Molybdenum acetylacetonate, oxidant

Molybdenum(VI) dioxyacetylacetonate (molybdenyl acetylacetonate) was first prepared by Gach1 by the action of acetylacetone upon molybdenum(VI) oxide at room temperature. Since he also isolated a small quantity of the same compound by the reaction between molybdenum (II) hydroxide and acetylacetone, he believed the compound to be Mo(C5H702)2. Rosenheim and Bertheim2 later prepared the compound by refluxing an ethanolic solution of acetylacetone with molybdic acid. They correctly identified the product as molybdenyl acetylacetonate. Morgan and Castell3 later duplicated the preparation of Rosenheim and Bertheim and verified their formula. 

Epoxides undergo deoxygenation upon treatment with vanadium or molybdenum acetylacetonate complexes, although their stereoselectivity is low. When the molybdenum(VI) oxo complex MoO(S2CNEt2)2 is employed, the deoxygenation proceeds with retention of configuration. For example, cw-2-butene oxide is converted to c -2-butene at 130 C in 83% yield. ... 

Methyloxirane (propylene oxide) is a colourless, water-miscible liquid, bp 35°C. It is produced commercially from propene and tert-hMtyX hydroperoxide in the presence of molybdenum acetylacetonate [8]. 

This is by far the most stable and best-known oxidation state for chromium and is characterized by thousands of compounds, most of them prepared from aqueous solutions. By contrast, unless stabilized by M-M bonding, molybdenum(III) compounds are sparse and hardly any are known for tungsten(III). Thus Mo, but not W, has an aquo ion [Mo(H20)g] +, which gives rise to complexes [MoXg] " (X = F, Cl, Br, NCS). Direct action of acetylacetone on the hexachloromolybdate(III) ion produces the sublimable (Mo(acac)3] which, however, unlike its chromium analogue, is oxidized by air to Mo products. A black cyanide,... 

The reaction of olefin epoxidation by peracids was discovered by Prilezhaev [235]. The first observation concerning catalytic olefin epoxidation was made in 1950 by Hawkins [236]. He discovered oxide formation from cyclohexene and 1-octane during the decomposition of cumyl hydroperoxide in the medium of these hydrocarbons in the presence of vanadium pentaoxide. From 1963 to 1965, the Halcon Co. developed and patented the process of preparation of propylene oxide and styrene from propylene and ethylbenzene in which the key stage is the catalytic epoxidation of propylene by ethylbenzene hydroperoxide [237,238]. In 1965, Indictor and Brill [239] published studies on the epoxidation of several olefins by 1,1-dimethylethyl hydroperoxide catalyzed by acetylacetonates of several metals. They observed the high yield of oxide (close to 100% with respect to hydroperoxide) for catalysis by molybdenum, vanadium, and chromium acetylacetonates. The low yield of oxide (15-28%) was observed in the case of catalysis by manganese, cobalt, iron, and copper acetylacetonates. The further studies showed that molybdenum, vanadium, and... 

We studied the oxidation of cyclohexene at 70°C in the presence of cyclopentadienylcarbonyl complexes of several transition metals. As with the acetylacetonates, the metal center was the determining factor in the product distribution. The decomposition of cyclohexenyl hydroperoxide by the metal complexes in cyclohexene gave insight into the nature of the reaction. With iron and molybdenum complexes the product profile from hydroperoxide decomposition paralleled that observed in olefin oxidation. When vanadium complexes were used, this was not the case. Variance in product distribution between the cyclopentadienylcarbonyl metal-promoted oxidations as a function of the metal center were more pronounced than with the acetylacetonates. Results are summarized in Table V. 

Among the most active transition metals are Mo and V, and both are effective in their highest oxidation state during reaction. Linden and Farona have foimd that Mo(V) is inactive for the epoxidation reaction and that V(IV) is converted to V (V) when contacted with a hydroperoxide [467]. The metals are added as compounds soluble in the reaction mixture, for example, Mo(CO)6, MoO2(acac), and VO(acac)2 (acac = monoanion of acetylacetone). Sheldon and Van Doom [266] have found that irrespective of the starting material, all molybdenum catalysts give rise to a common compound, a 1,2-diol complex (Fig. 1.11b). This is formed... 

Molybdenum, dichlorobis-one-electron oxidation, 493 Molybdenum, dioxybis(acetylacetone)-bond-length ratios, 57... 

Wang and Willey (19) synthesized fine iron oxide particles (FejOs) made out of a solution of iron (Ill)acetylacetonate in methanol and water this solution (no gel was formed at room temperature) was poured into an autoclave and evacuated with respect to the conditions of supercritical methanol. The iron oxide aerogel developed a specific surface area of 10 mVg. The primary particle dimensions were found to be 8-30 nm, as shown by XRD technique. The catalytic test run was the partial oxidation of methanol in the autoclave in the presence of supercritical COj at temperatures varying from 225 up to 325°C and the pressure was 91 bars. The main reaction product formed was dimethyl-ether, small amounts of formaldehyde, and methyl formate with a selectivity below 10% for both minor products. A 20% iron oxide-molybdenum oxide aerogel tested in the same supercritical conditions showed a very good selectivity of 94% for formaldehyde, the other product being only dimethyl-ether. 

The decomposition of cyclohexylhydroperoxide was also studied in the presence of molybdenum and chromium complexes [356]. The decomposition of cyclohexylhydroperoxide in benzene catalyzed by [Mo02(acac)2], has many characteristics of the [VO(acac)2]-catalyzed reaction [355]. The ketone/alcohol ratio in the product was 1 and the kinetic pattern of reaction is similar. When chromium(III) acetylacetonate is used, however, there is a substantial difference. The chromium complex selectively converts cyclohexyl hydroperoxide to cyclohexanone. It is suggested that in this case the extent of release of free radicals to the solution is small [356]. The ketone/alcohol ratio in this case is " 13.7. The predominant formation of cyclohexanone on decomposition of cyclohexyl hydroperoxide in the presence of [Cr(acac)3] is no doubt related to the much higher yield of ketone obtained in cyclohexane oxidation in the presence of chromium complexes than observed when Mo or V compounds are used as catalysts [356]. 

Metals can also be introduced by adsorption of the elemental vapor or melt, for instance in the case of mercury or alkali metals. Adsorption of molecular "precursors such as carbonyls of iron, cobalt, nickel and molybdenum, and subsequent thermal or photochemical decomposition has become an important approach for metals that are difficult to reduce. Other ligands such as alkyls or acetylacetonates have also been used for this purpose. In all these cases, thermal decomposition carries the risk of excessive mobility of the precursors or intermediates such that agglomeration and particle formation at the external surface of the zeolite crystals can occur. Barrer has described the synthesis of salt-bearing zeolites including the famous dry synthesis of ultramarin in 1828, which is sodalite containing intercalated Na-polysulphides. Adsorption of numerous non-ionic and salt species into zeolites was also described, either as such or as precursors for oxides, hydroxides, or metals. 

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