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64-19-7Relevant articles and documents
New insight on an old reaction - The aqueous hydrolysis of acetic anhydride
Wiseman, Floyd Landis
, p. 1105 - 1111 (2012)
Studies have shown that aqueous reactions generating a change in pH can be accurately monitored using a fast-response pH electrode. This technique has been successfully applied in this work to the aqueous hydrolysis of acetic anhydride, which is a reaction that has been studied using a variety of techniques for nearly one hundred years. Many of these techniques involve elaborate equipment and sophisticated analyses, making the pH technique an attractive alternative. Studies here have focused on the temperature effects of the simple hydrolysis and acetate-catalyzed hydrolysis reactions. Data analyses suggest the notion that if simple hydrolysis occurs by a two-step mechanism, it does so only at low temperatures, whereas acetate-catalyzed hydrolysis occurs almost assuredly by a single step mechanism. Results of this work yield the following values for the activation parameters for simple hydrolysis (subscripted with a "w") and acetate-catalyzed hydrolysis (subscripted with an "a") at atmospheric pressure: ΔHw?=39.90. 7kJ×mol-1,ΔSw?=-227(2)J×K-1×mol-1, ΔHa?=49.7(0.3)kJ×mol-1 and ΔS?a=-1571J×K- 1×mol-1. Implications of these results are discussed in this article. Copyright
Peroxy Acid Oxidations. II. A Kinetic and Mechanistic Study of Oxidation of α-Diketones
Panda, Radhasyam,Panigrahi, Akhil Krishna,Patnaik, Chakrapani,Sahu, Sabita Kumari,Mahapatra, Sabita Kumari
, p. 1363 - 1368 (1988)
The kinetics of Baeyer-Villiger oxidation of biacetyl and benzil by peroxomonophosphoric acid and peroxomonosulfuric acid have been studied in different pH ranges at 308 K.The reactions are second order; first order each in peroxy acid and in diketone concentrations at constant pH.The oxidation rate is strongly pH-dependent; the rate increases with increase in pH.From the pH-rate data the reactivity of different peroxo species, in the oxidation, has been determined.A mechanism consistent with rate-detemining nucleophilic attack of peroxo species on carbonyl carbon of the diketone molecule has been proposed.Acetic acid and benzoic acid are respectively found to be the products of oxidation of biacetyl and benzil.
Synthesis of Pd-Pt Ultrathin Assembled Nanosheets as Highly Efficient Electrocatalysts for Ethanol Oxidation
Choi, Sang-Il,Han, Yeji,Hong, Jong Wook,Kim, Jeonghyeon,Lee, Su-Un
, (2020)
Control over composition and morphology of nanocrystals (NCs) is significant to develop advanced catalysts applicable to polymer electrolyte membrane fuel cells and further overcome the performance limitations. Here, we present a facile synthesis of Pd?Pt alloy ultrathin assembled nanosheets (UANs) by regulating the growth behavior of Pd?Pt nanostructures. Iodide ions supplied from KI play as capping agents for the {111} plane to promote 2-dimensional (2D) growth of Pd and Pt, and the optimal concentrations of cetyltrimethylammonium chloride and ascorbic acid result in the generation of Pd?Pt alloy UANs in high yield. The prepared Pd?Pt alloy UANs exhibited the remarkable enhancement of the catalytic activity and stability toward ethanol oxidation reaction compared to irregular-shaped Pd?Pt alloy NCs, commercial Pd/C, and commercial Pt/C. Our results confirm that the Pd?Pt alloy composition and ultrathin 2D morphology offer high accessible active sites and favorable electronic structure for enhancing electrocatalytic activity.
Kinetics of formation of peroxyacetic acid
Dul'neva,Moskvin
, p. 1125 - 1130 (2005)
The kinetics of the reaction of acetic acid with hydrogen peroxide, leading to peroxyacetic acid, were studied at various molar reactant ratios (AcOH-H2O2 from 6 : 1 to 1 : 6) at 20, 40, and 60°C and sulfuric acid (catalyst) concentrations of 0 to 9 wt %. The reaction is reversible, and the equilibrium constant decreases as the temperature rises: K = 2.10 (20°C), 1.46 (40°C), 1.07 (60°C); Δr H 0 = - 13.7±0.1 kJ mol-1, Δr S = -40.5±0.4 J mol-1 K-1. The maximal equilibrium concentration of peroxyacetic acid (2.3 M) is attained at 20°C and a molar AcOH-to-H2O2 ratio of 2.5 : 1. The rate constants of both forward and reverse reactions increase with increase in sulfuric acid concentration from 0 to 5 wt %. Further raising the catalyst concentration does not affect the reaction rate. The reaction mechanism is discussed. 2005 Pleiades Publishing, Inc.
Rapid Aqueous Synthesis of Large-Size and Edge/Defect-Rich Porous Pd and Pd-Alloyed Nanomesh for Electrocatalytic Ethanol Oxidation
Teng, Yuxiang,Guo, Ke,Fan, Dongping,Guo, Hongyou,Han, Min,Xu, Dongdong,Bao, Jianchun
, p. 11175 - 11182 (2021)
In this work, a facile aqueous synthesis strategy was used (complete in 5 min at room temperature) to produce large-size Pd, PdCu, and PdPtCu nanomeshes without additional organic ligands or solvent and the volume restriction of reaction solution. The obtained metallic nanomeshes possess graphene-like morphology and a large size of dozens of microns. Abundant edges (coordinatively unsaturated sites, steps, and corners), defects (twins), and mesopores are seen in the metallic ultrathin structures. The formation mechanism for porous Pd nanomeshes disclosed that they undergo oriented attachment growth along the ?111? direction. Owing to structural and compositional advantages, PdCu porous nanomeshes with certain elemental ratios (e. g., Pd87Cu13) presented enhanced electrocatalytic performance (larger mass activity, better CO tolerance and stability) toward ethanol oxidation.
A high-throughput pH-based colorimetric assay: application focus on alpha/beta hydrolases
Paye, Mariétou F.,Rose, Harrison B.,Robbins, John M.,Yunda, Diana A.,Cho, Seonggeon,Bommarius, Andreas S.
, p. 80 - 90 (2018)
Research involving α/β hydrolases, including α-amino acid ester hydrolase and cocaine esterase, has been limited by the lack of an online high throughput screening assay. The development of a high throughput screening assay capable of detecting α/β hydrolase activity toward specific substrates and/or chemical reactions (e.g., hydrolysis in lieu of amidase activity and/or synthesis instead of thioesterase activity) is of interest in a broad set of scientific questions and applications. Here we present a general framework for pH-based colorimetric assays, as well as the mathematical considerations necessary to estimate de novo the experimental response required to assign a ‘hit’ or a ‘miss,’ in the absence of experimental standard curves. This combination is valuable for screening the hydrolysis and synthesis activity of α/β hydrolases on a variety of substrates, and produces data comparable to the current standard technique involving High Performance Liquid Chromatography (HPLC). In contrast to HPLC, this assay enables screening experiments to be performed with greater efficiency.
Polyoxometalate-Modified Fabrics: New Catalytic Materials for Low-Temperature Aerobic Oxidation
Xu, Ling,Boring, Eric,Hill, Craig L.
, p. 394 - 405 (2000)
The polyoxometalate H5PV2Mo10O40 (1) is deposited on cotton cloth, polyacrylic fiber, nylon fiber, carbon powder (Ambersorb 572), and the Japanese "self-deodorizing" fabric Smoklin by immersion of these materials in aqueous solutions of 1 followed by evaporation of the water. DRIFT spectra and chemical reactivity indicate that 1 is not damaged during deposition on the materials. More significantly, they catalyze O2-based oxidations of two representative and common toxics in air, acetaldehyde and 1-propanethiol, in addition to a representative thioether, tetrahydrothiophene. These aerobic oxidations proceed heterogeneously with the substrates in the liquid phase and under unusually mild conditions (mostly ambient temperature and pressure). One representative reaction, CH3CHO+O2→CH3COOH, catalyzed by several 1-fabric materials is examined in some detail. Kinetics, radical scavenging, and other experiments are consistent with the 1-fabric functioning primarily as a radical chain initiator. Surface area measurements and scanning electron microscopy of two representative materials, 1-polyacrylic and 1-Smoklin, before and after deposition of 1 and after catalysis indicate that the fibers are not demonstrably altered by deposition of 1, and that the 1-fabric catalysts are not significantly deactivated by use. In all cases, the surface areas are 2/g by BET N2 adsorption, and the deposition morphology is clumps of 1 microcrystals covering 2 oxidations in our evaluations. In contrast, 1-Smoklin is quite acti ve for all these processes.
Kinetic studies on the oxidation of iodide by peroxyacetic acid
Awad, Mohamed Ismail,Oritani, Tadato,Ohsaka, Takeo
, p. 253 - 256 (2003)
The kinetics of the oxidation of iodide by peroxyacetic acid (PAA) in aqueous media in the presence and absence of the heptamolybdate has been studied by a high time resolution spectrophotometric stopped-flow method. The time-dependent concentration of the liberated iodine was monitored by the change in absorbance at 352 nm. The effect of ammonium heptamolybdate as well as pH on the rate of the reaction was also studied and it was found that the rate of the reaction is independent of pH and molybdate concentration under the examined conditions. The results obtained show that the rate law of the reaction can be expressed as rate=k[PAA][I-] with a value of k=4.22×102 (mole/l)-1 s-1 at pH 3.5-5.4 and 25°C.
Substrate Specificity and Leaving Group Effect in Ester Cleavage by Metal Complexes of an Oximate Nucleophile
Lugo-González, José Carlos,Gómez-Tagle, Paola,Huang, Xiaomin,M. Del Campo, Jorge,Yatsimirsky, Anatoly K.
, p. 2060 - 2069 (2017)
Deprotonated zinc(II) and cadmium(II) complexes of a tridentate oxime nucleophile (1, OxH) show a very high reactivity, breaking by 2-3 orders of magnitude the previously established limiting reactivity of oximate nucleophiles in the cleavage of substituted phenyl acetates and phosphate triesters, but are unreactive with p-nitrophenyl phosphate di- and monoesters. With reactive substrates, these complexes operate as true catalysts through an acylation-deacylation mechanism. Detailed speciation and kinetic studies in a wide pH interval allowed us to establish as catalytically active forms [Cd(Ox)]+, [Zn(Ox)(OH)], and [Zn(Ox)(OH)2]? complexes. The formation of an unusual and most reactive zinc(II) oximatodihydroxo complex was confirmed by electrospray ionization mass spectrometry data and supported by density functional theory calculations, which also supported the previously noticed fact that the coordinated water in [Zn(OxH)(H2O)2]2+ deprotonates before the oxime. Analysis of the leaving group effect on the cleavage of phenyl acetates shows that the rate-determining step in the reaction with the free oximate anion is the nucleophilic attack, while with both zinc(II) and cadmium(II) oximate complexes, it changes to the expulsion of the leaving phenolate anion. The major new features of these complexes are (1) a very high esterolytic activity surpassing that of enzyme hydrolysis of aryl acetate esters and (2) an increased reactivity of coordinated oxime compared to free oxime in phosphate triester cleavage, contrary to the previously observed inhibitory effect of oxime coordination with these substrates.
Activity, recyclability, and stability of lipases immobilized on oil-filled spherical silica nanoparticles with different silica shell structures
Kuwahara, Yasutaka,Yamanishi, Takato,Kamegawa, Takashi,Mori, Kohsuke,Yamashita, Hiromi
, p. 2527 - 2536 (2013)
Candida antarctica lipaseA was immobilized on spherical silica nanoparticles with oil-filled core and oil-induced mesoporous silica shell with different silica shell structures. The immobilization of enzymes was achieved by directly adding enzymes to the oil-in-water emulsion system under ambient synthesis conditions, and the silica shell structure was controlled by the addition of the cosolvent ethanol to the initial synthesis medium. Detailed structural analysis revealed the formation of oil-filled spherical silica nanoparticles with 3.4-4.2nm mesopores randomly arranged in the silica shell; the thickness and pore characteristics of these pores markedly changed with the addition of ethanol. The retention of the enzyme activity during biocatalysis was significantly affected by the structural properties of the silica shells, and it was found that a thick and dense silica shell is essential to afford an active, recyclable, and stable biocatalyst. Furthermore, the oil encapsulated within the core cavity was found to play an important role in achieving a high catalytic efficiency. Trapped oil: Candida antarctica lipaseA is immobilized on oil-filled spherical silica nanoparticles with different silica shell structures through an anionic surfactant-induced self-assembly approach (see scheme) with ethanol as a cosolvent. The entrapped enzymes mostly retain their activities and exhibit recyclability and thermal and chemical stability, depending on the thickness and pore characteristics of the silica shells. TEOS=Tetraethoxyorthosilicate, APTES=3-aminopropyl triethoxysilane.