- Nanotitania catalyzes the chemoselective hydration and alkoxylation of epoxides
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Glycols and ethoxy– and propoxy–alcohols are fundamental chemicals in industry, with annual productions of millions of tons, still manufactured in many cases with corrosive and unrecoverable catalysts such as KOH, amines and BF3?OEt2. Here we show that commercially available, inexpensive, non–toxic, solid and recyclable nanotitania catalyzes the hydration and alkoxylation of epoxides, with water and primary and secondary alcohols but not with phenols, carboxylic acids and tertiary alcohols. In this way, the chemoselective synthesis of different glycols and 1,4–dioxanones, and the implementation of nanotitania for the production in–flow of glycols and alkoxylated alcohols, has been achieved. Mechanistic studies support the key role of vacancies in the nano–oxide catalyst.
- Ballesteros–Soberanas, Jordi,Leyva–Pérez, Antonio,Martínez–Castelló, Aarón,Oliver–Meseguer, Judit,Tejeda–Serrano, María
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- Method for preparing P-dioxanone from diethylene glycol and catalyst thereof
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The invention relates to the technical field of organic catalytic synthesis, in particular to a method for preparing p-dioxanone from diethylene glycol and a catalyst thereof. The method comprise the following steps of reacting the diethylene glycol under the action of the catalyst to generate the p-dioxanone, wherein the catalyst is a supported metal catalyst in which an active metal component is supported on a hydroxyapatite carrier. The method can be carried out in a green solvent or under a solvent-free condition, and p-dioxanone can be prepared from diethylene glycol at a conversion rate of up to 100%; moreover, the reaction process for preparing p-dioxanone from diethylene glycol is simple, the equipment is simple, the operation is simple and convenient, and the reaction conditions are very mild; meanwhile, the preparation process of the catalyst is simple, the cost is low, large-scale production can be realized, the thermal stability of the catalyst is high, and the recycling performance is good; reaction products, catalysts and solvent systems are easy to separate, reaction period is short, and the method is suitable for industrial production.
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Paragraph 0047-0075
(2021/05/01)
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- Flavin Nitroalkane Oxidase Mimics Compatibility with NOx/TEMPO Catalysis: Aerobic Oxidization of Alcohols, Diols, and Ethers
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Biomimetic flavin organocatalysts oxidize nitromethane to formaldehyde and NOx - providing a relatively nontoxic, noncaustic, and inexpensive source for catalytic NO2 for aerobic TEMPO oxidations of alcohols, diols, and ethers. Alcohols were oxidized to aldehydes or ketones, cyclic ethers to esters, and terminal diols to lactones. In situ trapping of NOx and formaldehyde suggest an oxidative Nef process reminiscent of flavoprotein nitroalkane oxidase reactivity, which is achieved by relatively stable 1,10-bridged flavins. The metal-free flavin/NOx/TEMPO catalytic cycles are uniquely compatible, especially compared to other Nef and NOx-generating processes, and reveal selectivity over flavin-catalyzed sulfoxide formation. Aliphatic ethers were oxidized by this method, as demonstrated by the conversion of (-)-ambroxide to (+)-sclareolide.
- Thapa, Pawan,Hazoor, Shan,Chouhan, Bikash,Vuong, Thanh Thuy,Foss, Frank W.
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p. 9096 - 9105
(2020/08/14)
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- (Cyclopentadienone)iron-Catalyzed Transfer Dehydrogenation of Symmetrical and Unsymmetrical Diols to Lactones
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Air-stable iron carbonyl compounds bearing cyclopentadienone ligands with varying substitution were explored as catalysts in dehydrogenative diol lactonization reactions using acetone as both the solvent and hydrogen acceptor. Two catalysts with trimethylsilyl groups in the 2- A nd 5-positions, [2,5-(SiMe3)2-3,4-(CH2)4(δ4-C4C= O)]Fe(CO)3 (1) and [2,5-(SiMe3)2-3,4-(CH2)3(δ4-C4C= O)]Fe(CO)3 (2), were found to be the most active, with 2 being the most selective in the lactonization of diols containing both primary and secondary alcohols. Lactones containing five-, six-, and seven-membered rings were successfully synthesized, and no over-oxidations to carboxylic acids were detected. The lactonization of unsymmetrical diols containing two primary alcohols occurred with catalyst 1, but selectivity was low based on alcohol electronics and modest based on alcohol sterics. Evidence for a transfer dehydrogenation mechanism was found, and insight into the origin of selectivity in the lactonization of 1°/2° diols was obtained. Additionally, spectroscopic evidence for a trimethylamine-ligated iron species formed in solution during the reaction was discovered.
- Tang, Yidan,Meador, Rowan I. L.,Malinchak, Casina T.,Harrison, Emily E.,McCaskey, Kimberly A.,Hempel, Melanie C.,Funk, Timothy W.
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p. 1823 - 1834
(2020/02/04)
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- Oxidative lactonization of diethylene glycol to high-value-added product 1,4-dioxan-2-one promoted by a highly efficacious and selective catalyst ZnO-ZnCr2O4
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For the first time, the desired product 1,4-dioxan-2-one (PDO) was successfully synthesized via the oxidative lactonization of diethylene glycol (DEG) under mild conditions. After screening several catalysts (M-Cr-O), we found ZnO-ZnCr2O4 (Zn-Cr-O) catalyst exhibited excellent catalytic performance and this chemical transformation obtained moderate to excellent selectivity (96.22%) and conversion (81.95%) within a 4 h reaction time. Subsequently, the morphology of calcined M-Cr-O was investigated by FT-IR, XRD, FESEM, TEM, and N2 adsorption-desorption tests for further study on catalytic performances. The strength and quantity of acid and base sites over Zn-Cr-O were also detected by NH3-TPD and CO2-TPD, and it was worth noting that the acid/base sites over ZnO-ZnCr2O4 (Zn-Cr-O) catalyst could promote this catalytic process well. Recycle studies demonstrated exceptional stability and recyclability of the prepared catalyst without significant efficiency and selectivity loss after 10 consecutive cycles.
- Cai, Menglu,Wang, Xiaozhong,Chen, Yingqi,Dai, Liyan
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- Pd-Catalyzed Aerobic Oxidation Reactions: Strategies to Increase Catalyst Lifetimes
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The palladium complex [(neocuproine)Pd(μ-OAc)]2[OTf]2 (1, neocuproine = 2,9-dimethyl-1,10-phenanthroline) is an effective catalyst precursor for the selective oxidation of primary and secondary alcohols, vicinal diols, polyols, and carbohydrates. Both air and benzoquinone can be used as terminal oxidants, but aerobic oxidations are accompanied by oxidative degradation of the neocuproine ligand, thus necessitating high Pd loadings. Several strategies to improve aerobic catalyst lifetimes were devised, guided by mechanistic studies of catalyst deactivation. These studies implicate a radical autoxidation mechanism initiated by H atom abstraction from the neocuproine ligand. Ligand modifications designed to retard H atom abstractions as well as the addition of sacrificial H atom donors increase catalyst lifetimes and lead to higher turnover numbers (TON) under aerobic conditions. Additional investigations revealed that the addition of benzylic hydroperoxides or styrene leads to significant increases in TON as well. Mechanistic studies suggest that benzylic hydroperoxides function as H atom donors and that styrene is effective at intercepting Pd hydrides. These strategies enabled the selective aerobic oxidation of polyols on preparative scales using as little as 0.25 mol % of Pd, a major improvement over previous work.
- Ho, Wilson C.,Chung, Kevin,Ingram, Andrew J.,Waymouth, Robert M.
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supporting information
p. 748 - 757
(2018/01/26)
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- Au NPs@ polystyrene resin for mild and selective aerobic oxidation of 1,4 dioxane to 1,4 dioxan-2-ol
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Supported gold nanoparticles of sizes 5–8 nm have been found as highly efficient catalyst for the oxidation of 1,4 dioxane, a saturated ether, using elemental oxygen at low temperature. GC–MS analysis of the reaction mixture showed > 85% conversion of 1,4 dioxane with a TON of 1120 h? 1 to 1,4 dioxan-2-ol with 90% selectivity. 1,4 Dioxan-2-one was obtained as the major byproduct along with traces of acetic acid and methoxy dioxalane. The catalyst displayed excellent stability and recyclability. TEM analysis of reused catalyst indicated that there was no significant change in the size, shape and morphology of gold nanoparticles.
- Sharma, Anuj S.,Kaur, Harjinder
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- Method for producing para-dioxanone using fixed bed reactor
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The present invention relates to a preparation method of para-dioxanone from diethylene glycol using a fixed bed reactor. More particularly, the present invention relates to a preparation method of para-dioxanone by dehydrogenation of diethylene glycol in vapor state in presence of a catalyst inside a fixed bed reactor. The preparation method injects diethylene glycol and hydrogen at the bottom part of a fixed bed reactor in the direction opposite to the gravitational gravity and can maintain high activity of the catalyst for a long period of time. Also, the preparation method of the present invention can have enhanced conversion rate of para-dioxanone, thereby cost-efficiently and effectively preparing para-dioxanone.(AA) GC purity of para-dioxanone(BB) Purity(%)(CC) Control - upper insertion(DD) Test - lower insertion(EE) Period(days)COPYRIGHT KIPO 2016
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Paragraph 0026-0027
(2017/04/05)
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- Efficient and Selective Cu/Nitroxyl-Catalyzed Methods for Aerobic Oxidative Lactonization of Diols
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Cu/nitroxyl catalysts have been identified that promote highly efficient and selective aerobic oxidative lactonization of diols under mild reaction conditions using ambient air as the oxidant. The chemo- and regioselectivity of the reaction may be tuned by changing the identity of the nitroxyl cocatalyst. A Cu/ABNO catalyst system (ABNO = 9-azabicyclo[3.3.1]nonan-N-oxyl) shows excellent reactivity with symmetrical diols and hindered unsymmetrical diols, whereas a Cu/TEMPO catalyst system (TEMPO = 2,2,6,6-tetramethyl-1-piperidinyl-N-oxyl) displays excellent chemo- and regioselectivity for the oxidation of less hindered unsymmetrical diols. These catalyst systems are compatible with all classes of alcohols (benzylic, allylic, aliphatic), mediate efficient lactonization of 1,4-, 1,5-, and some 1,6-diols, and tolerate diverse functional groups, including alkenes, heterocycles, and other heteroatom-containing groups.
- Xie, Xiaomin,Stahl, Shannon S.
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supporting information
p. 3767 - 3770
(2015/04/14)
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- Chemoselective Pd-catalyzed oxidation of polyols: Synthetic scope and mechanistic studies
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The regio- and chemoselective oxidation of unprotected vicinal polyols with [(neocuproine)Pd(OAc)]2(OTf)2 (1) (neocuproine = 2,9-dimethyl-1,10-phenanthroline) occurs readily under mild reaction conditions to generate α-hydroxy ketones. The oxidation of vicinal diols is both faster and more selective than the oxidation of primary and secondary alcohols; vicinal 1,2-diols are oxidized selectively to hydroxy ketones, whereas primary alcohols are oxidized in preference to secondary alcohols. Oxidative lactonization of 1,5-diols yields cyclic lactones. Catalyst loadings as low as 0.12 mol % in oxidation reactions on a 10 g scale can be used. The exquisite selectivity of this catalyst system is evident in the chemoselective and stereospecific oxidation of the polyol (S,S)-1,2,3,4-tetrahydroxybutane [(S,S)-threitol] to (S)-erythrulose. Mechanistic, kinetic, and theoretical studies revealed that the rate laws for the oxidation of primary and secondary alcohols differ from those of diols. Density functional theory calculations support the conclusion that β-hydride elimination to give hydroxy ketones is product-determining for the oxidation of vicinal diols, whereas for primary and secondary alcohols, pre-equilibria favoring primary alkoxides are product-determining. In situ desorption electrospray ionization mass spectrometry (DESI-MS) revealed several key intermediates in the proposed catalytic cycle.
- Chung, Kevin,Banik, Steven M.,De Crisci, Antonio G.,Pearson, David M.,Blake, Timothy R.,Olsson, Johan V.,Ingram, Andrew J.,Zare, Richard N.,Waymouth, Robert M.
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supporting information
p. 7593 - 7602
(2013/07/05)
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- Organocatalytic oxidative dimerization of alcohols to esters
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2,2,6,6-Tetramethylpiperidine-1-oxyl (TEMPO) catalyzes the direct oxidation of primary alkyl alcohols to symmetric esters at 1-2mol% loadings. These rapid reactions take place at room temperature to afford the products in yields of 55-99%. Georg Thieme Verlag Stuttgart ? New York.
- Abramovich, Adi,Toledo, Hila,Pisarevsky, Evgeni,Szpilman, Alex M.
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p. 2261 - 2265
(2012/11/07)
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- Dehydrogenation of alcohols under ambient atmosphere by a recyclable sol-gel encaged iridium pincer catalyst
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We demonstrate that a sol-gel entrapped iridium-pincer catalyst 1 is capable of promoting acceptorless dehydrogenation of primary and secondary alcohols. Although the dehydrogenations by the non-heterogenized catalyst are faster than by the sol-gel encaged complex, recyclability and significant stabilization of the organometallic species toward non-inert conditions represent a clear advantage from the environmental and practical points of view.
- Oded, Kobi,Musa, Sanaa,Gelman, Dmitri,Blum, Jochanan
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experimental part
p. 68 - 70
(2012/06/16)
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- Lactone metabolite common to the carcinogens dioxane, diethylene glycol, and N-nitrosomorpholine: Aqueous chemistry and failure to mediate liver carcinogenesis in the F344 rat
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1,4-Dioxan-2-one, 1, was synthesized, and the equilibrium constant between it and the hydrolysis product 2-(2-hydroxyethoxy) acetic acid, 2, was determined as KO = 70 ± 4 in acidic aqueous media, 25 °C, ionic strength 1 M (KCl), and 5% by volume acetonitrile. The carboxylic acid dissociation constant of 2 was determined under the same conditions to be pKa = 3.31 ± 0.02. On the basis of these two determinations, the equilibrium constant between 1 and carboxylic acid anion, 3, and the proton was calculated to be KOA = 0.034 ± 0.002 M. The stability of 1 was determined in the range of pH between 1 and 8.5 in buffered aqueous solutions under the conditions above by UV spectrophotometric methods and exhibited simple first order kinetics of decay. On the basis of buffer dilution plots, the values of ko, the rate constant for solvent mediated decomposition, were determined. The plot of log ko against pH is consistent with a three term rate law for solvolysis with a hydrogen ion catalyzed rate constant kH+ = 1.1 (±0.1) M-1 min-1, a water catalyzed rate constant, kw = 9.9 (±0.5) × 10-4 min-1, and a hydroxide ion catalyzed rate constant, kOH = 4.1 (±0.3) × 10 4 M-1 min-1. The t1/2 for decay at pH 7.0, at 25 °C, is ～2 h. Treatment of F344 rats with aflatoxin B 1 (AFB1) (positive control) elicited the expected preneoplastic foci in the livers of each rat tested, while subsequent administration of 1 (a total of 1.32 g over 12 weeks) failed to statistically increase focal number or focal volume percent. In 8 rats administered 1 (1.32 g, 12 weeks) alone, no increase above background foci was detected. This study does not support compound 1 as a common carcinogen.
- Koissi, Niangoran,Shah, Niti H.,Ginevan, Brandon,Eck, William S.,Roebuck, Bill D.,Fishbein, James C.
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experimental part
p. 1022 - 1028
(2012/08/08)
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- Ligand-metal cooperation in pcppincer complexes: Rational design and catalytic activity in acceptorless dehydrogenation of alcohols
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A helping hand: The dibenzobarrelene-based PCsp3Ppincer complex 1 was designed as a bifunctional catalyst for the acceptorless dehydrogenation of alcohols. The mechanism of the H2 release involves interaction between the hydride ligand and the acidic sidearm in the intermediate 2 (red O, yellow Cl, green P, blue Ir). The feasibility of the complete catalytic cycle was studied using a stoichiometric model and the reaction was subsequently realized in a catalytic fashion. Copyright
- Musa, Sanaa,Shaposhnikov, Irina,Cohen, Shmuel,Gelman, Dmitri
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supporting information; experimental part
p. 3533 - 3537
(2011/04/27)
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- PURIFICATION OF P-DIOXANONE
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The present disclosure provides methods for purifying p-dioxanone. In embodiments, crude p-dioxanone may be contacted with at least one isocyanate-functionalized scavenger. The at least one isocyanate-functionalized scavenger may react with hydroxyl compounds present with the crude p-dioxanone to form reaction products, in embodiments polyurethanes and/or polyureas, which may then be removed. The p-dioxanone thus obtained is of greater purity than the starting crude p-dioxanone.
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Page/Page column 3
(2010/02/16)
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- METHOD FOR MANUFACTURING ULTRAFINE P DIOXANONE
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The present invention relates to a method for preparing ultrafine p-dioxanone. The method comprises the steps of performing dehydrogenation cyclization of diethylene glycol in the presence of a pure silica catalyst (SiO ) or a copper-chromium (Cu-Cr) supported silica catalyst to obtain a crude reaction product including p-dioxanone and impurities, recrystallizing the crude reaction product using a mixture solvent of isopropyl alcohol and C -C saturated hydrocarbon as recrystallization solvent and distilling the recrystallized p-dioxanone under reduced pressure in the presence of a hydroxyl blocking agent and a dehydrating agent to obtain the wanted p- dioxanone. The p-dioxanone exhibits low water content and ultrafine purity.
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Page/Page column 6
(2009/03/07)
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- Supported gold nanoparticles as a reusable catalyst for synthesis of lactones from diols using molecular oxygen as an oxidant under mild conditions
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The oxidative lactonization of various diols using molecular oxygen as a primary oxidant can be efficiently catalyzed by hydrotalcite-supported Au nanoparticles (Au/HT). For instance, lactonization of 1,4-butanediol gave γ-butyrolactone with an excellent turnover number of 1400. After lactonization, the Au/HT can be recovered by simple filtration and reused without any loss of its activity and selectivity.
- Mitsudome, Takato,Noujima, Akifumi,Mizugaki, Tomoo,Jitsukawa, Koichiro,Kaneda, Kiyotomi
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experimental part
p. 793 - 797
(2010/04/23)
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- Synthesis and characterization of α,ω-dihydroxy-telechelic oligo(p-dioxanone)
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The homopolymer of 1,4-dioxane-2-one (pDO) is well known as an established biomaterial, especially for degradable surgical sutures. Well-defined α,ω-dihydroxy telechelics based on pDO are introduced in this paper. pDO was synthesized via a one step reaction modified to a literature procedure with a yield of 50-60%. The monomer was polymerized in bulk to oligomeric products via ring-opening polymerization. The polymerization was performed without or with dibutyltin oxide as catalyst using low molecular weight alcohols as initiators. The oligomeric products have number average molecular weights (Mn) between 1800 g mol-1 and 4200 g mol-1. They were soluble in 1,2-dichloroethane or chloroform as common solvents for further reaction in solution. The α,ω-dihydroxy-functionality of the obtained telechelics was investigated by MALDI-TOF MS and 1H NMR spectroscopy. Polymerization in the presence of the catalyst lead to macrocyclic byproducts which have been detected by MALDI-TOF MS. The telechelics were semicrystalline with melting points Tm between 86 °C and 95 °C, increasing with increasing molecular weight. The melting enthalpies ΔHm ranged from 67.7 to 82.3 J g-1. An example of the synthetic opportunities arising from the availability of well-defined telechelic oligomers as starting materials are multiblock copolymers, which were synthesized successfully from oligo(p-dioxane)diol, poly[(rac-lactide)-ran- glycolide]diol and trimethylhexane diisocyanate with weight average molecular weights Mw between 62000 and 149000 g mol-1. The Royal Society of Chemistry.
- Grablowitz, Hans,Lendlein, Andreas
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p. 4050 - 4056
(2008/12/23)
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- Oxidation of ethers with dimethyldioxirane
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Oxidation of a series of tert-butyl ethers ButOR (R = Me, Et, CH2CH2Cl, Pri, Bui), diethyl ether, diisopropyl ether, 1,2-dimethoxyethane, diisobutoxymethane, 1,4-dioxane, and tetrahydrofuran with dimethyldioxirane (DMDO) was studied. The reaction kinetics obeys the second-order equation w = k[DMDO][ether]. The rate constants in a range of 5-50°C and the activation parameters of the reaction were determined. The solvent effect on the oxidation rate was studied. The oxidation products are the corresponding alcohols and carbonyl compounds. The competition between the nonradical (oxygen insertion) and radical mechanisms of the reaction is discussed. The reactions of the parent dioxirane and DMDO with a series of methyl ethers MeOR′ (R′ = Me, Et, CH2CH2F, Pri) were studied by the density functional theory (DFT). The (U)B3LYP-6-311G(d,p) method was employed to calculate the geometry and energies of the reactants and transition states. The data obtained indicate a possible increase in the probability of oxidation via the radical route and an increase in the activation barrier for the substrates containing electron-withdrawing substituents.
- Grabovskiy,Timerghazin,Kabal'nova
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p. 2384 - 2393
(2007/10/03)
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- Oxoammonium salts. 9. Oxidative dimerization of polyfunctional primary alcohols to esters. An interesting β oxygen effect
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The use of the oxidant 4-acetylamino-2,2,6,6-tetramethylpiperidine-1- oxoammonium tetrafluoroborate in combination with pyridine for the oxidative, dimeric esterification of primary alcohols is described. The ester is the predominant product of the reaction with alcohols containing a β oxygen. In the absence of a β oxygen, the corresponding aldehyde is found in appreciable amounts, but a concentration effect can be observed. In the absence of pyridine, little ester is formed, and no appreciable reaction takes place with β-oxygenated compounds. δ Lactones have been prepared from diethylene glycol and 2,2′-thiodiethanol, without sulfur oxidation.
- Merbouh, Nabyl,Bobbitt, James M.,Brueckner, Christian
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p. 5116 - 5119
(2007/10/03)
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- Pd(II)-hydrotalcite-catalyzed selective oxidation of alcohols using molecular oxygen
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A novel heterogenized Pd catalyst, Pd supported by hydrotalcite [Pd(II)-hydrotalcite], was synthesized by a simple operation from commercially available hydrotalcite, Pd(OAc)2 and pyridine. The catalyst was effective for the oxidation of a wide range of alcohols using molecular oxygen as a sole oxidant. With this catalytic system, various alcohols were readily converted to the corresponding aldehydes or ketones selectively in high to excellent yields. Sterically less hindered substrates were converted to the corresponding ketones much faster than the hindered ones. For example, cyclohexanol was converted to cyclohexanone in 79% yield for 15 hr, while larger-sized cyclic alcohols were oxidized to the corresponding ketones only in 32-77% yields in the same reaction time. The catalyst was also applicable to the oxidation of unsaturated alcohols such as geraniol and nerol without any isomerization of an alkenic part. Modified Pd(II)-hydrotalcite [Pd(II)-hydrotalcite(m)] could be reused several times while keeping its activity.
- Uemura,Kakiuchi,Nishimura,Inoue
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p. 165 - 172
(2007/10/03)
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- Palladium(II)-catalyzed oxidation of alcohols to aldehydes and ketones by molecular oxygen
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A novel combination of Pd(OAc)2/pyridine/MS3A catalyzes the aerobic oxidation in toluene of a variety of primary and secondary alcohols into the corresponding aldehydes and ketones in high yields. Various substituents and protecting groups are compatible with this oxidation. The ca. 2:3 ratio of O2 uptake to product yield is observed, whereas in the absence of MS3A, the ratio is ca. 1:1, suggesting the in situ formation of H2O2 and its decomposition by MS3A into water and oxygen. A catalytic cycle including the formation of a Pd(II)-alcoholate followed by β-elimination of a Pd(II)H species and a carbonyl compound and then the formation of a Pd(II)OOH species is proposed.
- Nishimura, Takahiro,Onoue, Tomoaki,Ohe, Kouichi,Uemura, Sakae
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p. 6750 - 6755
(2007/10/03)
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- Synthesis of 1,4-dioxene from diethylene glycol in the presence of bifunctional copper-containing catalysts. Effect of support on the selectivity of dioxene formation
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In the synthesis of 1,4-dioxene from diethylene glycol in the presence of a bifunctional copper-containing catalyst, the composition of the by-products has been studied and the effect of the support on the overall direction of the reactions has been investigated. It has been established that on Cu/SiO2, 1,4-dioxanone is formed together with dioxene, the yield of the former increasing with an increase in the content of copper in the catalyst. This is due to an increase in the dehydrogenating function of the latter. On the more acidic Cu/Al2O3, 1,4-dioxane is mainly obtained together with, to a lesser degree, methyl-1,3-dioxolane. This is due to the predominance of dehydration reactions followed by isomerization. Dioxene, dioxane, and methyldioxolane are formed on Cu/HNaY, and the yield of the latter increases with an increase in the degree of acidity (degree of decationization) of the zeolite. It is possible to increase the selectivity of dioxene formation substantially with the use of a catalyst with a moderately acidic zeolite, by varying its copper content and by dilution with water vapor. 1996 Plenum Publishing Corporation.
- Gitis,Neumoeva,Isagulyants
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-
- Oxidation vs. fragmentation in radiosensitization. Reactions of α-alkoxyalkyl radicals with 4-nitrobenzonitrile and oxygen. A pulse radiolysis and product analysis study
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α-Monoalkoxyalkyl radicals produced from 1,4-dioxane (100percent), 1,3-dioxane (56percent), tetrahydrofuran (92percent) and dimethyl ether (100percent) by H-abstraction by hydroxyl radicals generated in the radiolysis of water were found to react with 4-nitrobenzonitrile (NBN) by addition to give N-alkoxyaminoxyl-type radicals, which have absorption maxima at about 310 nm and decay very slowly (k = 0.4 - 1.0 s-1).On the other hand, the reaction of the α-dialkoxyalkyl radical, 1,3-dioxan-2-yl 3 with NBN leads to the rapid formation of the radical anion NBN.The N-alkoxyaminoxyl-type radicals (A in the case of 1,4-dioxane and D in the case of dimethyl ether) react with ascorbate (k ca. 2*104 dm3 mol-1 s-1).They have a very low reactivity with oxygen (k 3 dm3 mol-1 s-1 in the case of tetrahydrofuran).On the other hand, they are rapidly reduced by NBN radical anion (k ca. 109 dm3 mol-1 s-1 as observed with A and with B derived from 1,3-dioxane).The products -7 mol J-1> in the γ-radiolysis of N2O-saturated solution of 1,4-dioxane in the presence of NBN are 1,4-dioxan-2-one (0.3), 2-hydroxy-1,4-dioxane (2.5), ethane-1,2-diol monoformate (2.1), ethane-1,2-diol diformate (0.7), formaldehyde (2.1), 4-nitrosobenzonitrile and other reduction products of 4-nitrobenzonitrile.These products are accounted for as resulting from the fragmentation of the aminoxyl radical A by (a) heterolysis of the C-O bond (45percent leading to the one-electron oxidation of the 1,4-dioxan-2-yl radical) and (b) homolysis of the N-O bond (55percent leading to the formation of the 1,4-dioxan-2-oxyl radical which undergoes further fragmentation.The products from the reaction of methoxymethyl radicals with NBN under γ-radiolysis conditions are formaldehyde (5.7), methanol (2.5) and methyl formate (1.3).It is concluded that also in this case the decay of the aminoxyl radical D occurs by two pathways: the heterolysis route (46percent) and the homolysis route (54percent).In the presence of oxygen the 1,4-dioxan-2-yl radicals are converted into the corresponding peroxyl radicals.Their bimolecular decay (2k = 2.0*108 dm3 mol-1 s-1) yields the same products as in the case of NBN (albeit with a different product distribution and the formation of some peroxides): 1,4-dioxan-2-one (0.4), 2-hydroxy-1,4-dioxane (0.4), ethane-1,2-diol monoformate (0.6), ethane-1,2-diol diformate (2.8) and formaldehyde (0.6).These results indicate that fragmentation reactions involving the carbon-skeleton of organic radicals are important not only in the case of peroxyl radicals but they can also be induced by nitroaromatic sensitizers.In cells, reduction of the long-lived sensitizer adduct radicals by reducing agents such as ascorbate to give (toxic) hydroxylamine type products may compete with the homolytic or heterolytic fragmentation of the N-alkoxyaminoxyl radicals.
- Nese, Chandrasekhar,Schuchmann, Man Nien,Steenken, Steen,Sonntag, Clemens von
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p. 1037 - 1044
(2007/10/02)
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- Catalytic oxidation of ethers with H2O2 over zeolites
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Titanium Silicates (TS-1 and TS-2) catalyzed efficiently the selective oxidation of both linear and cyclic ethers into the corresponding acids and lactones respectively, using dil, H2O2 as the oxidant.
- Sasidharan,Suresh,Sudalai
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p. 9071 - 9072
(2007/10/02)
-
- Process for production of oxazine diones
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N-substituted cyclic imides of diacids such as oxydiacetic acid and N-substituted iminodiacetic acid are produced by contacting a hydroxy amide of the formula with a reduced copper dehydrogenation catalyst at a temperature of about 200°-300° C, A representing --O--or STR1 and R and R' being hydrocarbon groups of 1-8 carbon atoms. The reaction is preferably conducted in the presence of hydrogen and the diol corresponding to the hydroxyamide. The process is essentially a means of making oxydiacetic acid or iminodiacetic acid from diethylene glycol or diethanolamine respectively as the original starting material. These dicarboxylic acids are useful chelating agents, particularly for Ca and Mg ions, they are intermediates in chemical syntheses, and they are difunctional monomers for making polyester plastics.
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