Molybdenum oxide alcohols

Methanol undergoes reactions that are typical of alcohols as a chemical class (3). Dehydrogenation and oxidative dehydrogenation to formaldehyde over silver or molybdenum oxide catalysts are of particular industrial importance. 

In this process, catalysts, such as boric acid, molybdenum oxide, zirconium, and titanium tetrachloride or ammonium molybdate, are used to accelerate the reaction. The synthesis is either carried out in a solvent (aUphatic hydrocarbon, trichlorobenzene, quinoline, pyridine, glycols, or alcohols) at approximately 200°C or without a solvent at 300°C (51,52). 

In order to circumvent this problem the rate-determining step was bypassed by using more reactive reagents, allyl alcohol and allyl iodide. These allylic probes were expected to adsorb on the molybdenum oxide surface to provide, respectively, M-O-C and M-C bonded intermediates. These studies were carried out with a sample of 9.0 wt% Mo03/Si02, which Raman spectroscopy and x-ray diffraction showed to consist of fine (- 5nm) crystallites of M0O3 (23). 

Reduction. Benzene can be reduced to cyclohexane [110-82-7], C5H12, or cycloolefins. At room temperature and ordinary pressure, benzene, either alone or in hydrocarbon solvents, is quantitatively reduced to cyclohexane with hydrogen and nickel or cobalt (14) catalysts. Catalytic vapor-phase hydrogenation of benzene is readily accomplished at about 200°C with nickel catalysts. Nickel or platinum catalysts are deactivated by the presence of sulfur-containing impurities in the benzene and these metals should only be used with thiophene-free benzene. Catalysts less active and less sensitive to sulfur, such as molybdenum oxide or sulfide, can be used when benzene is contaminated with sulfur-containing impurities. Benzene is reduced to 1,4-cydohexadiene [628-41-1], C6HS, with alkali metals in liquid ammonia solution in the presence of alcohols (15). 

Molybdenum-peroxo compounds have been shown to achieve a variety of selective oxidations they a-hydroxylate enolizable ketones, presumably via epoxidation of the enolate (equation 27) 163 they cause Baeyer-Villiger lactonization of cyclic ketones, probably via the formation of five-membered trioxametallacycles (equation 28) 164 they oxidize alcohols to carbonyl compounds... 

FIGURE 19 Changes during alcohol oxidation on supported molybdena catalysts (A) methanol oxidation (Reprinted from Journal of Catalysis 150, 407 (1994), M.A. Banares, H. Hu, I.E. Wachs, Molybdena on Silica Catalysts - Role of Preparation Methods on the Structure Selectivity Properties for the Oxidation of Methanol, copyright (1994) with permission from Elsevier). (B) ethanol oxidation (Reprinted with permission from Journal of Physical Chemistry, 99,14468 (1995) by W. Zhang, A. Desikan, S.T. Oyama, Effect of Support in Ethanol Oxidation on Molybdenum Oxide, copyright 1995, American Chemical Society). 

Aldehydes can be prepared by the dehydrogenation of a primary alcohol. Formaldehyde results from the dehydrogenation of methanol at high temperatures with an iron oxide-molybdenum oxide catalyst ... 

Ally alcohol oxidation into acrolein on the rhombic phase of molybdenum oxide modified with vanadium oxide has been studied by the kinetic molhod ami Ijy ESR of ions in situ. II was shown, that active sites for this reaction are V ions situated in the bulk of the catalyst, or near its surface, but not at the surface. Fast diffusion of e.lectrons and a more slower diffusion of oxygen ions between the surface and the bulk occur during the reaction. 

Hydrogen peroxide can be used with molybdenum and tungsten catalysts to provide a convenient source of bromine in situ from bromide ion.226 This mimics the action of haloperoxidase enzymes. It provides a less hazardous way to use bromine. Soybean peroxidase can be used with hydrogen peroxide to oxidize alcohols to aldehydes and ketones.227 The use of hydrogen peroxide with an immobilized lipase has allowed the oxidation of linoleic acid to a monoepoxide in 91% yield. The enzyme could be reused 15 times.228 Indole has been oxidized to oxindole in 95% yield using hydrogen peroxide with a chloroperoxi-dase (4.48a).229... 

Calcium molybdate Calcium molybdate(Vl) Calcium molybdenum oxide (CaMo04) EINECS 232-192-9 Molybdate (Mo042-), calcium (1 1) Molybdate, calcium Molybdic xid (H2M0O4), calcium salt (1 1). Alloying agent in production of iron and steel, crystals in optical and eixtronic applications, phosphors. Soiid d = 4.360 insoluble in H2O, alcohols, soluble in concentrated mineral xids. AAA Molybdenum Atomergic Chemetals Cerac Noah Chem. 

Formaldehyde occurs naturally in the atmosphere at a concentration of about 10 parts per billion (0.000 001%) partly as a by-product of plant and animal metabolism, and partly as a product of the reaction of sunlight with methane (CH4), a much more abundant component of the air. At such low concentrations, it is not a natural source of the compound for commercial or industrial uses and is produced instead by the oxidation of methanol (methyl alcohol CH3OH) or gases extracted from petroleum (such as methane) over a catalyst of silver, copper, or iron with molybdenum oxide. 

Oxygen-containing compounds such as alcohols also undergo dissociative chemisorption, an example being the adsorption of gaseous methanol on molybdenum oxide catalysts (Eq. 5-28). Such metal oxides, and in particular mixed metal oxides, act as redox catalysts, as we shall see in Section 5.3.3. 

For the second building block for verrucarin A (380), a derivative of verrucarinic acid (465) was synthesized in enantiomerically pure form from diester 461. Cleavage with pig liver esterase led to monoester 462, which was reduced to the alcohol with borane dimethylsulfide complex and protected with TBSCl to obtain the molecule 463. a-Hydroxylation with molybdenum oxide generated alcohol 464, and final protection and saponification afforded compound 465 (Scheme 8.16). 

Oxidation of Alcohols. Diphenyl sulfoxide has been employed as an oxidant in conjunction with molybdenum (VI) and osmium (VIII) catalysts for the conversion of alcohols to carbonyl compounds. Diphenyl sulfoxide in combination with catalytic quantities of Mo02(acac)2 oxidizes alcohols to ketones or aldehydes. Higher yields are obtained with allylic or benzylic alcohols. Catal)dic OSO4 in association with Ph2SO can oxidize primary and secondary alcohols to aldehydes and ketones in the... 

Itoh and coworkers [75] used ESI to identify a diiron complex of binaphthol-containing chiral ligand in the catalytic oxidation of alkane with m-CPBA to the corresponding alcohols. O Hair et al. [76] reported an example that involves the oxidation of methanol to formaldehyde in the gas phase using binuclear molybdenum oxides, [Mo206(OH)] and [Mo205(OH)], as catalysts and nitromethane as the oxidant. 

Usually prepared by the action of NaCN on benzaldehyde in dilute alcohol. It is oxidized by nitric acid to benzil, and reduced by sodium amalgam to hydrobenzoin PhCHOHCHOHPh by tin amalgam and hydrochloric acid to des-oxybenzoin, PhCH2COPh and by zinc amalgam to stilbene PhCH = CHPh. It gives an oxime, phenylhydrazone and ethanoyl derivative. The a-oxime is used under the name cupron for the estimation of copper and molybdenum. 

Both oae-step and two-step oxidation processes are known. A number of catalyst systems are known most use a molybdenum compound as the main component. The acryhc acid is esterified with alcohol to the desired acryhc ester ia a separate process (63—66). 

ARCO has developed a coproduct process which produces KA along with propylene oxide [75-56-9] (95—97). Cyclohexane is oxidized as in the high peroxide process to maximize the quantity of CHHP. The reactor effluent then is concentrated to about 20% CHHP by distilling off unreacted cyclohexane and cosolvent tert-huty alcohol [75-65-0]. This concentrate then is contacted with propylene [115-07-1] in another reactor in which the propylene is epoxidized with CHHP to form propylene oxide and KA. A molybdenum catalyst is employed. The product ratio is about 2.5 kg of KA pet kilogram of propylene oxide. 

The first-stage catalysts for the oxidation to methacrolein are based on complex mixed metal oxides of molybdenum, bismuth, and iron, often with the addition of cobalt, nickel, antimony, tungsten, and an alkaU metal. Process optimization continues to be in the form of incremental improvements in catalyst yield and lifetime. Typically, a dilute stream, 5—10% of isobutylene tert-huty alcohol) in steam (10%) and air, is passed over the catalyst at 300—420°C. Conversion is often nearly quantitative, with selectivities to methacrolein ranging from 85% to better than 95% (114—118). Often there is accompanying selectivity to methacrylic acid of an additional 2—5%. A patent by Mitsui Toatsu Chemicals reports selectivity to methacrolein of better than 97% at conversions of 98.7% for a yield of methacrolein of nearly 96% (119). 

Cobalt in Catalysis. Over 40% of the cobalt in nonmetaUic appHcations is used in catalysis. About 80% of those catalysts are employed in three areas (/) hydrotreating/desulfurization in combination with molybdenum for the oil and gas industry (see Sulfurremoval and recovery) (2) homogeneous catalysts used in the production of terphthaUc acid or dimethylterphthalate (see Phthalic acid and otherbenzene polycarboxylic acids) and (i) the high pressure oxo process for the production of aldehydes (qv) and alcohols (see Alcohols, higher aliphatic Alcohols, polyhydric). There are also several smaller scale uses of cobalt as oxidation and polymerization catalysts (44—46). 

The reaction scheme is rather complex also in the case of the oxidation of o-xylene (41a, 87a), of the oxidative dehydrogenation of n-butenes over bismuth-molybdenum catalyst (87b), or of ethylbenzene on aluminum oxide catalysts (87c), in the hydrogenolysis of glucose (87d) over Ni-kieselguhr or of n-butane on a nickel on silica catalyst (87e), and in the hydrogenation of succinimide in isopropyl alcohol on Ni-Al2Oa catalyst (87f) or of acetophenone on Rh-Al203 catalyst (87g). Decomposition of n-and sec-butyl acetates on synthetic zeolites accompanied by the isomerization of the formed butenes has also been the subject of a kinetic study (87h). 

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