- Phenol alkylation with isobutene - influence of heterogeneous Lewis and/or Bronsted acid sites
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Acidic solid catalysts with different types of acidity were used to study the liquid-phase alkylation of phenol with isobutene. A phosphonium ionic liquid immobilized on silica type carrier exhibiting pure Lewis acidity, Amberlyst 15 with pure Bronsted acidity as well as WO3/ZrO2 with both types of acid sites were used for this study. The active sites are postulated based on pyridine-FT-IR and NH3-TPD studies, BET analyses, MAS NMR and XRD measurements. The different properties of the chosen catalysts are mirrored in the product distribution of the reaction mixture. It was found that WO3/ZrO2 is a very active and selective catalyst for the production of 2,4-di-tert-butylphenol under mild reaction conditions.
- Modrogan, Elena,Valkenberg, Michael H.,Hoelderich, Wolfgang F.
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Read Online
- ACTIVITY OF SECONDARY AROMATIC AMINES AS CATALYSTS IN THE REACTION OF STERICALLY HINDERED AROXYL RADICALS WITH HYDROPEROXIDES
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Secondary aromatic amines AmH catalyze the reaction of the 2,4,6-tri-t-butylphenoxyl radical ArO* with cumyl hydroperoxide ROOH.This effect is closely connected with the antioxidant action of the mixtures of sterically hindered phenols and AmH which have a synergistic effect and which are used in practice.The present work is directed to a study of the dependence of the catalytic activity of AmH on the temperature and on the substituents on the aromatic rings.
- Varlamov, V. T.
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Read Online
- Visible-Light-Enhanced Cobalt-Catalyzed Hydrogenation: Switchable Catalysis Enabled by Divergence between Thermal and Photochemical Pathways
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The catalytic hydrogenation activity of the readily prepared, coordinatively saturated cobalt(I) precatalyst, (R,R)-(iPrDuPhos)Co(CO)2H ((R,R)-iPrDuPhos = (+)-1,2-bis[(2R,5R)-2,5-diisopropylphospholano]benzene), is described. While efficient turnover was observed with a range of alkenes upon heating to 100 °C, the catalytic performance of the cobalt catalyst was markedly enhanced upon irradiation with blue light at 35 °C. This improved reactivity enabled hydrogenation of terminal, di-, and trisubstituted alkenes, alkynes, and carbonyl compounds. A combination of deuterium labeling studies, hydrogenation of alkenes containing radical clocks, and experiments probing relative rates supports a hydrogen atom transfer pathway under thermal conditions that is enabled by a relatively weak cobalt-hydrogen bond of 54 kcal/mol. In contrast, data for the photocatalytic reactions support light-induced dissociation of a carbonyl ligand followed by a coordination-insertion sequence where the product is released by combination of a cobalt alkyl intermediate with the starting hydride, (R,R)-(iPrDuPhos)Co(CO)2H. These results demonstrate the versatility of catalysis with Earth-abundant metals as pathways involving open-versus closed-shell intermediates can be switched by the energy source.
- Mendelsohn, Lauren N.,MacNeil, Connor S.,Tian, Lei,Park, Yoonsu,Scholes, Gregory D.,Chirik, Paul J.
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p. 1351 - 1360
(2021/02/01)
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- Visible light enables catalytic formation of weak chemical bonds with molecular hydrogen
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The synthesis of weak chemical bonds at or near thermodynamic potential is a fundamental challenge in chemistry, with applications ranging from catalysis to biology to energy science. Proton-coupled electron transfer using molecular hydrogen is an attractive strategy for synthesizing weak element–hydrogen bonds, but the intrinsic thermodynamics presents a challenge for reactivity. Here we describe the direct photocatalytic synthesis of extremely weak element–hydrogen bonds of metal amido and metal imido complexes, as well as organic compounds with bond dissociation free energies as low as 31 kcal mol?1. Key to this approach is the bifunctional behaviour of the chromophoric iridium hydride photocatalyst. Activation of molecular hydrogen occurs in the ground state and the resulting iridium hydride harvests visible light to enable spontaneous formation of weak chemical bonds near thermodynamic potential with no by-products. Photophysical and mechanistic studies corroborate radical-based reaction pathways and highlight the uniqueness of this photodriven approach in promoting new catalytic chemistry. [Figure not available: see fulltext.].
- Park, Yoonsu,Kim, Sangmin,Tian, Lei,Zhong, Hongyu,Scholes, Gregory D.,Chirik, Paul J.
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p. 969 - 976
(2021/07/25)
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- Method for synthesizing 2, 4 and 6 -tert-butylphenol
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The invention belongs to the technical field of organic synthesis, and particularly relates to a method for synthesizing 2, 4 and 6 - tri-tert-butylphenol, which comprises the following steps: 1) adding phenol, a catalyst, demineralized water, heating and stirring. 2) To the isobutene, maintain temperature pressure, stirring. 3) Aqueous sodium carbonate aqueous solution, neutralization reaction, washing of the oil phase, separation of the oil phase and the aqueous phase. 4) The oil phase is rectified, and a reaction intermediate product is obtained at the top of the tower, which is used as a reaction material for the next kettle reaction to continue to be alkylated. 2, 4 and 6 -tert-butylphenol crude product is obtained in the tower kettle. 5) The crude product was recrystallized and dried with ethanol as a solvent to give 2, 4, 6 -tert-butylphenol product. The synthesis method provided by the invention is scientific and reasonable in design, adopts micro negative pressure pressure conditions as reaction pressure conditions, effectively avoids the self-polymerization phenomenon of isobutene, is mild and controllable in overall reaction conditions, and is low in reaction temperature, free of byproducts and high in product purity.
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Paragraph 0032-0082
(2021/11/14)
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- Multiple N-H and C-H Hydrogen Atom Abstractions through Coordination-Induced Bond Weakening at Fe-Amine Complexes
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We report the use of the reported Fe-phthalocyanine complex, PcFe (1; Pc = 1,4,8,11,15,18,22,25-octaethoxy-phthalocyanine), to generate PcFe-amine complexes 1-(NH3)2, 1-(MeNH2)2, and 1-(Me2NH)2. Treatment of 1 or 1-(NH3)2 to an excess of the stable aryloxide radical, 2,4,6-tritert-butylphenoxyl radical (tBuArO?), under NH3 resulted in catalytic H atom abstraction (HAA) and C-N coupling to generate the product 4-amino-2,4,6-tritert-butylcyclohexa-2,5-dien-1-one (2) and tBuArOH. Exposing 1-(NH3)2 to an excess of the trityl (CPh3) variant, 2,6-di-tert-butyl-4-tritylphenoxyl radical (TrArO?), under NH3 did not lead to catalytic ammonia oxidation as previously reported in a related Ru-porphyrin complex. However, pronounced coordination-induced bond weakening of both α N-H and β C-H in the alkylamine congeners, 1-(MeNH2)2 and 1-(Me2NH)2, led to multiple HAA events yielding the unsaturated cyanide complex, 1-(MeNH2)(CN), and imine complex, 1-(MeN═CH2)2, respectively. Subsequent C-N bond formation was also observed in the latter upon addition of a coordinating ligand. Detailed computational studies support an alternating mechanism involving sequential N-H and C-H HAA to generate these unsaturated products.
- Wang, Zongheng,Johnson, Samantha I.,Wu, Guang,Ménard, Gabriel
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p. 8242 - 8251
(2021/06/25)
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- A Bioinspired Disulfide/Dithiol Redox Switch in a Rhenium Complex as Proton, H Atom, and Hydride Transfer Reagent
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The transfer of multiple electrons and protons is of crucial importance in many reactions relevant in biology and chemistry. Natural redox-active cofactors are capable of storing and releasing electrons and protons under relatively mild conditions and thus serve as blueprints for synthetic proton-coupled electron transfer (PCET) reagents. Inspired by the prominence of the 2e-/2H+ disulfide/dithiol couple in biology, we investigate herein the diverse PCET reactivity of a Re complex equipped with a bipyridine ligand featuring a unique SH···-S moiety in the backbone. The disulfide bond in fac-[Re(S-Sbpy)(CO)3Cl] (1, S-Sbpy = [1,2]dithiino[4,3-b:5,6-b′]dipyridine) undergoes two successive reductions at equal potentials of-1.16 V vs Fc+|0 at room temperature forming [Re(S2bpy)(CO)3Cl]2- (12-, S2bpy = [2,2′-bipyridine]-3,3′-bis(thiolate)). 12- has two adjacent thiolate functions at the bpy periphery, which can be protonated forming the S-H···-S unit, 1H-. The disulfide/dithiol switch exhibits a rich PCET reactivity and can release a proton (G°H+ = 34 kcal mol-1, pKa = 24.7), an H atom (? G°H = 59 kcal mol-1), or a hydride ion (G°H- = 60 kcal mol-1) as demonstrated in the reactivity with various organic test substrates.
- Hua, Shao-An,Paul, Lucas A.,Oelschlegel, Manuel,Dechert, Sebastian,Meyer, Franc,Siewert, Inke
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supporting information
p. 6238 - 6247
(2021/05/07)
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- Aryl phenol compound as well as synthesis method and application thereof
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The invention discloses a synthesis method of an aryl phenol compound shown as a formula (3). All systems are carried out in an air or nitrogen atmosphere, and visible light is utilized to excite a photosensitizer for catalyzation. In a reaction solvent, ArNR1R2 as shown in a formula (1) and water as shown in a formula (2) are used as reaction raw materials and react under the auxiliary action of acid to obtain the aryl phenol compound as shown in a formula (3). The ArNR1R2 in the formula (1) can be primary amine and tertiary amine, can also be steroid and amino acid derivatives, and can also be drugs or derivatives of propofol, paracetamol, ibuprofen, oxaprozin, indomethacin and the like. The synthesis method has the advantages of cheap and easily available raw materials, simple reaction operation, mild reaction conditions, high reaction yield and good compatibility of substrate functional groups. The fluid reaction not only can realize amplification of basic chemicals, but also can realize amplification of fine chemicals, such as synthesis of drugs propofol and paracetamol. The invention has wide application prospect and use value.
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Paragraph 0121-0124
(2021/05/12)
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- Electron-rich phenoxyl mediators improve thermodynamic performance of electrocatalytic alcohol oxidation with an iridium pincer complex
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Electron-rich phenols, including α-rac-tocopherol Ar1OH, 2,4,6,-tri-tert-butylphenol Ar3OH, and butylated hydroxy-toluene Ar4OH, are effective electrochemical mediators for the electrocatalytic oxidation of alcohols by an iridium amido dihyride complex (PNP)Ir(H)2 (IrN 1, PNP = bis[2-diisopropylphosphino)ethyl]amide). Addition of phenol mediators leads to a decrease in the onset potential of catalysis from -0.65 V vs Fc+/0 under unmediated conditions to -1.07 V vs Fc+/0 in the presence of phenols. Mechanistic analysis suggests that oxidative turnover of the iridium amino trihydride (PNHP)Ir(H)3 (IrH 2, PNHP = bis[2-diisopropylphosphino)ethyl]amine) to IrN 1 proceeds through two successive hydrogen atom transfers (HAT) to 2 equiv of phenoxyl that are generated transiently at the anode. Isotope studies and comparison to known systems are consistent with initial homolysis of an Ir-H bond being rate-determining. Turnover frequencies up to 14.6 s-1 and an average Faradaic efficiency of 93% are observed. The mediated system shows excellent chemoselectivity in bulk oxidations of 2-propanol and 1,2-benzenedimethanol in THF and is also viable in neat 2-propanol.
- Galvin, Conor M.,Waymouth, Robert M.
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supporting information
p. 19368 - 19378
(2020/12/01)
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- Coordination-Induced N-H Bond Weakening in a Molybdenum Pyrrolidine Complex: Isotopic Labeling Provides Insight into the Pathway for H2Evolution
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The synthesis and characterization of a cationic molybdenum pyrrolidine complex are described that exhibits significant coordination-induced N-H bond weakening. The N-H bond dissociation free energy (BDFE) of the coordinated pyrrolidine in [(PhTpy)(PPh2Me)2Mo(NH(pyrr))][BArF24] ([1-NH(pyrr)]+PhTpy = 4′-Ph-2,2′,6′,2″-terpyridine, NH(pyrr) = pyrrolidine, ArF24 = [C6H3-3,5-(CF3)2]4) was determined to be between 41 and 51 kcal mol-1 by thermochemical analysis and supported by a density functional theory (DFT) computed value of 48 kcal mol-1. The complex [1-NH(pyrr)]+ underwent proton-coupled electron transfer (PCET) to 2,4,6-tri-tert-butylphenoxyl radical, as well as spontaneous H2 evolution upon gentle heating to furnish the corresponding molybdenum pyrrolidide complex [(PhTpy)(PPh2Me)2Mo(N(pyrr))][BArF24] ([1-N(pyrr)]+). Thermolysis of the deuterated isotopologue [1-ND(pyrr)]+ still produced H2 with concomitant incorporation of the isotopic label into the pyrrolidide ligand in the product [(1-N(pyrr-dn)]+ (n = 0-2), consistent with an H2 evolution pathway involving intramolecular H-H bond formation followed by an intermolecular product-forming PCET step. These observations provide the context for understanding H2 evolution in the nonclassical ammine complex [(PhTpy)(PPh2Me)2Mo(NH3)][BArF24] ([1-NH3]+) and are supported by DFT-computed reaction thermochemistry. Overall, these studies offer rare insight into the H2 formation pathway in nonclassical amine complexes with N-H BDFEs below the thermodynamic threshold for H2 evolution and inform the development of well-defined, thermodynamically potent PCET reagents.
- Bezdek, Máté J.,Pelczer, István,Chirik, Paul J.
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supporting information
p. 3050 - 3059
(2020/09/02)
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- Diazaphosphinanes as hydride, hydrogen atom, proton or electron donors under transition-metal-free conditions: Thermodynamics, kinetics, and synthetic applications
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Exploration of new hydrogen donors is in large demand in hydrogenation chemistry. Herein, we developed a new 1,3,2-diazaphosphinane 1a, which can serve as a hydride, hydrogen atom or proton donor without transition-metal mediation. The thermodynamics and kinetics of these three pathways of 1a, together with those of its analog 1b, were investigated in acetonitrile. It is noteworthy that, the reduction potentials (Ered) of the phosphenium cations 1a-[P]+ and 1b-[P]+ are extremely low, being-1.94 and-2.39 V (vs. Fc+/0), respectively, enabling corresponding phosphinyl radicals to function as neutral super-electron-donors. Kinetic studies revealed an extraordinarily large kinetic isotope effect KIE(1a) of 31.3 for the hydrogen atom transfer from 1a to the 2,4,6-tri-(tert-butyl)-phenoxyl radical, implying a tunneling effect. Furthermore, successful applications of these diverse P-H bond energetic parameters in organic syntheses were exemplified, shedding light on more exploitations of these versatile and powerful diazaphosphinane reagents in organic chemistry.
- Cheng, Jin-Pei,Yang, Jin-Dong,Zhang, Jingjing
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p. 3672 - 3679
(2020/04/21)
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- Diversion of Catalytic C-N Bond Formation to Catalytic Oxidation of NH3 through Modification of the Hydrogen Atom Abstractor
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We report that (TMP)Ru(NH3)2 (TMP = tetramesitylporphryin) is a molecular catalyst for oxidation of ammonia to dinitrogen. An aryloxy radical, tri-tert-butylphenoxyl (ArO·), abstracts H atoms from a bound ammonia ligand of (TMP)Ru(NH3)2, leading to the discovery of a new catalytic C-N coupling to the para position of ArO· to form 4-amino-2,4,6-tri-tert-butylcyclohexa-2,5-dien-1-one. Modification of the aryloxy radical to 2,6-di-tert-butyl-4-tritylphenoxyl radical, which contains a trityl group at the para position, prevents C-N coupling and diverts the reaction to catalytic oxidation of NH3 to give N2. We achieved 125 ± 5 turnovers at 22 °C for oxidation of NH3, the highest turnover number (TON) reported to date for a molecular catalyst.
- Bullock, R. Morris,Dunn, Peter L.,Johnson, Samantha I.,Kaminsky, Werner
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supporting information
p. 3361 - 3365
(2020/03/06)
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- Hydrogen on Cobalt Phosphide
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Cobalt phosphide (CoP) is one of the most promising earth-abundant replacements for noble metal catalysts for the hydrogen evolution reaction (HER). Critical to HER is the binding of H atoms. While theoretical studies have computed preferred sites and energetics of hydrogen bound to transition metal phosphide surfaces, direct experimental studies are scarce. Herein, we describe measurements of stoichiometry and thermochemistry for hydrogen bound to CoP. We studied both mesoscale CoP particles, exhibiting phosphide surfaces after an acidic pretreatment, and colloidal CoP nanoparticles. Treatment with H2 introduced large amounts of reactive hydrogen to CoP, ca. 0.2 H per CoP unit, and on the order of one H per Co or P surface atom. This was quantified using alkyne hydrogenation and H-atom transfer reactions with phenoxy radicals. Reactive H atoms were even present on the as-prepared materials. On the basis of the reactivity of CoP with various molecular hydrogen donating and accepting reagents, the distribution of binding free energies for H atoms on CoP was estimated to be roughly 51-66 kcal mol-1 (δG°H 0 to -0.7 eV vs H2). Operando X-ray absorption spectroscopy gave preliminary indications about the structure of hydrogenated CoP, showing a slight lattice expansion and no significant change of the effective nuclear charge of Co under H2-flow. These results provide a new picture of catalytically active CoP, with a substantial amount of reactive H atoms. This is likely of fundamental relevance for its catalytic and electrocatalytic properties. Additionally, the approach developed here provides a roadmap to examine hydrogen on other materials.
- Delley, Murielle F.,Wu, Zishan,Mundy, M. Elizabeth,Ung, David,Cossairt, Brandi M.,Wang, Hailiang,Mayer, James M.
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supporting information
p. 15390 - 15402
(2019/11/02)
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- Alkylation of Phenols with tert-Butanol Catalyzed by H-Form of Y Zeolites with a Hierarchical Porous Structure
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tert-Butyl-substituted phenols have been synthesized via the reaction of phenol, o-, m-, and p-cresols with tert-butanol under the action of CBr4-promoted Y-zeolites in the H-form with a hierarchical porous structure.
- Bayguzina,Makhiyanova,Khazipova,Khusnutdinov
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p. 1554 - 1559
(2019/10/14)
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- Conformational Change with Steric Interactions Affects the Inner Sphere Component of Concerted Proton-Electron Transfer in a Pyridyl-Appended Radical Cation System
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Proton-coupled electron transfer (PCET) model systems combine one-electron oxidants and bases to generate net hydrogen atom acceptors. We have generated two persistent pyridyl-appended radical cations: 10-(pyrid-2-yl)-10H-phenothiazinium (PPT?+) and 3-(pyrid-2-yl)-10-methyl-10H-phenothiazinium (MPTP?+). EPR spectra and corresponding calculations indicate phenothiazinium radical cations with minimal spin on the pyridine nitrogen. Addition of hindered phenols causes the radical cations to decay, and protonated products and the corresponding phenoxyl radicals to form. The ΔG° values for the formation of intermediates (determined through cyclic voltammetry and pKa measurements) rule out a stepwise mechanism, and kinetic isotope effects support concerted proton-electron transfer (CPET) as the mechanism. Calculations indicate that the reaction of PPT?+ + tBu3PhOH undergoes a significant conformational change with steric interactions on the diabatic surface while maintaining the hydrogen bond; in contrast, MPTP?+ + tBu3PhOH maintains its conformation throughout the reaction. This difference is reflected in both experiment and calculations with (Formula presented.) (Formula presented.). Experimental results with 2,6-di-tert-butyl-4-methoxyphenol are similar. Hence, despite the structural similarity between the compounds, differences in the inner sphere component for CPET affect the kinetics.
- Welker, Evan A.,Tiley, Brittney L.,Sasaran, Crina M.,Zuchero, Matthew A.,Tong, Wing-Sze,Vettleson, Melissa J.,Richards, Robert A.,Geruntho, Jonathan J.,Stoll, Stefan,Wolbach, Jeffrey P.,Rhile, Ian J.
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p. 8705 - 8712
(2015/09/15)
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- Protonation and proton-coupled electron transfer at S-ligated [4Fe-4S] clusters
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Biological [Fe-S] clusters are increasingly recognized to undergo proton-coupled electron transfer (PCET), but the site of protonation, mechanism, and role for PCET remains largely unknown. Here we explore this reactivity with synthetic model clusters. Protonation of the arylthiolate-ligated [4Fe-4S] cluster [Fe4S4(SAr)4]2- (1, SAr=S-2,4-6-(iPr)3C6H2) leads to thiol dissociation, reversibly forming [Fe4S4(SAr)3L]1- (2) and ArSH (L=solvent, and/or conjugate base). Solutions of 2+ArSH react with the nitroxyl radical TEMPO to give [Fe4S4(SAr)4]1- (1ox) and TEMPOH. This reaction involves PCET coupled to thiolate association and may proceed via the unobserved protonated cluster [Fe4S4(SAr)3(HSAr)]1- (1-H). Similar reactions with this and related clusters proceed comparably. An understanding of the PCET thermochemistry of this cluster system has been developed, encompassing three different redox levels and two protonation states. Transfer target: S-Ligated [4Fe-4S] clusters undergo proton-coupled electron transfer involving the reassociation of a thiol ligand (see figure). An understanding of the proton-coupled electron-transfer (PCET) thermochemistry of this cluster system has been developed, encompassing three different redox levels and two protonation states.
- Saouma, Caroline T.,Morris, Wesley D.,Darcy, Julia W.,Mayer, James M.
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p. 9256 - 9260
(2015/06/16)
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- Saturation kinetics in phenolic O-H bond oxidation by a mononuclear Mn(III)-OH complex derived from dioxygen
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The mononuclear hydroxomanganese(III) complex, [MnIII(OH)(dpaq)] +, which is supported by the amide-containing N5 ligand dpaq (dpaq = 2-[bis(pyridin-2-ylmethyl)]amino-N-quinolin-8-yl-acetamidate) was generated by treatment of the manganese(II) species, [MnII(dpaq)] (OTf), with dioxygen in acetonitrile solution at 25 °C. This oxygenation reaction proceeds with essentially quantitative yield (greater than 98% isolated yield) and represents a rare example of an O2-mediated oxidation of a manganese(II) complex to generate a single product. The X-ray diffraction structure of [MnIII(OH)(dpaq)]+ reveals a short Mn-OH distance of 1.806(13) A, with the hydroxo moiety trans to the amide function of the dpaq ligand. No shielding of the hydroxo group is observed in the solid-state structure. Nonetheless, [MnIII(OH)(dpaq)]+ is remarkably stable, decreasing in concentration by only 10% when stored in MeCN at 25 °C for 1 week. The [MnIII(OH)(dpaq)]+ complex participates in proton-coupled electron transfer reactions with substrates with relatively weak O-H and C-H bonds. For example, [Mn III(OH)(dpaq)]+ oxidizes TEMPOH (TEMPOH = 2,2′-6,6′-tetramethylpiperidine-1-ol), which has a bond dissociation free energy (BDFE) of 66.5 kcal/mol, in MeCN at 25 °C. The hydrogen/deuterium kinetic isotope effect of 1.8 observed for this reaction implies a concerted proton-electron transfer pathway. The [Mn III(OH)(dpaq)]+ complex also oxidizes xanthene (C-H BDFE of 73.3 kcal/mol in dimethylsulfoxide) and phenols, such as 2,4,6-tri-t- butylphenol, with BDFEs of less than 79 kcal/mol. Saturation kinetics were observed for phenol oxidation, implying an initial equilibrium prior to the rate-determining step. On the basis of a collective body of evidence, the equilibrium step is attributed to the formation of a hydrogen-bonding complex between [MnIII(OH)(dpaq)]+ and the phenol substrates.
- Wijeratne, Gayan B.,Corzine, Briana,Day, Victor W.,Jackson, Timothy A.
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supporting information
p. 7622 - 7634
(2014/08/05)
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- Photo-induced proton-coupled electron transfer reactions of acridine orange: Comprehensive spectral and kinetics analysis
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The triplet excited state of acridine orange (3*AO) undergoes a proton-coupled electron transfer (PCET) reaction with tri-tert-butylphenol (ttbPhOH) in acetonitrile. Each of the reaction components possesses a spectroscopic signature, providing a rare opportunity to monitor the individual proton transfer, electron transfer, and H ?-transfer components in parallel via transient absorption spectroscopy. This enhanced optical tracking, along with excited-state thermochemical analysis, facilitates assignment of the mechanism of excited-state PCET reactivity. 3*AO is quenched via concerted proton-electron transfer (CPET) from ttbPhOH to form acridine radical (AOH?) and ttbPhO? (kCPET = 3.7 × 108 M-1 s-1, KIE = 1.3). Subsequently, AOH? reduces the phenoxyl radical (kET = 5.5 × 109 M-1 s-1), forming AOH + and ttbPhO-, followed by proton transfer (kPT = 1.0 × 109 M-1 s-1) to regenerate the starting reactants.
- Eisenhart, Thomas T.,Dempsey, Jillian L.
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supporting information
p. 12221 - 12224
(2014/11/08)
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- Solvolysis of 4-halogeno-4-alkyl-2,6-di-tert-butylcyclohexa-2,5-dienones induced by positive halogen donors as electrophiles
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Positive halogen donors such as N-iodosuccinimide (NIS) induce solvolysis of dienones 1, as model 4-halogenocyclohexa-2,5-dienones, in different hydroxylic solvents (ROH), yielding the 4-RO-cyclohexa-2,5-dienones (2). The rate of the solvolysis with NIS is highly dependent on the structure of ROH. The problem of such dependency is overcome by running the reaction in ROH diluted with MeCN, a polar aprotic solvent, in place of pure ROH; the rate of the reaction in the ROH-MeCN solvent mixture is almost independent of the structure (or the polarity) of ROH, and the reaction is completed faster or markedly faster than in neat ROH. The results suggest that the solvolysis rate is controlled by the polarity of the solvent system, although the hydrogen-bond acceptability of MeCN for dilution also accelerates the reaction. A mechanism for the solvolysis is proposed, involving electrophilic attack of a positive halogen donor at the halogen atom of 1, generating the 4-oxocyclohexa-2,5-dienyl cation intermediates (8) via the rate-limiting polar transition states. CSIRO 2013.
- Omura, Kanji
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p. 1386 - 1392
(2013/12/04)
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- Oxidative C-C bond cleavage of α-keto acids by cobalt(II) complexes of nitrogen donor ligands
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Four cobalt(II) complexes, [(6Me3TPA)CoII(BF)] (BPh4) (1), [(TPA)CoII(BF)](BPh4) (2), [{(6Me3TPA)CoII}2(PP)](BPh4) 2 (3), and [(TPA)CoII(PPH)](BPh4) (4) [where 6Me3TPA = tris(6-methyl-2-pyridylmethyl)amine, TPA = tris(2-pyridylmethyl)amine, BF = monoanionic benzoylformate, PP = dianionic phenylpyruvate, and PPH = monoanionic phenylpyruvate], of α-keto acid derivatives have been isolated to show their versatile reactivity with dioxygen. The X-ray crystal structure of 2 suggests a five-coordinate cobalt(II) center coordinated by a monodentate benzoylformate and a tetradentate nitrogen-donor supporting ligand. Conversely, complex 3 is a dinuclear cobalt complex where two cobalt(II) centers are bridged by PP. While complex 1 is unreactive towards dioxygen, 2 reacts slowly with oxygen to exhibit quantitative decarboxylation of coordinated benzoylformate to benzoate. An active cobalt-oxygen intermediate, intercepted by external substrates, is proposed to initiate the decarboxylation reaction. Complex 3 also reacts with dioxygen but to cleave the C2-C3 bond of PP with concomitant formation of benzaldehyde and an oxalate-bridged dicobalt(II) complex [{(6Me3TPA)CoII}2(oxalate)](BPh 4)2 (5). The mononuclear PPH-cobalt(II) complex (4), unlike 2 and 3, does not undergo oxidative decarboxylation or C-C bond cleavage of PPH. In the reaction with dioxygen, 4 is oxidized to a PP-cobalt(III) complex, [(TPA)CoIII(PP)](BPh4) (6), as established from the X-ray single-crystal structure. Cobalt(II) complexes of N4 donor ligands oxidatively cleave the C-C bond of α-keto acids in the presence of dioxygen. Copyright
- Chakraborty, Biswarup,Halder, Partha,Banerjee, Priya Ranjan,Paine, Tapan Kanti
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p. 5843 - 5853
(2013/02/23)
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- β-Hydroxyalkylation of sterically hindered phenols with epoxides in acid medium
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Reactions of 2,6-dialkylphenols with ethylene oxide, propylene oxide and epichlorohydrin in the presence of SnCl4 at the temperature from -5 to +5°C leads to the formation of respective phenols containing a hydroxy group in the β-position of the aliphatic chain of the para-substituent. The conditions for maximum selectivity of the reaction of 2,6-di-tert-butylphenol with ethylene oxide were determined. By HPLC-MS method the directions of the side reactions were explored. The method has been successfully tested in a pilot installation. With 2,6-dimethylphenol instead of 2,6-di-tert-butylphenol a sharp increase occurs in the content of ethers in the reaction product. With epichlorohydrin, 2,6-di-tert-butylphenol affords a product, which is easily converted into an epoxide containing a sterically hindered phenol in its structure.
- Krysin,Amitina,Egorova,Vasiliev
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experimental part
p. 354 - 360
(2011/06/27)
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- LIQUID ALKYLATED TRISARYL PHOSPHITE COMPOSITIONS HAVING TWO ALKYL GROUPS WITH DIFFERENT CARBON NUMBER
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A composition comprising at least two different alkylaryl phosphites, wherein some alkyl groups have a different number of carbon atoms than other alkyl groups and wherein the composition is a liquid at ambient conditions.
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Page/Page column 42
(2011/02/24)
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- Organochalcogen substituents in phenolic antioxidants
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Little is known about the ED/EW character of organochalcogen substituents and their contribution to the O-H bond dissociation enthalpy (BDE) in phenolic compounds. A series of ortho- and para-(S,Se,Te)R-substituted phenols were prepared and investigated by EPR, IR, and computational methods. Substituents lowered the O-H BDE by >3 kcal/mol in the para position, while the ortho-effect was modest due to hydrogen bonding (~3 kcal/mol) to the O-H group.
- Amorati, Riccardo,Pedulli, Gian Franco,Valgimigli, Luca,Johansson, Henrik,Engman, Lars
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scheme or table
p. 2326 - 2329
(2010/07/20)
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- Chloroindate(iii) ionic liquids as catalysts for alkylation of phenols and catechol with alkenes
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Chloroindate(iii) ionic liquids are shown to be versatile catalysts for the alkylation of phenols with alkenes, giving high conversions to alkylated phenols with high selectivities.
- Gunaratne, H. Q. Nimal,Lotz, Tobias J.,Seddon, Kenneth R.
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scheme or table
p. 1821 - 1824
(2011/01/07)
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- Electron transfer between protonated and unprotonated phenoxyl radicals
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(Chemical Equation Presented) The reaction of phenoxyl radicals with acids is investigated. 2,4,6-Tri-tert-butylphenoxyl radical (13), a persistent radical, deteriorates in MeOH/PhH in the presence of an acid yielding 4-methoxycyclohexa-2,5-dienone 18a and the parent phenol (14). The reaction is facilitated by a strong acid. Treatment of 2,6-di-tert-butyl-4-methylphenoxyl radical (2), a short-lived radical, generated by dissociation of its dimer, with an acid in MeOH provides 4-methoxycyclohexa-2,5-dienone 4 and the products from disproportionation of 2 including the parent phenol (3). A strong acid in a high concentration favors the formation of 4 while the yield of 3 is always kept high. Oxidation of the parent phenol (33) with PbO2 to generate transient 2,6-di-tert-butylphenoxyl radical (35) in AcOH/H2O containing an added acid provides eventually p-benzoquinone 39 and 4,4′-diphenoquinone 42, the product from dimerization of 35. A strong acid in a high concentration favors the formation of 39. These results suggest that a phenoxyl radical is protonated by an acid and electron transfer takes place from another phenoxyl radical to the protonated phenoxyl radical, thus generating the phenoxyl cation, which can add an oxygen nucleophile, and the phenol (eq 5). The electron transfer is a fast reaction.
- Omura, Kanji
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p. 858 - 867
(2008/09/19)
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- ALKYLATION OF HYDROXYARENES WITH OLEFINS, ALCOHOLS AND ETHERS IN IONIC LIQUIDS
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Hydroxyarenes are alkylated using an ionic liquid catalyst system with olefins, alcohols, or ethers as alkylating agents. The ionic liquid catalyst system comprises chloroindate (III) anions. The reactions may be conducted at moderate temperatures and pressures to yield commercially relevant alkylated hydroxyarene compounds.
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Page/Page column 19-20
(2008/06/13)
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- Alkyl substituted phenoxyl decay in a hydrogen transfer equilibrium
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The kinetics of radical decay in the equilibrium: 2,4.6-tri-tert- butylphenoxyl radical 1 + 2,6-di-tert-butyl-4-methylphenol 2 = 2.4,6-tri-tert-butylphenol 3 + 2,6-di-tert-butyl-4-methylphenoxyl radical 4 was studied at 298 and 273 K by means of EPR spectroscopy. At 298 K second order prevails, whereas at 273 K the best fit was order 3/2. The extinction of 4 takes place in two steps: dimerization followed by disproportionation of the dimer, but the stable radical 1 enters in crossed dimerization with 4 to yield nonradical products. The mechanism ensures a constant |4|/|1| ratio along the decay. 2004 Wiley Periodicals, Inc.
- Coronel, Marta E. J.
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- Reactivity of tris(trimethylsilyl)silane toward diarylaminyl radicals
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Absolute rate constants for the reaction of tri-tert-butylphenoxyl radical (ArO·) with (TMS)3SiH were measured spectrophotometrically in the temperature range 321-383 K. Rate constants for the hydrogen abstraction from (TMS)3SiH by diarylaminyl radicals of type (4-X-C6H4)2N· were determined by using a method in which the corresponding amines catalyze the reaction of ArO· with (TMS)3SiH. At 364.2 K, rate constants·are in the range of 2-50 M-1 s-1 for X = H, CH3, CH3O, and Br, whereas the corresponding value for ArO· is 3 orders of magnitude lower. A common feature of these reactions is the low preexponential factor [log(A/M-1 s-1) of 4.4 and 5.2 for ArO· and Ph2N·, respectively], which reflects high steric demand in the transition state. A semiempirical approach based on intersecting parabolas suggests that the observed reactivity is mainly related to the enthalpy of the reaction and allowed to estimate activation energies for the reaction of (4-X-C6H4)2N· and ArO· radicals with a variety of silicon hydrides.
- Varlamov,Denisov,Chatgilialoglu
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p. 6317 - 6322
(2007/10/03)
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- The selective functionalization of saturated hydrocarbons. Part 47, investigation of the size of the reagent involved in the Fe(II)-Fe(IV) manifold
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Competition experiments between cyclohexane and various aromatic substrates have been carried out in pyridine-acetonitrile in order to ascertain the steric requirements of the Fe(II)-H2O2 reagent in comparison with the Fe(III)-H2O2 reagent already studied. The latter is distinctly larger and much less reactive than the former. Although these results might indicate that the Fe(II)H2O2 reagent is simply the hydroxyl radical, the chemistry observed is strictly dependent on the presence of picolinic acid. Without the latter, no significant oxidation of any substrate is observed. Hydroxyl radical formation (Fenton Chemistry) is not considered to be ligand dependent in preceding investigations.
- Barton, Derek H.R.,Launay, Franck
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p. 12699 - 12706
(2007/10/03)
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- Radical ion probes, 8. Direct and indirect electrochemistry of 5,7-di-tert-butylspiro[2.5]octa-4,7-dien-6-one and derivatives
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Results pertaining to the direct and indirect electrochemistry of 5,7-di-tert-butylspiro[2.5]octa-4,7-dien-6-one (1a), 1-methyl-5,7-di-tert-butylspiro[2.5]octa-4,7-dien-6-one (1b), and 1,1,-dimethyl-5,7-di-tert-butylspiro[2.5]octa-4,7-dien-6-one (1c) are reported. Product analyses reveal that reduction of all these substrates leads to cyclopropane ring-opened products; ring opening occurs with modest selectivity leading to the more substituted (stable) distonic radical anion. The direct electrochemistry of these compounds is characterized by rate limiting electron transfer (with α ~ 0.5), suggesting that while ring opening is extremely rapid, the radical anions do have a discrete lifetime (i.e., electron transfer and ring opening are not concerted). Utilizing homogeneous redox catalysis, rate constants for electron transfer between 1a, 1b, and 1c and a series of aromatic radical anions were measured; reduction potentials and reorganization energies were derived from these rate constants by using Marcus theory.
- Phillips, J. Paige,Gillmore, Jason G.,Schwartz, Phillip,Brammer Jr., Larry E.,Berger, Daniel J.,Tanko
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p. 195 - 202
(2007/10/03)
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- Effect of Solvation on the Bond Dissociation Energies of Phenolic Antioxidants
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The effect of solvent on the bond dissociation energies (BDEs) of the oxygen-hydrogen bond in substituted phenolic antioxidants has been investigated by means of an EPR technique.On changing the solvent from benzene to tert-butanol the BDE's were found to increase by ca. 2.2 kcal/mol for phenols without ortho substituents, by ca. 1 kcal/mol for 2,6-dimethyl substituted phenols while in 2,6-di-tert-butyl phenols they seem to be substantially unaffected.This behaviour has been interpreted by admitting that the BDE increase observed in tert-butanol is essentially due to the solvation of the hydroxylic hydrogen which stabilises the phenol, leaving the energy of the phenoxyl radical unaltered.Thus, solvation effects are expected to be large with unhindered phenols and relatively unimportant in phenols containing bulky substituents in the proximity of the OH group.
- Pedrielli, Pamela,Pedulli, Gian Franco
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p. 509 - 512
(2007/10/03)
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- On the Structures of the Intermediates from Reversible Coupling between Hindered Phenoxy Radicals
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Hindered phenoxy radicals 1 and 2 are found to undergo reversible, C-C rather than C-O cross-coupling, and give bis(cyclohexadienone)s 14 and 17.These primary products are not isolable but are recovered as phenolic cyclohexadienones 15 and 18, respectively, after treatment with Et3N or as biphenols 16 and 12, respectively, after treatment with TFA.The other products obtained after treating the reaction mixture with Et3N or TFA are phenol 5 and 4,4'-diphenoquinone 13 alone.Dienones 14 and 17 are interconvertible with each other via dissociation into the parent radicals, and 14 appears to be thermodynamically more stable than 17.Phenoxy radical 1 and other, less hindered 2,6-dialkylphenoxy radicals 24 also form intermediates of reversible cross-coupling.Treatment with TFA of the mixtures containing the intermediates provides 2,4'-biphenols 25 preferentially.
- Omura, Kanji
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p. 6901 - 6910
(2007/10/02)
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- Utilization of 1,1-Dimethyl-4,6-di-tert-butylspiroocta-3,6-dien-5-one as a 'Hypersensitive' Probe for Single Electron Transfer to Carbonyl Compounds
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The use of 1,1-dimethyl-4,6-di-tert-butylspiroocta-3,6-dien-5-one 1 as a 'hypersensitive' probe for single electron transfer in the reaction of several nucleophiles (RMgX, RLi and R2CuLi) with carbonyl compounds is demonstrated.
- Tanko, James M.,Brammer, Larry E.
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p. 1165 - 1166
(2007/10/02)
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- Novel Reduction of 2,6-Di-t-butyl-p-quinols with Sodium Borohydride
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Reduction of 2,6-di-t-butyl-p-quinols with NaBH4 results unexpectedly in the regio- and stereoselective formation of the corresponding dihydro-p-quinols.The novel reduction occurs via a quinoxyborohydride anion intermediate, which regulates the stereochemistry of the 4- and 6-positions in the products.Aromatization of the products is blocked by the t-butyl groups.
- Nishinaga, Akira,Kojima, Shinya,Mashino, Takahiro,Maruyama, Kazushige
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p. 961 - 964
(2007/10/02)
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- Free Radical Reactions of N-Heterocyclic Compounds. XIII. Oxidation of Cyclic Hydrazo Compounds with 2,4,6-Tri-tert-butyl-phenoxy Radical and Reactions of Radical Combination Products
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H-Heterocyclic compounds 1a,b containing the hydrazo structure were oxidized with 2,4,6-tri-tert-butyl-phenoxy radical (2).It was shown that the oxidation did not lead to the azo compounds 5a,b, but rather to radical combination products 6a,b of 2 via the intermediate hydrazyls 4a,b.The decomposition of adducts 6a,b was found to be similar to the reaction of radical combination products of aryl hydrazyls and CH-acidic compounds.The main reactions consisted of cleavage to starting radicals or elimination of isobutene forming the respective phenolic compounds 13a-c.
- Schulz, Manfred,Meske, Michael,Kluge, Ralph
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p. 350 - 354
(2007/10/02)
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- Bond Dissociation Enthalpy of α-Tocopherol and Other Phenolic Antioxidants
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The equilibrium constants, K1, for the reaction between galvinoxyl and a series of phenolic antioxidants have been determined by means of EPR spectroscopy.With aroxyl radicals decaying at appreciable rates, K1 was obtained by performing kinetic analyses of the time dependence of the concentrations of the equilibrating radicals after mixing the reactants.In two cases the temperature dependence of K1 was also studied and the entropy change for the equilibration reaction was determined.Bond dissociation enthalpies, DH, of the ArO-H bond of the examined phenols were calculated by comparison with the known value of 2,4,6-tri-tert-butylphenol (81.24 kcal mol-1).A larger than expected DH value was found for probucol (81.03 kcal mol-1) and an explanation of this behavior was given in terms of the preferred conformation adopted by the para alkylthio group.The DH value of α-tocopherol (78.93 kcal mol-1) was found to be very close to that of the phenolic precursor of galvinoxyl (78.80 kcal mol-1) and somewhat larger than that of 2,6-di-tert-butyl-4-methoxyphenyl (77.61 kcal mol-1).
- Lucarini, Marco,Pedulli, Gian Franco,Cipollone, Marta
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p. 5063 - 5070
(2007/10/02)
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- Characterization of a 'Hypersensitive' Probe for Single Electron Transfer to Carbonyl Compounds
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The radical anion generated from 1,1-dimethyl-5,7-di-tert-butylspiroocta-4,7-dien-6-one (1) undergoes facile ring opening yielding both the 3o and 1o distonic radical ions in a ratio of 9:1 with a rate constant 107 s-1 (relief of cyclopropane ring strain and the generation of an aromatic ring provide the thermodynamic driving force for this rearrangement), the facility of C-C bond cleavage in this radical anion and the observed electrochemistry are reminiscent of the reductive cleavage of carbon-halogen bonds in alkyl and benzylic halides: on the basis of these results, 1 emerges as a viable substrate for use as a hypersensitive SET probe in mechanistic studies.
- Tanko, James M.,Brammer, Larry E.,Hervas, Manuel,Campos, Kevin
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p. 1407 - 1410
(2007/10/02)
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- Cyclopentenone formation via hydrogen activation in the reactions of chromium carbene complexes with alkynes
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The reactions of alkyl chromium carbene complexes with alkynes have been found to give cyclopentenones. Mechanisms are proposed to account for the formation of these products that involve metal hydride intermediates. As has been previously reported for tungsten, molybdenum alkyl complexes have been found to give 1,3-dienes rather than cyclopentenones. The difference between chromium and molybdenum and tungsten may be that a metal hydride intermediate can re-add to an olefin in the case of chromium rather than undergo reductive elimination. A mechanism for the formation of cyclopentenones involving a free vinylketene was ruled out on the basis of an experiment in which the free vinylketene was generated via thermolysis of a cyclobutenone and found not to give a cyclopentenone product but rather an intramolecular [2 + 2] cycloadduct.
- Challener, Cynthia A.,Wulff, William D.,Anderson, Benjamin A.,Chamberlin, Steve,Faron, Katherine L.,Kim, Oak K.,Murray, Christopher K.,Xu, Yao-Chang,Yang, Dominic C.,Darling, Stephen D.
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p. 1359 - 1376
(2007/10/02)
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- Free Radical Reactions of N-Heterocyclic Compounds, X. - Radical Reactions of Cyclic 1,2-Diacylhydrazines
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Cyclic 1,2-diazylhydrazyls 3 have been detected by ESR spectroscopy during oxidation of the corresponding NH compounds 2.The N coupling constants are determined and confirmed by simulation and by (15)N labeling.The hydrazyls 3 react by dimerization to the corresponding tetrazenes of type 5 or by β scission to the diazyl azo compounds 4 and C radicals.The β scission of the radicals 3 is elucidated by UV/Vis detection of the azo compound 4b and reaction of 4b to Diels-Alder adducts.The alkyl radicals are trapped by nitrosobenzene (8) (ESR). Key Words: Hydrazines, cyclic, 1,2-diacyl- / Oxidation / Hydrazyls / Hydrazine oxyls / ESR
- Kluge, Ralph,Omelka, Ladislav,Reinhardt, Michael,Schulz, Manfred
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p. 2075 - 2080
(2007/10/02)
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- STUDY OF THE REVERSIBLE REACTION BETWEEN THE DIPHENYLAMINYL RADICAL AND STERICALLY HINDERED PHENOL
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Two methods of determining the equilibrium constant of the reaction of the diphenylaminyl radical with 2,4,6-tri-tert-butylphenol were proposed; they are based on the high reactivity of aminyl radicals in cleavage of a H atom from phenol and phenoxyl radicals in cleavage of an H atom from an amine.In the first method (generation of aminyl radicals in a system containing phenol and amine), the forward reaction goes into quasiequilibrium, and the maximum concentration of phenoxyl radical formed and the concentrations of the other components calculated from the stoichiometry are used for calculating the equilibrium constant.In the second method (kinetic features of consumption of the phenoxyl radical in the presence of amine and phenol), the reverse reaction goes into quasiequilibrium, and the equilibrium constant is calculated in this case using the initial segments of the kinetic curve of consumption of phenoxyl.Both methods give similar values of the equilibrium constant.
- Varlamov, V. T.
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p. 1601 - 1606
(2007/10/02)
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- Trimethylsilyl Cyanide - A Reagent for Umpolung, XVI. - Effect of Umpolung Moieties on the Diastereoselectivity of the Nucleophilic Acylation of α-Chiral Carbonyl Compounds
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Umpolung of benzaldehyde leads to derivatives 1a-h, which add to the aldehydes 2a and 2c as well as to the ketones 2b and 2d in high yields, if side reactions are excluded by proper choice of conditions.Determined with the acyloins 4 or their silyl ethers 5, the diastereoselectivity of this reaction depends only slightly on the groups used for umpolung (1e > 1c > 1d > 1a ca. 1b ca. 1g > 1h > 1f).Strong effects are observed for the substituents at the center of chirality of the electrophiles 2.Whereas a syn/anti selectivity of ca. 95:5 in products 4 and 5 is obtained by an α-phenyl group in 2, only a 52:48-71:29 ratio is produced by an α-ethyl group.In case of 4d the syn/anti ratio is raised from 63:37 to 80:20 by optimizing the conditions.The observed Cram selectivity is explained by the model of Anh. - Key Words: Umpolung/ Diastereoselectivity/ Acyloins/ Substituent effects/ Nucleophilic acylation
- Huenig, Siegfried,Marschner, Claus
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p. 1329 - 1340
(2007/10/02)
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- ELECTRON-TRANSFER PROCESSES. PART 40. REACTION OF ALKYL RADICALS WITH DIPHENYLPHOSPHIDE ANION
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The anion Ph2P- (K+, 18-crown-6) reacts with t-BuHgCl in HMPA to form Ph2PCMe3 by a free radical chain mechanism.In Me2SO, PhP(O)CMe3 is produced.Reaction of Ph2P- with PhCOCH2HgCl yields the oxidative dimerization product isolable from HMPA but readily converted to Ph2P(O)P(O)Ph2 in Me2SO.
- Russell, Glen A.,Khanna, Rajive K.
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p. 271 - 274
(2007/10/02)
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- Kinetics and Mechanisms of Oxygen Transfer in the Reaction of p-Cyano-N,N-Dimethylaniline N-Oxide with Metalloporphyrin Salts. 3. Catalysis by iron(III) Chloride
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Decomposition of p-cyano-N,N-dimethylaniline N-oxide (NO) catalyzed by iron(III) chloride ((Cl8TPP)FeIIICl) yields as products p-cyano-N,N-dimethylaniline (DA), p-cyano-N-methylaniline (MA), and formaldehyde (CH2Cl2 solvent, 25 deg C, N2 atmosphere).Intermediate in the reaction are mono and bis NO complexes (Cl8TPP(Cl)FeIIINO and Cl8TPP(NO)FeIIINO, respectively).Oxygen transfer from the complexed NO species to the iron porphyrin is rate-limiting and provides the higher valent iron(IV) salts (IVO>+. and IVO>+.) and DA.The observed kinetics for reactions involving 10-100 turnovers of catalyst dictate that the catalyst is saturated in the formation of Cl8TPP(Cl)FeIIINO and that formation of Cl8TPP(NO)FeIIINO is unfavorable.The two iron(IV)-oxo porphyrin ?-cation radical species are converted back to the iron(III) porphyrin catalytic moieties by oxidation of DA -> MA + CH2O and oxidation of CH2O.Addition of 2,4,6-tri-tert-butylphenol (TBPH), 2,3-dimethyl-2-butene (TME), and cyclohexene results in the formation of TBP. and the respective epoxides, thus inhibiting the oxidation of DA and CH2O.The kinetics of the overall reaction and formation of each product may be simulated by employing the reactions of Scheme II and eq l-r, and from the simulations, the rates and equilibria, leading to the formation of the two iron(IV)-oxo porphyrin ?-cation radical species may be determined as can minimal rate constants for the oxidations of DA, CH2O, and TBPH and the epoxidation of TME and cyclohexene.The results obtained herein with the electron-deficient porphyrin, (Cl8TPP)Fe(III)Cl, are discussed and compared to those obtained previously when employing (TPP)FeIIICl as the catalyst.
- Dicken, C. Michael,Woon, T. C.,Bruice, Thomas C.
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p. 1636 - 1643
(2007/10/02)
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- Some Rearrangements of 2,4,6-Tri-t-butyl-4-nitrocyclohexa-2,5-dienone
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Rearrangement of 2,4,6-tri-t-butyl-4-nitrocyclohexa-2,5-dienone (20) in benzene gives the 4-hydroxy dienone (21) and the mono-de-t-butylated 1,2-benzoquinone (22).The rearrangement is not affected by the addition of mesitylene, but the phenol-coupling product (26) is formed in the presence of p-cresol, and the nitromethyl phenol (31) is formed when the nitro dienone (20) rearranges in the presence of 2,4,6-trimethylphenol (29).The rearrangements of the nitro dienone (20) in methanol are described.
- Hartshorn, Michael P.,Kennedy, James A.,Simpson, Richard W.,Vaughan, John,Wright, Graeme J.
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p. 735 - 743
(2007/10/02)
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- Cyclodienones. X. Reaction of Halo-cyclohexadien-1-ones with Phenols in the Presence of α-Picoline and Preparation of 4-Hydroxy- and 2-Hydroxyphenyl Aryl Ethers
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Reaction of 4-halocyclohexadienones such as 4-bromo-(1a), 4-chloro-2,4,6-tri-t-butyl-(1b), 2,4-dichloro-4,6-di-t-butyl-2,5-cyclohexadien-1-one, and 2,4-dichloro-2,6-di-t-butyl-3,5-cyclohexadien-1-one with phenols in the presence of α-picoline was carried out under various conditions.The reaction of 1a and 1b with phenols afforded the corresponding 2-aryloxy-4,6-di-t-butyl phenols together with various by-products.The AlCl3 catalyzed trans-t-butylation of 2-aroxy-4,6-di-t-butyl-phenols, which were obtained by the above reaction, afforded the corresponding 2-hydroxyphenyl aryl ethers.The similar reaction of 4-aroxy-2,4,6-tri-t-butyl-2,5-cyclohexadien-1-ones also afforded the corresponding 4-hydroxyphenyl aryl ethers.
- Tashiro, Masashi,Itoh, Takashi,Fukata, Gouki
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p. 416 - 420
(2007/10/02)
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- Silica Gel as an Effective Catalyst for the Alkylation of Phenols and Some Heterocyclic Compounds
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In the presence of silica gel, the reaction of phenol with t-BuBr was examined under a variety of conditions and it was found that silica gel is an effective catalyst for the alkylation.As a result of this work 2-tert-butyl-, 2,6-di-tert-butyl-, and 2,4,6-tri-tert-butylphenols, all of which are hard to obtain directly by the Friedel-Crafts process, could be prepared easily by this one-step reaction.Several other alkyl halides were also used in this reaction.The alkylations of some heterocyclic aromatic compounds which cannot be alkylated by the conventional Friedel-Crafts method were also succesfully performed by this reaction.
- Kamitori, Yasuhiro,Hojo, Masaru,Masuda, Ryoichi,Izumi, Tatsuo,Tsukamoto, Shuichi
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p. 4161 - 4165
(2007/10/02)
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- Ring Opening Reactions of Methyl 2-Siloxycyclopropanecarboxylates to Oxoalkanoic Acid Derivatives
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A great variety of methyl 2-(trialkylsiloxy)cyclopropanecarboxylates C1 - C31 are cleaved under very mild conditions and with excellent yields providing 4-oxoalkanoic esters D1 - D31 which are important synthetic building blocks.Even sensible esters with formyl, vinyl ketone, or trimethylsiloxy functions can be prepared.Corresponding to the regioselective synthesis of C isomeric pairs of D can deliberately be constructed.In the presence of an electrophile alkylating ring opening delivers 4-oxoalkanoates substituted in position 2, however, the degree of alkylation does not exceed 60percent.Several other cleavage variations allow syntheses of other 4-oxoalkanoic acid derivatives in effective one-pot procedures.
- Kunkel, Elisabeth,Reichelt, Ingrid,Reissig, Hans-Ulrich
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p. 802 - 819
(2007/10/02)
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