Isomerization Of Oxide Research Articles

Isomerization of cyclooctatetraene oxide in the reaction with organometallic reagents : Possible involvement of homotropylium cation intermediate

The reaction of cyclooctatetraene oxide ( 1) with several organometallic reagents and metal salts were investigated with reference to skeletal change of the ring. LAH causes ring cleavage to yield octa-2,4,6-trienal along with the formation of cycloocta-3,5-dienol. Ethylmagnesium bromide and triethylaluminum afford ethyl(cyclohepta-2,4,6-trienyl)methanol in good yields, but the addition of HMPA in the Grignard reaction results in reduction of the reactivity and formation of the isomerized cyclic trienone. A similar medium effect by HMPA or solvent is found in the reaction of 1 with ethyllithium which affords 5-ethylcycloocta-2,6-dienone (70·2%) in ether, and also in the metal salts (MgBr 2, LiBr, and LiClO 4) induced isomerization giving cycloheptatrienylcarboxyaldehydes and phenylacetaldehyde. The diverse nature of the products in the reactions is accounted for by the formation of homotropylium cation intermediates.

Positive ion fragmentation mechanisms of some simple aldehydes and epoxides and trimethylene oxide

AbstractThe metastable ion spectra of ethylene oxide, acetaldehyde, acetaldehyde‐d4, propylene oxide, propionaldehyde and trimethylene oxide are presented. They reveal no reason to suppose that electron‐impact‐induced isomerisation of oxide to aldehyde structure occurs, although many spectral features are common to various members of this set. The spectra of phenylacetaldehyde and styrene oxide are compared, and the more plausible possibility of partial isomerisation in this case is discussed.

Heterogeneous Isomerization of Ethylene Oxide to Acetaldehyde

Surface catalyzed isomerization of (CH2)2O to CH3CHO occurs in a small, Pyrex reactor containing 15 or 230 Torr (CH2)2O at temperatures in the range 339.2 °C to 461.4 °C. Ro(CH3CHO), the initial rate of formation of CH3CHO, depends on the number of successive pyrolyses and on the evacuation time between pyrolyses, which is not true of the initial rates of formation of H2, CO, CH4, CH2CO, and C2H6. Ro(CH3CHO) also depends on the reactor S/V and on pretreatment of the reactor with product gases, particularly H2. The reproducible and limiting values of Ro(CH3CHO) are independent of the (CH2)2O pressures used. Above 385 °C these initial rates exhibit an Arrhenius temperature dependence while below 385 °C they pass through a maximum.Analysis of the Langmuir–Hinshelwood, low surface coverage mechanism shows that the T > 385 °C isomerization is partially or totally controlled by CH3CHO desorption and that −ΔHads < (55 ± 10) kcal mol−1, for CH3CHO on this surface.Ea = 57 kcal mol−1 for the homogeneous first order decomposition of (CH2)2O, in the 15 Torr pyrolysis at temperatures in the range 374.0 to 406.7 °C, and any vibrationally excited CH3CHO, formed in the gas phase at this pressure (and possibly even at 230 Torr), dissociates into chain initiating radicals.

The Isomerization of Propylene Oxide on Metal Oxides and Silica-Magnesia Catalysts

Abstract The isomerization of propylene oxide was carried out over silica-magnesia catalysts and metal oxides at 260–270°C using a pulse reactor. The main products of the reaction were propionaldehyde, acetone, allyl alcohol, 1-propanol, and acrolein. Propionaldehyde and acetone are produced on acidic and basic sites respectively. Allyl alcohol is formed over acid-base bifunctional catalysts. 1-Propanol and acrolein are mainly produced through hydrogen-transfer reactions between allyl alcohol and propionaldehyde and propylene oxide. As regards these reactions, acid-base bifunctional catalysts are favorable and the reaction rate depends on the electron-donating power of the hydrogen acceptor and the basic strength of the catalyst. The acid sites on silica-magnesia catalysts are attributed to the forsterite produced by the reaction of magnesium oxide and silica gel, and the basic sites, to the magnesium oxide remaining. The metal oxides, such as magnesium and calcium oxides, are considered to have very weak acid sites.

The Isomerization of Propylene Oxide on Zeolite Catalysts

Abstract The selectivity and activity of propylene oxide isomerization have been investigated over zeolite catalysts at 100°C. It has been found that the acid strength of a catalyst is a dominant factor in the selectivity and activity. The stronger the acid strength, the larger the ratio of acetone to propionaldehyde. The reaction intermediates are deduced to be a propylene oxide protonated or that adsorbed on a Lewis-acid site. It has also been found that, in the cases of HY, Silnex (SiO2), and HY treated with pyridine, the selectivity and activity correlate with the strength of the interaction between the propylene oxide and the surface hydroxyl group. Moreover, it has been clarified that the H0 value of the surface hydroxyl group observed at 3660 cm−1 on HY is −8.2–−5.6, while that found at 3540 cm−1 is +4.0–+4.8.

Arene oxides as intermediates in the oxidative metabolism of aromatic compounds. Isomerization of methyl-substituted arene oxides.

Arene oxides as intermediates in the oxidative metabolism of aromatic compounds. Isomerization of methyl-substituted arene oxides.

The Isomerization of Propylene Oxide on Metal Phosphate Catalysts

Abstract The isomerization of propylene oxide was carried out on metal phosphate catalysts. The main products were allyl alcohol, propionaldehyde, acetone, and 1-propanol. It was found that allyl alcohol is produced by acid-base bifunctional catalysts, acetone, by basic-site catalysts only, and propionaldehyde, by acid-site catalysts. 1-Propanol may be produced by the hydrogen-transfer reaction of allyl alcohol. The conversion to propionaldehyde is proportional to the acidity of the catalyst, the strength of which is stronger than H0=+4.8. The sum of the conversions to allyl alcohol, acetone, and 1-propanol correlate linearly with the observed basicity (H0≥+7.2) of the catalyst. The selectivity and activity are determined by the basic and acidic properties of the catalyst. The mechanisms of the propylene oxide isomerization are also discussed.

Arene oxides as intermediates in the metabolism of aromatic substrates: alkyl and oxygen migrations during isomerization of alkylated arene oxides.

Phenolic products obtained on isomerization of the three arene oxides of toluene, the nine arene oxides of ortho-, meta-, and para-xylene, the arene oxide of mesitylene, and 2-methyl and 1,2-dimethylnaphthalene-1,2-oxides are compared to the phenolic products obtained by hepatic metabolism of the parent aromatic hydrocarbons. The results are compatible with the intermediacy of certain of these arene oxides in the metabolic pathway from hydrocarbons to phenols. Migrations of methyl groups as well as a remarkable apparent migration of oxygen are observed. The isomerization of 1,4-dimethylbenzene oxide to 2,4-dimethylphenol is analogous to the methyl migration observed in the enzymatic conversion of 4-methylphenylalanine to 3-methyltyrosine with phenylalanine hydroxylase. There are multiple pathways of isomerization of alkylarene oxides to phenols and they are determined by environmental and structural factors. The proportion and nature of products vary greatly with pH, which suggests the presence of different mechanisms for acid-catalyzed or spontaneous isomerizations of arene oxides.

Derivatives of perfluoroisobutyric acid

1. The interaction of perfluoroisobutylene oxide with ammonia and dimethylamine leads to dimethylamides ofα-aminoperfluoroisobutyric acids. 2. The isomerization of perfluoroisobutylene oxide is a convenient comparative method for the production of perfluoroisobutyryl fluorides.

The copper‐catalysed oxidation of unsaturated carbonyl compounds: II. Base‐catalysed isomerization of isomesityl oxide and Δ5‐cholestenone

AbstractThe mechanism of the base‐catalysed isomerization of the βγ‐unsaturated ketones isomesityl oxide and Δ5‐cholestenone to their αβ‐unsaturated isomers was studied. The results are interpreted on the basis of a reaction scheme in which a dienolate anion, formed by deprotonation of the starting material, is an intermediate. The factors determining the rate of deprotonation of unsaturated ketones are discussed.Methoxide ions were found to deprotonate both ketones studied, whereas triethylamine, which deprotonates isomesityl oxide directly, was found to react with Δ5‐cholestenone only via the intermediate formation of methoxide ions from the solvent methanol.

Studies of the Organic Reactions of Metal Carbonyl. III. The Hydroformylation of Olefin Oxides

Abstract The hydroformylation reactions of ethylene oxide and propylene oxide have been carried out; the character of this type of reaction may be summarized as follows: 1) Propylene oxide reacts with water gas, in the presence of dicobalt octacarbonyl serving as a catalyst, to give β-hydroxy-n-butyraldehyde as the major product, but it is important to keep the reaction temperature between 80 to 100°C in order to hold the high selectivity of this reaction. 2) At temperatures below 80°C, the reaction does not take place; on the other hand, at temperatures above 100°C, the isomerization of propylene oxide to acetone predominates, and the other side-reactions, such as the dehydration of the hydroformylation products, hydrogenation, condensation and polymerization, take place simultaneously. 3) Ethylene oxide seems to undergo hydroformylation under the same conditions as those used for the propylene oxide, but only a small amount of acrolein is obtained as the hydroformylation product. The expected product, i.e., β-hydroxypropionaldehyde, is formed, but this compound is easily converted into acrolein and the latter seems to polymerize to give a large amount of a resinous or oily material.

Studies on Catalytic Isomerization of Ethylene Oxide

Catalytic isomerization of ethylene oxide to acetaldehyde was carried out by the flow method in order to obtain the suitable catalyst and the kinetic equation for this reaction.The conclusions obtained were as follows.1. The acidic catalysts such as alumina and silica-alumina promoted high polymerization of ethylene oxide but degraded rather rapidly.2. Active charcoal, magnesia and zinc oxide promoted low polymerization of ethylene oxide, accompanying some isomerization reaction.3. Silica gel had especially high activity and selectivity at 150∼300°C and thus proved to be an excellent catalyst for this reaction.4. This reaction was carried out at 150∼300°C and with space velocity 1, 500∼4, 000hr-1 using silica gel catalyst pretreated at 700°C.The results obtained were expressed satisfactorily by the following rate equation which was derived on the assumption of the surface reaction controlling.W/F=αx-βln(1-x), where W: weights of catalyst (g)F: feed rate (mol/hr)x: fraction of ethylene oxide convertedα, β: constants at various temperatures

Catalytic Isomerization of Ethylene Oxide by the Pulse Reactor

Recently, a pulse flow method using a gaschromatotechnique has been applied for the catalytic reactions. In this paper, isomerization reaction of ethylene oxide to acetaldehyde over silica gel was studied by applying this method. The adsorption behavior of ethylene oxide during the reaction, the degradation of catalytic activity with reaction time and also the reaction rate at several reaction temperatures were investigated.The conclusions obtained were as follows.(1) It was reconfirmed that isomerization of ethylene oxide to acetaldehyde tooks place selectively on silica gel catalyst in the temperature range of 110∼200°C, accompanied with very small amount of polymerized substances.(2) The results obtained were expressed satisfactorily by the first order rate equation in terms of the ethylene oxide concentration. The activation energy of reaction and the heat of ethylene oxide adsorption were observed to be nearly 9kcal/mol and 11kcal/mol respectively.(3) The adsorption amount during the initial short period of reaction and the initial change in catalytic-activity with reaction time, which were difficult to determine by the ordinary flow method, were obtained by utilizing this pulse flow technique.

Vapor-phase hydration of propylene oxide over tricalcium phosphate

1. The catalytic activity of tricalcium phosphate in the vapor-phase hydration of propylene oxide to propylene glycol was studied. 2. Calcium phosphate is a stable and selective catalyst for this reaction. 3. The effect of temperature, contact time, and water excess on the glycol yield was studied. Considerable amounts of glycol were formed under the optimal conditions and the glycol yield reached 50–57% at 232°, for example similar results were obtained in the hydration of ethylene oxide. 4. The high specificity of the phosphate catalyst in the hydration of propylene oxide is in accord with the fact that it hardly catalyzes the isomerization of oxide to allyl alcohol and propionaldehyde. 5. The reaction mechanism is discussed.

The mechanism of the catalytic oxidation of ethylene - I. Experiments using a flow system

Experiments have been made using a flow system to determine the mechanism of the catalytic oxidation of ethylene on a silver catalyst. The effects of time of contact of the gases with the catalyst, gas concentration, and temperature have been investigated. The products of reaction are ethylene oxide, and carbon dioxide and water. There appear to be two processes whereby the carbon dioxide is formed: (1) by direct oxidation of the ethylene not via ethylene oxide, and (2) by the further oxidation of the ethylene oxide. The isomerization of ethylene oxide to acetaldehyde by the catalyst in the absence of any oxygen has also been examined. By comparison with the oxidation of ethylene oxide, it has been shown that this latter reaction proceeds to a large extent, and possibly entirely, through a preliminary isomerization of the ethylene oxide to acetaldehyde. The rate of oxidation of acetaldehyde is extremely rapid and no trace of acetaldehyde is found during the oxidation of ethylene or of ethylene oxide. Ethylene oxide forms on the catalyst an involatile deposit, which is oxidized away by oxygen, so that during oxidation reactions the quantity of it on the catalyst is kept low. The kinetics of the oxidation of ethylene, i.e. rate of reaction proportional to the oxygen concentration and slightly dependent on the ethylene pressure, are consistent with the view that ethylene reacts with oxygen adsorbed on the catalyst and that the slowest step in the whole series of reactions is the rate of adsorption of the oxygen. An energy of activation of about 27 kcal. was found for the production of ethylene oxide, and slightly less for the production of carbon dioxide and consumption of oxygen.

The mechanism of the catalytic oxidation of ethylene. III. The reactions between ethylene and oxygen in a static system

Static experiments have been carried out between ethylene and oxygen on the silver catalyst at different pressures and temperatures, and the rates of the several reactions occurring were determined. It was found at 263° C that ( a ) the rate of oxidation of ethylene to ethylene oxide is proportional to the ethylene pressure and to the first power of the concentration ( θ ) of adsorbed oxygen on the catalyst; ( b ) the rate of the direct oxidation of ethylene to carbon dioxide is proportional to the ethylene pressure and to the square of θ ; ( c ) the rate of oxidation of ethylene oxide is proportional to the ethylene oxide pressure and independent of θ . The Kinetic equations for the course of reaction with time, although incapable of analytical solution, were integrated by means of the Bush differential analyser, the numerical constants being fitted to one series of experiments. The goodness of fit and the accuracy of the predictions for other conditions were confirmation of the kinetics deduced. These results confirm previous findings that the main steps in the reactions are (1) chemisorption of oxygen as atoms on the catalyst surface, (2) reaction of gaseous or weakly adsorbed ethylene either with one oxygen atom to form ethylene oxide, or with two atoms to form products which are oxidized rapidly to carbon dioxide, and (3) isomerization of ethylene oxide to acetaldehyde followed by the rapid oxidation of this to carbon dioxide. Energies of activation have been measured for these steps. An attempt was made to measure directly the concentration of oxygen adsorbed on the catalyst during reaction, by cleaning it up with hydrogen after pumping out the reaction mixture; a value of 0.31 was found which is in fair agreement with that expected from the machine solutions.