Propene gas-phase

Acknowledgment The authors express their thanks for financial support from the DFG grants JE 267/2-1 and 436 RUS 113/788/0-1 and the Program N 1 of the Russian Academy of Sciences. Jutta Krohnert is acknowledged for propene gas phase measurements. 

The Bemene/Isoprene/Propene Gas Phase System. In this ternary system, following the selective ionization of benzene direct and coupled charge transfer reactions can take place aconding to reactions 1 and 2, respectively. The observed reaction products include IPb (n ), tPn (n )> (n=2-5), BP ... 

The hydrofluonnation of alkenes also occurs in the gas phase, generally at somewhat higher temperatures [J]. Huoroethane is obtained m yields as high as 98% at 100 to 160 C by reaction in the presence of minor amounts of higher ot-olefms [6], and 2-fluoropropane is prepared in greater than 90% yield at <.80 "C from hydrogen fluonde and propene in the presence of activated carbon [7]... 

The irradiation of the thiophene in gas phase yields ethylene, allene, methyl-acetylene, carbon disulfide, and vinylacetylene. No Dewar thiophene or cyclo-propene derivatives were isolated (69CJC2965). The irradiation in liquid phase gave the Dewar thiophene which can be trapped as a Diels-Alder adduct with furan (85JA723). The Dewar thiophene and cyclopropene-3-thiocarbaldehyde can be obtained by irradiation in argon matrices at 10 K (86JA1691). 

Reaction conditions are generally mild, but they differ from one process to another. In the newer Unipol process (Eigure 12-1) used to produce both HDPE and LLDPE, the reaction occurs in the gas phase. Ethylene and the comonomers (propene, 1-butene, etc.) are fed to the reactor containing a fluidized bed of growing polymer particles. Operation temperature and pressure are approximately 100°C and 20 atmospheres. A single-stage centrifugal compressor circulates unreacted ethylene. The circulated gas fluidizes the bed and removes some of the exothermic reaction heat. The product from the reactor is mixed with additives and then pelletized. New modifications for gas-phase processes have been reviewed by Sinclair. ... 

B.S. Uphade, M. Okumura, S. Tsubota, and M. Haruta, Effect of physical mixing of CsCl with Au/Ti-MCM-41 on the gas-phase epoxidation of propene using H2 and02 Drastic depression of H2 consumption, Appl. Catal. A 190, 43-50 (2000). 

CO6-OO6I. Acrylonitrile is an important starting material for the manufacture of plastics and synthetic mbber. The compound is made from propene in a gas-phase reaction at elevated temperature ... 

Sketch plausible transition states for (a) the dissociation of a molecule in the gas phase (b) the reaction of cyclopropane to give propene (c) the isomerization of CH3CN to CH3NC (d) the desorption of an atom from a surface (e) the dissociation of an adsorbed molecule such as CO on a metal surface. 

Fig. 2 Quantification in the gas phase of 3,3-dimethylbutene and 4,4-dimethyl-2-pentene during propene metathesis (500 equiv.) catalyzed with 13(1 equiv.) at 25 °C...

Examples for necessary process improvements through catalyst research are the development of one-step processes for a number of bulk products like acetaldehyde and acetic acid (from ethane), phenol (from benzene), acrolein (from propane), or allyl alcohol (from acrolein). For example, allyl alcohol, a chemical which is used in the production of plasticizers, flame resistors and fungicides, can be manufactured via gas-phase acetoxylation of propene in the Hoechst [1] or Bayer process [2], isomerization of propene oxide (BASF-Wyandotte), or by technologies involving the alkaline hydrolysis of allyl chloride (Dow and Shell) thereby producing stoichiometric amounts of unavoidable by-products. However, if there is a catalyst... 

Last, McClain disclosed the gas phase hydroamination of ethylene and propene with NH3 over palladium on alumina (Eq. 4.4) [46]. 

Figure 5.11 Variation in the catalytic activity of an Mg(0001) surface when exposed to a propene-rich propene- oxygen mixture at room temperature. The surface chemistry is followed by XPS (a), the gas phase by mass spectrometry (b) and surface structural changes by STM (c, d). Initially the surface is catalytically active producing a mixture of C4 and C6 products, but as the surface concentrations of carbonate and carbonaceous CxHy species increase, the activity decreases. STM images indicate that activity is high during the nucleation of the surface phase when oxygen transients dominate. (Reproduced from Ref. 39).

A heterogeneous olefin epoxidation catalyst containing both V and Ti in the active site was prepared by sequential non-hydrolytic grafting. The silica was exposed first to VO(OiPr)3 vapor followed by Ti(0 Pr)4 vapor. Formation of propene is evidence for the creation of Ti-O-V linkages on the surface. Upon metathesis of the 2-propoxide ligands with BuOOH, the catalyst becomes active for the gas phase epoxidation of cyclohexene. The kinetics of epoxidation are biphasic, indicating the presence of two reactive sites whose activity differs by approximately one order of magnitude. 

Table 1. Absolute intensities A (IMECs) of different bands of propene in the gas phase and adsorbed in different cationic forms of Y zeolite.

Acetylene is sufficiently acidic to allow application of the gas-phase proton transfer equilibrium method described in equation l7. For ethylene, the equilibrium constant was determined from the kinetics of reaction in both directions with NH2-8. Since the acidity of ammonia is known accurately, that of ethylene can be determined. This method actually gives A f/ acid at the temperature of the measurement. Use of known entropies allows the calculation of A//ac d from AG = AH — TAS. The value of A//acij found for ethylene is 409.4 0.6 kcal mol 1. But hydrocarbons in general, and ethylene in particular, are so weakly acidic that such equilibria are generally not observable. From net proton transfers that are observed it is possible sometimes to put limits on the acidity range. Thus, ethylene is not deprotonated by hydroxide ion whereas allene and propene are9 consequently, ethylene is less acidic than water and allene and propene (undoubtedly the allylic proton) are more acidic. Unfortunately, the acidity of no other alkene is known as precisely as that of ethylene. 

One of the earliest measurements of the gas-phase equilibrium acidity of propene involved measuring the rates of reaction of propene with hydroxide ion in both directions33. The resulting equilibrium constant gave A//acid = 391 1 kcalmol-1. In the case of ethylene, the acidity and independently measured electron affinity of vinyl radical were used to determine the bond dissociation energy, a quantity difficult to obtain accurately by other means8. 

Fig. 48. Infrared difference spectrum recorded immediately after loading of 6.5 mbar propene gas into TS-1 molecular sieve containing TiOOH. Although the main peaks originate from adsorbed C3H6, the small shoulders of the bands at 1443,1646,2980, and 3081 cm-1 are attributed to gas-phase propene [Reprinted from Lin and Frei (133) with permission. Copyright (2002) American Chemical Society].

Cyclopropane isomerizes into propene when heated to 500°C in the gas phase. The amount converted at various times with various initial pressures has been followed by gas chromatography. In the table, t is in sec and pressures are in Torr. Find the rate equation. 

This is related to reaction (X) for propene, but for isobutene this process is unlikely because it involves formation of a 2-methylallyl ion and destruction of a tertiary ion in the gas phase this reaction would be highly endothermic [113] because the ionisation potential of the 2-methylallyl radical [114] is appreciably greater than that of the tertiary butyl radical [115], and the difference in the homolytic C—H bond dissociation energies is in the same... 

If photolyzed with light of the intensity I, HBr adds to propadiene (la) in the gas phase with a rate given by v=kexp[HBr]I<). This transformation affords within the detection limit (GC) 2-bromo-l-propene (5a) as sole reaction product (Table 11.1). The conversion of methyl-substituted allenes, such as lc and If, under these conditions follows the same kinetic expression [37]. Results from competition experiments indicate that the reactivity of an allene towards HBr increases progressively with the number of methyl substituents from propadiene (la) (= 1.00) to 2,4-dimethylpenta-2,3-diene (If) (1.65). In all instances, Br addition occurs exclusively at Cp to furnish substituted allyl radicals, which were trapped in the rate determining step by HBr. 

A second example of an inverse statistical weight isotope effect is that of the secondary H/D KIE on C-C bond rupture during the gas phase unimolecular isomerization of cyclopropane to propene. Theory and experiment are compared in Fig. 14.2 for reactions 14.37 and 14.38. 

A. Zwijnenburg, M. Saleh, M. Makkee, and J. A. Moulijn, Direct gas-phase epoxidation of propene over bimetallic Au catalysts, Catal. Today 72(1—2), 59—62 (2002). 

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