Isomerization catalyst effect

The catalytic isomerization of 1-methylnaphthalene and all lation of 2-methylnaphtha-lene with methanol were studied at ambient pressure in a flow-type fixed bed reactor. Acid zeolites with a Spaciousness Index between ca. 2 and 16 were found to be excellent isomerization catalysts which completely suppress the undesired disproportionation into nwhthalene and dimethylnaphthalenes due to transition state shape selectivity. Examples are HZSM-12, H-EU-1 and H-Beta. Optimum catalysts for the shape selective methylation of 2-methylnaphthalene are HZSM-5 and HZSM-li. All experimental finding concerning this reaction can be readily accounted for by conventional product shape selectivity combined with coke selectivation, so there is no need for invoking shape selectivity effects at the external surface or "nest effects", at variance with recent pubhcations from other groups. 

The photochemical cis trans isomerization is effected by direct irradiation or in the presence of a sensitiser or a catalyst. 

Mechanism. The proven acidity of the effective alkane isomerization catalysts suggests that carbocations are involved in acid-catalyzed alkane isomerization. Such a mechanism was first proposed by Schmerling and coworkers54 on the basis of the pioneering ideas of Whitmore55 for the skeletal isomerization of alkanes and cycloalkanes in the presence of aluminum chloride and a trace of olefin or other promoter. Subsequently these concepts were used to explain the mechanism of the acid-catalyzed isomerizations in general. 

In the Phillips neohexene process147 2,4,4-trimethyl-2-pentene (8) is converted by cleavage with ethylene to neohexene (9) used in the production of a perfume musk. The starting material is commercial diisobutylene. Since it is a mixture of positional isomers (2,4,4-trimethyl-2-pentene and 2,4,4-trimethyl-l-pentene) and the latter (7) participates in degenerative metathesis, effective utilization of the process requires the isomerization of 7 into 8. A bifunctional catalyst system consisting of an isomerization catalyst (MgO) and a heterogeneous metathesis catalyst is employed 131... 

The possibility that isomerization may effect the selectivity is important to note. A convenient method of removing 1,9-octalin from a mixture of the 1,9- and the 9,10-octalins is to hydrogenate the mixture over a Pt catalyst. Pd is ineffective because it is more active than Pt in catalyzing the interconversion of the isomers, eqn. (5) (procedure suggested by Hussey given in ref. 30). 

The Rh-BINAP catalysts are very sensitive to impurities such as oxygen, moisture, and carbon dioxide. If an excess of water ([H20]/[Rh] = 15) is present in the reaction mixture, the isomerization is stopped aftera few turnovers with precipitation of air-stable red-brown crystals, which were found to be [ Rh(BINAP) 3()I3-0H)2 C104. X-Ray analysis of this complex (H20 was replaced by DzO) revealed a unique structure of a triangular Rh3 core capped with two triply bridging OH groups (Fig. 3.1). This Rh(I)-trinuclear complex was totally inactive as an isomerization catalyst, which suggests a catalyst deactivation mechanism [12], The effect of several additives on the isomerization of 2 with [Rh(BINAP)(COD)]+ has been examined, and the results are summarized in Table 3.3. 

It has been observed that rapid isomerization accompanies the cobalt carbonyl-catalyzed hydrosilation of olefins (18). The reaction of equimolar amounts of a trisubstituted silane and dicobalt octacarbonyl has been shown to result in the formation of cobalt hydrocarbonyl (cf. Section IV). A very effective isomerization catalyst may be prepared by treatment of a solution of Co2(CO)8 in olefin ( 0.01 M) with a silicon hydride in sufficient quantity to slightly exceed the cobalt carbonyl concentration. 

Carrying the analogy between the photochemistry of Fe(C0)ij and Fe(C0)3[l,4-Me2N4] one step further we note that both compounds (25,26) behave as photoassisted olefin hydrosilation and isomerization catalysts. One distinction between the two catalyst systems is the latter (26) operates effectively with long wavelength radiation, Table II. Hydrosilation activity requires continuous photolysis ... 

We examined the ability of our bis-imidazole cyclodextrin artificial enzymes to perform other bifunctionally-catalyzed reactions, where again the availability of the A,B and A,C and A.D isomers let us learn mechanistic details. As an important example, we examined three isomeric catalysts ability to promote the enolization of substrate 48, which binds into the cyclodextrin cavity in water [138]. Here there was again a strong preference among the isomers, but it was the A,D isomer 49 that was the effective catalyst It was also more effective than a cyclodextrin mono-imidazole that cannot use the bifunctional mechanism. 

Isomerization/cyclization of ct-dienyl-to-allyl acetates (carbonates). This Pd catalyst effects isomerization and cyclization of these substrates to vic-disubsti-... 

Both decay processes are due to minor side reactions of some of the same carbenium ions as those propagating the "fhiitful" reactions of cracking and isomerization. Their effects combine to yield an equation for the kinetics of catalyst decay which can be anywhere from first to second order in site concentration. In practice, small molecules of the type studied as model compounds generally exhibit almost pure second-order decay in site concentration, while the large molecules found in gas oils tend to show a lower kinetic order, often approaching first-order decay. 

A special case of a transannular cycloisomerization occurs with the ethyl acrylate derivative 22. lO a.b Nickel(O), as well as palladium(O), catalysts effect this reaction in generally high yields, leading to the formation of the [3.3.3]propellane derivative 23. Even in the nickel(0)-catalyzed reaction, no isomeric compound arising from proximal cleavage of the methylenecyelopropane is formed, presumably due to activation of the distal bond arising from the tetrasubstitution of the methylene group. 

Aluminum halide catalysts are not effective isomerization catalysts for hydrogenated chlorofluorocarbons because of HCl elimination to form alkenes which are catalyst poisons. HF elimination from hydrofluorocarbons is not as facile, thus AIF3 [63] and AIClxF, 02 (x + y + 2z = 3) [64] are effective catalysts for the isomerization of 134 to 134a (eq 13). 

ISOMERIZATION OF FISCHER-TROPSCH PRODUCT The conditions for operating the tungsten isomerization catalyst are compatible with the composition of the exit stream from a Fischer-Tropsch reactor. The presence of unreacted hydrogen and water vapour together with CO and C02 provides an effective oxygen partial pressure equivalent to that required by the isomerization catalyst. 

Experiments were designed to investigate whether a catalyst inactive for 1-butene isomerization could effectively isomerize 1-pentene and also to determine the level of 1-butene isomerization for a catalyst that has been... 

Cycloaromatization. These catalysts effect isomerization/cyclization of conjugated... 

Numerous catalysts that are used for hydrogenation or hydroformyla-tion are also active isomerization catalysts. These catalysts require the presence of hydrogen to be activated, probably to form a metal hydride. Carbonyls of cobalt, iron, and osmium are activated in this manner and effect hydrogen shifts. 

In the case of isomerization which proceeds according to the 7c-allyl mechanism, 1,3-hydrogen transfer takes place. These reactions are catalyzed by palladium(II) complexes which easily form 7r-allyl complexes from 7r-olefin compounds. Also, compounds of nickel, rhodium, iron, etc., are utilized as catalysts. Effective isomerization is possible if the hydrogen addition to both terminal carbon atoms of the 7r-allyl asymmetric grouping takes place. 

Zhang, A., Nakamura, I., Fujimoto, K. (1995). Isomerization of n-pentane and other light hydrocarbons on hybrid catalyst, effect of hydrogen spillover. Industrial and Engineering Chemistry, 34, 1074. 

Masuda, T. Izunukawa, H. Misumi, Y Higashimura, T. Stereospecific polymerization of reri-butylacetylene by molybdenum catalysts. Effect of acid-catalyzed geometric isomerization. Macromolecules 1996, 29,1167-1171. 

For most of applications, it is required to purity BPA from the mentioned byproducts before its further processing. Therefore, the BPA production line consists of a condensation reactor and the units responsible for the BPA purification. Among them, there is usually a unit for crystallization of the BPA-phenol adduct and stripping tower, where the adduct is cracked and phenol is recovered (as it was described earlier). There are also a recrystallization unit, a cracker for the o,p-isomers of BPA and a wastewater treatment facility. Additionally, there may be an isomerization unit, where the mother liquor is contacted with an acidic or amine-based ion-exchange resin as the isomerization catalyst under the conditions effective to convert the BPA byproducts to BPA. Next, the effluent from the isomerization zone can be contacted with a solid particle guard bed, composed of alumina, titanium oxide, silica, zirconium oxide, tin oxide, charcoal or silicon carbide [55]. This guard... 

Inspection of the formulas of an epoxide and cyclic anhydride side by side reveals that an equimolecular mixture has the elemental composition of a polyester. Only a catalyst is needed to isomerize, in effect, such a mixture to a linear polyester. In such a plymerization, both epoxide and anhydride must be strictly bifunctional toward each other. Careful studies of the uncatalyzed reaction have been made by Fisch and Hoffman [80,81], who showed that some epoxide homopolymerization occurs. This gives systems in which the anhydride is only 0.5 to 0.85 mol per mol of epoxide. 

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