Liquid-phase oxidation of tert-butyldimethylsilane

Kinetics and mechanism of liquid-phase oxidation of tert-butyldimethylsilane t-BuMe₂SiH with molecular oxygen in the temperature range 297–350K were studied. Reaction orders in silane, initiator, and oxygen were evaluated. The major product of the oxidation of t-BuMe₂SiH is tert-butyldimethylsilyl hydroperoxide t-BuMe₂SiOOH. It was shown for the first time that the major reaction product is a silyl hydroperoxide. A kinetic scheme of the oxidation of t-BuMe₂SiH is offered and discussed.Translated from Zhurnal Obshchei Khimii, Vol. 74, No. 10, 2004, pp. 1625–1630.Original Russian Text Copyright © 2004 by Lutsik-Maksim, Timokhin, Zaborovskii, Pristanskii, Turovskii, Chatgilialoglu.This revised version was published online in April 2005 with a corrected cover date.     

Liquid-phase oxidation of alkyl-substituted cyclohexylbenzenes

The reactivity of alkyl-substituted cyclohexylbenzenes in liquid-phase oxidation was estimated by the k ₂/?k ₆ value which considerably decreased as the number of methyl groups in the substrate molecule increased. The observed difference in the reactivity of the title compounds was attributed to the degree of coplanarity of intermediate radical species.     

Liquid-phase oxidation of thiols with chlorine dioxide

The products and kinetics of the liquid-phase oxidation of 11 aliphatic and aromatic thiols with chlorine dioxide were studied at –10—+70 °C in organic media. The rate constants and activation parameters of the reaction were determined. The influence of the thiol structure on its reactivity was studied. A strong solvent effect on the reaction rate constant was found, and the reaction mechanism was proposed.     

Liquid-phase oxidation of isopropyl-meta-xylene to tertiary hydroperoxide

Fundamental aspects and the mechanism of the reaction of liquid-phase oxidation of isopropyl-meta-xylene to a tertiary hydroperoxide by atmospheric oxygen, initiated by isopropylbenzene hydroperoxide or catalyzed by N-hydroxyphthalimide were studied. It was found that using N-hydroxyphthalimide in the course of oxidation of isopropyl-meta-xylene makes it possible to raise, compared with the initiator (isopropylbenzene hydroperoxide), the oxidation rate and the conversion of the hydrocarbon by a factor of 2–2.5 at a 90–95% formation selectivity of a tertiary hydroperoxide of isopropyl-meta-xylene up to a conversion of 20–25%.     

Liquid-phase noncatalytic butene oxidation with nitrous oxide

The kinetics and mechanism of noncatalytic liquid-phase oxidation of but-1-ene and but-2-ene with nitrous oxide in a benzene solution in the temperature range from 180 to 240°C were studied. Oxidation proceeds via the 1,3-dipolar cycloaddition mechanism to form carbonyl compounds. Both of these reactions occur with close rates and activation energies and have the first orders with respect to the alkene and N₂O. A considerable fraction (39%) of but-1-ene involved in oxidation undergoes cleavage at the double bond yielding propanal and an equivalent amount of methylene, the latter producing ethylcyclopropane and cycloheptatriene. The oxidation of but-2-ene proceeds with a minimum bond cleavage and affords methyl ethyl ketone with 84% selectivity. Regularities of the oxidation of terminal and internal alkenes C₂—C₈ with nitrous oxide were analyzed using the previously published data. __________ Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 925–933, April, 2005.     

Liquid-phase catalytic oxidation of methyl derivatives of biphenyl

Liquid-phase catalytic oxidation into acids by air was studied for the following hydrocarbons: isomers of cyclohexyltoluenes and cyclohexyl derivatives of para-xylene, mesitylene, pseudocumene, cyclopentyltoluene, cyclohexyladamantane, 4-methylbiphenyl, 2,4-, 2,5- and 3,4-dimethylbiphenyls, hydroxymethylbiphenyls, and hydroxymethylbenzenes. The oxidation of cyclohexyltoluenes involves a methyl group and proceeds without participation of the -CH bond of the cyclohexyl fragment in the oxidative conversions. The reactivity of the hydrocarbons increases in the order ortho < meta < para. Consecutive conversions of the methyl groups to carboxyls occur during the oxidation of dimethylbiphenyls. In 3,4- and 2,5-dimethylbiphenyls, the methyl groups in the para and ortho positions, respectively, are first oxidized, whereas the reactivity of both of the methyl groups in 2,4-dimethylbiphenyl is virtually the same. The mechanism of the oxidation of hydroxymethylbiphenyls and hydroxymethylbenzenes involves the formation of an unstable cation radical, which is then stabilized by emitting a proton, giving hydroxybenzyl, a more stable radical.Translated from Kinetika i Kataliz, Vol. 45, No. 6, 2004, pp. 872–876.Original Russian Text Copyright © 2004 by G. Koshel, S. Koshel, Postnova, Lebedeva, Kuznetsova, Belysheva, Yunkova.     

Liquid-phase oxidation of bromovinyl compounds with molecular oxygen

Liquid-phase oxidation of bromovinyl compounds with the aim to obtain the corresponding α-bromo acids was studied. Original Russian Text R.B. Bayatyan, B.E. Bayatyan, L.A. Saakyan, 2006, published in Zhurnal Prikladnoi Khimii, 2006, Vol. 79, No. 11, pp. 1870–1873.     

Liquid-phase oxidation of hydrogen sulfide in centrifugal bubbling apparatus

Liquid-phase oxidation of H₂S in centrifugal-bubbling apparatus in the presence of catalysts [manganese(II) chloride, cobalt phthalocyanine disulfonic acid, and a catalytic system including cobalt phthalocyanine disulfonic acid and MnCl₂] was studied.     

Liquid-phase oxidation of ethylamine to acetaldehyde oximes over tungsten-doped zeolites

The liquid-phase oxidation of ethylamine with hydrogen peroxide was studied over tungsten-doped zeolites to develop a clean and simple route for producing acetaldehyde oxime. The investigations were firstly performed over W/MOR, where the coordinated state as well as the acidity of the W species were characterized. The reaction parameters, including H_2O_2 amount, solvent,temperature, tungsten content as well as catalyst amount, governed the activity and oxime selectivity. Under optimized reaction conditions, W/MOR showed an ethylamine conversion and corresponding oxime selectivity of 18.3% and 88.9%. W/MOR showed a superior performance in comparison to other tungsten-containing zeolites of W/Beta, W/MWW and W/Y. Although W/MOR exhibited lower amine conversion than titanosilicates of TS-1 and Ti-MWW, it gave higher selectivity to the main product of oxime. Moreover, W/MOR proved to be a robust catalyst, exhibiting a stable catalytic performance after being reused at least for 5 times.     

Liquid-phase oxidation of isobutane—a reanalysis of the data

Data on the liquid-phase oxidation of isobutane at 50 and 100°C have been reexamined, using a modified mechanism to take into account the termination by isobutylperoxy radicals. Algebraic expressions are derived from steady-state methods. Using Arrhenius parameters fitted by transition-state A factors and activation energies derived from observed “best” rate constants, new sets of parameters are derived for the rate constants for propagation by t? BuO₂ + t? BuH → t-BuO₂H + t? Bu^?: where θ = 2.303RT in kcal/mol. This, together with new values for the termination parameters and rates of i-butyl production by k_4B, is shown to give good agreement with the published data. An important reaction: is shown to quench the possible contributions to termination of adventitious radicals such as CH₃O^?₂.     

Liquid-phase oxidation of hydrocarbons in the presence of different types of phase-transfer reagents

The autoxidation of cyclohexene, tetralin and cumene was investigated in the presence of non-ionic, anionic and cationic surfactants and it was found that all three types of phase-transfer reagents are able to influence the rate of oxidation. If their HLB values are not too low (> 3) or not too high (< 15) all the non-ionic surfactants increase the rate of oxidation, otherwise they exert a slight inhibitory effect. If present in acid form, anionic surfactants all increase the rate of oxidation, while their Na-salts slightly inhibit the oxidation. Cationic surfactants all increase the autoxidation rate, but their catalytic efficiencies depend strongly on the experimental conditions. It was shown that the phosphonium ion-type surfactants are quickly oxidized by hydroperoxide present, but their catalytic and phase-transfer capabilities are not detectably reduced. In biphasic systems, the catalytic activities of cationic surfactants are strongly reduced by the presence of water as a separate phase. Light scattering measurements demonstrated that all three types of surfactants are prone to self-association when their concentrations are increased, and this limits their influence on the rate of oxidation. The oxidation rate is strongly reduced when non-ionizing but strongly solvating solvents are simultaneously applied in the reaction mixture. The rate-diminishing effect seems to correlate with the sequence of solvating ability of the solvents. It was pointed out that the presence of hydroperoxide is essential for the PTC-catalyzed oxidation of hydrocarbons. It is thought that the cationic and the anionic surfactants interact with the more nucleophilic (the inner one) and the more electrophilic (the outer one) O-atom of hydroperoxide, respectively, whereby homolysis of the O---O bond is facilitated. The non-ionic surfactants exert their rate-influencing effects through H-bond formation. In the PTC-catalyzed oxidation of hydrocarbons, the rate changes linearly only in a narrow range of PTC, hydroperoxide and substrate concentrations, and consequently the turnover number is not suitable to characterize the oxidation.     

Catalyst-free and atom-economic synthesis of substituted 1-acetyl and 1-hydroxyl carbazoles

The first-ever Diels-Alder reactions of 3-alkenyl indoles with a conjugated alkynyl ketone are reported. These reactions proceed in an atom-economic manner without a catalyst and give various substituted 1-acetyl carbazoles in moderate to excellent yields. These products can be converted to 1-hydroxyl carbazoles in high yields under mild reaction conditions.     

Liquid-phase oxidation of anthracene by hydrogen peroxide in the presence of heterogenized vanadyl acetylacetonate

The synthesis of heterogenized vanadyl acetylacetonate was accomplished by alkylation of a chloromethylated styrene—divinylbenzene copolymer via activation by Co(II) complexes. The effect of heterogenization on the structure of the complexes and their catalytic properties in the peroxide oxidation of anthracene was investigated by kinetic studies and EPR spectroscopy. Increased stability during oxidation of the catalytic centers of the polymer sample as compared with homogeneous vanadyl acetylacetonate was demonstrated.Department of Fine Organic Synthesis, Institute of Chemistry, Bashkir Science Center, Ural Branch, Russian Academy of Sciences, Ekaterinburg 620219. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 4, pp. 800–804, April, 1992.     

A new efficient synthesis of pyranoquinolines from 1-acetyl N-aryl cyclopentanecarboxamides

A new efficient synthesis of pyrano[2,3-b]quinoline derivatives is developed via the H2SO4-mediated tandem cyclization/ring-opening/recyclization reaction of readily available 1-acetyl N-aryl cyclopentanecarboxamides, during which a novel ring-cleavage fashion of the cyclopentane unit is involved and possible mechanisms are discussed.     

Liquid-phase catalytic oxidation of organic substrates by a recyclable polymer-supported copper(II) complex

Chloromethylated polystyrene beads cross-linked with 6.5 % divinylbenzene were functionalized with 2-(2′-pyridyl) benzimidazole (PBIMH) and on subsequent treatment with Cu(OAc)₂ in methanol gave a polymer-supported diacetatobis(2-pyridylbenzimidazole)copper(II) complex [PS-(PBIM)₂Cu(II)], which was characterized by physicochemical techniques. The supported complex showed excellent catalytic activity toward the oxidation of industrially important organic compounds such as phenol, benzyl alcohol, cyclohexanol, styrene, and ethylbenzene. An effective catalytic protocol was developed by varying reaction parameters such as the catalyst and substrate concentrations, reaction time, temperature, and substrate-to-oxidant ratio to obtain maximum selectivity with high yields of products. Possible reaction mechanisms were worked out. The catalyst could be recycled five times without any metal leaching or much loss in activity. This catalyst is truly heterogeneous and allows for easy work up, as well as recyclability and excellent product yields under mild conditions.