Selenium dioxide catalyst

Ishii, Y., Mural, S., Sonoda, N. Oxidation of aldehydes by hydrogen peroxide in the presence of selenium dioxide catalyst. Technol. Rep. Osaka Univ. 1976, 26, 623-626. 

Estr-5(10)-en-3-ones also react with methanol to give dimethyl ketals. Weak acid catalysts such as malonic and oxalic acid or selenium dioxide, which are unable to promote conjugation of the double bond, are conveniently used. ... 

Selective ketalization at C-3 in the presence of a 20-ketone is achieved by the selenium dioxide procedure, at room temperature with " or without an additional acid catalyst. 

The preparation of Pans-1,2-cyclohexanediol by oxidation of cyclohexene with peroxyformic acid and subsequent hydrolysis of the diol monoformate has been described, and other methods for the preparation of both cis- and trans-l,2-cyclohexanediols were cited. Subsequently the trans diol has been prepared by oxidation of cyclohexene with various peroxy acids, with hydrogen peroxide and selenium dioxide, and with iodine and silver acetate by the Prevost reaction. Alternative methods for preparing the trans isomer are hydroboration of various enol derivatives of cyclohexanone and reduction of Pans-2-cyclohexen-l-ol epoxide with lithium aluminum hydride. cis-1,2-Cyclohexanediol has been prepared by cis hydroxylation of cyclohexene with various reagents or catalysts derived from osmium tetroxide, by solvolysis of Pans-2-halocyclohexanol esters in a manner similar to the Woodward-Prevost reaction, by reduction of cis-2-cyclohexen-l-ol epoxide with lithium aluminum hydride, and by oxymercuration of 2-cyclohexen-l-ol with mercury(II) trifluoro-acetate in the presence of ehloral and subsequent reduction. ... 

Selenium dioxide (SeO ) is used as an oxidizing agent, as a catalyst, and as an antioxidant for lubricating oils and grease. 

Oxidation of 2-Methylpropene over Copper Oxide Catalysts in the Presence of Selenium Dioxide... 

The air oxidation of 2-methylpropene to methacrolein was investigated at atmospheric pressure and temperatures ranging between 200° and 460°C. over pumice-supported copper oxide catalyst in the presence of selenium dioxide in an integral isothermal flow reactor. The reaction products were analyzed quantitatively by gas chromatography, and the effects of several process variables on conversion and yield were determined. The experimental results are explained by the electron theory of catalysis on semiconductors, and a reaction mechanism is proposed. It is postulated that while at low selenium-copper ratios, the rate-determining step in the oxidation of 2-methylpropene to methacrolein is a p-type, it is n-type at higher ratios. 

This paper reports the effect of various amounts of selenium dioxide under different operating conditions on the conversion of 2-methylpropene to methacrolein and proposes a hypothesis for the hydrocarbon oxidation, which explains particularly the reactivity and selectivity of selenium-copper oxide catalysts in oxidizing 2-methylpropene. 

The flow rate of the inlet air to the selenium vaporizer was kept constant, and different amounts of selenium dioxide vapor carried by air were obtained by adjusting the temperature of the vaporizer. Thus, selenium and its compounds (oxides) were uniformly distributed over the thin layer of catalyst bed. Since the catalyst was present in small amounts, selenium retained by the catalyst could not be determined accurately. However, most of it was recovered from the product stream by condensation. An air condenser was installed in the exit line of the reactor to remove the condensed selenium, thereby ensuring that selenium did not pollute the air. 

The selectivity for methacrolein first increased rapidly with increased amounts of selenium dioxide, and then decreased. The optimal amount of selenium dioxide giving the highest selectivity was about Z = 0.03 (corresponding to about 0.7% by weight of the pumice-supported catalyst) under different operating conditions. 

For higher amounts of selenium dioxide in the feed (Z > 0.02), while the surface concentration of adsorbed oxygen ions gradually decreases, the surface concentration of adsorbed products becomes significant, and possibly results in the modifier s entering the catalyst lattice substitutionally, rather than interstitially, Cu2+, Cu+, or O" is replaced by selenium, forming a small unit of a covalent compound. Thus, both free... 

The rate of formation of water would increase with increased rates of conversion of 2-methylpropene and decrease with decreased rate formation. The yield of water, therefore, increased first and then decreased because of the combined effects of these two processes. On the other hand, if methacrolein is formed by Reaction I and subsequently further oxidized by Reaction II, its yield will depend on the extent of Reactions I and II, and an optimum will exist. In agreement with this, it was found that the optimal amount of selenium dioxide giving the highest selectivity under operating conditions was about 0.7% by weight of the catalyst. 

The oxidation of 2-butene with selenium dioxide in acetic acid solution produces l-acetoxy-2-butene as the oxidation product of the olefin and bis(l-methyl-2-acetoxypropyl)-selenide (I) as the final reduced state of the oxidant instead of elemental selenium. Further, (I) may act as a catalyst for the oxidation of 2-butene with peracetic acid or oxygen to 3-acetoxy-1-butene. A mechanism is proposed to explain the formation of selenides in the oxidation of olefins with selenium dioxide and their catalytic activity in the oxidation of olefins with other oxidants. 

The chief advantages of the contact process are the high purity of the product and the fact that the product is a concentrated acid. Disadvantages are the high cost of the catalysts and the fact that if sulfides are used as raw materials, costly purification of the sulfur dioxide is necessary, because impurities such as arsenic trioxide and selenium dioxide poison the catalyst (i.e., render the catalyst inactive). Platinum catalysts are particularly sensitive to these impurities, while vanadium catalysts are claimed to be free from this disadvantage. 

It is well known that other non-metal oxides can react with hydrogen peroxide to form similar compounds which can be viewed as inorganic peracids. Such species include boron(III), arsenic(III) and selenium(IV). For example, selenium dioxide can be used as a catalyst for epoxidations or amine oxidations through perselenous acid (Figure 2.29).86... 

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