Oxidation 1-hexene, catalytic

Figure 4. Catalytic oxidation of cis-2-hexene [Pd/OAcje] = 0.00162M, [cis-2-hexene] =0.316M...

Fig. 60. Correlations between catalytic activity and oxidizing ability for (a) oxidation of acetaldehyde (surface reaction) and (b) oxidative dehydrogenation of cyclohexene (bulk-type 11 reaction). (From Ref. 327.) r(aldehyde) and r(hexene) show the rates of catalytic oxidation of acetaldehyde and oxidative dehydrogenation of cyclohexene, respectively. (From Ref. 337.) r( CO) is the rate of reduction of catalysts by CO r(H2) is the rate of reduction of catalysts by H2. M, denotes M,H3-,PMO 2O40. Na2-1, 2, 3, and 4 are Na2HPMoi2O40 of different lots, of which the surface areas are 2.8, 2.2, 1.7, and 1.2 m2 g, respectively.

As mentioned above, catalytic oxidation of olefins via coordination catalysis with an intermediate such as LnM (olefin) 02 seemed an attractive possibility, and Collman s group (45) tentatively invoked such catalysis in the 02-oxidation of cyclohexene to mainly 2-cyclo-hexene-1-one promoted by IrI(CO)(PPh3)2, a complex known to form a dioxygen adduct. Soon afterwards (4, 46, 47) such oxidations involving d8 systems generally were shown to exhibit the characteristics of a radical chain process, initiated by decomposition of hydroperoxides via a Haber-Weiss mechanism, for example Reactions 10 and 11. Such oxidations catalyzed by transition-metal salts such as... 

Figure 6. Correlations between catalytic activity and oxidizing ability (a) oxidation of acetaldehyde (surface type) and surface oxidizing ability (b) oxidative dehydrogenation of cyclohexene (bulk type) and bulk oxidizing ability [4, 38] (/(aldehyde) and /(hexene) are the rates of catalytic oxidation of acetaldehyde and cyclohexene, respectively).

The catalytic dehydrogenation of 1-butene gives 1,3-butadiene,12 which can be dimerized to 4-vinyl-1-cyclo-hexene by a copper(I)-containing zeolite, with over 99% selectivity.13 This material is converted to styrene by catalytic oxidation with oxygen in the presence of steam... 

The following figure shows data on the catalytic oxidation of 1-hexene at three different gas flow rates using a single screen. At a fixed fl ow rate, the fractional conversion of hexene increases rapidly with the temperature of the feed gas when the temperature is low. However, at temperatures greater than about 420 °C, conversion is virtually independent of temperature. 

In the stoichiometric ADH of ( )-3-hexene the highest ee was achieved using the ligand 4b (88% ee). On the other hand, the catalytic process (Table 10.4, entries 1-3) was carried out by slow addition of ( )-3-hexene (1 equiv.) to a mixture of 4a (0.25 equiv.), A-methylmorpholine A-oxide (NMO, 1.5 equiv.) and OSO4 (0.004 equiv.) in acetone-water (10/1, v/v) at 0 °C, followed by working-up with Na2S205. Although the catalytic reaction was slow and required a slower addition... 

In order to assess whether intramolecular cooperativity could occur within the dendrimeric [Co(salen)]catalyst the HKR of racemic l-cyclohexyl-l,2-ethenoxide was studied at low catalyst concentrations (2xl0 " M). Under these conditions the monomeric [Co(salen)] complex showed no conversion at all, while the dendritic [G2]-[Co(salen)]catalyst gave an impressive enantiomeric excess of 98% ee of the epoxide at 50% conversion. Further catalytic studies for the HKR with 1,2-hexen-oxide revealed that the dendritic catalysts are significantly more active than a dimeric model compound. However, the [Gl]-complex represents already the maximum (100%) in relative rate per Go-salen unit, which was lower for higher generations [G2] (66%) and [G3] (45%). 

A chiral dinuclear Ti(IV) oxide 20 has been successfully designed by Maruoka and coworkers and can be used for the strong activation of aldehydes, thereby allowing a new catalytic enantioselective allylation of aldehydes with allyltributyltin (Scheme 12.18). ° The chiral catalyst 20 can be readily prepared either by treatment of bis(triisopropoxy)titanium oxide [(/-Pr0)3Ti-0-Ti(0/-Pr)3] with (S)-BINOL or by the reaction of ((5)-binaphthoxy)isopropoxytitanium chloride with silver(I) oxide. The reaction of 3-phenylpropanal with allyltributyltin (1.1 equiv) under the influence of 20 (10 mol%) gives l-phenyl-5-hexen-3-ol... 

Lee and coworkers have reported on the use of the highly active and selective cobalt(III) catalyst depicted in Fig. 12 for the terpolymerization of propylene oxide and various epoxides with CO2, including cyclohexene oxide, 1-hexene oxide, and 1-butene oxide [61]. Catalytic activities ranged from 4,400-14,000 h at a CO2... 

Several preparation methods have been reported for the synthesis of TS-1. In this work, we have investigated the physicochemical properties of TS-1 samples synthesized by different preparation metiiods and tested these materials as catalysts for the oxidation of n-octane, 1-hexene and phenol using aqueous hydrogen peroxide (30 wt%) as oxidant at temperatures below 100 C. For comparison, Ti02 (anatase) and the octahedral titanium-containing silicate molecular sieve (ETS-10) (5) have been studied. The effect of the presence of aluminum and/or sodium on the catalytic activity of TS-1 is also discussed. 

It is now possible to understand the curious phenomenon whereby the reaction of palladium acetate with I in vacuo first rapidly produces a metal precipitate and then slows at about 20% conversion and finally stops with much of the palladium (II) unreacted. These stages in the reaction correspond to oxidation first by Pd3(OAc)6 and then by IVa with ultimate formation of the inert species Va. A complex mixture of hexenyl acetates is formed in the oxidation of which the major constituent l-hexen-2-yl acetate (VI) is 0.68 mole fraction of the whole mixture. Overall the mixture is closely similar to that obtained in the catalytic reactions of 02 described later, suggesting that the same active palladium-containing species is involved. Much of I is isomerized to a 5 1 mixture of trans- and ds-2-hexene (85% at 6 hrs) with only 3% each of the 3-hexene isomers. This aspect of the selectivity problem in which only one shift of the double bond takes place is also reproduced in the catalytic reaction, but oxygen suppresses the rate of isomerization relative to oxidation. 

However the catalyst can be easily reactivated in flow of o2/Ar at 350°C (compare runs 2 and 2.1, Table 1) using the procedure reported in the previous section. Catalytic activity can be restored also by a thermal treatment in flow of He (350°C, 15 h), and this suggests that strongly adsorbed produts could be responsible for catalyst deactivation. The amount of 4-hexen-3-one converted depends on the nature of the catalyst precursor and on its thermal pretreatment. Thus, over a non activated commercial Mgo (obtained by thermal decomposition of MgC03, surface area 17 m2/g), 0.5 moles of 4-hexen-3-one/mole Mgo are converted, while when the same Mgo was activated at 350°C (surface area 34 m2/g), 2 moles of 4-hexen-3-one/mole MgO are converted. Over a high surface area Mgo (prepared by thermal decomposition of Mg(OH)2r surface area 281 m2/g) up to 5 moles of 4-hexen-3-one/mole Mgo can be converted. Conversion of 4-hexen-3-one depends also on reaction temperature 250°C is found to be the best one, since both at higher and lower temperatures side reaction are favoured (runs 2.2 and 2.3, Table 1). Since different oxides were employed, the product distributions reported in Table 1 were measured in stationary conditions after 1 hour of reaction. 

Despite the presence of sites that strongly chemisorb a variety of molecules, pure silica gel is catalytically inactive for skeletal transformations of hydrocarbons. However, as has recently been emphasized by West et al. (79), only trace amounts of acid-producing impurities such as aluminum need be present in pure silica gel to provide catalytic activity— especially when a facile reaction such as olefin isomerization is used as a test reaction. They found that addition of 0.012% Al to silica gel resulted in a 10,000-fold increase in the rate of hexene-1 isomerization at 100°C over the pure gel. An earlier study by Tamele et al. (22) showed that introduction of 0.01% wt Al in silica gel produces a 40-fold increase in cumene conversion when this hydrocarbon is cracked at 500°C. The more highly acidic solids that are formed when substantial concentrations of metal oxides are incorporated with silica are discussed in following sections. 

Although the catalytic properties of titanosilicates are related to their crystalline structures and/or characters, the hydrophilicity caused by the presence of more defect sites in titanosilicates would be unfavorable for the oxidation of hydrocarbon reactants, as suggested by the following facts (1) compared with TS-1, Ti-MWWand Ti-beta with more defect sites showed very low activity for the oxidation of hexane, styrene and benzene (2) Ti-MCM-41, with a low Q4/Q3 ratio, showed very low activity in the oxidation of hexane and 1-hexene however, silylation resulted in a remarkable... 

Figure 4.3 Catalytic results of the oxidation of various organic substrates over the YNU-20 and A-50 catalysts. H202 based conv. (%) the percent used for the oxidation of substrates. Reaction conditions for 1-hexene, 0.05 g catalyst, 10 mL methanol, 10 mmol substrate, 10 mmol H202, 60°C, 2 h for n-hexane, 0.1 g...

Large-pore titanosilicates developed after TS-1, for example, Ti-beta, Ti-ITQ-7, Ti-MCM-41 and Ti-MCM-48, have been claimed to have advantages for the oxidation of bulky alkenes because of their pore size [15-17, 66, 67]. However, none of them is intrinsically more active than TS-1 in the reactions of small substrates that have no obvious diffusion problem for the medium pores. Therefore, in parallel with developing large pore titanosilicates, the search for more intrinsically active ones than TS-1 is also an important research subject. The catalytic performance of Ti-MWW is compared in the oxidation of 1-hexene with H202 with that of TS-1 and Ti-beta. Consistent with the results reported elsewhere [15-17], TS-1 showed higher conversion than Ti-beta with a similar Ti content. However, Ti-MWW exhibited activity about three times as high as TS-1 based on the specific conversion per Ti site (TON). 

It has long been known that acetonitrile should be the solvent of choice for the oxidation of 1 -hexene over Ti-beta and Ti-MWW while methanol is preferred by TS-1. In contrast, for cyclohexene oxidation, methanol is favorable for Ti-beta, whereas acetonitrile is the best for TS-1 and Ti-MWW. The effect of hydrophilicity/hydropho-bicity is demonstrated by a series of catalytic results, but this can not interpret the solvent effect on the oxidation of cydohexene over Ti-beta. 

It has also been shown that the catalytic activity can be enhanced when appropriate amounts of mixed solvents are present in the oxidation system, compared to a single solvent [98]. In particular, converse results are obtained when the same titanosilicate is used for catalyzing the oxidation of 1-hexene and cyclohexene. Thus, further insight into the solvent effect is required. 

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