- Experimental study on the mechanism of gas-phase aromatic nitration by protonated methyl nitrate
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The mechanism of gas-phase aromatic substitution by (CH3ONO2)H+ ions has been studied by a combination of FT-ICR mass spectrometry and atmospheric pressure radiolytic techniques. Clarifying a long-standing ambiguity, the ICR results characterize the CH3OH-NO2+ complex (1), in essence a nitronium ion solvated by a methanol molecule, as the nitrating agent, whereas the CH3NO2H+ isomer (2) is devoid of nitrating properties and reacts with benzene exclusively as a Br?nsted acid. Indeed, the reaction with benzene has been exploited as an ICR "titration" technique to evaluate the relative abundances of 1 and 2 in mixed populations of (CH3ONO2)H+ ions from different preparative procedures. Radiolytic nitration of p-H-toluene-d7 and p-D-toluene-h7 leads to intraannular hydron migration from the ipso nitrated position, whose rate has been estimated to be ca. 1.6 × 106 s-1 at 315 K. The mutually supporting evidence from the ICR and the radiolytic experiments outlines a reaction mechanism involving preliminary formation of a Wheland intermediate from the attack of 1 on the arene, followed by its isomerization into the more stable O-protonated nitrobenzene structure via a proton shift whose rate is estimated to be ca. 3.6 × 107s-1 at 315 K. The results are compared with those of a recent theoretical analysis of the mechanism of aromatic nitration by isomeric (CH3ONO2)H+ ions, and their correlation with condensed-phase nitration is briefly discussed.
- Aschi, Massimiliano,Attinà, Marina,Cacace, Fulvio,Ricci, Andreina
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Read Online
- Hydrogenation of CO2 to Methanol by Pt Nanoparticles Encapsulated in UiO-67: Deciphering the Role of the Metal-Organic Framework
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Metal-organic frameworks (MOFs) show great prospect as catalysts and catalyst support materials. Yet, studies that address their dynamic, kinetic, and mechanistic role in target reactions are scarce. In this study, an exceptionally stable MOF catalyst consisting of Pt nanoparticles (NPs) embedded in a Zr-based UiO-67 MOF was subject to steady-state and transient kinetic studies involving H/D and 13C/12C exchange, coupled with operando infrared spectroscopy and density functional theory (DFT) modeling, targeting methanol formation from CO2/H2 feeds at 170 °C and 1-8 bar pressure. The study revealed that methanol is formed at the interface between the Pt NPs and defect Zr nodes via formate species attached to the Zr nodes. Methanol formation is mechanistically separated from the formation of coproducts CO and methane, except for hydrogen activation on the Pt NPs. Careful analysis of transient data revealed that the number of intermediates was higher than the number of open Zr sites in the MOF lattice around each Pt NP. Hence, additional Zr sites must be available for formate formation. DFT modeling revealed that Pt NP growth is sufficiently energetically favored to enable displacement of linkers and creation of open Zr sites during pretreatment. However, linker displacement during formate formation is energetically disfavored, in line with the excellent catalyst stability observed experimentally. Overall, the study provides firm evidence that methanol is formed at the interface of Pt NPs and linker-deficient Zr6O8 nodes resting on the Pt NP surface.
- Gutter?d, Emil S.,Lazzarini, Andrea,Fjermestad, Torstein,Kaur, Gurpreet,Manzoli, Maela,Bordiga, Silvia,Svelle, Stian,Lillerud, Karl P.,Skúlason, Egill,?ien-?Degaard, Sigurd,Nova, Ainara,Olsbye, Unni
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supporting information
p. 999 - 1009
(2020/02/20)
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- Formation of Glyoxylic Acid in Interstellar Ices: A Key Entry Point for Prebiotic Chemistry
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With nearly 200 molecules detected in interstellar and circumstellar environments, the identification of the biologically relevant α-keto carboxylic acid, glyoxylic acid (HCOCOOH), is still elusive. Herein, the formation of glyoxylic acid via cosmic-ray driven, non-equilibrium chemistry in polar interstellar ices of carbon monoxide (CO) and water (H2O) at 5 K via barrierless recombination of formyl (HCO) and hydroxycarbonyl radicals (HOCO) is reported. In temperature-programmed desorption experiments, the subliming neutral molecules were selectively photoionized and identified based on the ionization energy and distinct mass-to-charge ratios in combination with isotopically labeled experiments exploiting reflectron time-of-flight mass spectrometry. These studies unravel a key reaction path to glyoxylic acid, an organic molecule formed in interstellar ices before subliming in star-forming regions like SgrB2(N), thus providing a critical entry point to prebiotic organic synthesis.
- Eckhardt, André K.,Bergantini, Alexandre,Singh, Santosh K.,Schreiner, Peter R.,Kaiser, Ralf I.
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supporting information
p. 5663 - 5667
(2019/03/29)
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- Synthesis of ethanol via a reaction of dimethyl ether with CO2 and H2
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Ethanol is currently produced via the catalytic hydration of ethylene or fermentation of foods. The synthesis of ethanol from cheap and renewable CO2 is of great importance, but the state of the art routes encounter difficulties, especially in reaction selectivity and activity. Here we show a strategy of ethanol synthesis from CO2, dimethyl ether (DME) and H2. The reaction can be effectively promoted with a Ru-Co bimetallic catalyst using LiI as a promoter in 1,3-dimethyl-2-imidazolidinone (DMI) solvent. The predominant product of this reaction was ethanol and the selectivity of ethanol in total products could reach 71.7 C-mol%. The selectivity of ethanol in the liquid product could reach 94.1%, which was higher than the reported routes using CO2/CO. To the best of our knowledge, this is the first work on ethanol synthesis from DME, CO2 and H2. The reaction mechanism is discussed based on a series of control experiments.
- Qian, Qingli,Cui, Meng,Zhang, Jingjing,Xiang, Junfeng,Song, Jinliang,Yang, Guanying,Han, Buxing
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supporting information
p. 206 - 213
(2018/01/12)
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- Aqueous phase hydrodeoxygenation of polyols over Pd/WO3-ZrO2: Role of Pd-WO3 interaction and hydrodeoxygenation pathway
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Aqueous phase processing of biomass derived sugar alcohols is one of the promising routes to convert biomass into fuels and chemicals. Bifunctional catalysts are critical in the aqueous phase hydrodeoxygenation of sugar alcohol. Understanding the interaction between metal and acidic metal oxides as well as the hydrodeoxygenation pathways will help develop more efficient bifunctional catalysts. Here, tungstated zirconia supported palladium catalysts were prepared and further characterized using nitrogen sorption, X-ray diffraction, FT-IR analysis of adsorbed pyridine, CO chemisorption and diffuse reflectance UV-vis. Strong interaction between palladium and WO3 in addition to a synergetic effect of the acidic and metallic sites were found to promote the aqueous phase hydrodeoxygenation of ethylene glycol. H-D exchange experiments using 13C{1H} NMR spectroscopy confirmed that the aqueous phase hydrodeoxygenation follows a dehydration-hydrogenation pathway. The hydrogenation of the dehydration products shifts the dehydration-hydration equilibrium toward the dehydration pathway and leads to highly selective C-O cleavage.
- Liu, Changjun,Sun, Junming,Brown, Heather M.,Marin-Flores, Oscar G.,Bays, J. Timothy,Karim, Ayman M.,Wang, Yong
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p. 103 - 109
(2016/05/11)
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- Transfer hydrogenation of organic formates and cyclic carbonates: An alternative route to methanol from carbon dioxide
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Transfer hydrogenation of organic formates and cyclic carbonates was achieved for the first time using a readily available ruthenium catalyst. Nontoxic and economical 2-propanol was used, both as a solvent and hydrogen source, without the need of using flammable H2 gas under high pressure. This method provides an indirect strategy to produce methanol from carbon dioxide under mild conditions as well as an operationally simple and environmentally benign way to reduce formates and carbonates.
- Kim, Seung Hyo,Hong, Soon Hyeok
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p. 3630 - 3636
(2015/02/19)
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- Using reduced catalysts for oxidation reactions: Mechanistic studies of the "periana-catalytica" system for CH4 oxidation
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Designing oxidation catalysts based on CH activation with reduced, low oxidation state species is a seeming dilemma given the proclivity for catalyst deactivation by overoxidation. This dilemma has been recognized in the Shilov system where reduced PtII is used to catalyze methane functionalization. Thus, it is generally accepted that key to replacing Pt IV in that system with more practical oxidants is ensuring that the oxidant does not over-oxidize the reduced PtII species. The "Periana-Catalytica" system, which utilizes (bpym)Pt IICl2 in concentrated sulfuric acid solvent at 200 C, is a highly stable catalyst for the selective, high yield oxy-functionalization of methane. In lieu of the over-oxidation dilemma, the high stability and observed rapid oxidation of (bpym)PtIICl2 to PtIV in the absence of methane would seem to contradict the originally proposed mechanism involving CH activation by a reduced PtII species. Mechanistic studies show that the originally proposed mechanism is incomplete and that while CH activation does proceed with PtII there is a solution to the over-oxidation dilemma. Importantly, contrary to the accepted view to minimize PtII overoxidation, these studies also show that increasing that rate could increase the rate of catalysis and catalyst stability. The mechanistic basis for this counterintuitive prediction could help to guide the design of new catalysts for alkane oxidation that operate by CH activation.
- Mironov, Oleg A.,Bischof, Steven M.,Konnick, Michael M.,Hashiguchi, Brian G.,Ziatdinov, Vadim R.,Goddard, William A.,Ahlquist, Maisrten,Periana, Roy A.
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supporting information
p. 14644 - 14658
(2013/10/22)
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- Stepwise photocatalytic dissociation of methanol and water on TiO 2(110)
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We have investigated the photocatalysis of partially deuterated methanol (CD3OH) and H2O on TiO2(110) at 400 nm using a newly developed photocatalysis apparatus in combination with theoretical calculations. Photocatalyzed products, CD2O on Ti5c sites, and H and D atoms on bridge-bonded oxygen (BBO) sites from CD3OH have been clearly detected, while no evidence of H2O photocatalysis was found. The experimental results show that dissociation of CD3OH on TiO2(110) occurs in a stepwise manner in which the O-H dissociation proceeds first and is then followed by C-D dissociation. Theoretical calculations indicate that the high reverse barrier to C-D recombination and the facile desorption of CD2O make photocatalytic methanol dissociation on TiO2(110) proceed efficiently. Theoretical results also reveal that the reverse reactions, i.e, O-H recombination after H2O photocatalytic dissociation on TiO2(110), may occur easily, thus inhibiting efficient photocatalytic water splitting.
- Guo, Qing,Xu, Chenbiao,Ren, Zefeng,Yang, Wenshao,Ma, Zhibo,Dai, Dongxu,Fan, Hongjun,Minton, Timothy K.,Yang, Xueming
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supporting information; experimental part
p. 13366 - 13373
(2012/10/07)
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- Enantioselective synthesis of stephacidin B
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We describe an enantioselective synthetic route to the antiproliferative alkaloid stephacidin B (1) proceeding in 18 steps and 4.0% yield from 4,4-(ethylenedioxy)-2,2-dimethylcyclohexanone (3). Key features of the synthetic sequence include the use of the Corey-Bakshi-Shibata (CBS) reduction to introduce asymmetry early in the synthetic route, use of the novel electrophile N-(tert-butoxycarbonyl)-5-(isopropylsulfonyloxymethyl)-2,3-dihydropyrrole in a stereoselective enolate alkylation, a diastereoselective Strecker-type addition of hydrogen cyanide to an N-Boc enamine substrate in the solvent hexafluoroisopropanol, platinum-catalyzed nitrile hydrolysis under neutral conditions, cyclization of an acylamino radical intermediate to form the diketopiperazine core of stephacidin B, and implementation of a convergent procedure for introduction of the key 3-alkylidene-3H-indole 1-oxide functional group in the final stage of the route to prepare the structure 2, previously proposed to be the fungal metabolite avrainvillamide (17 steps, 4.2% yield). We observed that synthetic (-)-2 dimerized in the presence of triethylamine to form (+)-stephacidin B (>95%). We also obtained evidence that 2 can form 1 under mild conditions, and that 2 reacts with nucleophiles, such as methanol, by conjugate addition. Copyright
- Herzon, Seth B.,Myers, Andrew G.
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p. 5342 - 5344
(2007/10/03)
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- Methanol formation from dichloromethane under hydrothermal conditions
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CH2Cl2 (1 mole) mixed with NaOH (2 moles) was treated under hydrothermal conditions at 250 °C. The chlorinated methane was completely hydrolyzed to form methanol and the formate by the Cannizzaro reaction. The reactant and products were analyzed by 1H-, 2H-, and 13C-NMR. Solvent isotope effect on the transformation was also investigated. The hazardous and environmentally troublesome organic solvent was safely converted into the useful compounds.
- Yamasaki, Yuki,Enomoto, Heiji,Yamasaki, Nakamichi,Nakahara, Masaru
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- Hydrogen-deuterium-exchange reactions of methoxide-methanol clusters
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The tandem flowing afterglow-selected ion flow tube has been employed to measure rate coefficients for a series of 12 bimolecular isotope-exchange reactions of methoxide-methanol clusters. From these kinetic measurements the dissociation energies of several hydrogen-bonded dimers were determined: CH3O-·DOCH3 (28.3 ± 0.1 kcal/mol), CH3O-·HOCD3 (28.5 ± 0.1 kcal/mol), CH3O-·DOCD3 (28.1 ± 0.1 kcal/mol) CD3O-·HOCD3 (28.9 ± 0.1 kcal/mol), and CD3O-·DOCD3 (28.5 ± 0.1 kcal/mol). Differences in the bond strengths of these cluster ions can be understood in terms of the acidity of the neutral molecule and the basicity of the anion involved in the cluster; a given ion makes a stronger bond with a stronger acid while a given neutral molecule makes a stronger bond with a stronger base. By use of literature values of the electron affinity of the methoxy radicals along with the known RO-H and RO-D bond strengths, the gas-phase acidities (ΔH° acid) of CD3OD (383.9 ± 0.7 kcal/mol), CH3OD (383.5 ± 0.7 kcal/mol), and CD3OH (382.0 ± 0.7 kcal/mol) were calculated. A simple model is employed to predict reaction efficiencies and branching ratios for these isotope-exchange reactions.
- Barlow,Dang, Thuy Thanh,Bierbaum, Veronica M.
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p. 6832 - 6838
(2007/10/02)
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- Broensted Basicity of Atomic Oxygen on the Au(110) Surface: Reactions with Methanol, Acetylene, Water, and Ethylene
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The adsorption and reactions of methanol, acetylene, water, and ethylene were investigated on clean and oxidized Au(110) surfaces by temperature-programmed reaction spectroscopy.All of these molecules are only weakly and molecularly adsorbed on the clean Au(110) surface.Methanol, acetylene, and water, however, react with the oxidized surface.Methanol, activated by 0.25 monolayer of oxygen adatoms, reacts to form water, methyl formate, hydrogen, and carbon dioxide.A stable methoxy intermediate is identified in these reactions.Acetylene reacts to form water and carbon dioxide, and water is more strongly bonded to the Au(110) surface in the presence of oxygen adatoms.Ethylene is the only one of these molecules which does not react with oxygen adatoms on Au(110).This pattern of reactivity parallels that associated with the acidity of these molecules as measured in the gas phase which has been observed on Cu(110) and Ag(110) surfaces.These results complete the studies necessary to demonstrate the Broensted base character of oxygen adatoms on all of the group 1B metals.
- Outka, Duane A.,Madix, R. J.
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p. 1708 - 1714
(2007/10/02)
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- Relative Acidities of Water and Methanol and the Stabilities of the Dimer Anions
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The difference between ΔH0acid of H2O and CH3OH was directly measured to be 9.6 +/- 0.2 kcal/mol at 600 K by variable-temperature pulsed high pressure mass spectrometry.This result defines ΔH0acid(CH3OH) at 300 K as 381.6 +/- 0.7 kcal/mol and also confirms published values of EA(CH3O) and ΔH0D(CH3O-H), H2O was also used as a reference to measure ΔH0acid(C6H6) as 400.7 +/- 0.8 kcal/mol at 600 K.The dissociation energies of the hydrogen-bonded dimers OH-*H2O (26.8 kcal/mol), CH3O-*H2O (23.9 kcal/mol), and CH3O-*CH3OH (28.8 kcal/mol) were also measured.The former two are found to be in very good agreement with pu blished ab initio results.
- Meot-Ner (Mautner), Michael,Sieck, L. Wayne
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p. 6687 - 6690
(2007/10/02)
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- Decomposition of 1,3-Dialkyltriazenes in Aqueous Buffers: Kinetic and Mechanistic Studies
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1,3-Dialkyltriazenes, prepared by the reaction of alkyl azides with alkyllithiums, are stable as pure liquids or in aprotic solutions.The kinetics of decomposition of 1,3-dimethyltriazene (DMT) were investigated in buffered, aqueous solutions over the pH range of 9-12.The reaction is acid-catalyzed since the rate is inversely proportional to pH.The invariance of the rate with (cyclohexylamino)propanesulfonic acid (CAPS) buffer concentration at pH 9.5 and the finding of an inverse solvent isotope effect of 0.35 suggest that the reaction follows simple specific acid catalysis in that buffer.Decomposition of DMT in phosphate and carbonate buffers, however, indicated dependence of rate on buffer concentration, although the solvent isotope effects were still less than 1.These data suggested that the reaction in those buffers is catalyzed by specific acid, followed by general base.The kinetics of decomposition of 1,3-diethyltriazene (DET) and 1,3-diisopropyltriazene (DIT) were also studied.DET decomposed slightly more rapidly than DMT in phosphate and carbonate buffers but showed a similar dependence of the rate on the buffer concentration.This triazene also exhibited an inverse solvent isotope effect.DIT, on the other hand, showed a rate that was invariant with phosphate buffer concentration and exhibited a biphasic profile of rate vs. carbonate buffer concentration.The rate of decomposition of DIT was also invariant with the pKa of various buffers and showed an inverse solvent isotope effect.Decomposition of DMT in buffered deuterium oxide resulted in incorporation of deuterium into the product methanol, which indicated that an intermediate product of the reaction was the methyldiazonium ion.The dependence of the rate of decomposition on buffer concentration of DMT and DET is explained in terms of nucleophilic attack of buffer anions on N-2 of the protonated triazenes.The proponated DIT, on the other hand, is seen as dissociating directly to the isopropyl carbonium ion in phosphate buffer and in low concentrations of carbonate buffer.
- Smith, Richard H.,Denlinger, Cheryl L.,Kupper, Robert,Mehl, Andrew F.,Michejda, Christopher J.
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p. 3726 - 3730
(2007/10/02)
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- The Methyldiazonium Ion in Water: Competition Between Hydrolysis and Proton Exchange
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The methyldiazonium ion, generated from four different precursors, was found to undergo proton exchange with deuteriated phosphate buffer solutions.
- Smith, Richard H.,Koepke, Steven R.,Tondeur, Yves,Denlinger, Cheryl L.,Michejda, Christopher J.
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p. 936 - 937
(2007/10/02)
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- Phosphoric Amides. Part 8. The Effect of the Ethyleneimine Substituent on the Solvolytic Reactivity of Phosphate and Phosphoramidate Bonds
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Rates and products of the base-catalysed hydrolysis of some amidoesters of phosphoric acid have been determined in the N,N-dimethyl derivative, the P-N bond is resistant, and the P-O bond deactivated towards hydrolysis, while in the N-methyl substrate, the reactivity of the ester link is similar to that in trimethyl phosphate.In the N-ethylene compound, both P-O and P-N bonds are strongly activated.The N-(β-chloroethyl) substrate reacts via fast, base-catalysed cyclization to the N-ethylene amidate.
- Davidowitz, Bette,Modro, Tomasz A.
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p. 303 - 306
(2007/10/02)
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- Gas-Phase Hydrogen-Deuterium Exchange Reactions of Anions: Kinetics and Detailed Mechanism
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Rate coefficients and branching ratios for anionic hydrogen-deuterium exchange reactions between isotopically labeled hydroxide, amide, hydrogen sulfide, and methoxide ions and their corresponding neutral compounds have been measured in the gas phase by using the selected ion flow tube (SIFT) technique.The kinetic data for the methoxide-methanol systems lead to a determination of the relative base strength of CD3O(1-) and CH3O(1-).The reaction efficiencies and branching ratios of hydroxide-water, amide-ammonia, and amide-water systems are discussed in terms of the mechanism by which exchange occours; the multiply labeled systems reveal that more proton transfer occur than one might expect upon initial inspection of the data.The product distributions are discussed in terms of relative ion-molecule complex lifetimes and dissociation of the complex is competition with scrambling.Efficient H/D exchange was also observed to occur between compounds containing second-row elements and the implications of this are discussed.
- Grabowski, Joseph J.,DePuy, Charles H.,Doren, Jane M.Van,Bierbaum, Veronica, M.
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p. 7384 - 7389
(2007/10/02)
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- Deuterium-Protium Separation Factor between Hydrogen and Liquid Methanols
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The overall deuterium-protium isotope separation factor, α, between hydrogen and the hydroxyl group of liquid methanols containing both CH3 and CD3 substituents has been measured directly between -30 and +64 deg C.The temperature dependence of the respective separation factors is given by the equations ln α(CH3) = -0.4641 + (540.4/T) + (9849.5/T2) and ln α(CD3) = -0.8183 + (708.4/T) - (15263/T2) where T is the absolute temperature.The α values are about 12percent larger than that for liquid water.The equilibrium constants, K1 and K2, for isotopic exchange between hydrogen and the isotopically substituted methanol vapors were calculated from the α values and the corresponding liquid-vapor separation factors αv.At 25 deg C the experimental values of K1 and K2 differ by 7percent, indicating that methyl deuteration exerts a significant secondary isotope effect on deuterium-protium fractionation between methanol vapor and hydrogen.A comparison of equilibrium constants is made with theoretical values calculated from the ratios of partition functions of molecular hydrogen and those derived from the available spectroscopic data of the isotopically substituted methanols.
- Rolston, J.H.,Gale, K.L.
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p. 163 - 167
(2007/10/02)
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- Hydrolysis of Diazomethane - Kinetics and Mechanism
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The reaction between diazomethane and the hydronium ion was studied in a THF-water (60:40 v/v) mixture at 25 deg C.When a large excess of diazoalkane was used, the kinetics were zero order in diazoalkane and first order in acid for the pH range 4 8 M-1s-1.Isotope-exchange studies showed that water deprotonates the methanediazonium ion less rapidly than it displaces nitrogen; however, the hydroxide ion reacts more rapidly as a base than as a nucleophile.The rates of nucleophilic attack of water and the hydroxide ion on the methanediazonium ion were estimated as 1.8 s-1 and 1*104 M-1s-1, respectively, in THF-water (60:40 v/v).The pKa of the methanediazonium ion in this medium was ten.
- McGarrity, John F.,Smyth, Timothy
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p. 7303 - 7308
(2007/10/02)
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