Cyclohexenes, conversion

Cyclohexene, conversion to cyclopen-tanecarboxaldehyde, 44, 26 purification of, 41, 74 reaction with zinc-copper couple and methylene iodide, 41, 73 Cyclohexene oxide, 44, 29 2-Cyclohexenone, 40,14 Cyclohexylamine, reaction with ethyl formate, 41,14... 

After reduction, Pd nanoparticles in the range of 5.2 nm were obtained. Particle size could be controlled by the ratio of -OH groups to Pd. Hydrogenation of cyclohexene in toluene gave a TON of 20 000 corresponding to a TOP of 700 h atm(H2) at 75% cyclohexene conversion. The catalyst was easily separated from the product by vacuum distillation and/or dialysis or membrane filtration [76]. 

Catalysts tor epoxidation" Ti (wt%) (pretreatment) Cyclohexene conversion (%)" Epoxide selectivity Epoxide TON... 

Addition of benzene in methanol to an excess (25-100%) of sodium in liquid ammonia afforded 84-88% yields of 1,4-cyclohexadiene [392]. o-Xylene under the same conditions gave 70%-92% yield of 1,2-dimethyl-1,4-cyclohexadiene [392, 395]. Lithium in neat ammonia at 60° gave 91% of 1,4-cyclo-hexadiene and 9% of cyclohexene (conversion 58.4%), while calcium under the same conditions yielded 21% of cyclohexadienes and 79% of cyclohexene in conversions of 13-60% [393]. If benzene dissolved in ether was added to the compound Ca(NH3)s, preformed by dissolving calcium in liquid ammonia and evaporating ammonia, a 75% conversion to pure cyclohexene was achieved [394]. 

In a recent study, Xu et al. managed to lower temperatures to 100 °C by using gold catalyst and oxygen as oxidant. The authors compared the Au/C catalyst and supported Pd or Pt catalysts, and concluded that these systems offered similar performance and that selectivity generally depended on cyclohexene conversion [226]. 

Gaseous Reactant, Composition, mole % Cyclohexene Cyclohexene, Conversion ... 

Moreover, this catalytic reaction could be employed in a continuously operated membrane reactor [105,106]. A stirred membrane reactor module equipped with a solvent-stable Koch MPF-50 membrane [107] was operated at 40 atm. After exchange of a few reactor volumes a steady conversion is achieved, e.g., 30% cyclohexene conversion for the example shown in Fig. 9 [32], corresponding to a catalytic activity of 1200 TO h 1. Over 30 exchanged reactor volumes, corresponding to a time of operation of 30 h, a productivity of a total of 29 000 turnovers was observed. 

The cyclohexene conversion to paraffins and olefins which is well known as the Hydrogen Transfer Index (HTl) ratio was used to evaluate the catalytic activity of the fi sh and deactivated materials at constant conversion (30 mol %) varying the contact time and at 250°C. The HTl results were related with the REO content, cell parameter and total acidity and are plotted in figures 5,6 and 7, respectively. 

Titanium framework-substituted aluminophosphate, TAPO-5, gave a 30.3% selectivity to AA at total cyclohexene conversion, in 72 h reaction time at 80 °C [35c]. However, when the filtered TAPO-5 catalyst was reused its activity was significantly diminished. The major by-product was 1,2-cyclohexanediol, which is formed as reaction intermediate. The trans isomer was more slowly transformed into 2-hydroxycyclohexanone than the cis isomer. A detailed investigation of the mechanism indeed showed that the trans-diol formed by ring opening of the cyclohexene epoxide, whereas the cis isomer formed via a free-radical mechanism. Scheme 7.14 shows the mechanism proposed. 

Following the generation of initial reactive surface species from hydrocarbon feedstocks the product distribution is largely governed by the balance of moncroolecular processes such as isomerisation and Beta scission and bimolecular processes (for example oligomerisation and bimolecular hydrogen transfer). A measure of the relative contribution of bimolecular versus monomolecular carbenium-ion like processes can be provided from the distribution of products from cyclohexene conversion... 

Figure 3 shows the effect of feed tenperature on the axial temperature profile. In all these cases, the cyclohexene conversion is 80% with total selectivity toward cyclohexene. The hot spot tenq)erature in the bed increases proportionally to the feed temperature and does not show any runaway tendencies. This is... 

Fig. 2. Cyclohexene conversion as a function of Hexene-1 conversion at identical conditions.

Initial experiments were done in water and resulted in low cyclohexene conversions, low product selectivities, and extensive palladium deactivation by Pd black formation. The low cyclohexanone yield originated from overoxidation of cyclohexanone to 2-cyclohexenone, which undergoes further oxidation to a plethora of by-products. The low cyclohexene conversion can be attributed to the aforementioned low reactivity of the internal double bond as well as the low solubility of cyclohexene in water. Several reaction media have been described in which higher alkenes are oxidized to ketones in organic solvent-based systems. Some typical examples are DMF [4], water mixtures with chlorobenzene, dodecane, sulfolane [5], 3-methylsulfolane andM-methylpyrrolidone [6], or alcohols [7]. These solvent systems indeed lead to increased cyclohexene conversions but still suffer from overoxidation and catalyst deactivation by Pd black formation. Hence, the goal of our research was to find a variation to the Wacker oxidation without over-oxidation of the product and deactivation of the palladium catalyst. 

A measure of the relative contribution of bimolecular verses monomolecular carbenium-ion-like processes can be provided from the distribution of products from cyclohexene conversion [54]. This is evident from Scheme 5. 

More information was obtained by direct analysis of the coke components recovered after dissolution of the zeolite in hydrofluoric acid solutions. Thus during cyclohexene conversion on USHY at 350 C the coke was totally soluble in methylene chloride and composed of alkyl pyrenes and alkylnaphtenopyrenes [8]. At 450 0 only 40 % of coke was soluble in methylene chloride, 60 % appearing as black particles constituted of highly polyaromatic compounds. Soluble coke contained alkylcyclopentapyrenes and alkylindenopyrenes. The composition of coke formed from propene [7] in the same conditions was practically identical. In contrast the coke formed from 1-hexene on HZSM5 at 320°C contained mainly alkylindanes and alkylnaphtalenes [42]. 

Fig. 2. Effect of reaction temperature on cyclohexene conversion when using catalysts fresh (A) spent (B) decoked before (D) and after (E) leached by 2%.

Figure 10.5 (a) Cyclohexene conversion and (b) benzene selectivity versus mean residence time [27]. 

Figure 10.7 Effect of temperature on (a) cyclohexane (solid symbols) and benzene selectivity (open symbols) and (b) cyclohexene conversion.

Fig. 12. Comparison of temporal cyclohexene conversion and cyclohexane selectivity profiles with 180 ppm and <6 ppm of organic peroxides in feed T = 343 K, P = 13.6 MPa, OWHSV = 20h-i (49).

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