Kinetics Of Condensation Reactions Research Articles

Hydrolysis and condensation kinetic studies of mercaptopropyl trimethoxysilane using in-situ Raman spectroscopy

The hydrolysis and condensation kinetic parameters of mercaptopropyl trimethoxysilane (MPTMS, HS(CH2)3Si(OCH3)3) have rarely been quantitatively studied due to the fast reaction rate with the presence of catalysts. In this work, we employed the in-situ Raman spectroscopy to monitor the hydrolysis and condensation reactions of MPTMS in real time. First, with CH3OH as the solvent and NH4OH as the catalyst, the hydrolysis kinetics of MPTMS was investigated via the initial rate method. The reaction orders with respect to MPTMS, H2O, and NH4OH are 1.0, 1.0, and 1.0, respectively. The activation energy (Ea) and pre-exponential factor (A) of MPTMS hydrolysis reaction are (28.4 ± 1.1) kJ/mol and 938.1 (mol/L)-2·min−1, respectively. Then, an ‘acid-catalyzed hydrolysis and base-catalyzed condensation’ two-step strategy was employed to decouple the hydrolysis and condensation reactions. With the hydrolysates, trihydroxy silanols HS(CH2)3Si(OH)3, as the starting reactant, the early-stage condensation reaction kinetics was studied. The reaction orders with respect to HS(CH2)3Si(OH)3 and NH4OH are 1.4 and 2.8, respectively. The activation energy (Ea) and pre-exponential factor (A) of the condensation reaction are (52.2 ± 0.4) kJ/mol and 7.5 × 1013 (mol/L)-3.2·min−1, respectively. The kinetic parameters determined in this work could provide quantitative guidance for the design and control of MPTMS reaction process.

Synthesis and Kinetics of the N-(2-Methyl-6-ethyl phenyl)-1-methoxypropyl-2-imine Schiff Base Catalyzed by NKC-9 Cation Exchange Resin.

The kinetics of condensation reaction of methoxyacetone with 2-methyl-6-ethyl aniline catalyzed by NKC-9 cation exchange resin was studied for the first time. The reaction temperature of Schiff base synthesis was determined in the range of 367.15 to 401.15 K by the batch experiments, and influences of reactant molar ratio, temperature, catalyst dosage, and particle size on the ultimate conversion were also studied. The dynamic data were used to be relevant with PH, ER(1), ER(2), and Langmuir Hinshelwood Hougen Watson homogeneity models. Model parameters, including reaction equilibrium constants, activation energy, enthalpy change, entropy change, and rate constants, were solved. The accuracy of the model was validated by means of both experimental proofs and standard deviation between the predicted and experimental data. Finally, a series of characterization tests such as Fourier transform infrared spectroscopy, X-ray diffraction, and polarizing microscopy were performed to investigate the structure and properties of NKC-9.

The Influence of β-Ammonium Substitution on the Reaction Kinetics of Aminooxy Condensations with Aldehydes and Ketones.

The click-chemistry capture of volatile aldehydes and ketones by ammonium aminooxy compounds has proven to be an efficient means of analyzing the carbonyl subset in complex mixtures, such as exhaled breath or environmental air. In this work, we examine the carbonyl condensation reaction kinetics of three aminooxy compounds with varying β-ammonium ion substitution using Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS). We determined the activation energies for the reactions of the aminooxy compounds ATM, ADMH and AMAH with a panel of ketones and aldehydes that included acrolein and crotonaldehyde. The measurements indicate that the activation energies for the oximation reactions are quite low, less than 75 kJ mol-1 . ADMH is observed to react the fastest with the carbonyls studied. We postulate this result may be attributed to the ADMH ammonium proton effecting a Brønsted-Lowry acid-catalyzed elimination of water during the rate-determining step of oxime ether formation. A theoretical study of oxime ether formation is presented to explain the enhanced reactivity of ADMH relative to the tetraalkylammonium analog ATM.

Improvement in Char Strength with an Open Cage Silsesquioxane Flame Retardant.

Different characterization techniques were used to study the hydrolysis and condensation reaction kinetics of 3-methacryloxypropyltrimethoxysilane (MAPTMS) to obtain open cage silsesquioxane oligomers. The formation of hydrogen bonds, which condition the chemical structures of the resulting products, was identified. Improved thermal and fire resistant behavior of unsaturated polyester (UP) composites prepared with aluminium trihydroxide (ATH) and the synthesized oligomer were registered. Opened silsesquioxane structures also showed an improvement in the mechanical properties of the char formed after firing.

Kinetics of Condensation Reactions between Ethanolamine (Amino-Alcohol) and Dicarboxylic Acids at 413 K

Kinetics of Condensation Reactions between Ethanolamine (Amino-Alcohol) and Dicarboxylic Acids at 413 K

A study on the kinetics of condensation reaction of phenol‐modified cardanol–formaldehyde resin

AbstractPhenol‐modified cardanol–formaldehyde novolac resins have been synthesized using equal proportions of phenol and cardanol. To this mixture of phenol and cardanol, 0.6 and 0.8 mol of formaldehyde were added separately, under acidic conditions, at five different temperatures ranging between 80 and 120°C with an interval of 10°C. This was carried out for a maximum period of 6 h. The free formaldehyde and free phenol contents were determined at regular time intervals to check the completion of the reaction. The synthesized novolacs have been studied by infrared spectroscopic analysis (FT‐IR). The reaction between cardanol, phenol, and formaldehyde was found to follow a second‐order rate kinetics. The overall rate constant (k) increased with the increase of temperature. Based on the value of rate constants, various other parameters such as activation energy (Ea), change in enthalpy (Δ H) and entropy (Δ S), and free energy change (Δ G) of the reaction were also evaluated. It was found that the condensation reaction of phenol and cardanol with formaldehyde was nonspontaneous and irreversible. © 2010 Wiley Periodicals, Inc. Int J Chem Kinet 42: 380–389, 2010

A study on the kinetics of condensation reaction of cardanol and formaldehyde, part I

AbstractNovolac resins having cardanol‐to‐formaldehyde mole ratios of 1:0.4, 1:0.5, and 1:0.6 were prepared by using aromatic sulphonic acid as the catalyst at four different temperatures ranging between 90°C and 120°C, with an interval of 10°C. Free formaldehyde and free phenol contents were determined at regular time intervals to check the completion of the reaction. The synthesized novolacs were characterized by Fourier‐transform infrared spectroscopic analysis, nuclear magnetic resonance, and gel permeation chromatography. The reaction between cardanol and formaldehyde was found to follow second‐order kinetics. The overall rate constant (k) increased with the increase of temperature. On the basis of the value of k, various other activation parameters such as activation energy (Ea), change in enthalpy (ΔH), entropy (ΔS), and free energy (ΔG) of the reaction were also evaluated. It was found that the condensation reaction of cardanol and formaldehyde with aromatic sulphonic acid was nonspontaneous and irreversible. © 2009 Wiley Periodicals, Inc. Int J Chem Kinet 41: 559–572, 2009

Surfactant Effect on Kinetic of Reaction of Some Sulphonamides withp-Dimethylaminobenzaldehyde: Surfactant-Modified Determination of Sulphonamides in Aqueous Solution

Kinetics of condensation reactions of six sulpha drugs (I-VI) with p-dimethylaminobenzaldehyde (DAB) in a weakly acidic EthOH/H2O solution have been studied spectrophotometrically. The reaction was found to be first order with respect to DAB and zero order with respect to sulphonamide. The rate constants, activation energies, and other related thermodynamic functions have been determined. The effect of the presence of anionic surfactant sodium dodecyl sulphate (SDS) on the kinetics of this reaction in aqueous solution has been investigated. The observed rate constants increase with increasing the amount of SDS except for those of sodium sulphacetamide (VI). The surfactant molecules enhance the reaction rates (14–113 times) in concentrations less than critical micellar concentration (cmc). A developed spectrophotometric method for determining sulphonamides in aqueous solution by their reactions with an excess of DAB in the presence of SDS and HCl (pH = 2) at a wavelength of 447 nm has been introduced. Microgram amounts of sulphonamides can be estimated with accuracy better than ± 1.5% and reproducibility less than ± 0.064%. The results of application to sulphonamides in pure form indicate that the presented method is simple, sensitive, precise, accurate, and comparable to the colorimetric Bratton-Marshall standard procedure. The effect of interferences and application of the presented method to two pharmaceutical preparations have been investigated.

Influence of molecular weight and chemical structure of soft segment in reaction kinetics of polycarbonate diols with 4,4′-diphenylmethane diisocyanate

This third paper in this series regarding the mechanism and kinetics of urethane systems presents the results obtained in the study of the influence of molecular weight and chemical structure of several polycarbonate diols on the polycondensation reaction with 4,4′-diphenylmethane diisocyanate (MDI), comparing them with those obtained previously for condensation reaction with p-tolyl isocyanate ( p-TI). The substitution effect induced in the second isocyanate group by the reaction of the first isocyanate group of a symmetric diisocyanate likes MDI has been studied by size exclusion chromatography (SEC) using a model monoalcohol. The condensation reaction kinetics is adequately described by an autocatalyzed third order rate equation. The values obtained for rate constants, using a Runge–Kutta mathematical model, suggest association phenomena by hydrogen bonding implying hydroxyl groups but also urethane groups. In bulk and in stoichiometric conditions, the association phenomena observed increase proportionally on one hand, to the decrease of molecular weight of macrodiol and on the other hand, to the tendency to form intramolecular hydrogen bonds. The activation energies were obtained from the evaluation of kinetic data at different temperatures in the range 45–65 °C. As association phenomena increase, activation energies decrease. The slightly higher activation energies obtained for polycondensation compared to condensation are explained because of the rapid increase of viscosity of the medium.

Determination of Carbohydrazide and Kinetics of Condensation reaction of Carbohydrazide with Malachite Green by Spectrophotometry

AbstractThe kinetics of the condensation reaction of malachite green and carbohydrazide was studied by spectrophotometry in aqueous solution in the temperature range of 15.0–22.0 °C. The reaction was found to be second‐order overall, first‐order with respect to each reactant. The effect of ionic strength on the reaction has negative salt effect in the range of 0.2–1.0 mol˙L–1. A mechanism of the reaction between malachite green and carbohydrazide was proposed, and the rate equation derived from the mechanism can explain all experimental observations properly. Based on this reaction, a method of determining the content of carbohydrazide in the concentration range of (0.02–0.5)×10−3 mol·L−1 was proposed.

The influence of molecular weight and chemical structure of soft segment in reaction kinetics with tolyl isocyanate

The influence of molecular weight and chemical structure of several polycarbonate diols on the kinetics of condensation reaction with p-tolyl isocyanate has been studied. Size exclusion chromatography has been used to monitor the reaction. The condensation reaction kinetics is adequately described by an autocatalysed third order rate equation. The values obtained for rate constants, using a Runge–Kutta mathematical model, suggest an association phenomena by hydrogen bonding implying hydroxyl groups but also urethane groups. In bulk and in stoichiometric conditions, the association phenomena observed increases proportionally, on one hand to the decrease of molecular weight of macrodiol, and on the other hand to the tendency to form intramolecular hydrogen bonds.

Microstructural Studies of Transparent Silica Gels and Aerogels

ABSTRACTTransmission electron microscopy, spectroscopy, light scattering and surface area measurements have been used to characterize the microstructural details of transparent silica aerogels. Light scattering intensity measurements have also been used to differentiate acid and base catalyzed hydrolysis and condensation reaction kinetics of Si(OC2H5)4. A plot of logarithm of the light scattering intensity vs. logarithm of time diring gelation gives distinctly different slopes for acid and base catalyzed systems (6 for acid and 2 for base). These slopes for the two systems can be explained on the basis of the point of zero charge of silica and the resulting interactions of the uncharged and charged particles in the systems.

The kinetics of phosphotriester condensation reactions on solid support.

A study has been made of the kinetics of condensation reactions in phosphotriester synthesis of oligonucleotides on polystyrene copolymer resin support, using monomers, dimers, and trimers as the coupling units. The condensations follow pseudo first order kinetics, with a rate constant that decreases from monomers to dimers to trimers. Arrhenius plots indicate a nearly constant activation energy of around 10.4 kcal mol-1. Extrapolation to find the Arrhenius preexponential factor, A, is inaccurate because of the limited temperature range studied. But if the assumption is made that Ea is the same for monomer, dimer, and trimer reactions, then the A values are inversely proportional to the surface areas of the coupling units, reinforcing the interpretation of A as a collision efficiency factor.

Kinetics of Condensation Reactions of Model Phenolic Compounds

Kinetics of Condensation Reactions of Model Phenolic Compounds

Effect of equilibrium in aqueous formaldehyde solutions on its condensation reaction kinetics

1. The effect of the equilibrium which establishes itself in an aqueous solution of formaldehyde and an anionic catalyst on the kinetics of the formaldehyde condensation reaction has been studied. 2. The kinetics of the Cannizzaro reaction have been studied. The reaction rate as a function of the initial formaldehyde concentration is represented by a curve with a maximum. The experimental data have been interpreted on the assumption that the reaction is based on the interaction of monomeric formaldehyde with the free form of the catalyst, which are in equilibrium with their polymeric compounds.