Data Treatment and Error Analysis in Kinetics

Methods of data treatment in kinetics are reviewed from a practical viewpoint. The equations to describe the kinetics of chemical reactions and the methodology to obtain the models are presented. Moreover, the integration methods that are needed for the simulation of complex reactions are explained, from the simple first-order reaction to the complex general mechanism. However, it is essential to know the main sources of error in data treatment in order to reduce their effects on the results. Stress is put on the analysis of the errors due to the simplification of complex models. The different factors that influence the kinetics of the reaction are reviewed. How to take advantage of the kin…

Pore Length Effect on Drug Uptake and Delivery by Mesoporous Silicas

The capability of UVM-7 silicas to work as supports for drug storage and delivery is investigated using ibuprofen as a model. UVM-7 silicas are surfactant-assisted synthesised mesoporous materials displaying a characteristic bimodal pore architecture related to their nanoparticulate texture. Strict control of the drug-charge protocol allows the achievement of high ibuprofen loads, not only because of the availability of intra-nanoparticle mesopores and large textural voids, but also owing to the decrease in pore-blocking effects (with regard to related unimodal mesoporous materials such as MCM-41) achieved through the shortening of the mesopore length. The UVM-7/ibuprofen nanocomposites are…

Precatalyst or dosing-device? The [Pd2{μ-(C6H4) PPh2}2{μ-O2C(C6H5)}2] complex anchored on a carboxypolystyrene polymer as an effective supplier of palladium catalytically active nanoparticles for the Suzuki-Miyaura reaction

Abstract A new catalyst has been synthesized from the precursor [Pd2{μ-(C6H4) PPh2}2 {μ-O2C(C6H5)}2] immobilized on a carboxypolystyrene polymer that exhibits an excellent dispersion of the Pd (II) centers, reusability, and catalytic activity in front of phenyl bromides. The activity of this new material was studied in detail for the Suzuki-Miyaura reaction and compared to that of Pd nanoparticles (NPs) supported on UVM-7 (a mesoporous silica), and Pd NPs stabilized with polyvinylpirrolydone. The homogeneous/heterogeneous character of the catalytic process was determined from the results of the hot-filtration, centrifugation, poisoning, three phases tests, and from differential sensitivity …

Colloidally Confined Crystallization of Highly Efficient Ammonium Phosphomolybdate Catalysts

Nanodroplets in inverse miniemulsions provide a colloidal confinement for the crystallization of ammonium phosphomolybdate (APM), influencing the resulting particle size. The effects of the space confinement are investigated by comparing the crystallization of analogous materials both in miniemulsion and in bulk solution. Both routes result in particles with a rhombododecahedral morphology, but the ones produced in miniemulsion have sizes between 40 and 90 nm, 3 orders of magnitude smaller than the ones obtained in bulk solution. The catalytic activity of the materials is studied by taking the epoxidation of cis-cyclooctene as a model reaction. The miniemulsion route yields APM particles ca…

Highly Active Hydrogenation Catalysts Based on Pd Nanoparticles Dispersed along Hierarchical Porous Silica Covered with Polydopamine as Interfacial Glue

New catalysts based on Pd(0) nanoparticles (Pd NPs) on a bimodal porous silica of the UVM-7/polydopamine (PDA) support have been synthesized following two preparative strategies based on the sequential or joint incorporation of two components of the composite (Pd and PDA). We analyzed the role played by the PDA as &lsquo

DFT Study on the Interaction of Tris(benzene-1,2-dithiolato)molybdenum Complex with Water. A Hydrolysis Mechanism Involving a Feasible Seven-Coordinate Aquomolybdenum Intermediate

In the present work, the reactivity of the tris(benzene-1,2-dithiolato)molybdenum complex ([Mo(bdt)3]) toward water is studied by means of the density functional theory (DFT). DFT calculations were performed using the M06, B3P86, and B3PW91 hybrid functionals for comparison purposes. The M06 method was employed to elucidate the reaction pathway, relative stability of the intermediate products, nature of the Mo–S bond cleavage, and electronic structure of the involved molybdenum species. This functional was also used to study the transference of electrons from the molybdenum center toward the ligands. The reaction pathway confirms that [Mo(bdt)3] undergoes hydrolysis, yielding dihydroxo-bis(…

Improving epoxide production using Ti-UVM-7 porous nanosized catalysts

Nanosized Ti-UVM-7 materials with a hierarchical system of pores at two different length scales have been prepared through a one-pot procedure by using a simple template agent; the catalytic activity and selectivity of the resulting materials in bulky olefin epoxidation by organic peroxides are the highest reported to date.

The reduction of tris-dithiolene complexes of molybdenum(vi) and tungsten(vi) by hydroxide ion: kinetics and mechanism

The kinetic study of the spontaneous reduction of some neutral tris-dithiolene complexes [ML3] of molybdenum(VI) and tungsten(VI), (L = S2C6H42−, S2C6H3CH32− and S2C2(CH3)22−; M = Mo or W) by tetrabutylammonium hydroxide in tetrahydrofuran-water solutions demonstrates that OH− is an effective reductant. Their reduction is fast, clean and quantitative. Depending upon both the molar ratio in which the reagents are mixed and the amount of water present, one- or two-electron reductions of these tris-dithiolene complexes were observed. If Bu4NOH is present in low concentration or/and at high concentrations of water, the total transformation of the neutral M(VI) complex into the monoanionic M(V) …

Nitroarene hydrogenation catalysts based on Pd nanoparticles glued with PDA on inorganic supports: Multivariate Curve Resolution as an useful tool to compare the catalytic activity in multi-step reactions

[EN] Two green catalysts based on Pd(0) nanoparticles (Pd NPs) anchored through PDA on porous silica and magnetite have been synthesized using a generalized simple and reproducible "two-step" methodology. Both catalysts were tested for a model reaction, the hydrogenation of 4-nitrophenol using NaBH4 as the hydrogenating agent, and especially good activity has been achieved in the case of the catalysts containing magnetite as inorganic core (Pd NPs-PDA@Fe3O4). We analyzed the effect associated with the catalyst separation method (centrifugation or magnetically) that affect to the distribution and aggregation degree of the Pd NPs. In addition, we also correlate the final catalyst morphology w…

Hydrolysis of DCNP (a Tabun mimic) catalyzed by mesoporous silica nanoparticles

[EN] The hydrolysis of diethylcyanophosphonate, DCNP (a Tabun simulant) in the presence of mesoporous silica nanoparticles (MSN) has been studied in acetonitrile:water (99.5:0.5 v/v) mixtures using 31P NMR as a suitable technique to follow the DCNP hydrolysis. MSN alone was not capable to induce DCNP hydrolysis, yet MSN in combination with the presence of the bases potassium carbonate, triethylamine or DABCO enhanced DCNP degradation. When MSN was used combined with K2CO3, a hydrolysis of ca. 95% of the initial DCNP after 60 min was observed. In the presence of DABCO, MSN was able to induce the hydrolysis of ca. 90% of DCNP after the same time. However, the DCNP hydrolysis using MSN in the …

A new efficient, highly dispersed, Pd nanoparticulate silica supported catalyst synthesized from an organometallic precursor. Study of the homogeneous vs. heterogeneous activity in the Suzuki-Miyaura reaction

[EN] A new Pd(0) catalyst supported on silica UVM-7 has been synthesized from the organometallic [Pd-2(mu-(C6H4) Pp(2))(2)(CH3CN)(4)](BF4)(2) precursor, characterized by the high dispersion, activity, and small size of the palladium nanoclusters fixed on the silica surface. The catalyst was tested for the Suzuki-Miyaura (SM) reaction of different 4-substitutedphenyl halides with phenylboronic acid. The kinetic study concurs with most of the catalytic action was carried out by Pd species originated by the partial solubilization of Pd immobilized on mesoporous silica. The Schmidt's analysis of differential selectivity (SADS) in several competitive SM reactions, together the STEM-HAADF and HRT…

Reduction of tris(benzene-1,2-dithiolate)molybdenum(VI) by hydroxide ions in dry tetrahydrofuran solution.

Tris(benzene-1,2-dithiolate)molybdenum(VI) reacts rapidly and quantitatively with tetrabutylammonium hydroxide to yield the corresponding Mo(V) and Mo(IV) complexes and hydrogen peroxide; the reaction has been executed in dry tetrahydrofuran where the reaction rate shows a fair dependence on complex and OH2 concentrations. Cervilla Avalos, Antonio, Antonio.Cervilla@uv.es ; Perez Pla, Francisco, Francisco.Perez@uv.es ; Llopis Jover, Elisa, Elisa.Llopis@uv.es

Layered-Expanded Mesostructured Silicas: Generalized Synthesis and Functionalization

Mesostructured layered silicas have been prepared through a surfactant-assisted procedure using neutral alkylamines as templates and starting from atrane complexes as hydrolytic inorganic precursors. By adjusting the synthetic parameters, this kinetically controlled reproducible one-pot method allows for obtaining both pure and functionalized (inorganic or organically) lamellar silica frameworks. These are easily deconstructed and built up again, which provides a simple way for expanding the interlamellar space. The materials present high dispersibility, which results in stable colloidal suspensions.

Data Treatment in Kinetics

Chemical kinetics is an important part of chemistry devoted to study how reactions proceed and quantify the rate of the process. The reaction mechanism is the chemical model that describes how the chemical change occurs. From the proposed mechanism, a mathematical model can be obtained to explain the evolution of the chemical species with time. In many cases, the mechanism can be simplified to a single rate law that relates the reaction rate with concentrations. In the last decades, the study of kinetic systems has benefited from the development of instrumentation, the increasing availability of specialized computer software, and the advances in data treatment techniques. A comprehensive re…

Zirconium oxocluster/polymer hybrid nanoparticles prepared by photoactivated miniemulsion copolymerization

The photoactivated free radical miniemulsion copolymerization of methyl methacrylate (MMA) and the zirconium oxocluster Zr4O2(methacrylate) 12 is used as an effective and fast preparation method for polymer/inorganic hybrid nanoparticles. The oxoclusters, covalently anchored to the polymer network, act as metal-organic cross-linkers, thus improving the thermomechanical properties of the resulting hybrid nanoparticles. Benzoin carbonyl organic compounds were used as photoinitiators. The obtained materials are compared in terms of cross-linking, effectiveness of cluster incorporation, and size distribution with the analogous nanoparticles produced by using conventional thermally induced free …

Towards the design of organocatalysts for nerve agents remediation: The case of the active hydrolysis of DCNP (a Tabun mimic) catalyzed by simple amine-containing derivatives

We report herein a study of the hydrolysis of Tabun mimic DCNP in the presence of different amines, aminoalcohols and glycols as potential suitable organocatalysts for DCNP degradation. Experiments were performed in CD3CN in the presence of 5% D2O, which is a suitable solvent mixture to follow the DCNP hydrolysis. These studies allowed the definition of different DCNP depletion paths, resulting in the formation of diethylphosphoric acid, tetraethylpyrophosphate and phosphoramide species as final products. Without organocatalysts, DCNP hydrolysis occurred mainly via an autocatalysis path. Addition of tertiary amines in sub-stoichiometric amounts largely enhanced DCNP depletion whereas non-te…

A kinetic model for the oxidation of benzenethiol catalyzed by the [MoVIO2(O2CC(S)(C6H5)2)2]2− complex intercalated in a Zn(II)–Al(III) layered double hydroxide host

Abstract The heterogeneous oxidation of benzenethiol catalyzed by the dianionic bis(2-sulfanyl-2,2-diphenylethanoxycarbonyl) dioxomolybdate (VI) complex intercalated into a Zn(II)–Al(III) layered double hydroxide (LDH) host have been investigated under aerobic conditions. The kinetics of the system has been analysed in detail. In ethanol, the benzenethiol is cleanly oxidized to diphenyl disulfide in the acidic media provided by the protonic resin Amberlite IR-120(H). The reaction is second-order in benzenethiol, and the apparent rate coefficient has been found to be proportional to the catalyst weight and inversely proportional to the initial concentration of the substrate. A catalytic cycl…

The different kinetic and mechanistic behaviors of molybdenum and tungsten in the reduction of tris(benzene-1,2-dithiolato)Mo(VI) and W(VI) complexes by ascorbic acid in aqueous media

The mono-electronic reduction of tris(benzene-1,2-dithiolato)Mo(VI) and W(VI) complexes (ML3: M = Mo, W; L = S2C6H2−4, S2C6H3CH2−3) to their anionic forms ML−3 by L(+)-ascorbic acid (H2A) has been studied in tetrahydrofurane (THF):water and THF:methanol by means of diode-array, stopped-flow, and mass spectrometry–electrospray ionization (MS-ESI) spectroscopy. The kinetic study in methanol demonstrates that the reaction is first order in each reactant, the electron transfer being rate limiting. This fact was assessed by the absence of a primary saline effect and by the correlation observed between the activation free enthalpy (ΔG≠) and the reduction potentials measured by cyclic voltamperome…

Increased Stability of Polysaccharide/Silica Hybrid Sub‐Millicarriers for Retarded Release of Hydrophilic Substances

Magnetically enhanced polymer-supported ceria nanocatalysts for the hydration of nitriles.

The heterogeneous catalysis of the hydration of nitriles to amides is a process of great industrial relevance in which cerium(IV) oxide (also referred to as ceria) has shown an outstanding catalytic performance. The use of non-supported ceria nanoparticles is related to difficulties in the purification of the product and the recovery and recyclability of the catalyst. Therefore, in this work, ceria nanoparticles are supported on a polymer matrix either by synthesizing polymer particles by so-called Pickering miniemulsions while using ceria nanoparticles as emulsion stabilizers or, as a comparison, by in-situ crystallization on preformed polymer particles. The former strategy presents signif…