 1-butene, which is isomerized to 2-butene (cis/trans) during the reaction. The C₆-Olefins are formed by the reaction of ethylene with 1-butene and with the 2-butenes. The following primary reaction products are obtained: 3-hexene (cis/trans), 1-hexene, 2-ethyl-1-butene, 3-methyl-1-pentene and 3-methyl-2-pentene (cis/trans). The effect of other phosphines on the reaction was also studied. The relative composition of the reaction product is strongly dependent upon the amount and the LEWIS base strength of the phosphine present. The results are in accordance with a coordinative mechanism on nickel.     

Laser photolysis study of trans→cis photoisomerization of trans-1-phenyl-2-(2-naphthyl) ethylene

The direct trans→cis photoisomerization of trans-1-phenyl-2-(2-naphthyl) ethylene (trans-PNE) in liquid solution at room temperature was studied by the nanosecond laser photolysis technique. The time-resolved S_n←S₁ and T_n←T₁ absorption spectra were observed with trans-PNE at 300 K and 77 K. The lifetime of the triplet state of trans-PNE was found to be much shorter in liquid solution at room temperature than in rigid solution at 77 K. This fact and the effect of a triplet quencher shows that the photoisomerization of trans-PNE occurs mainly via the triplet state.     

Oxidising properties of MgO formed by thermal decomposition of Mg(OH)2

To clarify whether trans-cis photoisomerization can be induced by an infrared laser in low temperature matrices, argon matrices of trans-2-butene and rans-1,2-dichloroethylene were irradiated with a TEA CO₂ laser. The results were negative, indicating that the multiple-photon absorption is suppressed in low-temperature matrices.     

Evidence for π-allylic nickel complexes as intermediates in the reactions of nickelocene with allylic chlorides

Reactions of trans-1-chloro-2-butene and of 3-chloro-1-butene with nickelocene give mixtures of (1-methyl-2-propenyl)-, (trans-2-butenyl)-, and (cis-2-butenyl)-cyclopentadienes. The reaction between π-crotyl-π-cyclopentadienylnickel and 5-chlorocyclopentadiene yields identical products. In the presence of tetrahcloromethane, 5-(trichloromethyl)cyclopentadiene is formed. Mechanisms involving oxidative addition and π-allylic nickel complexes are discussed.     

Experimental determination of dissociation pressures for hydrates of the cis- and trans-isomers of 2-butene below the ice temperature

The three-phase (vapor + ice + hydrate) (VIH) hydrate equilibrium was determined for cis- and trans-2-butene using a new and a simple experimental technique. The equilibrium measurements were done at temperatures between 248 to 272 K and pressures between 16.7 to 67.6 kPa for cis-2-butene, and for trans-2-butene between 245 to 272 K and 15.4 to 70.4 kPa. The accuracy of the experimental technique was verified by measuring hydrate dissociation pressures for pure propane below the ice temperature; the results obtained were in good agreement with those in the literature for pure propane.     

Cyclic oligomers in the cationic polymerization of cis- and trans-2,3-dimethylthiirane

Under the influence of triethyloxonium tetrafluoroborate in methylene chloride, cis- and trans-2,3-dimethylthiirane are transformed to their corresponding polymers almost instantaneously (at temperatures between 0 and 20 °) but within a few hours these polymers completely degrade to form a mixture of low molecular weight substances. The cis-monomer leads to a mixture of cyclic tetramer, cis-butene and two geometric isomers of 3,4,6,7-tetramethyl-1,2,5-trithiepane. By ¹H-NMR it was shown that these two isomers are the trans-cis-trans and the trans-trans-trans forms. The trans-monomer leads to a mixture of trans-butene and 3,4,6,7-tetramethyl-1,2,5-trithiepane which is present as a mixture of the cis-cis-cis and the cis-trans-cis isomers. In both cases, the butene and the trithiepanes were formed in equimolar quantities. The formation of these oligomers is explained by assuming that polymerization occurs via an SN2 propagation reaction between the three-membered cyclic sulphonium ion (the active species) and monomer, followed by a degradation reaction occurring via a back-biting mechanism.     

Formation yields of epoxides and O(3P) atoms from the gas-phase reactions of O3 with a series of alkenes

Reactions of ozone with propene, 1-butene, cis-2-butene, trans-2-butene, 2,3-dimethyl-2-butene, and 1,3-butadiene were carried out in N₂ and air diluent at atmospheric pressure and room temperature and, by monitoring the formation of the epoxides and/or a carbonyl compound formed from the reactions of O(³P) atoms with these alkenes, the formation yields of O(³P) atoms from the O₃ reactions were investigated. No evidence for O(³P) atom formation was obtained, and upper limits to O(³P) atom formation yields of <4% for propene, <5% for 1.3-butadiene, and <2% for the other four alkenes were derived. The reaction of O₃ with 1,3-butadiene led to the direct formation of 3,4-epoxy-1-butene in (2.3 ± 0.4)% yield. These data are in agreement with the majority of the literature data and show that O(³P) atom formation is not a significant pathway in O₃—alkene reactions, and that epoxide formation only occurs to any significant extent from conjugated dienes. © 1994 John Wiley & Sons, Inc.     

Efficient synthesis of cis-thiazolidinethiones derived from ephedrines

The reaction of chlorodeoxypseudoephedrine or chlorodeoxynorpseudoephedrine hydrochlorides with sodium dithiocarbonate in stirring ethanol at 0 °C to stereoselectively afford the corresponding cis-thiazolidinethiones in good yields (81% and 95%) is reported. The in situ formation of a cis-aziridine to explain the presence of trans-thiazolidinethione as a side product is proposed when the same reaction was carried out at room temperature. In addition, a 70:30 mixture of trans-isomers of a thiazolidinethione/isothiazolidinethione was formed when a cis-aziridine NH was reacted with carbon disulfide in refluxing ethanol. The analogous reaction with cis-aziridine N-Me stereoselectively affords the corresponding cis-thiazolidinethione. The ¹H and ¹³C NMR data of the thiazolidinethiones were assigned. cis-3,4-Dimethyl-5-phenylthiazolidine-2-thione was crystallized from ethanol and its X-ray diffraction structure was analyzed.     

Quantitative estimation of trans-1,4 and cis-1,4 isomers in polychloroprene by high-resolution NMR

In the ¹H-NMR spectrum of polychloroprene dissolved in C₆D₆, the ?CH proton signal was separated into two triplet peaks. These triplet signals were assigned to the ?CH proton in the trans-1,4 and cis-1,4 isomers by measurement of ¹H-NMR spectra of 3-chloro-1-butene and a mixture of trans- and cis-2-chloro-2-butene as model compounds for the 1,2, trans-1,4 and cis-1,4 isomers. In ¹H-NMR spectra (220 Mcps) of polychloroprene dissolved in C₆D₆, two triplet signals were separated completely from which the relative concentrations of trans-1,4 and cis-1,4 isomers could be obtained quantitatively.     

Hydrodesulfurization of thiophene over CoMo/AlMCM-41

In this paper the application of a series of CoMo/AlMCM-41 catalysts with different Si/Al ratios was studied in the model reaction of thiophene hydrodesulfurization. The results obtained showed good catalytic activity for the formation of H₂S, isobutene, 1-butene, n-butane, 2-trans-butene-and 2-cis-butene.     

Stabilization and isomerization of radical cations generated by fast electron irradiation of unsaturated organic molecules in a solid argon matrix

Matrix isolation EPR spectroscopy was used to study the fate of “hot” unsaturated radical cations produced by fast electron irradiation in solid argon. It was found that the radical cations of cis-2-butene, trans-2-butene and ethyl vinyl ether resulting from highly exothermic hole transfer (excess energy>6 eV) underwent effective relaxation in an argon matrix. 1-Butene radical cation exhibits isomerization to cis-2-butene radical cation. The role of molecular structure of organic radical cations in excess energy relaxation is discussed.     

Thermal isomerization of cis- or trans-2-butene. The unimolecular elimination of hydrogen from cis-2-butene around 500°C

An analytical and kinetic study of the thermal reaction of cis- or trans-2-butene has been performed in a static system over the temperature range of 480–550°C and at a low extent of reaction and initial pressures of 10–100 torr. The rate constant of the unimolecular cis–trans isomerization of cis-2-butene, determined under the conditions (2.3 RT in cal/mole) is in good agreement with previous measurements made at lower pressures. A comparison between the formation rates of hydrogen from the thermal reactions of cis- and trans-2 butene around 500°C leads to the rate constant value (2.3 RT in cal/mole) for the unimolecular 1,4? hydrogen elimination from cis? 2? butene.     

Formation of O(3P) atoms and epoxides from the gas- phase reaction of O3 with isoprene

The formation yields of 1,2-epoxy-2-methyl-3-butene and 1,2-epoxy-3-methyl-3-butene have been measured from the reaction of O₃ with isoprene at room temperature and one atmosphere total pressure of N₂ and air diluents, with and without cyclohexane to scavenge the OH radicals formed in this reaction system. In addition, a relative rate method was used to determine a rate constant for the gas-phase reaction of O₃ with 1,2-epoxy-2-methyl-3-butene of (2.5 ± 0.7) x 10^-18 cm³ molecules^-1 s^-1 at 296 ± 2 K. Our data show that the epoxide yields in N₂ and air diluents are the same, with formation yields of 1,2-epoxy-2-methyl-3-butene of 0.028 ± 0.007 and of 1,2-epoxy-3-methyl-3-butene of 0.011 ± 0.004. These data further show that the epoxides arise from the primary O₃ reaction with isoprene, and not via the formation of O(³P) atoms from the O₃ - isoprene reaction followed by reaction of these O(³P) atoms with isoprene.     

Metals in organic syntheses: XIV. NMR,IR, and reactivity studies on the olefin hydroformylation catalyzed by Pt-Sn complexes

Among the several hydrides formed when trans-[PtHClL₂] (L = PPh₃) reacts with Sncl₂, only trans-[PtH(SnCl₃)L₂] rapidly inserts ethylene, at −80°C, to yield cis-[PtEt(SnCl₃)L₂]. At −10°C, cis-[PtEt(SnCl₃)L₂] irreversibly rearranges to the trans-isomer, thus indicating that the cis-isomer is the kinetically controlled species, and that the trans-isomer is thermodynamically more stable.At −50°C, a mixture of trans-[PtHClL₂] and trans[PtH(SnCl₃)L₂] reacts with ethylene to give cis-[PtEtClL₂] and cis-[PtEt(SnCl3)L₂] and this has been attributed to the catalytic activity of SnCl₂ which dissociates from cis-[PtEt(SnCl₃)L₂] at this temperature.Carbon monoxide promotes the cis-trans isomerization of cis[PtEt(SnCl₃)L₂], which occurs rapidly even at −80°C. This rearrangement is followed by a slower reaction leading to the cationic complex trans-[PtEt(CO)L₂]⁺ SnCl₃⁻. At −80°C, this complex does not react further, but when it is kept at room temperature ethyl migration to coordinated carbon monoxide takes place, to give several Pt-acyl complexes, i.e. trans-[PtCl(COEt)L₂], trans-[Pt(SnCl₃)(COEt)L₂], trans-[PtCl(COEt)l₂ · SnCl₂], and trans-[Pt(COEt)(CO)L₂]⁺ SnCl₃⁻. This mixture of Pt-acyl complexes reacts with molecular hydrogen to yield n-propanal and the same complex mixture of platinum hydrides as is obtained by treating trans-[PtHClL₂] with SnCl₂.Trans-[PtH(SnCl₃)L₂] reacts with carbon monoxide to yield the five-coordinate complex [PtH(SnCl₃)(CO)₂L₂], which has been characterized by NMR and Ir spectroscopy; ethylene does not insert into the PtH bond of this complex at low temperature. At room temperature, trans-[PtH(SnCl₃)L₂] reacts with a mixture of CO and ethylene to yield the same mixture of Pt-acyl species as is obtained when trans-[PtEt(SnCl₃)L₂] is allowed to react with CO.The role of a PtSn bond in these reactions is discussed in relation to the catalytic cycle for the hydroformylation of olefins.