Alkane hydroperoxidation with peroxides catalysed by copper complexes

Various copper(I) and copper(II) derivatives, both "simple" ones (copper acetate, perchlorate and a complex with CH3CN) and compounds containing N,O-chelating ligands, catalyse very efficient (turnover numbers attain 2200) oxidation of saturated hydrocarbons with peroxyacetic acid (PAA) or tert-butyl hydroperoxide (TBHP) in acetonitrile solution at 60 degrees C. Alkyl hydroperoxide, alcohol and ketone are formed, the main product being an alkyl hydroperoxide in the oxidation with PAA and an alcohol for the case of TBHP. It has been proposed that the oxidation with PAA is induced via the attack of species r* [HO* or CH3C(=O)O*] on the alkane, RH. A competitive attack of r* on the solvent, CH3CN, also occurs. It has been assumed that in the case of the reaction catalysed by complex Cu(CH3CN)4BF4, copper is present mainly in the form of Cu+ cation, and the rate-limiting step of the oxidation process is the formation of r* via reaction (1): CH3C(=O)OOH + Cu+ --> CH3C(=O)O* + HO- + Cu2+ or/and CH3C(=O)OOH + Cu+ --> CH3C(=O)O- + HO* + Cu2+ with initial rate W1 = k1[PAA][Cu(CH3CN)4BF4] and k1 = 1.7 mol(-1) dm3 s(-1) at 60 degrees C. The activity of the Cu-catalyst is dramatically changed on a small modification of N,O-chelating ligands in the catalyst.     

Kinetics of 2-methyl-2-pentene epoxidation with tert-butyl hydroperoxide

The reaction rate at the initial period during the epoxidation of 2-methyl-2-pentene with tert-butyl hydroperoxide in the presence of Mo(CO)₆ as catalyst varies linearly in the range of lower concentrations of olefin, hydroperoxide and catalyst. The reaction is losing the first order character in the region of higher concentrations due to the inhibition with the reaction products. This finds the confirmations in a discrepancy between the concentration and the instantaneous (temporal) reaction order.     

Kinetics of chalcone oxidation by peroxide anion catalysed by poly-l-leucine

An insight into the kinetics, mechanism and optimum reaction conditions of the Julia-Colonna epoxidation has been gained using a soluble polyleucine catalyst.     

Isotope effects and the mechanism of epoxidation of cyclohexenone with tert-butyl hydroperoxide

The mechanism of the epoxidation of 2-cyclohexen-1-one with tert-butyl hydroperoxide mediated by DBU was studied by a combination of experimental kinetic isotope effects (KIEs) and theoretical calculations. A large 12C/13C (k(12C)/k(13C)) isotope effect of approximately equal to 1.032 was observed at the C3 (beta) position of cyclohexenone, while a much smaller 12C/13C isotope effect of 1.010 was observed at the C2 (alpha) position. Qualitatively, these results are indicative of nucleophilic addition to the enone being the rate-limiting step. Theoretical calculations support this interpretation. Transition structures for the addition step lead to predicted isotope effects that approximate the experimental values, while the predicted isotope effects for the ring-closure step are not consistent with the experimental values. The calculations correctly favor a rate-limiting addition step but suggest that the barriers for the addition and ring-closure steps are crudely similar in energy. The stereochemistry of these epoxidations is predicted to be governed by a preference for an initial axial addition, and the role of this preference in experimental diastereoselectivity observations is discussed.     

Etherification of glycerol with tert-butyl alcohol catalysed by ion-exchange resins

The reaction of glycerol with tert-butyl alcohol in the liquid phase on acid Amberlyst-type ion-exchange resins was studied. The influence of temperature, mole ratio n(TBA)/n(G), water and swelling of gel, and macroreticular type of polymer catalysts on etherification reaction was investigated. The most favourable reaction temperature is 75°C. The conversion of glycerol and yield of glycerol tert-butyl ethers has increased with the mole ratio n(TBA)/n(G). Dry form of macroreticular catalysts provided the best results. Etherification reaction of glycerol with isobutylene in non-aqueous conditions gives the highest yield of desired ethers. The influence of water was studied. The gel forms of ion-exchange resins have very low catalytic activity. It can be concluded that water has an inhibition effect on ion-exchange resins. By comparing the gel and macroreticular forms of Amberlyst ion-exchange resins it can be concluded that very acid forms of macroreticular ion-exchange resins with a high degree of crosslinking are more active catalysts for the studied reaction due to their pores which are sufficiently large so that the voluminous tert-butyl ethers of glycerol can be formed. It was estimated that tert-butyl alcohol as tert-butylation agent is not suitable for etherification of glycerol with the formation of di-and triethers.     

Kinetics and mechanism of the reaction of 1,2-diethoxyethane hydroperoxide with ozone

The kinetics and products of the reaction of 1,2-diethoxyethane hydroperoxide with ozone in CCl₄ solution at 9 and 22°C have been studied. A reaction mechanism is proposed.

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I,I- CCl₄ (9; 22°C). .

     

Kinetics and mechanism of the liquid-phase oxidation of tert-butyl phenylacetate

The oxidation of tert-butyl phenylacetate in ortho-dichlorobenzene at 140°C occurs with short chains. The primary nonperoxide reaction products (tert-butyl α-hydroxyphenylacetate, tert-butyl α-oxophenylacetate, and benzaldehyde) are formed by the decomposition of a hydroperoxide (tert-butyl α-hydroperoxyphenylacetate) and (or) by the recombination of peroxy radicals with and without chain termination. Benzaldehyde and tert-butyl α-hydroxyphenylacetate undergo radical chain oxidation in a reaction medium to result in benzoic acid and tert-butyl α-oxophenylacetate. Homolytic hydroperoxide decomposition is responsible for process autoacceleration and results in benzaldehyde, which is also formed from hydroperoxide by a nonradical mechanism, probably, via a dioxetane intermediate. Both of the reactions are catalyzed by benzoic acid. Benzoic acid has no effect on hydroperoxide conversion into tert-butyl α-oxophenylacetate, which most likely occurs as a result of hydroperoxide decomposition induced by peroxy radicals. The rate constants of the main steps of the process and kinetic parameters have been calculated by solving an inverse kinetic problem.     

Ruthenium-catalyzed oxidation of alkanes with tert-butyl hydroperoxide and peracetic acid

The ruthenium-catalyzed oxidation of alkanes with tert-butyl hydroperoxide and peracetic acid gives the corresponding ketones and alcohols highly efficiently at room temperature. The former catalytic system, RuCl(2)(PPh(3))(3)-t-BuOOH, is preferable to the oxidation of alkylated arenes to give aryl ketones. The latter system, Ru/C-CH(3)CO(3)H, is suitable especially for the synthesis of ketones and alcohols from alkanes. The ruthenium-catalyzed oxidation of cyclohexane with CH(3)CO(3)H in trifluoroacetic acid/CH(2)Cl(2) at room temperature gave cyclohexyl trifluoroacetate and cyclohexanone with 90% conversion and 90% selectivity (85:15). The mechanistic study indicates that these catalytic oxidations of hydrocarbons involve oxo-ruthenium species as key intermediates.     

Epoxidation of cyclohexene with tert-butyl hydroperoxide catalyzed by polymer anchored molybdenum complexes

Catalytic activity of molybdenum hexacarbonyl anchored on various polymers was investigated for the epoxidation of cyclohexene with tert-butyl hydroperoxide. The activity was increased by anchoring on the polymer. The catalyst on polystyrene showed much higher activity than Mo(CO)₆ used under homogeneous conditions.

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, , .— . . ]qt, Mo(CO)₆, .

     

Selective catalytic oxidation of organosulfur compounds with tert-butyl hydroperoxide

Rates and selectivities for the oxidation of various organosulfur compounds with tert-butyl hydroperoxide were measured on CoAPO-5 (APO = aluminophosphate; Co/P = 0.05), Co/H-Y (Co/Al = 0.15), and MoO(x)/Al2O3 (15 % wt MoO3). Rates increased with increasing electron density at the sulfur atom (methyl phenyl sulfide>diphenyl sulfide>4-methyldibenzothiophene>2,5-dimethyl thiophene). Rates (per metal atom) were significantly higher on CoAPO-5 than on Co/H-Y, MoO(x)/Al2O3, or homogeneous Co acetate catalysts. Small amounts of sulfoxides (1-oxide) were detected on all catalysts at low reactant conversions, together with their corresponding sulfones; at higher conversions, only sulfones (1,1-dioxide) were detected, indicating that the oxidation of sulfoxides is much faster than for organosulfur reactants in the sequential oxidation pathways prevalent on these catalysts. Framework Co cations were not leached from CoAPO-5 during the oxidation of 4-methyldibenzothiophene, but most exchanged Co cations in H-Y and >20 % of Mo cations in MoO(x)/Al2O3 were extracted during these reactions. The fraction of redox-active Co cations in CoAPO-5 and Co/H-Y was measured by reduction-oxidation cycles using H2 and O2 and by UV-visible spectroscopy. This fraction was much larger in CoAPO-5 (0.35) than in Co/H-Y (0.01), consistent with the higher oxidation rates measured on CoAPO-5 and with the involvement of redox-active species in kinetically-relevant steps in catalytic oxidation sequences. Redox-active Co cations at framework positions within accessible channels are required for catalytic activity and structural stability during oxidative desulfurization, whether hydroperoxides are used as reactants or as intermediates (when O2 is used as the oxidant).     

Kinetics and mechanism of ruthenium tetroxide catalysed oxidation of cyclic alcohols by bromate in a base

Summary Kinetic investigations on the RuO₄-catalysed oxidation of cyclopentanol (Cypol) and cyclohexanol (Cyhol) in alkaline KBrO₃ in the presence of Hg(OAc)₂ which acts as a bromide ion scavenger have been made in the 30°–45°C range. The reaction exhibits zero order kinetics in OH^– and is first order with respect to BrO ₃ ^– , substrate and RuO₄. The influence of Hg(OAc)₂ and ionic strength is insignificant. A transient complex, formed between HRuO ₅ ^– (the active species of RuO₄) and the cyclic alcohol, reacts with BrO ₃ ^– in a slow, rate determining step to give the products; the catalyst is regenerated.     

Kinetics and mechanism of aniline hydroxylation by cumene hydroperoxide in the presence of catalase

In a phosphate buffer with pH=7.4 at 20°C the kinetics of aniline hydroxylation to p-aminophenol by the catalase-cumene hydroperoxide system has been studied. The reaction mechanism of this system is discussed.

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20°C pH 7,4 - . .

     

X-ray crystallographic and quantum-chemical investigation of tert-butyl hydroperoxide

An MNDO calculation and an x-ray crystallographic investigation of tert-butyl hydroperoxide (I) were undertaken. The two symmetrically independent molecules of (I), which in fact have identical geometric parameters, form infinite chains along the y axis through staggered hydrogen bonds. The chains have local symmetry, described by a noncrystallographic slip plane. The difference between the experimental value of the COOH dihedral angle (average 100°) and the calculated value (128.5°) is most likely due to the formation of intermolecular hydrogen bonds in the crystal, the energies of which (30 kJ/mole) are considerably larger than the calculated excess energy of the conformers observed in the crystal (3.4 and 1.9 kJ/ mole).Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 25, No. 1, pp. 82–87, January–February, 1989.     

Kinetics and mechanism of peroxydisulphate oxidation of benzamide catalysed by silver(I)

Summary The kinetics of the Ag^I-catalysed peroxydisulphate oxidation of benzamide in 30% (v/v) MeCO₂HH₂O at constant ionic strength have been studied. The rate at which peroxydisulphate disappears is proportional to the peroxydisulphate and Ag^I ion concentrations, but independent of benzamide concentration. Allyl acetate, an effective radical scavenger for the sulphate radical ion, inhibits the reaction. The different thermodynamic parameters are evaluated. A free radical mechanism involving Ag^II is proposed on the basis of products.