Oxidation with bismuth oxide

Oxidation of acyloins to a-diketones with bismuth oxide [51JCS793] 

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Veracevine (11), cevine (15), or cevagenine (14) may be oxidized with bismuth oxide to the same 8-lactone (27) (45,52). This undergoes the simple reactions shown in Scheme 7 to give the other five-membered ring A derivatives 28-31. Two natural products (32,33) having five-membered A rings and 8-lactone structures have been isolated and are recorded along with their synthetic derivatives in Table IX. 

The pyrometaHurgical processes, ie, furnace-kettle refining, are based on (/) the higher oxidation potentials of the impurities such as antimony, arsenic, and tin, ia comparison to that of lead and (2) the formation of iasoluble iatermetaUic compounds by reaction of metallic reagents such as 2iac with the impurities, gold, silver and copper, and calcium and magnesium with bismuth (Fig. 12). 

Catalytic oxidation ia the presence of metals is claimed as both nonspecific and specific for the 6-hydoxyl depending on the metals used and the conditions employed for the oxidation. Nonspecific oxidation is achieved with silver or copper and oxygen (243), and noble metals with bismuth and oxygen (244). Specific oxidation is claimed with platinum at pH 6—10 ia water ia the presence of oxygen (245). Related patents to water-soluble carboxylated derivatives of starch are Hoechst s on the oxidation of ethoxylated starch and another on the oxidation of sucrose to a tricarboxyhc acid. AH the oxidations are specific to primary hydroxyls and are with a platinum catalyst at pH near neutraUty ia the presence of oxygen (246,247). Polysaccharides as raw materials ia the detergent iadustry have been reviewed (248). 

Another example of the use of neutron diffraction to understand the role of atomic vacancies in producing a superconducting metal oxide phase is work that has been performed on Bao Kq 4fii03. This work demonstrates that at the synthesis temperature (700° C), under the proper conditions, oxygen vacancies are created to allow the formation of the parent phase with bismuth largely in the +3 oxidation state. The presence of the vacancies allows the incorporation of potassium in the... 

Another important difference in the poison formation reaction is observed when studying this reaction on Pt(lll) electrodes covered with different adatoms. On Pt(lll) electrodes covered with bismuth, the formation of CO ceased at relatively high coverages only when isolated Pt sites were found on the surface [Herrero et al., 1993]. For formic acid, the formation takes place only at defects thus, small bismuth coverages are able to stop poison formation [Herrero et al., 1993 Macia et al., 1999]. Thus, an ideal Pt(lll) electrode would form CO from methanol but not from formic acid. This important difference indicates that the mechanism proposed in (6.17) is not vahd. It should be noted that the most difhcult step in the oxidation mechanism of methanol is probably the addition of the oxygen atom required to yield CO2. In the case of formic acid, this step is not necessary, since the molecule has already two oxygen atoms. For that reason, the adatoms that enhance formic acid oxidation, such as bismuth or palladium, do not show any catalytic effect for methanol oxidation. 

Herteto E, Rodes A, Perez JM, Feliu JM, Aldaz A. 1995d. CO adsorption and oxidation on Pt(lll) electrodes modified by irreversibly adsorbed arsenic in sulfimc-acid medium— Comparison with bismuth-modified electrodes. J Electroanal Chem 393 87-96. 

See Table III.) Bismuth formate Bi(OOCH)3 is prepared by reacting bismuth oxide with a 40% formic acid solution under reflux conditions (50, 64). The solid-state structure shows three different Bi-0 distance ranges [avg. 2.38, 2.52, and 2.77 A] and all oxygen atoms interacting with bismuth, which occupies a six-coordinate, distorted octahedral environment. The octahedra are linked via the carbon centers re-... 

We have previously reported that when the rearrangement of trans-stilbene oxide was carried out with CF3SO3H, the solution turned red and the product diphenylacetaldehyde was less pure than that obtained with bismuth triflate. This observation points to the role of bismuth(III) triflate as a Lewis acid in the rearrangement of epoxides and not to protic acid catalysis by triflic acid released by hydrolysis of bismuth triflate. 

Amorphous boron and bismuth oxide Amorphous boron reacts vigorously with bismuth oxide to form fusible metallic bismuth and volatile boric oxide (Equation 5.10) ... 

The hypothesis of a bifunctional mechanism involving allyl radical formation and oxygen incorporation on distinct sites is advocated by Haber et al. [147,152], This hypothesis is particularly based on experiments with Mo03, Bi203 and mechanical mixtures of these oxides, which are compared with bismuth molybdate catalysts. The reaction was carried out in cyclic operation (alternating feeds of oxygen and of propene diluted with nitrogen). The results are collected in Table 5. The authors con-... 

A commercial iron-promoted catalyst (Sn/Sb/Fe = 1/4/0.25) was studied by Germain et al. [92,93,135,137]. Iron is reported to improve the ammoxidation qualities of the catalyst although it has no effect on the oxidation [93], The kinetics, determined in a flow reactor at 445°C and with a feed ratio C3H6/NH3/air = 1/1.2/10, are essentially similar for this catalyst and bismuth molybdate. The initial selectivity is 80% and the maximum yield is 65% (at 445°C). The initial selectivity markedly depends on the temperature (e.g. 91% at 415°C and 72% at 507°C). The effect of water is hardly significant for this catalyst the acrylonitrile formation is slightly inhibited, while some more acrolein is formed. Presumably, water and ammonia compete in the interaction with the catalyst, which is much less reactive with respect to ammonia than bismuth molybdate. The acrolein ammoxidation is very rapid (about six times the propene ammoxidation rate) and selective (86%). A comparison of the Sn—Sb—Fe—O catalyst with bismuth molybdate is presented in Table 14. 

Villa et al. [340] have shown that the bismuth tungstates are comparable with bismuth molybdates with respect to dehydrogenation catalysis, although activities and selectivities are somewhat lower. Although the phase structures are different, interesting catalysts are formed in a similar composition range Bi/W = 2/3 to 2/1. (Note that, in case of propene (amm)oxidation, tungstates are definitely inferior to molybdates.)... 

Finally, Ven yaminov et al. [338] compare a Sn/Sb = 4/1 catalyst with bismuth molybdate (2/3) at 450°C and note that the Sn—Sb catalyst is less hampered by a drop in selectivity at high degrees of conversion. On the other hand, lower yields are found in the oxidation of 2-butene (compared with 1-butene). The superiority of the bismuth molybdate catalyst in this respect is probably connected with its greater isomerizing capacity. 

The conversion of toluene to benzene was studied by Steenhof de Jong et al. (302—304), by both pulse and flow experiments. In the absence of oxygen, selectivities of up to 70% are obtained with bismuth uranate catalysts at 400—500° C. The best catalyst is Bi2U06. The catalyst is reduced in the oxidation process, as gas phase oxygen is absent. The reduction proceeds to metallic bismuth and U02. The activity decreases during reduction, but is completely restored by reoxidation with air. Therefore, a regenerative mode of operation is proposed for practical application of this process. 

In scheelite-type systems containing divalent ions, the tolerance for vacancies was more limited than in systems containing substantial amounts of monovalent ions. A vacancy limit of about 7.5% appeared to prevail at calcination temperatures between 550° and 800°C (97). The results for the oxidation of propylene over A2i3xBi J(f>xMo0.i, (A2+ = Pb, Cd, or Ca), compositions showed that when x = 0, the activity was very low but increased rapidly with increasing defect concentration. When bismuth was absent, the activity and selectivity were very poor on comparison with bismuth containing defect scheelites. 

Daniel and Keulks (104) investigated Bi-Fe-Mo oxide catalysts prepared by reacting the a-bismuth molybdate with ferric hydroxide. Comparison of these catalysts with bismuth molybdate and ferric oxide indicated that mechanistically the Bi-Fe-Mo oxide catalysts resembled bismuth molybdate in their ability to form an allyl species. Under the same reaction conditions, the composition with Bi-Fe-Mo atomic ratio equal to 6 9 10 exhibited higher conversion than and the same selectivity as the bismuth molybdate catalysts. In contrast to bismuth molybdate, the Bi-Fe-Mo oxide catalysts were found to maintain their activity and se-... 

Some examples of ceramic semiconductors are magnetite (Fe304), doped barium titanate and doped zinc oxide. By for instance doping zinc oxide with bismuth, cobalt, manganese or antimony, you can vary the resistance of zinc oxide. 

The rate of oxidation of acetophenoximes with bismuth(V) fluoride in a mixture of hydrogen fluoride and perchloric acid follows first-order kinetics in both the oxime and Bi(V). The reaction is acid catalysed. A bridged outer-sphere mechanism, involving formation of an iminoxy radical, has been suggested.81... 

Bacteria, antimicrobials against, 12, 456 Baeyer-Villiger oxidation, via tin amides, 9, 370 Barbier-Grignard-type reactions, and sonochemical metal insertions, 1, 315 Barbier-type reactions allenyl and propargyl tins, 9, 358 with allylic tins, 9, 357 with antimony(III) compounds, 9, 426 with bismuth(III) compounds, 9, 433 with cerium reagents, 10, 409 with indium compounds, 9, 685... 

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