Propyl dehydrogenation

A kinetic model of DHP over a commercial Pt-Sn/Al203 catalyst was obtained by Faijoo et al. (2011). The temperature used in this study was 580-620 °C and a iaxed H2/C3Hg molar ratio of 0.8 was used. Four L-IT models were developed by assuming dissociative adsorption of propane or propyl dehydrogenation as the RDS. The L-Fl model (see Table 2.4) with the dissociative adsorption of propane as RDS provided the best agreement with experimental data. 

If the propyl dehydrogenation (2.6) was determined to be the RDS, the rate expression became... 

An important structure property of the Pt catalyst for DHP is the particle size. It is beheved that the surface is mostly terminated by steps and edges on smaller particles, while the surface is mosdy terminated by terraces and planes on larger particles (Van Hardeveld and Hartog, 1969). As shown in Table 2.2, the energy barrier for both propane and propyl dehydrogenation on Pt(l 11)... 

The modeling results were summarized in Table 2.10. It can be seen that the RDS of DHP over Pt-Sn catalyst was propane dehydrogenation (Eq. 2.24) instead of propyl dehydrogenation (Eq. 2.25). The adsorbed H was the most abundant surface species. 

Worldwide propylene production and capacity utilization for 1992 are given in Table 6 (74). The world capacity to produce propylene reached 41.5 X 10 t in 1992 the demand for propylene amounted to 32.3 x 10 t. About 80% of propylene produced worldwide was derived from steam crackers the balance came from refinery operations and propylene dehydrogenation. The manufacture of polypropylene, a thermoplastic resin, accounted for about 45% of the total demand. Demand for other uses included manufacture of acrylonitrile (qv), oxochemicals, propylene oxide (qv), cumene (qv), isopropyl alcohol (see Propyl alcohols), and polygas chemicals. Each of these markets accounted for about 5—15% of the propylene demand in 1992 (Table 7). 

Other typical reactions of carbenium ions are alkene loss, provided sufficient chain length is available (Chap. 6.6.1), and dehydrogenation in case of the smaller ions such as ethyl, propyl, or butyl ion (Chap. 6.2.4.). 

Styrene is produced by the catalytic vapor phase dehydrogenation of ethylbenzene. Ethylbenzene is made by the Friedel-Crafts condensation of ethylene and benzene. Styrene is also produced by the palladium acetate-catalyzed condensation of ethylene and benzene and by the dehydration of methylphenylcarbinol obtained by the propylation of ethylbenzene. Because of the toxicity of styrene, its concentration in the atmosphere must be severely limited. 

The behavior of ethane is different from the other alkanes. It is the only alkane that undergoes significant dehydrogenation on the VPO catalyst, as well as the only one for which combustion is the predominant reaction on VMgO. However, an ethyl species is too small to interact with two V ions simultaneously on any of the three catalysts. A phenomenological explanation of this behavior of ethane has been suggested [10]. In this explanation, the possible reactions of ethyl, propyl, and 2-methylpropyl species were compared by statistically counting the number of various types of bonds in each species ... 

Desaturation of alkyl groups. This novel reaction, which converts a saturated alkyl compound into a substituted alkene and is catalyzed by cytochromes P-450, has been described for the antiepileptic drug, valproic acid (VPA) (2-n-propyl-4-pentanoic acid) (Fig. 4.29). The mechanism proposed involves formation of a carbon-centered free radical, which may form either a hydroxy la ted product (alcohol) or dehydrogenate to the unsaturated compound. The cytochrome P-450-mediated metabolism yields 4-ene-VPA (2-n-propyl-4pentenoic acid), which is oxidized by the mitochondrial p-oxidation enzymes to 2,4-diene-VPA (2-n-propyl-2, 4-pentadienoic acid). This metabolite or its Co A ester irreversibly inhibits enzymes of the p-oxidation system, destroys cytochrome P-450, and may be involved in the hepatotoxicity of the drug. Further metabolism may occur to give 3-keto-4-ene-VPA (2-n-propyl-3-oxo-4-pentenoic acid), which inhibits the enzyme 3-ketoacyl-CoA thiolase, the terminal enzyme of the fatty acid oxidation system. 

The difference between propane and 2-methy]propane on Mg2V207 cannot be explained by the size of the C3 chain. It is then proposed that although with difficulties, a C3 species still has a finite probability to interact with both vanadium ions in a V207 unit in the catalyst to lead to the formation of combustion products. This probability is twice as large for 2-methylpropene (or 2-methylpropyl) than propene (or propyl), which may account for the lower selectivity for dehydrogenation for 2-methylpropane on this catalyst. 

In some cases, the reaction of silicon and methanol has been optimized for formation of (MeO)4Si. As discussed above, thiophene addition favored formation of (MeO SiH. Both thiophene and propyl chloride poison copper copper poisoning seems to favor formation of the trialkoxysilane. High-temperature pretreatment disfavors trialkoxysilane formation copper is formed on the surface of the silicon during pretreatment at 450 °C98. Metallic Cu catalyzes dehydrogenation of alcohols and favors formation of (RO)4Si. Workers from Tonen Corporation reported 50% conversion of silicon to make (MeO Si with 92% selectivity if silicon, methanol and Cu(OMe)2 were pretreated (lower conversion and selectivity without pretreatment) and then reacted at 180 °C and 1 atmosphere99. 

Acetone is made from Ao-propyl alcohol by either dehydrogenation (preferred) or air oxidation. These are catalytic processes at 500°C and 40 to 50 psi. The acetone is purified by distillation, boiling point 56°C and the conversion per pass is 70 to 85 percent, with the overall yield being in excess of 90 percent. 

Figure 5. Separation of C,4 C,- alkylbenzenes and o-dialkylbenzenes obtained4from dehydrogenation of n-alkanes in columns with Carbowax 2CM and MEAB l=l-butyl-2-butylbenzene, 2=l-propyl-2-pentylbenzene 3=i-ethyl-2-hexylbenzene, 4=l-methyl-2-heptylbenzene, 5=n-octylbenzene 6=l-butyl-2-pentylbenzene, 7=l-pro-pyl-2-hexylbenzene 8=l-etyl-2-heptylbenzene, 9=l-me-thyl-2-oktylbenzene, 10=n-nonylbenzene, ll=l-pentyl-2-pentylbenzene, 12=l-butyl-2-hexylbenzenev 13=l-pro-pyl-2-heptylbenzene, 14=l-ethyl-2-octylbenzene, 15=1-methyl-2-nonylbenzene, 16=n-decylbenzene, 17=l-pentyl-2-hexylbenzene, 18= 1-butyl-2-heptylbenzenev 19=l-pro-pyl-2-octylbenzene, 20= l-ethyl-2-nonylbenzene, 21=1-methyl-2-decylbenzene, 22=n-undecylbenzene ...

Aromatization of short alkanes can be carried out on a purely acidic HZSM-5 zeolite. In this case, activation of the alkane is thought to occur by protonation on the zeolite acid sites, with formation of a penta-coordinated carbonium ion (1). In the case of propane, protonation at a C-H bond will lead to the formation of H2 and a sec-propyl cation (dehydrogenation), while protonation at a C-C bond will produce methane and a primary ethyl cation (cracking) ... 

To 2-methyl-2-imidazoline (0.5 g, 5.95 mmol) dissolved in dry dioxane (15 ml) under nitrogen is added, in small portions with stirring, potassium permanganate (1.5 g, 9.5 mmol). The mixture is then refluxed (12 h), allowed to cool to room temperature, and filtered through Celite. The filtrate is evaporated under reduced pressure to a yellowish solid, which is recrystallizcd from toluene (0.352 g, 72%), m.p. 140-142°C. Similar dehydrogenations of the 2-ethyl-and 2-propyl-2-imidazolines were accomplished with 48 and 50% efficiencies, respectively. 

Kassahun, K., Baillie, T. A. Cytochrome P-450-mediated dehydrogenation of 2-n-propyl-2(E)-pentenoic acid, a pharmacologically active metabolite of valproic acid in rat liver microsomal preparations. Drug Metab. Dispos. 1993, 21, 242-248. 

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