Orthovanadate catalyst

Synthesis from Linalool. A 96% pure synthetic geraniol prepared by isomerization of linalool has become commercially available. Orthovanadates are used as catalysts, to give a >90% yield of a geraniol nerol mixture [31]. Geraniol of high purity is finally obtained by fractional distillation. 

Synthesis from Dehydrolinalool. Dehydrolinalool is produced on a large scale from 6-methyl-5-hepten-2-one and acetylene and can be isomerized to citral in high yield by a number of catalysts. Preferred catalysts include organic orthovanadates [55], organic trisilyl oxyvanadates [56], and vanadium catalysts with silanols added to the reaction system [57]. 

Another important use of a-pinene is the hydrogenation to ttf-pinane (21). One use of the oy-pinane is based on oxidation to as- and /tt .f-pinane hydroperoxide and their subsequent catalytic reduction to as- and // J/w-pinanol (22 and 23) in about an 80 20 ratio (53,54). Pyrolysis of the r/r-pinanol is an important route to linalool overall the yield of linalool (3) from a-pinene is about 30%. Linalool can be readily isomerized to nerol and geraniol using an orthovanadate catalyst (55). Because the isomerization is an equilibrium process, use of borate esters in the process improves the yield of nerol and geraniol... 

The catalysts based on vanadium oxide are one of the better studied systems. A V-Mg oxide in which Mg orthovanadate (Mg2(V04)2) and MgO were the only identifiable phases was a rather selective catalyst (27). Since MgO was relatively inactive in alkane activation, Mg orthovanadate was assumed to be the active component. Indeed, Mg orthovanadate prepared as a stoichiometric compound showed high selectivities for the oxidative dehydrogenation of propane (29). In this latter study, it was shown interestingly that Mg orthovanadate was the only alkali or alkali earth orthovanadate that... 

Mg pyrovanadate (Mg2V207) was also found to be a selective catalyst for this reaction (30). A later study further showed that the catalytic performance of Mg2V207 was insensitive to the method of preparation, such that there were only minor differences whether or not the oxide contained small amounts of potassium (25). In contrast, the presence of K in Mg orthovanadate degraded its selectivity noticeably. Temperature-programmed reduction with H2 and electrical conductivity characterization in the presence of propane showed that Mg pyrovanadate could be reduced by both H2 and propane faster than Mg orthovanadate containing K (31). 

The performance of the V-Mg oxide catalyst was found to depend on its composition and the method of preparation. As to the composition, it was found that catalysts containing very small or very large amounts of vanadium were not selective. The better catalysts in terms of both activity and selectivity consisted of from about 10 to 60 wt% V2O5 (35). Analyses of these catalysts by X-ray diffraction, Auger electron spectroscopy, and infrared spectroscopy showed that they contained only two identifiable phases Mg orthovanadate (Mg3(V04)2) and MgO. Since MgO had low activity and poor selectivity under the reaction conditions employed, it was concluded that the active phase was Mg orthovanadate (Mg3(V04)2). Indeed, it was later shown that this compound was a selective catalyst (26). 

The pulse experiments using orthovanadates and V/y-AFCb catalysts showed that high selectivity for dehydrogenation of butane could be obtained by reaction of butane with lattice oxygen. This has also been demonstrated with other oxides, including Mg-Mo oxide (43, 44). 

Preparation. The catalyst can also be prepared in situ from tri-n-propyl orthovanadate and triphenylsUanol (Arapahoe). ... 

Propane conversions and propene selectivities over rare-earth orthovanadates (La, Pr, Yb, Er, Sm, Ce, Tb, Nd) at 673 K suggests that the activity (conversion) was higher with Er and Sm orthovanadates ( 11.5%) with 29% propene selectivity [54]. Fang et al. [55] studied a series of rare-earth orthovanadate catalysts for the low-temperature ODH of propane. At 773 K and for a propane/oxygen molar ratio of 2 1 Y-doped VO4 was able to form propene with a selectivity of 49% at 23% conversion [55,56]. Michaels et al. [15] carried out the ODH of propane over Mg-V-Sb oxide catalysts and observed that the propene selectivity decreases from 75 to 5% as the propane conversion increases from 2 to 68%. 

Fang, Z.M., Hong, Q., Zhou, Z.H., Dai, S.J., Zheng, W., and Wan, H.L. Oxidative dehydrogenation of propane over a series of low-temperature rare earth orthovanadate catalysts prepared by the nitrate method. Catal Lett 1999, 61, 39. 

Chaar, M.A., Patel, D., Kung, M.C., and Kung, H.H. Selective oxidative dehydrogenation of butane over V-Mg-O catalysts. J. Catal 1987,105, 483. Kung, M.C. and Kung, H.H. The effect of potassium in the preparation of magnesium orthovanadate and pyrovanadate on the oxidative dehydrogenation of propane and butane. J. Catal 1992, 134, 668. 

Hydrochlorination of isoprene [78-79-5] (1) produces prenyl chloride (56), together with some of the isomeric 3-chloro-3-methylbut-l-ene (57), the ratio between the two depending on reaction conditions. The former undergoes Sn2 reactions while the latter prefers Sn2, hence both alkylate preferentially at the primary carbon atom. Therefore, treatment of the chlorides with acetone in the presence of base, gives methylheptenone [110-93-0] (19), as shown in Fig. 8.13 (62). This is the basis of a process developed by Rhone-Poulenc in which a phase-transfer catalyst is used to assist in the alkylation of acetone [63-65]. A similar process is operated by Kuraray (66). Linalool produced in this way can be isomerized to geraniol using an orthovanadate catalyst (67). 

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