Gibbs Free Energy Of Activation Research Articles

The catalytic effects of a thiazolium salt in the oxa-Diels-Alder reaction between benzaldehyde and Danishefsky's diene: a molecular electron density theory study.

The oxa-Diels-Alder (ODA) reaction of benzaldehyde with Danishefsky's diene in the presence of a [thiazolium][Cl] salt, as a model of an ionic liquid, has been studied within Molecular Electron Density Theory (MEDT) at the M06-2X/6-311G(d,p) computational level. The formation of two hydrogen bonds (HBs) between the thiazolium cation and the carbonyl oxygen of benzaldehyde modifies neither the electrophilic character of benzaldehyde nor its electronic structure substantially but accelerates the reaction considerably. This ODA reaction presents an activation energy of 4.5 kcal mol-1; the formation of the only observed dihydropyranone is strongly exothermic by -28.8 kcal mol-1. The presence of the [thiazolium][Cl] salt decreases the Gibbs free energy of activation of the ODA reaction between benzaldehyde and Danishefsky's diene by 5.9 kcal mol-1. This ODA reaction presents total para regioselectivity and high endo stereoselectivity. This ODA reaction takes place through a highly asynchronous polar transition state structure (TS) associated with a non-concerted two-stage one-step mechanism. ELF analysis of para/endo TSs associated with the ODA reactions in the absence and presence of the [thiazolium][Cl] salt shows that the formation of the HBs at the TSs does not modify their electronic structure substantially. This MEDT study makes it possible to conclude that the acceleration found in the ODA reaction of benzaldehyde with Danishefsky's diene in ILs is a consequence of an increase of the global electron density transfer at TS3-pn, resulting from HB formation, and the greater strength of the HBs at the polar TS3-pn compared to that at the benzaldehyde : [thiazolium][Cl] complex, and that the strength in the HB formed is more relevant that than an increase of the electrophilic character of the interaction between reagent.

Kinetic-thermodynamic study of the oxidative stability of Arbequina olive oils flavored with lemon verbena essential oil

Arbequina extra-virgin olive oils were flavored with lemon verbena (Aloysia citrodora) essential oil (0.1–0.4%, w/w), being evaluated quality parameters (free acidity, peroxide value, UV-extinction coefficients), oxidative stability, antioxidant and total reducing capacity. The kinetic-thermodynamic nature of the lipid oxidation was evaluated by Rancimat (110–150 °C). The essential oil addition promoted the antioxidant and total reducing capacities but, unfortunately, increased primary and secondary related quality parameters. Moreover, flavoring decreased the oils' oxidative stability. The kinetic-thermodynamic data showed that unflavored oils had significantly lower oxidation reaction rates (0.055–0.06492 h−1), more negative temperature coefficient (−0.0268°C−1), higher temperature acceleration factor (1.852), greater activation energy (82.7 kJ mol−1) and frequency factor (10.9 × 109 h−1), higher positive enthalpy of activation (79.4 kJmol-1), lower negative entropy of activation (−131.8 J mol−1K−1) and greater positive Gibbs free energy of activation (129.95–135.23 kJ mol−1), showing that oils’ oxidation was negatively influenced by the essential oil incorporation. Overall, oxidation had a non-spontaneous, endothermic and endergonic nature. Finally, olive oils could be satisfactorily classified (principal component and linear discriminant analysis) according to the flavoring level, using quality-antioxidant-stability or kinetic-thermodynamic datasets. The latter showed a less predictive performance, although ensuring the full discrimination of unflavored from flavored oils.

An adsorption technique applied by plants and factories for purifying gas emissions using modified wastes available at power plants

the paper proposes an adsorption-based method of how to remove sulfur dioxide from the gas emissions produced by industrial companies. A power plant waste – chemical water treatment sludge from Kazan CHPP-1 – was used as an adsorption material. The authors refere here to the chemical composition of the sludge and describe the method of its modification. A new sorption material based on power plant waste was tested for removal sulfur dioxide from the gases. This was resulted in kinetic dependence and adsorption isotherm. The mechanism of how the sulfur dioxide can be adsorbed by a new sorption material at different temperatures was studied. The tests revealed Gibbs free energy, differential heat, and adsorption activation energy. The economic and environmental effect of upgrading the process of removal of sulfur dioxide from gas emissions was calculated for the sodium bisulfite production line of L. Ya. Karpov Chemical Plant JSC

Self-polymerization reaction of cyclohexanone: Kinetics and thermodynamics

The self-polymerization reaction of cyclohexanone was carried out in a stirred glass batch reactor in presence of a base catalyst to prepare a ketonic resin. The effect of reaction parameters such as reaction time, temperature and catalyst concentration on cyclohexanone (monomer) conversion and resin product properties was studied. The reaction time was varied from 7 to 10 hrs, temperature was varied from 90 to 110 °C and catalyst concentration was varied from 10 to 20 wt%. The obtained product was in the form of viscous liquid with a number average molecular weight range of 300–400 g/mol. It has been observed that the rate of reaction increased with the increase in reaction time, temperature and catalyst loading. An effort has been taken to estimate the kinetic and thermodynamic parameters such as, rate constant ( k ), apparent activation energy ( E a ), entropy (Δ S* ), enthalpy (Δ H* ), and Gibbs free energy (Δ G* ) of activation of the polymerization reaction from experimentally obtained monomer conversion data. It has been observed that the reaction order varied mostly between 2 and 3 depending upon the reaction conditions. The estimated activation energy of the self-polymerization reaction of cyclohexanone was around 379 kJ/mol. Based on the obtained enthalpy and free energy data, it can be concluded that self-polymerization reaction of cyclohexanone is endothermic and non-spontaneous respectively in nature.

Water Phase Synthesis Method of CuInS2 Nanoparticles and Its Application for Photovoltaic Device

CIS (CuInS2) is one of the most effective photovoltaic devices with high stability and efficiency, because of its suitable bandgap (1.5eV). Moreover, it does not contain toxic materials, such as Se, within its components. However, productivity and utilization of natural resources under the gas phase synthesis method is relatively low, since vaporizing temperature of elements is extremely different. Thus, it is required to develop a synthesis method of CIS solar cell materials within liquid phase.Here, we have already developed a synthesizing method of single phase and homogenous CI (CuIn) alloy nanoparticles in aqueous solution. In this method, the concentration of the metal complexes in the solution are calculated by using the critical stability constants, and the reduction reaction rate of both metal ions is also controlled. Synthesized CI nanoparticles were spin coted onto Mo/glass substrate and selenized, consequently it shows the photo voltaic effect. Thus, printable solar cells can be formed by using this method. The synthesizing method contains the selenization which is a sort of evaporation method, so it is not liquid process completely. To synthesize CIS solar cells without the selenization, we tried to sulfurize CI nanoparticles but CIS particles were not synthesized. It is difficult to sulfurize CI nanoparticles because they are stable and hard to react with sulfur ions, so it is necessary to synthesize from copper ions and indium ions to CuInS2 particles directly.However, nobody can synthesize CuInS2 particles in aqueous solution because there is a difference between the sulfurization reaction rate of copper and indium ions. If the sulfurization reaction rate of both metal ions is different, they are sulfurized independently to form their own sulfides, such as Cu2S or CuS and In2S3. It is necessary to control and approximate the sulfurization reaction rate of both metal ions for synthesis of CuInS2 particles. Here, in the sulfurization process, the sulfurization reaction rate is correlation with potential energy such as gibbs free energy (ΔG) or activation energy (Ea ). Hence, CuInS2 particles can be synthesized under the condition that the ΔG or Ea in the sulfurization reaction of copper and indium ions are approximated.To synthesize CuInS2 particles in aqueous solution, we tried to approximate the ΔG of the sulfurization reaction of copper and indium ions.By calculating ΔGCu2S and ΔGIn2S3 , we obtained the correlation of KIn and KCu and we were able to select appropriate complexing agents, so we tried to synthesize CuInS2 particles by using these reagents.XRD data indicates that several peaks with a dominant CuInS2 peak were observed. From the above results, it can be said that the synthesis of the precursor of CuInS2 particles in aqueous solution was successful because the Ea of the sulfurization process are approximated in both metal ions.In addition, it was found that the ΔG of copper and indium ions are approximated in the sulfurization system (Cu-In-IDA), so it is necessary to control and approximate both the ΔG and Ea for synthesis of CuInS2 particles in aqueous solution.Although the precursor of CuInS2 were synthesized in aqueous solution, the size and shape of the particles were not uniform. Therefore, for preventing degradation of conversion efficiency, it is needed to develop a technique for homogenizing the shape and the size of the particles.Detailed and another results will be introduced in our presentation. This work has been supported by the Grant-in-Aid for Scientific Research (B) (18H03416).

Kinetics Study of Dye Decolorization by Oxidation in Aqueous and Aqueous Alcohol Medium

The kinetics of oxidation of methylene blue with potassium bromate was investigated by observing decolorization of methylene blue in aqueous, aqueous methanol and aqueous isopropanol solvent system. The rate of reaction was studied as function of concentrations of methylene blue and potassium bromate in acidic medium at temperature 303 and 313 K. The increase in concentration of potassium bromate enhances the rate of decolorization of methylene blue in acidic medium; no significant change in rate was observed with variation of methylene blue. The rate of decolorization was found to be fastest in aqueous methanol compared to aqueous isopropanol and slow in aqueous medium. From the investigation, it was observed the reaction follows pseudo-first-order kinetics. The kinetic data were used to propose the mechanism of reaction. Thermodynamic parameters, enthalpy of activation (ΔH*), entropy of activation (ΔS*) and Gibbs free energy of activation (ΔG*), were also calculated to support kinetic results.

Understanding the Influence of the Trifluoromethyl Group on the Selectivities of the [3+2] Cycloadditions of Thiocarbonyl S‐methanides with α,β‐Unsaturated Ketones. A MEDT study

AbstractExperimentally (G. Mlostoń et al., J. Fluor. Chem. 2016, 190, 56–60), it has been found that the type of the obtained cycloadduct of the [3+2] cycloaddition (32CA) reaction of thiocarbonyl S‐methanides with α,β‐unsaturated ketones depends strongly on the location of the trifluoromethyl group. In the case of enones containing the CF3CH=CH moiety, the 32CA reaction occurs chemo‐ and regioselectively onto the C=C double bond giving trifluoromethylated tetrahydrothiophene derivatives. On the other hand, enones containing the CF3−C=O fragment react as carbonyl heteroethylenes leading to trifluoromethylated 1,3‐oxathiolanes also in a chemo‐ and regioselective manner. Our aim in the present work is to perform a theoretical study of the all chemo‐, regio‐, and stereo‐isomeric reaction paths of these 32CA reactions within the Molecular Electron Density Theory. Activation Gibbs free energies, calculated at the B3LYP/6‐311G(d,p) level in tetrahydrofurane at −40 °C, show that the ortho/endo reaction path giving the trifluoromethylated tetrahydrothiophene is more favoured, while the meta/endo reaction path leading to trifluoromethylated 1,3‐oxathiolanes is more preferred in total agreement with experimental findings. The low activation barriers in combination of the Electron Localization Function topological analysis of the most relevant points along the Intrinsic Reaction Coordinate reveals the pseudomonoradical character of the studied 32CA reactions.

Effect of formaldehyde properties on SnO2 clusters gas sensitivity: A DFT study

Formaldehyde (CH2O) properties such as flash point and autoignition temperature have a great effect on the temperature range of sensitivity of sensors applied to detect CH2O gas. Tin dioxide nanocrystal interaction with formaldehyde is investigated from room temperature to 500 °C using transition state and density functional theory. Gibbs free energy, enthalpy, and entropy of activation and reaction are evaluated as a function of temperature. The sensitivity and response time of SnO2 clusters towards formaldehyde are evaluated. Results show that the activation energy of SnO2 clusters with formaldehyde increases with the rise of temperature while the reaction energy decreases (in negative value) with the rise of temperature. Response time is inversely proportional to formaldehyde concentration. The highest CH2O gas-sensitive range of SnO2 is confined between the formaldehyde flash point at 64 °C and the autoignition temperature at 430 °C. The effect of partial oxidation and dissociation of formaldehyde is discussed.

Effect of seaweed extracts on improving the oxidation kinetic of black cumin (Nigella sativa) oil

In this study, effects of red (Palisada perforata and Gracilaria corticata), brown (Sargassum angustifolium and Polyclada indica) and green (Ulva compressa and Caulerpa taxifolia) Persian Gulf seaweed extracts on thermal kinetic parameters of black cumin (Nigella sativa) oil was investigated in comparison with those of BHT and α-tocopherol. Oxidative stability of black cumin oil samples were investigated using Rancimat at 363, 383, and 403 K. Apart from P. indica extract, all other seaweed extracts were effective on improving oxidative stability indices of black cumin oil samples. Red seaweed extracts were the most effective in reducing the severity of temperature-related effects on black cumin oil oxidation rate. In addition, these antioxidants were able to reduce black cumin oil oxidation by forming an activated complex with more structured configuration. The extent of decrease in frequency factor and entropy were 80.77% and 14.83% for G. corticata extract, respectively and also 82.66% and 15.45% for P. perforata extract, respectively. The highest increase in Gibbs free-energy of activation was observed for G. corticata extract followed by BHT, P. perforata extract, and α-tocopherol. In conclusion, red seaweed extracts can be proposed as suitable sources of natural antioxidants for improving oxidation kinetic of black cumin oil.

Adsorptive kinetics, isotherm and thermodynamic analysis of fishpond effluent coagulation using chitin derived coagulant from waste Brachyura shell

High grade chitin extracted from Brachyura shell waste was successfully used for adsorptive de-colorization of highly turbid fishpond effluent. Brachyura shell chitin was characterized via Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), X-ray diffraction (XRD), thermo-gravimetric analysis (TGA) and differential scanning calorimetry (DSC). Results obtained from the characterization indicated that the extracted chitin possessed significant features required for surface phenomenon driven matrices. The best efficiency obtained for turbidity and color removal were 88% and 91%, respectively, at BSC dosage of 1.8 g/L, pH of 6.0 and temperature of 45°C. The maximum adsorption capacity of the de-colorization process onto BSC was found to be 265.59 mg/g. Results from kinetic analysis suggested that pseudo-second order model was most accurate (R2 > 0.99) in predicting the experimental data. Webber-Morris intraparticle diffusion rate constant (Kipd) demonstrated that the adsorptive process depended more on film diffusion mechanism. Equilibrium study was carried out using Langmuir, Freundlich, Temkin, Dubinin Radushkevich and Brunauer-Emmett-Teller isotherm model at 30, 40 and 50°C. Fitness appraisal analysis of the isotherm models pointed out that experimental data aligned significantly with Langmuir and Temkin isotherm (R2 > 0.94), suggesting the homogenous and monolayer mode of the adsorptive process. Values of Gibbs free energy (− ΔG0= 1.7816 – 2.6706 kJ /mol), enthalpy (ΔH0= 11.6867kJ/ mol), activation energy (EA= 13.2330kJ/ mol) and entropy (ΔS0= 44.4511J / molK) obtained from thermodynamic analysis confirmed the spontaneous, endothermic, favorable and physical nature of the process.

Adsorption isotherms, kinetics and thermodynamic studies of methylene blue dye removal using Raphia taedigera seed activated carbon

This present work revealed the isotherm, kinetic, and thermodynamic behaviour of methylene blue (MB) dye adsorbed onto acidic activated carbon (AAC) and base activated carbon (BAC) prepared from Raphia taedigera seed by carbonization and chemical activation. AAC and BAC were activated with sulphuric acid and sodium hydroxide respectively. Batch equilibrium studies were done under different experimental conditions such as MB dye concentration and temperature. The equilibrium data were modelled using Langmuir, Freundlich, Elovich, Temkin and Dubinin-Radushkevich isotherms. The Langmuir isotherm model best describes the uptake of MB dye onto AAC and BAC with R2 > 0.998 in all cases. The pseudo-first-order, pseudo-second-order and intra-particle diffusion equations were used to evaluate the kinetic properties. It was observed that the adsorption of MB dye onto the two activated carbons could best be described by the pseudo-second order equation with 0.999 < R2 ≤ 1. Thermodynamic parameters such as Gibbs free energy (ΔG0), standard enthalpy (ΔH0), standard entropy (ΔS0), and activation energy (Ea) were determined. The results of ΔG0indicated a spontaneous and feasible for AAC and non-spontaneous but feasible for BAC. Results of ΔH0 confirmed that the adsorption of MB onto AAC and BAC are endothermic and physical in nature. It can be concluded that AAC and BAC prepared from Raphia taedigera seed could be used as low-cost adsorbent for the removal of MB dye from the wastewater.

DFT Investigation of Hydrogen Atom Abstraction from NHC-Boranes by Methyl, Ethyl and Cyanomethyl Radicals-Composition and Correlation Analysis of Kinetic Barriers.

Understanding the hydrogen atom abstraction (HAA) reactions of N-heterocyclic carbene (NHC)-boranes is essential for extending the practical applications of boron chemistry. In this study, density functional theory (DFT) computations were performed for the HAA reactions of a series of NHC-boranes attacked by •CH2CN, Me• and Et• radicals. Using the computed data, we investigated the correlations of the activation and free energy barriers with their components, including the intrinsic barrier, the thermal contribution of the thermodynamic reaction energy to the kinetic barriers, the activation Gibbs free energy correction and the activation zero-point vibrational energy correction. Furthermore, to describe the dependence of the activation and free energy barriers on the thermodynamic reaction energy or reaction Gibbs free energy, we used a three-variable linear model, which was demonstrated to be more precise than the two-variable Evans–Polanyi linear free energy model and more succinct than the three-variable Marcus-theory-based nonlinear HAA model. The present work provides not only a more thorough understanding of the compositions of the barriers to the HAA reactions of NHC-boranes and the HAA reactivities of the substrates but also fresh insights into the suitability of various models for describing the relationships between the kinetic and thermodynamic physical quantities.

Kinetic/thermodynamic study of immobilized β-fructofuranosidase from Aspergillus tamarii URM4634 in chitosan beads and application on invert sugar production in packed bed reactor

β-fructofuranosidase (FFase) from Aspergillus tamarii URM4634 was immobilized covalently in chitosan beads. It was characterized biochemically, studied in terms of kinetic and thermodynamic parameters, and applied on conversion of sucrose for invert sugar production in a packed bed reactor (PBR). The optimum reactional conditions were determined and obtained at pH 5.0 and 60 °C. FFase was thermostable at 50–55°C. At 50°C, the enzyme shows longer half-life (t1/2) (594.13 min) and a higher D-value (1,973.64 min). This indicates that immobilized FFase was stable at temperature commonly used in invert sugar production. The following thermodynamic parameters were obtained: activation energy (E*d = 301.57 kJ mol−1), enthalpy (298.76 ≤ ΔH*d ≤ 298.89 kJ mol−1), entropy (579.88 ≤ ΔS*d ≤ 589.27 J K−1 mol−1) and Gibbs free energy (100.29 ≤ ΔG*d ≤ 108.47 kJ mol−1). The high E*d, ΔH*d and ΔG*d values confirmed FFase thermostability. The high and positive values for ΔS*d indicate an increase in disorder due opening of the enzyme structure. The sucrose hydrolysis in PBR showed a maximum invert sugar yield (96.0%) at 15 min of operation. The hydrolysis process remained efficient up to 100 min (70.22%). The results obtained in the present study provide a good indication that immobilized FFase on chitosan beads in PBR is efficient to invert sugar production for food industry.

Insight into solute-solute and solute-solvent interactions of l-proline in aqueous-D-xylose/L-arabinose solutions by using physicochemical methods at temperatures from 293.15 to 318.15 K

The interactions of l-proline with carbohydrates are investigated by using volumetric, viscometric and acoustic properties. The measurements of the densities, ρ, ultrasonic speeds, u and viscosities, η of the l-proline in water and in aqueous-D-xylose/L-arabinose (2.5% and 5% D-xylose/L-arabinose in water) solvents were carried out at temperatures (293.15–318.15) K and at atmospheric pressure of 101 kPa by using digital vibrating tube density and sound analyzer and microviscometer. The experimental data have been used to evaluate the apparent molar volumes, Vϕ, limiting apparent molar volumes, Vϕ°, apparent molar compressibilities, Ks, ϕ, limiting apparent molar compressibilities, Ks,ϕ°, transfer volumes, Vϕ,tr° and transfer compressibilities, Ks,ϕ,tr°. The viscosity A and B coefficients, Gibbs free energies of activation of viscous flow per mole of solvent, Δμ1°# and of solute, Δμ2°#, enthalpies, ΔH∘# and entropies, ΔS∘# of viscous flow, were obtained using the viscosity data. The effect of concentration, temperature and solute structure were discussed in terms of solute-solvent and solute-solute interactions prevailing in these systems. The structure making/breaking ability of l-proline is examined in from the sign of temperature derivative of B-coefficient, dB/dT. The thermodynamic parameters of viscous flow for the solutions are also calculated and discussed using transition state theory.

Thermodynamic and transport properties of ternary mixture (ethyl oleate + n-hexadecane +1-butanol) and its binary constituents (ethyl oleate +1-butanol and ethyl oleate + n-hexadecane) at different temperatures and atmospheric pressure

Densities, viscosities, speeds of sound and refractive indices have been measured for the ternary system ethyl oleate + n-hexadecane +1-butanol, and for the corresponding binaries ethyl oleate +1-butanol and ethyl oleate + n-hexadecane, in the temperature range from T = (293.15 to 343.15) K and at atmospheric pressure. Experimental data were employed to calculate some derived thermodynamic parameters, i.e. excess molar volumes (VE), viscosity deviations (Δη) and deviations in refractive index (ΔnD). Additionally, molar excess Gibbs free energies of activation of viscous flow (ΔG⁎E) and deviations in isentropic compressibility (Δκs) were calculated. A graphical representation of excess molar volumes and refractive indices show positive deviation from ideal behavior for both binary systems whereas deviation in viscosity shows negative nature for the ethyl oleate + n-hexadecane system and an inversion sign for ethyl oleate +1-butanol binary system. A negative deviation in isentropic compressibility was confirmed for the systems ethyl oleate +1-butanol while positive deviation was observed in ethyl oleate + n-hexadecane system. It can be concluded that dispersive forces predominate between the components in binary systems and the observed behavior seems to suggest that the properties obtained for the ternary mixture are dominated by the binary effects. The viscosities of the binary systems were modeled by UNIFAC-VISCO, ASOG-VISCO, Teja-Rice and McAllister models. The results showed that McAllister's multibody model is suitable to describe viscosities for binary systems with maximum percentage deviations less than 0.5%.

Viscosity-Temperature Stability, Chemical Characterization, and Fatty Acid Profiles of some Brands of Refined Vegetable Oil

Oils of vegetable origin are of great importance in food, soap, and cosmetic industries and they may also be used as lubricants and raw materials for biodiesel production depending on their viscosity and thermal stability. This work provides insight into the fatty acid components, physicochemical properties and thermal stability of some refined vegetable oils. The Saponification values, peroxide values, acid values, iodine values and refractive index of these oils range from 185.38 to 209.26 mg/g KOH, 2.00 to 37.00 meq O2/ kg, 2.50 to 5.50 mg KOH/ g, 31.09 to 89.46 g / 100g and 1.441 to 1.488 respectively The activation energies obtained from Arrhenius-type equation range from 11.32 to 3.85 kJ mol-1, while the enthalpy (∆H҂) and entropy (∆S҂) of activation obtained from Eyring-type equation range from 6.852 to 14.317 kJ mol-1 and -31.85 to -29.06 J mol-1 K-1 respectively. The Gibbs free energy of activation (∆G҂) ranges from 15.51 to 23.81 k J mol-1. The Pw oil brand has the highest thermal stability and resistance to shear stress due to its high activation energy and a low degree of unsaturation. The heat was absorbed during the process, the reaction mechanism was associative and the entire process was non-spontaneous.

Photocatalytic Reduction of Fluorescent Dyes in Sunlight by Newly Synthesized Spiroindenoquinoxaline Pyrrolizidines.

Spiroindenoquinoxaline pyrrolizidines (SIQPs)—7-nitro-2′-phenyl-5′,6′,7′,7a′-tetrahydrospiro[indeno[1,2-b]quinoxaline-11,3′-pyrrolizine]-1′,1′(2′H)-dicarbonitrile (SIQP I), 2′-(4-cyanophenyl)-7-nitro-5′,6′,7′,7a′-tetrahydrospiro[indeno[1,2-b]quinoxaline-11,3′-pyrrolizine]-1′,1′(2′H)-dicarbonitrile (SIQP II), and 2′-(4-methoxyphenyl)-7-nitro-5′,6′,7′,7a′-tetrahydrospiro[indeno[1,2-b]quinoxaline-11,3′-pyrrolizine]-1′,1′(2′H)-dicarbonitrile (SIQP III)—have been synthesized through a one-pot cascade Knoevenagel condensation reaction in acetonitrile (ACN) with 91, 98, and 87% yields, respectively. Structures are characterized by 1H NMR and 13C NMR spectroscopy, nuclear Overhauser enhancement spectroscopy (NOESY), Fourier transform infrared (FT-IR) and UV–vis spectroscopy, thermogravimetric analysis (TGA), high-resolution mass spectroscopy (HRTEM), fluorescence and Raman spectroscopy, and energy-dispersive analysis by X-ray (EDX) spectroscopy. SIQPs in ACN photocatalyzed methylene blue (MB) but not phenolphthalein (HIn). SIQPs distinguished the quaternary atoms and dipoles of the fluorescent dye (MB) contrary to the quinonoid HIn structure. In sunlight, SIQPs without electricity input acted as a photonic sensor to detect fluorescent dyes in waste effluents of textile, paper, dyes, and other industries. Activation energy (Ea), enthalpy (ΔH), entropy (ΔS), and Gibbs free energy (ΔG) calculated from UV–vis absorption spectra show photocatalytic reduction (PCR) activities in the order SIQP II > III > I. The N-atom of pyrrolizidine and −NO2 of nitro-indenoquinoxaline (NIQ) induced the highest occupied molecular orbital (HOMO) to the lowest unoccupied molecular orbital (LUMO) electrodynamics to enable the SIQPs to catalyze biochemical activities.

Studies on Volumetric and Viscometric Properties of L-Glutamic Acid in Aqueous Solution of Glucose over a Range of Temperatures (298K to 323K)

In this work, volumetric and viscometric properties of L-glutamic acid in water and aqueous glucose solutions (5%, 10%, 15%, and 20% of glucose, w/w in water) have been measured as a function of molal concentration (0.02 mol.kg-1 to 0.16 mol.kg-1) of L-glutamic acid at different temperatures T= (293.15, 303.15, 308.15, 313.15 and 323.15) K. By using experimental densities (ρ) and viscosities (η) data, apparent molar volume (φv), experimental slope (Sv), limiting apparent molar volume (φv0), limiting apparent molar volume transfer (Δφv0)tra, limiting apparent molar expansibilities (Eφ0), Hepler’s constant (δEφ0/δT)p, Falkenhagen coefficient A, and Jones-Dole coefficient B have been computed. Gibbs free energies of activation of viscous flow per mole of solvent (μ_1^(0#)) and per mole of solute 〖(μ〗_2^(0#)), hydration number (Hn) is also calculated. The results are discussed based on solute-solute and solute-solvent interactions in these systems. From the results, it is observed that there exists a structure making propensity of L-glutamic acid in water and in the different mass fraction of aqueous glucose solutions, which increases with the increase of glucose concentrations.

Investigation of the Effect of Diisocyanate on the Thermal Degradation Behavior and Degradation Kinetics of Polyether-Based Polyurethanes

Low molecular weight polyether (PE) or polyester polyols can produce novel elastomeric urethane products when cured with diisocyanate which are then utilized for formation of castable energetic composites in addition to many more applications. In this work four different kinds of diisocyanates, isophorone diisocyanate (IPDI), methylenediphenyl diisocyanate (MDI), 2,2,4-trimethyl hexamethylene diisocyanate (TMDI), and toluene diisocyanate (TDI), were used to react with a PE to form PE-based polyurethanes (PUs); they were denoted PE/IPDI, PE/MDI, PE/TMDI, and PE/TDI, respectively. The effect of the four diisocyanate groups in the PE-based PUs on the thermal degradation behavior, thermal degradation kinetics, reaction model, and thermodynamic parameters of the PE/IPDI, PE/MDI, PE/TMDI, and PE/TDI samples were investigated by thermogravimetric analysis (TGA) and derivative thermal gravimetric analysis (DTGA) methods. On the basis of the degradation peak temperature at a high heating rate, the thermal stability of the PU followed the order PE/TDI > PE/TMDI > PE/MDI > PE/IPDI. The activation energy for the thermal degradation was derived using the Flynn–Wall–Ozawa (FWO) method from the TGA data and the average values of the PE/IPDI, PE/MDI, PE/TMDI, and PE/TDI samples were found to be 136.9, 148.0, 132.3, and 155.7 kJ mol‒1, each at various conversions from 0.05 to 0.95, respectively. In addition, the results of the activation energies obtained from the Kissinger–Akahira–Sunnse (KAS) method were in good agreement and consistent with those obtained the FWO method. The reaction models of the degradation reaction were investigated through the Coats–Redfern method and all PUs samples were probably best described by the Avarami–Erofeyev (A 2) and reaction order (F 1) models. The kinetic and thermodynamic parameters for formation of the activated complex of all PUs, such as the activation energy (Ea ), enthalpy of activation (ΔH #), Gibbs free energy of activation (ΔG #), and entropy of activation (ΔS #), were investigated. The investigated thermal kinetic and thermodynamic parameters indicated that there was significant variation in the properties of the PUs containing the different diisocyanate groups.

Mechanism of promotion of SN2 fluorination by [Bmim]F in solvent-free environment: Quantum chemical analysis

Quantum chemical analysis is presented for the mechanism of promotion of SN2 fluorination by 1-Butyl-3-methylimidazolium fluoride ([Bmim]F) reported by Magnier and co-workers (2014). At [Bmim]F: substrate molar ratio of 2:1, one of the fluorides acts as the nucleophile, but the second F− plays the role as Lewis base on the two counter-cations to facilitate the reaction. We find that the Gibbs free energy(at 80 °C) of activation decreases as the [Bmim]F: substrate ratio increases from 1:1 to 2:1, in good agreement with the experimental observations of improved yield from 47 to 84%.