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110-89-4Relevant articles and documents
Role of platinum deposits on titanium(IV) oxide particles: Structural and kinetic analyses of photocatalytic reaction in aqueous alcohol and amino acid solutions
Ohtani, Bunsho,Iwai, Kunihiro,Nishimoto, Sei-Ichi,Sato, Shinri
, p. 3349 - 3359 (1997)
Photocatalytic reaction at 298 K by platinum-loaded titanium(IV) oxide (TiO2-Pt) particles suspended in deaerated aqueous solutions of 2-propanol or (S)-lysine (Lys) was investigated. The TiO2 catalysts with various amounts of Pt loadings were prepared by impregnation from aqueous chloroplatinic acid solution onto a commercial TiO2 (Degussa P-25) followed by hydrogen reduction at 753 K. The physical properties of deposited Pt, e.g., particle size, surface area, and electronic state, were studied respectively by transmission electron microscopy, volumetric gas adsorption measurement, and X-ray photoelectron spectroscopy as well as infrared spectroscopy of adsorbed carbon monoxide. The increase in Pt amount mainly resulted in an increase of the number of Pt deposits, not of their size. The catalysts were suspended in the aqueous solutions and photoirradiated at a wavelength >300 nm under an argon (Ar) atmosphere. The overall rate of photocatalytic reactions for both 2-propanol and Lys, corresponding to the rate of consumption of these substrates, was negligible without Pt loading, increased drastically with the loading up to ca. 0.3%, and was almost constant or a little decreased by the further loadings. However, the rate of formation of pipecolinic acid (PCA) from Lys was improved gradually with a increase of Pt loading up to ca. 2 wt %. These dependences were discussed as a function of Pt surface area, which is employed as a measure that includes the properties of both number and size of Pt deposits. For the photocatalytic dehydrogenation of 2-propanol, the rate dependence could be interpreted semiquantitatively with the model that only the TiO2 particles loaded with at least one Pt deposit can photocatalyze, but the reaction rate is independent of the number of Pt deposits. Therefore, the overall rate is proportional to the number of Pt-loaded TiO2 particles. On the other hand, for the interpretation of the rate of PCA and H2 productions, the number of Pt deposits on each TiO2 particle had to be taken into account. The efficient production of PCA at higher Pt loadings was attributed to the reduction of a Schiff base intermediate produced via oxidation of Lys with positive holes and subsequent intramolecular condensation at the Pt deposit that is close to the site for the oxidation. Otherwise, photoexcited electrons are consumed for H2 production and the intermediate remains unreduced or undergoes further oxidation. It was suggested that the intermediate produced at the TiO2 surface sites within a distance of several nanometers from the Pt deposit undergoes efficient reduction to PCA. Thus, the importance of the distribution of Pt deposits for the preparation of highly active and selective TiO2-Pt photocatalyst has been clearly demonstrated.
Nucleophilic Addition to Olefins. 21. Substituent and Solvent Effects on the Reaction of Benzylidene Meldrum's Acids with Piperidine and Morpholine
Bernasconi, Claude F.,Panda, Markandeswar
, p. 3042 - 3050 (1987)
Rate (k1) and equilibrium constants (K1) for piperidine and morpholine addition to benzylidene Meldrum's acid (BMA) and substituted BMA's (Z=4-NO2, 3-Cl, 4-CN, 4-OMe, 4-NMe2, 4-NEt2) were determined in water and in 50percent, 70percent, and 90percent aqueous Me2SO.The equilibrium for addition is highly favorable, with K1 values (piperidine) as high as 7.8*107M-1, which is the highest value measured in a series of olefins of the type PhCH=CXY.The rates are also quite high (k1 up to 2.1*106M-1s-1), indicating a relatively high intrinsic rate constant (k0=k1 for K1=1) which ranks BMA second among seven PhCH=CXY-type olefins with respect to kinetic reactivity.This ranking is "reasonable" based on a correlation between k0 for nucleophilic addition to PhCH=CXY and k0 for deprotonation of carbon acids of the type CH2XY.βnucn (d log k1/ d log K1, variation of amine) is very amall, particularly in aqueous solution.This result appears to be part of a trend toward lower βnucn values with increasing thermodynamic stability of the adducts of PhCH=CXY. αnucn (d log k1/ d log K1, variation of Z) is significantly larger than βnucn, implying a substantial imbalance in these reactions.However, after correction of αnucn for the effect of the developing positive charge on the amine nitrogen the remaining "true" imbalance is quite small.The small imbalance as well as the high k0 value are consistent with the Meldrum's acid anion deriving most of its exceptional stability from its bislactone structure rather than from resonance.Strong ?-donor substituents (4-NMe2, 4-NEt2) have a strong stabilizing effect on the olefin, leading to a large reduction in K1.Contrary to expectations based on the principle of nonperfect synchronization (PNS), this resonance effect does not lead to a strong reduction of the intrinsic rate constant, probably because the polarization in the olefin (Me2N+=C6H4+CHC(COO)2-C(CH3)2) helps in partially offsetting the PNS effect caused by delayed development of resonance on the carbanionic side of the adduct
An experimental-theoretical study of the factors that affect the switch between ruthenium-catalyzed dehydrogenative amide formation versus amine alkylation
Nova, Ainara,Balcells, David,Schley, Nathan D.,Dobereiner, Graham E.,Crabtree, Robert H.,Eisenstein, Odile
, p. 6548 - 6558 (2010)
A ruthenium(II) diamine complex can catalyze the intramolecular cyclization of amino alcohols H2N(CH2)nOH via two pathways: (i) one yields the cyclic secondary amine by a redox-neutral hydrogen-borrowing route with loss of water; and (ii) the second gives the corresponding cyclic amide by a net oxidation involving loss of H2. The reaction is most efficient in cases where the product has a six-membered ring. The amide and amine pathways are closely related: DFT calculations show that both amine and amide formations start with the oxidation of the amino alcohol, 5-amino-1-pentanol, to the corresponding amino aldehyde, accompanied by reduction of the catalyst. The intramolecular condensation of the amino aldehyde takes place either in the coordination sphere of the metal (path I) or after dissociation from the metal (path II). Path I yields the Ru-bound zwitterionic form of the hemiaminal protonated at nitrogen, which eliminates H2, forming the amide product. In path II, the free hemiaminal dehydrates, giving an imine, which yields the amine product by hydrogenation with the reduced form of the catalyst generated in the initial amino alcohol oxidation. For amide to be formed, the hemiaminal must remain metal-bound in the key intermediate and the elimination of H2 must occur from the same intermediate to provide a vacant site for β-elimination. The elimination of H2 is affected by an intramolecular H-bond in the key intermediate. For amine to be formed, the hemiaminal must be liberated for dehydration to imine and the H2 must be retained on the metal for reduction of the imine intermediate.
Kinetics of Reactions of Cyclic Secondary Amines with 2,4-Dinitro-1-naphthyl Ethyl Ether in Dimethyl Sulfoxide Solution. Spectacular Difference between the Behavior of Pyrrolidine and Piperidine
Bunnett, Joseph F.,Sekiguchi, Shizen,Smith, Lewis A.
, p. 4865 - 4871 (1981)
The reactions named in the title, which form N-(2,4-dinitro-1-naphthyl) derivatives of these heterocyclic amines, occur in two distinct stages.In stage I, the spectrum of a ?-adduct intermediate develops at a rate which is measurable in a stopped flow apparatus; in stage II, it decays at a slower and easily measurable rate.The kinetics of both stage I and stage II have been studied.Pyrrolidine and piperidine are similar in their stage I behavior, but reactivity in stage II is about 11000 times greater in the pyrrolidine system.This huge difference between systems apparently so similar is judged to arise from steric interactions forced by differences in conformation between the amino moieties in the intermediate ? adducts as they release the nucleofuge.It calls into question the rate-limiting proton transfer interpretation of base catalysis in analogous aminodephenoxylation reactions in protic solvents.
Catalytic Homogeneous Hydrogenation of CO to Methanol via Formamide
Kar, Sayan,Goeppert, Alain,Prakash, G. K. Surya
, p. 12518 - 12521 (2019)
A novel amine-assisted route for low temperature homogeneous hydrogenation of CO to methanol is described. The reaction proceeds through the formation of formamide intermediates. The first amine carbonylation part is catalyzed by K3PO4. Subsequently, the formamides are hydrogenated in situ to methanol in the presence of a commercially available ruthenium pincer complex as a catalyst. Under optimized reaction conditions, CO (up to 10 bar) was directly converted to methanol in high yield and selectivity in the presence of H2 (70 bar) and diethylenetriamine. A maximum TON of 539 was achieved using the catalyst Ru-Macho-BH. The high yield, selectivity, and TONs obtained for methanol production at low reaction temperature (145 °C) could make this process an attractive alternative over the traditional high temperature heterogeneous catalysis.
Synthesis of: N -heterocycles from diamines via H2-driven NADPH recycling in the presence of O2
Al-Shameri, Ammar,Borlinghaus, Niels,Weinmann, Leonie,Scheller, Philipp N.,Nestl, Bettina M.,Lauterbach, Lars
, p. 1396 - 1400 (2019)
Herein, we report an enzymatic cascade involving an oxidase, an imine reductase and a hydrogenase for the H2-driven synthesis of N-heterocycles. Variants of putrescine oxidase from Rhodococcus erythropolis with improved activity were identified. Substituted pyrrolidines and piperidines were obtained with up to 97% product formation in a one-pot reaction directly from the corresponding diamine substrates. The formation of up to 93% ee gave insights into the specificity and selectivity of the putrescine oxidase.
The True Fate of Pyridinium in the Reportedly Pyridinium-Catalyzed Carbon Dioxide Electroreduction on Platinum
Olu, Pierre-Yves,Li, Qi,Krischer, Katharina
, p. 14769 - 14772 (2018)
Protonated pyridine (PyH+) has been reported to act as a peculiar and promising catalyst for the direct electroreduction of CO2 to methanol and/or formate. Because of recent strong incentives to turn CO2 into valuable products, this claim triggered great interest, prompting many experiments and DFT simulations. However, when performing the electrolysis in near-neutral pH electrolyte, the local pH around the platinum electrode can easily increase, leading to Py and HCO3? being the predominant species next to the Pt electrode instead of PyH+ and CO2. Using a carefully designed electrolysis setup which overcomes the local pH shift issue, we demonstrate that protonated pyridine undergoes a complete hydrogenation into piperidine upon mild reductive conditions (near 0 V vs. RHE). The reduction of the PyH+ ring occurs with and without the presence of CO2 in the electrolyte, and no sign of CO2 electroreduction products was observed, strongly questioning that PyH+ acts as a catalyst for CO2 electroreduction.
The elimination kinetics and mechanisms of ethyl piperidine-3-carboxylate, ethyl 1-methylpiperidine-3-carboxylate, and ethyl 3-(piperidin-1-yl)propionate in the gas phase
Monsalve, Angiebelk,Rosas, Felix,Tosta, Maria,Herize, Armando,Dominguez, Rosa M.,Brusco, Doris,Chuchani, Gabriel
, p. 106 - 114 (2006)
The gas-phase elimination kinetics of the above-mentioned compounds were determined in a static reaction system over the temperature range of 369-450.3°C and pressure range of 29-103.5 Torr, The reactions are homogeneous, unimolecular, and obey a first-order rate law. The rate coefficients are given by the following Arrhenius expressions: ethyl 3-(piperidin-1-yl) propionate, log κ1(s-1) = (12.79 ± 0.16) - (199.7±2.0) kJ mol-1 (2.303 RT)-1; ethyl 1-methylpiperidine-3-carboxylate, log κ1(s-1) = (13.07 ± 0.12)-(212.8 ± 1.6) kJmol-1 (2,303 RT) -1; ethyl piperidine-3-carboxylate, log κ1(s -1) = (13.12 ± 0.13) - (210.4 ± 1.7) kJ mol -1 (2.303 RT)-1 and 3-piperidine carboxylic acid, log κ1(s-1) = (14.24 ± 0.17) - (234.4 ± 2.2) kJ mol-1 (2.303 RT)-1. The first step of decomposition of these esters is the formation of the corresponding carboxylic acids and ethylene through a concerted six-membered cyclic transition state type of mechanism. The intermediate β-amino acids decarboxylate as the α-amino acids but in terms of a semipolar six-membered cyclic transition state mechanism.
Vapor-phase synthesis of piperidine over SiO2 catalysts
Tsuchiya, Takuma,Kajitani, Yoshihiro,Ohta, Kaishu,Yamada, Yasuhiro,Sato, Satoshi
, p. 42 - 45 (2018)
Vapor phase dehydration of 5-amino-1-pentanol to produce piperidine was investigated over various oxide catalysts such as ZrO2, TiO2, Al2O3 and SiO2. Among the tested catalysts, SiO2 selectively produced piperidine at 300 °C. A high 5-amino-1-pentanol conversion of 99.9% with a piperidine selectivity of 94.8% was achieved over weak acidic SiO2. In an experiment using isotope such as deuterated water, surface hydroxy groups of SiO2 are concluded to be the active centers.
Microwave-assisted synthesis of azoniaspiro compounds using a novel catalyst, 1-azaphenothiazine
Gupta, Archana,Sakhuja, Rajeev,Kushwaha, Khushbu,Jain, Subhash C.
, p. 411 - 416 (2011)
1-Azaphenothiazine catalyses the intramolecular cyclization of N-(bromoalkyl)phthalimides in the presence of anhydrous K2CO 3 to form spiro cyclic quaternary ammonium salts, namely azoniaspiro compounds, under microwave irradiation. A novel and ecofriendly method was developed for the synthesis of azoniaspiro compounds, and the role of azaphenothiazine as a catalyst in such reactions has been established for the first time. In the future, this protocol can be extended to the synthesis of various substituted N-heterocycles by hydrolyzing the resulting azoniaspiro compounds.