- Design of stable mixed-metal MIL-101(Cr/Fe) materials with enhanced catalytic activity for the Prins reaction
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This work highlights the benefit of designing mixed-metal (Cr/Fe) MOFs for enhanced chemical stability and catalytic activity. A robust and stable mixed-metal MIL-101(Cr/Fe) was prepared through a HF-free direct hydrothermal route with Fe3+ content up to 21 wt%. The incorporation of Fe3+ cations in the crystal structure was confirmed by 57Fe M?ssbauer spectrometry. The catalytic performance of the mixed metal MIL-101(Cr/Fe) was evaluated in the Prins reaction. MIL-101(Cr/Fe) exhibited a higher catalytic activity compared to MIL-101(Cr), improved chemical stability compared to MIL-101(Fe) and a higher catalytic activity for bulky substrates compared to MIL-100(Fe). In situ infra-red spectroscopy study suggests that the incorporation of Fe3+ ions in MIL-101 structure leads to an increase in Lewis acid sites. It was thus concluded that the predominant role of Cr3+ ions was to maintain the crystal structure, while Fe3+ ions enhanced the catalytic activity.
- álvaro, Mercedes,García, Hermenegildo,Giménez-Marqués, Mónica,Gkaniatsou, Effrosyni,Greneche, Jean-Marc,Navalón, Sergio,Santiago-Portillo, Andrea,Serre, Christian,Sicard, Clémence,Steunou, Nathalie,Vallés-García, Cristina
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supporting information
p. 17002 - 17011
(2020/09/16)
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- Selective Allylic Oxidation of Terpenic Olefins Using Co-Ag Supported on SiO2 as a Novel, Efficient, and Recyclable Catalyst
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Co-Ag supported on the SiO2 catalyst was synthesized by the sol-gel method and characterized using XRD, FT-IR, TG-DTG, BET, CV, and SEM/EDX analysis. The catalytic performance of the resulting catalyst was examined by the oxidation of mono and sesquiterpenic olefins using hydrogen peroxide and tert-butyl peroxide as oxidant agents. Various parameters such as catalyst amount, temperature, and solvents have been studied. The Co-Ag supported on the SiO2 catalyst showed a high activity, selectivity, and recyclability for the selected oxidation reaction.
- Aberkouks, Abderrazak,Mekkaoui, Ayoub Abdelkader,Ait Ali, Mustapha,El Firdoussi, Larbi,El Houssame, Soufiane
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- Solvent and additive-free selective aerobic allylic hydroxylation of β-pinene catalyzed by metalloporphyrins
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Metallodeuteroporphyrins (MDPs) were employed as the catalysts for aerobic oxidation of β-pinene in absence of solvents and additives. Allylic hydroxylation products were found to be the main products from this protocol. The catalytic activity of MDPs with different metal nuclei and the influences of technological conditions on this reaction were investigated. This catalytic system has bright application prospect since only eco-friendly and readily available dioxygen were needed.
- Xu, Shi-Chao,Zhu, Shou-Ji,Bi, Liang-Wu,Chen, Yu-Xiang,Wang, Jing,Lu, Yan-Ju,Gu, Yan,Zhao, Zhen-Dong
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p. 575 - 578
(2017/06/19)
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- Biologically Inspired and Magnetically Recoverable Copper Porphyrinic Catalysts: A Greener Approach for Oxidation of Hydrocarbons with Molecular Oxygen
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An efficient synthetic method for magnetically recoverable hybrid copper porphyrinic nanomaterials is reported. These functionalized magnetic materials prove to be efficient bioinspired oxidation catalysts of olefins and thiols, using molecular oxygen as oxidant, in total absence of reductants and solvents, with the highest TON (turnover number) yet achieved for this reaction (≈200 000). A comparative study between homogeneous and heterogeneous oxidation of cyclohexene is discussed, revealing the heterogeneous system to be the most promising concerning stability and reusability of the catalysts. The full characterization of the magnetic hybrid porphyrinic nanomaterials, by transmission electron microscopy, flame atomic absorption spectrometry, thermogravimetry, N2 sorption, and infrared spectroscopy, is also described.
- Henriques, César A.,Fernandes, Auguste,Rossi, Liane M.,Ribeiro, M. Filipa,Calvete, Mário J. F.,Pereira, Mariette M.
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p. 3359 - 3368
(2016/06/06)
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- Synthesis of bimetallic Zr(Ti)-naphthalendicarboxylate MOFs and their properties as Lewis acid catalysis
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Bimetallic Zr(Ti)-NDC based metal-organic frameworks (MOFs) have been prepared by incorporation of titanium(iv) into zirconium(iv)-NDC-MOFs (UiO family). The resulting materials maintain thermal (up to 500 °C), chemical and structural stability with respect to parent Zr-MOFs as can be deduced from XRD, N2 adsorption, FTIR and thermal analysis. The materials have been studied in Lewis acid catalyzed reactions, such as, domino Meerwein-Ponndorf-Verley (MPV) reduction-etherification of p-methoxybenzaldehyde with butanol, isomerization of α-pinene oxide and cyclization of citronellal.
- Rasero-Almansa, Antonia M.,Iglesias, Marta,Sánchez, Félix
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p. 106790 - 106797
(2016/11/23)
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- Beta-pinene selective hydroxylation oxidation method and product thereof
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The invention discloses a beta-pinene selective hydroxylation oxidation method and a product thereof. The beta-pinene selective hydroxylation oxidation method uses ordinary-pressure oxygen or oxygen-enriched air as an oxidant, uses metal porphyrin or their solid carriers as a catalyst and is performed in the absence of an additional solvent or a co-oxidation reducer, and the beta-pinene hydroxylation oxidation product is obtained by means of the method in a high-selectivity mode. Main oxidation products include pinocarveol, 2,10-epoxy pinane and myrtenol, wherein the overall selectivity of the hydroxylation oxidation products 1 and 3 is above 90%. The usage amount of the catalyst used in method is small, a reaction process is simple, the temperature is low, the initiation rate is high, the selectivity is good, homogeneous catalysis can be achieved, and heterogeneous catalysis can also be performed after immobilization.
- -
-
Paragraph 0032; 033; 0334;
(2016/10/10)
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- H- and Fe-modified zeolite beta catalysts for preparation of trans-carveol from α-pinene oxide
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The isomerisation of a-pinene oxide has been intensively investigated for selective preparation of campholenic aldehyde, a compound used in the synthesis of fragrances. Selective preparation of another product of α-pinene oxide rearrangement, trans-carveol, still remains a challenging task. Trans-carveol is a highly valuable compound used in perfume bases, food flavour compositions and as an active pharmaceutical substance in chemoprevention of mammary carcinogenesis. In the present work zeolite beta with different SiO2/Al2O3 molar ratios was modified by iron, characterised and tested per se and in the modified form for trans-carveol preparation from a-pinene oxide. The isomerisation reaction was carried out in a polar basic solvent N, N-dimethylacetamide at 140 °C. The activities and selectivities of the catalysts were correlated with their acid properties and with the iron content.
- Stekrova,Kumar,Daz,M?ki-Arvela,Murzin
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p. 237 - 245
(2015/03/14)
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- Continuous flow photooxygenation of monoterpenes
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Photooxygenation of monoterpenes was conducted in two continuous flow reactors. The first, suitable for lab-scale research, had a maximum yield of 99.9%, and the second, focused on industrial applications, showed a daily output that was 270.0-fold higher than that in batch systems. The use of sunlight instead of an LED lamp gave 68.28% conversion.
- Park, Chan Yi,Kim, Young Joon,Lim, Hyo Jin,Park, Jeong Hyeon,Kim, Mi Jin,Seo, Seung Woo,Park, Chan Pil
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p. 4233 - 4237
(2015/02/19)
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- Hydrocarbon oxidation over Fe- and Cr-containing metal-organic frameworks MIL-100 and MIL-101-a comparative study
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Catalytic properties of Fe- and Cr-based metal-organic frameworks (MOFs) MIL-100 and MIL-101 have been assessed in two liquid-phase reactions: solvent-free allylic oxidation of alkenes (cyclohexene, α- and β-pinenes) with molecular oxygen and oxidation of anthracene (AN) with tert-butyl hydroperoxide (TBHP). In the oxidation of alkenes, the product selectivity strongly depends on the nature of metal (Fe or Cr) but, for the same metal, only slightly differs for the MIL-100 and MIL-101 structures. The Fe-containing MOFs afford the formation of unsaturated alcohols while Cr-based MOFs give mainly unsaturated ketones. Both Cr-MIL-100 and Cr-MIL-101 favor decomposition of cyclohexenyl hydroperoxide to produce 2-cyclohexen-1-one with 67-69% selectivity. Stability toward destruction reduced in the order Cr-MIL-101, Cr-MIL-100 > Fe-MIL-100 > Fe-MIL-101. In the oxidation of anthracene over both Cr-MOFs and Fe-MIL-101, the selectivity toward 9,10-anthraquinone (AQ) attained 100% at 92-100% AN conversion. The turnover frequency (TOF) decreased in the order Cr-MIL-101 > Fe-MIL-101 > Cr-MIL-100 > Fe-MIL-100. Cr-MIL-101 revealed superior catalytic performance in terms of AN conversion, AQ selectivity and TOF. Nearly quantitative yield of AQ was obtained after 1.5 h at 100 °C in chlorobenzene as solvent. No leaching of active metal occurred under optimal reaction conditions and the MOFs could be recycled several times without deterioration of the catalytic properties.
- Kholdeeva, Oxana A.,Skobelev, Igor Y.,Ivanchikova, Irina D.,Kovalenko, Konstantin A.,Fedin, Vladimir P.,Sorokin, Alexander B.
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- Isomerization of α-pinene oxide using Fe-supported catalysts: Selective synthesis of campholenic aldehyde
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α-Pinene oxide, an oxygenated derivative of α-pinene, can be converted into various valuable substances useful as flavour, fragrance and pharmaceutical compounds. Campholenic aldehyde is one of the most desired products of α-pinene oxide isomerization being a valuable intermediate for the production of sandalwood-like fragrances. Iron modified zeolites Beta-75 and ZSM-5, mesoporous material MCM-41, silica and alumina were prepared by two methods (impregnation and solid-state ion exchange) and tested for selective preparation of campholenic aldehyde by isomerization of α-pinene oxide. The characterization of tested catalyst was carried out using scanning electron microscope analysis, nitrogen adsorption measurements, pyridine adsorption-desorption with FTIR, X-ray absorption spectroscopy measurements, XPS-analysis, 29Si MAS NMR and 27Al MAS NMR and X-ray diffraction. The isomerization of α-pinene oxide was carried out in toluene as a solvent at 70 C. The main properties influencing the activity and the selectivity are the acidic and structural properties of the tested catalysts. The highest selectivity of 66% was achieved at complete conversion of α-pinene oxide with Fe-MCM-41.
- Stekrova, Martina,Kumar, Narendra,Aho, Atte,Sinev, Ilia,Grünert, Wolfgang,Dahl, Johnny,Roine, Jorma,Arzumanov, Sergey S.,M?ki-Arvela, P?ivi,Murzin, Dmitry Yu.
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p. 162 - 176
(2014/01/06)
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- A novel Fe(III) salt-catalyzed monoterpene aerobic oxidation in methyl alcohol
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The Fe(III)-catalyzed aerobic oxidation of monoterpenes in CH3OH has been developed, in which simple Fe(III) salts are used as catalysts in the absence of stabilizing ligands. Remarkably, Fe(NO3)3 catalyst efficiently promotes the oxidation of monoterpenes under air or dioxygen. The highest TON and TOF reached 476 and 162 h- 1, respectively. In general, reactions with 1.0-9.0 mol% of catalyst reached high conversions (ca. 90-99%) and high oxidation products selectivity (ca. 80%). Notably, α-pinene and β-pinene were selectively oxidized into only allylic product, myrtenol methyl ether. The significant breakthroughs of this simple oxidative process are the use of inexpensive Fe(III) salts as catalysts and environmentally-friendly oxidants (air or dioxygen).
- Ferreira De Paula, Fabiano Gomes,Berllini, Lilian,Da Silva, Márcio José
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p. 129 - 133
(2013/10/01)
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- Homo- and heterogeneous α-pinene photooxidation using a protoporphyrin-derived amide
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6,7-Bis[3-(NIμ-tert-butyloxycarbonyllysine methyl ester)]-1,3,5,8-tetramethyl-2,4-divinylporphyrin (3) was synthesized and successfully immobilized in a silica matrix by a sol-gel method. Protoporphyrin (PP)-derived amide 3 showed much higher photostability than its parent PP-IX. Its UV/Vis absorption, excitation, and fluorescence spectra as well as its ability to generate 1O2 were measured both in solution and in the matrix. Subsequently, free and immobilized porphyrins 3 were used as sensitizers in the photooxidation of α-pinene, and their photocatalytic properties were compared. Newly synthesized protoporphyrin (PP)-derived amide 3 is more photostable than PP-IX. Because it is able to generate 1O2, it could be used as a biomimetic catalyst for the oxidation of α-pinene under visible light. After successful immobilization in a silica matrix, a transparent organic-inorganic hybrid was obtained that shows intensive luminescence. Copyright
- Trytek, Mariusz,Lipke, Agnieszka,Majdan, Marek,Pisarek, Sabina,Gryko, Dorota
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p. 1653 - 1658
(2013/04/23)
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- Nanosized sulfated zinc ferrite as catalyst for the synthesis of nopol and other fine chemicals
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A nanosized highly ordered mesoporous zinc ferrite (ZnFe2O 4; ZF) was synthesized via co-precipitation method, further sulfated with ammonium sulfate solution to obtain sulfated ZF (SZF) and have been used for the synthesis of nopol by Prins condensation of β-pinene and paraformaldehyde. The NH3-TPD and pyridine sorption DRIFT-IR studies revealed the significant enhancement in Lewis acidic sites of the zinc ferrite on sulfatation. The influence of various reaction parameters such as reaction temperature, effect of substrate stoichiometry and catalyst loading has been investigated. It gave 70% conversion of β-pinene with 88% selectivity to nopol. The spent catalyst was regenerated and reused successfully up to four cycles with slight loss in catalytic activity. The nanosized SZF catalyst was found to be highly active towards several other commercially important acid catalyzed reactions such as isomerization, acetalization and aldol condensation.
- Jadhav, Sumit V.,Jinka, Krishna Mohan,Bajaj, Hari C.
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- Acid/vanadium-containing saponite for the conversion of propene into coke: Potential flame-retardant filler for nanocomposite materials
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Vanadium-containing saponite samples were synthesized in a one-pot synthetic procedure with the aim of preparing samples for potential application as fillers for polymeric composites. These vanadium-modified materials were prepared from an acid support by adopting a synthetic strategy that allowed us to introduce isolated structural V species (H/V-SAP). The physicochemical properties of these materials were investigated by XRD analysis and by DR-UV/Vis and FTIR spectroscopy of CO that was adsorbed at 100 K; these data were compared to those of a V-modified saponite material that did not contain any Bronsted acid sites (Na/V-SAP). The surface-acid properties of both samples (together with the fully acidic H-SAP material and the Na-SAP solid) were studied in the catalytic isomerization of α-pinene oxide. The V-containing solids were tested in the oxidative dehydrogenation reaction of propene to evaluate their potential use as flame-retardant fillers for polymer composites. The effect of tuning the presence of Lewis/Bronsted acid sites was carefully studied. The V-containing saponite sample that contained a marked presence of Bronsted acid sites showed the most interesting performance in the oxidative dehydrogenation (ODH) reactions because they produced coke, even at 773 K. The catalytic data presented herein indicate that the H/V-SAP material is potentially active as a flame-retardant filler. In questo lavoro e stato sintetizzata tramite metodologia one-pot una saponite contenente in struttura vanadio, di interesse come additivo per compositi polimerici. La metodologia di sintesi adottata ha permesso di ottenere un solido acido contenente siti di vanadio strutturale isolati (H/V-SAP). Le proprieta chimico-fisiche di tale materiale sono state studiate tramite XRD, DR-UV-Vis e FT-IR di CO adsorbito a 100 K e confrontate con quelle di una V-saponite priva di acidita di Bronsted (Na/V-SAP). Le proprieta acide di entrambi i materiali (e di saponiti acidi H-SAP e sodica Na-SAP) sono state investigate sottoponendo i campioni ad un test catalitico di isomerizzazione dell' ossido di α-pinene. I campioni contenenti vanadio sono stati infine testati come catalizzatori per la reazione di deidrogenazione ossidativa del propene, con l'obiettivo di valutarne i loro potenziale uso come additivi ritardanti di fiamma per compositi polimerici. La saponite contenente vanadio strutturale e caratterizzata da una marcata acidita di Bronsted ha mostrato le migliori prestazioni catalitiche, producendo prodotti carboniosi anche ad alte temperature di esercizio (773 K). I dati catalitici qui mostrati indicano che il campione H/V-SAP e potenzialmente attivo come ritardante di fiamma per compositi polimerici. A hard day's saponite: An acid/vanadium-containing saponite (H/V-SAP) was synthesized and its physicochemical properties were compared to those of a V-modified saponite material that did not contain acid sites. Both samples were tested in the oxidative dehydrogenation (ODH) reaction of propene to study the capability of the samples to form coke species. H/V-SAP was the most interesting catalyst for the production of coke. Copyright
- Ostinelli, Luca,Recchia, Sandro,Bisio, Chiara,Carniato, Fabio,Marchese, Leonardo,Guidotti, Matteo,Psaro, Rinaldo
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p. 2394 - 2402,9
(2020/08/24)
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- Influence of the Br?nsted and Lewis acid sites on the catalytic activity and selectivity of Fe/MCM-41 system
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The system Fe2O3/MCM-41, with high iron dispersion, was synthesized in order to introduce Lewis acid sites into the MCM-41 structure. Two calcination atmospheres (inert and oxidant) were used to produce iron nanoclusters with different structural properties. Besides, a silylation treatment was realized on both solids with the aim of neutralizing the Br?nsted acidity associated with the MCM-41 silanol groups. The samples were characterized by atomic absorption spectroscopy, X-ray diffraction at low angles, N2 adsorption, temperature-programmed reduction, Fourier transform infrared spectroscopy, nuclear magnetic resonance of 29Si, and M?ssbauer spectroscopy. The influence of the structural changes of the nanoclusters and the effect of the simultaneous presence of Lewis and Br?nsted acid sites were evaluated studying the product distribution from the α-pinene oxide isomerization reaction. It was determined that the Br?nsted acidity of the Fe/MCM-41 system has not the sufficient acid strength to modify the product distribution which is mainly governed by the Lewis sites.
- Fellenz,Bengoa,Marchetti,Gervasini
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scheme or table
p. 187 - 196
(2012/10/08)
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- β-pinene oxidation by hydrogen peroxide catalyzed by modified niobium-MCM
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Although solid niobium has a high surface area, its high Lewis and Br?nsted acidity is a drawback that always compromises its catalytic performance in oxidation reactions. In this work, treating the niobium catalyst with hydrogen peroxide circumvents this disadvantage and results in a significant increase in the selectivity of the oxidation of β-pinene. In addition, the efficiency of the niobium catalysts supported on MCM was investigated. Nb-MCM//H2O2 and Nb-MCM were the most active catalysts. Good selectivity of up to 85% at a 93-97% substrate conversion has been achieved. The catalyst can easily be recovered and reused several times without loss in activity.
- Coelho, Jakelyne V.,Oliveira, Luiz C.A.,Moura, Flavia C.C.,De Souza, Patterson P.,Silva, Cesar Augusto,Batista, Kenia Barros,Silva, Márcio José Da
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experimental part
p. 215 - 220
(2012/06/29)
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- Selective photosensitized oxidation and its catalytic regulation of monoterpene with molecular oxygen in different reaction media
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The photo-catalytic oxidation of α-pinene, β-pinene and limonene with molecular oxygen sensitized by tetrachlorotetraiodo-fluorescein sodium salt (RB) has been studied in different reaction media under green light irradiation. Simple and efficient photosensitized oxidation equipment was employed successfully to improve the efficiency of the photosensitized reaction. The results indicate that the photosensitized oxidation products can be directly obtained without after-treatment by reductive reagent. Furthermore, it was found that the product distributions are remarkably affected by reaction media, and that N,N-dimethylformamide (DMF) can regulate the selectivity to products. In particular, the good selectivity (85%) to the main product (myrtenal) and the excellent conversion (99%) were obtained in the absence of any other catalysts when DMF was used as reaction solvent in the photosensitized oxidation of β-pinene. Moreover, the possible photosensitized oxidation reaction mechanism in different media was suggested in the present work.
- You, Kuiyi,Yin, Dulin,Mao, Liqiu,Liu, Pingle,Luo, He'An
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experimental part
p. 321 - 325
(2011/10/13)
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- Peculiarities of β-pinene autoxidation
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The thermal oxidation of the renewable olefin β-pinene with molecular oxygen was experimentally and computationally investigated. Peroxyl radicals abstract weakly bonded allylic hydrogen atoms from the substrate, yielding allylic hydroperoxides (i.e., myrtenyl and pinocarvyl hydroperoxide). In addition, peroxyl radicals add to the C=C bond of the substrate to form an epoxide. It was found that a relatively high peroxyl radical concentration, together with the high rate of peroxyl cross-reactions, make radical-radical reactions surprisingly important for this particular substrate. Approximately 60% of these peroxyl cross-reactions lead to termination (radical destruction), keeping a radical chain length of approximately 4 at 10% conversion. Numerical simulation of the reaction-based on the proposed reaction mechanism and known or predicted rate constants-demonstrate the importance of peroxyl cross-reactions for the formation of alkoxyl radicals, which are the precursor of alcohol and ketone products. Copyright
- Neuenschwander, Ulrich,Meier, Emanuel,Hermans, Ive
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experimental part
p. 1613 - 1621
(2012/03/11)
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- Silica- and polymer-supported platinum(II) polypyridyl complexes: Synthesis and application in photosensitized oxidation of alkenes
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Square-planar polypyridine platinum(II) complexes have been introduced into a silica/polymer matrix by covalent ligand modification. The photophysical properties of the supported matrices are well retained as their model complexes, and the quantum yields for singlet oxygen (1O2) generation are comparable with that of TPP (tetraphenylporphyrin) under similar conditions. A preliminary application in photosensitized oxidation indicates the silica/polymer-supported matrices are promising, which can be reused without loss of reactivity by a simple filtration. Moreover, the polymer-supported matrix exhibits excellent compatibility in various solvents. The Royal Society of Chemistry 2009.
- Feng, Ke,Peng, Ming-Li,Wang, Deng-Hui,Zhang, Li-Ping,Tung, Chen-Ho,Wu, Li-Zhu
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scheme or table
p. 9794 - 9799
(2010/03/04)
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- Palladium catalyzed oxidation of monoterpenes: NMR study of palladium(II)-monoterpene interactions
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Reactions of the monoterpenes β-pinene, limonene and myrcene with Pd(II) complexes in acetic acid solutions were studied by 1H NMR spectroscopy. Various π-allyl palladium complexes were detected in situ and their interaction with CuCl2 has been investigated. The results clarify the mechanism of allylic oxidation of these substrates mediated by Pd(II)/Cu(II)-based catalytic systems. Originally introduced to regenerate reduced palladium species, CuCl2 has been shown to play an important role in the formation and/or decomposition of key reaction intermediates - π-allyl palladium complexes. β-Pinene and myrcene readily react with Pd(OAc)2 giving corresponding π-allyls, with two complexes acyclic and cyclic being formed from myrcene. On the other hand, the formation of π-allyl complexes from limonene occurs at a significant rate only in the presence of CuCl2. NMR observations, including selective paramagnetic enhancement of spin-lattice relaxation, indicate that π-allyl palladium intermediates specifically interact with Cu(II) ions in the reaction solutions. Such interaction probably involves Cu(II) bonding to Pd(II) via bridging ligands, and seems to be responsible for the accelerative effect of CuCl 2 in the palladium catalyzed oxidation of the monoterpenes. Indeed, most of these reactions do not occur at all in the absence of CuCl2.
- Gon?alves, José Ailton,Da Silva, Márcio José,Piló-Veloso, Dorila,Howarth, Oliver W.,Gusevskaya, Elena V.
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p. 2996 - 3003
(2007/10/03)
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- Controllable selectivity of photosensitized oxidation of olefins included in vesicles
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9,10-Dicyanoanthracene (DCA) sensitized photooxidation of α-pinene, trans-stilbene and trans,trans-1,4-diphenyl-1,3-butadiene in mixed surfactant vesicles was investigated. While the oxidation in homogeneous solution yields the products derived from both the energy transfer and the electron transfer pathways, that within Vesicles selectively yields either the singlet oxygen mediated or the superoxide radical anion mediated products depending on the status and location of the substrate and sensitizer molecules in the reaction medium. Upon incorporating the alkene in the bilayer membranes of one set of vesicles and DCA in another set of vesicles, the isolation of the substrate from the sensitizer prevents them from undergoing electron transfer. The singlet oxygen produced in the DCA-containing vesicles diffuses into the alkene-containing vesicles and reacts with the alkene. Thus, only the singlet oxygen oxidation products are obtained, and no product derived from the superoxide radical anion is detected. In contrast, incorporating both the sensitizer and the substrate within the same set of vesicles results in the two dissimilar molecules close to one another in the restricted space of the bilayer membranes of the vesicles. Thus, electron transfer from the alkenes to 1DCA* is enhanced, and the efficiency of the intersystem crossing from 1DCA* to 3DCA* is reduced. The photosensitized oxidation in this case only gives the products derived from the electron transfer pathway. Moreover, the reaction of singlet oxygen with DPB in vesicles results exclusively in the 1,2-cycloaddition products rather than the 1,4-cycloaddition product. This result indicates that the organized semirigid environment in vesicles prevents the olefin molecules from conformational change. (C) 2000 Elsevier Science Ltd.
- Li, Hong-Ru,Wu, Li-Zhu,Tung, Chen-Ho
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p. 7437 - 7442
(2007/10/03)
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- Vesicle controlled selectivity in photosensitized oxidation of olefins
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The photooxidation of α-pinene (α-PE) and trans,trans-1,4-diphenyl- 1,3-butadiene (DPB) sensitized by 9,10-dicyanoanthracene (DCA) in mixed surfactant vesicles was selectively directed toward either the singlet oxygen mediated or the superoxide radical an
- Li, Hong Ru,Wu, Li Zhu,Tung, Chen Ho
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p. 1085 - 1086
(2007/10/03)
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- Metal-Catalyzed Oxidations with Pinane Hydroperoxide: A Mechanistic Probe to Distinguish between Oxometal and Peroxometal Pathways
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The relative reactivities of tert-butyl hydroperoxide (TBHP) and pinane hydroperoxide (PHP) in metal (Cr, Mo, Ru, Se, V, and Zr)-catalyzed oxidations were compared. When these oxidations involve rate-limiting oxygen transfer from a peroxometal species to the substrate huge differences between TBHP and PHP were observed, e.g., molybdenum-catalyzed epoxidation of cyclohexene with TBHP gave a 98% yield while PHP gave 0%. When the reaction involves reaction of an oxometal species with the substrate as the rate-limiting step, little or no difference is observed, e.g., the selenium-catalyzed allylic oxidation of β-pinene gave a 96% and 99% yield with TBHP and PHP, respectively. Small but significant differences are observed when reoxidation of the catalyst by the hydroperoxide to the active oxometal species is the rate-limiting step; e.g., the chromium-catalyzed oxidation of carveol gave carvone in 89% and 24% yield with TBHP and PHP, respectively. Hence, the effect of RO2H structure on rate is dependent on the rate-limiting step.
- Lempers,Ripolles i Garcia,Sheldon
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p. 1408 - 1413
(2007/10/03)
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- Cobalt catalyzed oxidation of cyclic alkenes with molecular oxygen: Allylic oxidation versus double bond attack
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Cobalt (II) Schiff's base complex 1 and 2 exhibit a remarkable chemoselectivity during oxidation of cyclic alkenes with molecular oxygen in the presence of 2-methylpropanal. Catalyst 1 encourages the oxidation of double bond to give epoxide as the major product whereas catalyst 2 promotes mainly the allylic oxidation leading to allylic alcohols or enones.
- Madhava Reddy,Punniyamurthy,Iqbal, Javed
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p. 159 - 162
(2007/10/02)
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- Novel allylic oxidation reagents
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Pentafluorobenzeneseleninic acid and 2-(N-oxido)pyridineseleninic anhydride were prepared and used efficiently in the oxidation of alcohols and in the allylic oxidation of alkenes.
- Barton, Derek H. R.,Wang, Tie-Lin
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p. 5149 - 5152
(2007/10/02)
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- Photokatalytische Oxygenierung von Cycloalkenen mit Mangan(III) Tetraarylporphyrin-Komplexen
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The catalytic oxygenation of cyclohexene, 1-methylcyclohexene, α-pinene, 1,5-dimethylcycloocta-1,5-diene, and cis,trans-cyclodeca-1,5-diene with (tetraarylporphyrinato)manganese(III) complexes in the presence of molecular oxygen and visible light is reported.The photocatalytic reaction results in the formation of epoxides and allylic oxygenation products due to allylic hydrogen abstraction.
- Weber, L.,Behling, J.,Haufe, G.,Hennig, H.
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p. 265 - 268
(2007/10/02)
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- Carbon-Carbon Bond Scission during the Reactions of Allylic Hydroperoxides with some Transition Metal Compounds. Result Relevant to a Recent Proposal
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The proposal that 4-exo closure of an allylic peroxyl radical can account for the titled reactions of pinocarveyl hydroperoxide has been considered in the light of literature data, along with the results of reactions carried out with a range of alternative copper and iron reagents and with the previously examinated reagents in the presence or absence of suitable traps: an acid-catalysed pathway is proposed to account for the observed scission reaction.
- Courtneidge, John L.
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p. 381 - 383
(2007/10/02)
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- IMMOBILISATION DE PHOTOSENSIBILISATEURS SUR DES SUPPORTS SOLIDES DERIVES DE L'ACIDE CYANURIQUE
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The synthesis of photosensitizers insoluble in common organic solvents used in photooxidation reactions is described.Bengal Rose and Toluidine Blue have been immobilized via covalent bonding on an original support: tri-(hydroxymethyl)-isocyanurate (THMIC).The photosensitizers prepared have been successfully used in the photooxidation reaction of α-pinene.Their recovery is easy (filtration) and they can be reused several times without important loss of yield.
- Dorgham, K.,Richard, B.,Richard, M.,Lenzi, M.
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p. 579 - 582
(2007/10/02)
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- A CONVENIENT "ONE-POT" SYNTHESIS OF EPOXY ALCOHOLS VIA PHOTOOXYGENATION OF OLEFINS IN THE PRESENCE OF TITANIUM(IV) CATALYST
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The ene reaction of singlet oxygen with alkenes in the presence of titanium alkoxides was employed to prepare epoxy alcohols in high diastereoselectivity; enantioselectivity could be achieved by use of diethyl tartrate as chiral auxiliary.
- Adam, Waldemar,Griesbeck, Axel,Staab, Eugen
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p. 2839 - 2842
(2007/10/02)
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- THE ALLYLIC REARRANGEMENT OF HYDROPEROXIDES : THE ALLYLPEROXYL RADICAL
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The free-radical rearrangement of pinocarveyl hydroperoxide (1) or myrtenyl hydroperoxide (2) in hexane produces an equilibrium mixture of both hydroperoxides.The absence of carbon skeletal rearrangement suggests that the intermediate radical involved in hydroperoxide isomerization has its unpaired electron localized elsewhere than the α-carbon atom.The failure of oxygen to react with pinocarveyl, myrtenyl, and acyclic hydroperoxides (8) and (9) during the allylic rearrangement supports this suggestion.The kinetics of the rearrangement of 1-isopropyl-2-methylallyl hydroperoxide (8) is compatible with a mechanism in wich the intermediate is a common allylperoxyl radical produced directly from either allylic isomer.
- Brill, William F.
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p. 621 - 628
(2007/10/02)
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