Gibbs Free Energy Of Activation Research Articles

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%.

Purification and characterization of a novel Aspergillus heteromorphus URM 0269 protease extracted by aqueous two-phase systems PEG/citrate

A novel Aspergillus heteromorphus URM 0269 protease (EC 3.4.21) was extracted by aqueous two-phase systems PEG/citrate (ATPS). Extraction was performed by factorial design 24 for analyzing the independent variable effects named PEG molar mass (MPEG), PEG concentration (CPEG), sodium citrate concentration (CCIT) and pH. Afterwards, extracted protease was characterized in terms of kinetic and thermodynamic parameters. Protease partitioned preferentially for the PEG rich phase displaying the highest purification factor of 7.83 with a 157.53% yielded. Despite the enzyme acted optimally at 50 °C and pH 8.0, it was more stable in lower temperatures (10–40 °C) and pH conditions (5.0–10.0). The kinetic parameters of activation for casein hydrolysis revealed higher affinity by casein (KM = 2.8 mg/mL) with maximum catalysis rate of 45.0 U/mL. The reaction activation energy and the standard enthalpy variation of enzyme unfolding were 24.2 and 54.2 kJ/mol, respectively. Protease catalyzed casein hydrolysis at 25 °C, showed activation Gibbs free energy, enthalpy and entropy of 65.8 kJ/mol, 21.8 kJ/mol and −146.7 J/mol·K, respectively. The thermodynamic parameters of protease thermoinactivation suggested a predominating mechanism of reversible unfolding since the inactivation Gibbs free energy increased from 91.0 to 102.3 kJ/mol. These results displayed the great potential of the protease to be exploited in industrial applications.

Thermodynamic Study on Density and Viscosity of Binary Mixtures of Ethyl acetoacetate with (C4-C9) Aliphatic Ketones at (303.15 and 308.15) K

Investigation on Density (ρ) and viscosity (η) of various binary mixtures of ethylacetoacetate and straight chain aliphatic ketones (butan-2-one, pentan-2- one, hexan-2-one, heptan-2-one, octan-2-one and nonan2-one) have been carried out over the entire solvents composition range at temperatures of 303.15K and 308.15K. From the data obtained, the excess molar volumes (V E ), the excess viscosity (η E ) and excess Gibbs free energy of activation for viscous flow (ΔG*E) have been calculated from the experimental density and viscosity measurements at the working temperatures. Excess molar volumes, V E results are negative and positive over the entire range of mole fractions and become more positive as the chain length increases. The excess viscosities, η E were both positive and negative over the entire mole fraction range. While the observed excess Gibbs free energies of activation of viscous flow, ΔG*E data are positive throughout the entire mole fraction range of solvents composition at all investigated temperatures. These observed results of the excess functions have been interpreted in terms of possible molecular interactions in the binary mixtures.

Transition state theory application to ZnO nanocluster sensitivity to H2 gas

The sensitivity of zinc oxide nanoclusters to hydrogen molecules is discussed using transition state theory. Thermodynamic quantities of activation and reaction are calculated that includes Gibbs free energy, enthalpy, and entropy in the temperature range 25−500 °C. Results show that Gibbs free energy of activation that controls the reaction rate, and the values of response and recovery times increase with temperature. The oxygen recovery reaction rate is higher than the response reaction rate because of the low value of its activation energy. The response time is inversely proportional to the concentration of H2 molecules, while the recovery time increases with the concentration of H2 molecules due to diffusion. The variation of the sensitivity, response, and recovery times with the concentration of H2 molecules agree with available experimental results.

Magnetic nanocomposite cobalt-multiwalled carbon nanotube and adsorption kinetics of methylene blue using an ultrasonic batch

Herein, cobalt (0) metals loaded on multiwalled carbon nanotube nanoadsorbents were synthesized by a straightforward ultrasonic technique, and the removal efficiency of cobalt (0) multiwalled carbon nanotube nanoadsorbents were evaluated in the adsorption of methylene blue at various experimental conduction in an ultrasonic bath. Nanoadsorbents amount, solution pH, ultrasonic power, methylene blue concentrations, temperature, and H2O2 concentrations were studied as experimental parameters in the study. The synthesized cobalt (0) multiwalled carbon nanotube nanoadsorbents were characterized using some advanced spectroscopic techniques. The adsorption mechanism of methylene blue using the as-synthesized nanoadsorbents was evaluated by investigating some kinetic models including intra-particles diffusion, the pseudo-first-order, and the second-order models. The experimental findings of methylene blue adsorption by cobalt multiwalled carbon nanotube was found to be compatible with the pseudo-second-order model. Additionally, some kinetic activation studies like Gibbs free energy, enthalpy, and activation energy for the methylene blue adsorption were investigated. The enthalpy of the process was found to be 25.29 kJ mol−1 that shows the adsorption process is endothermic. The maximum adsorption efficiency of the nanoadsorbents was found to be 1.04 × 10−3 mol g−1 (324.34 mg g−1). The comparisons of results to the previous studies revealed that the synthesized nanoparticles were found to be very effective for the removal of methylene blue from the aquatic mediums.

Better late than never! Transition state character involved in the neutral solvolysis of an oxalic ester determined by the ionizing power of ethanol/water and methanol/water mixtures

Solvation effects and solvolysis extent are major aspects of the decomposition of esters, particularly in polar protic media. Among the many different ester derivatives, oxalic esters are substances that have two ester groups in the same molecular framework, but with potentially different reactivities. Aryl oxalic esters are commonly used in efficient organic chemiluminescent reactions, leading to important analytical and biological applications. We studied the decomposition of bis(2,4,6-trichlorophenyl) oxalate (TCPO) in 100, 98, 95, 90, 80, 70, 60, and 50% ethanol/water (EtOH/W) and 100, 90, 80, and 70% methanol/water (MeOH/W) mixtures (% in v/v). In these media, one phenolic residue is generated in a fast addition–elimination (step 1), followed by a second slower addition–elimination (step 2), thus, two rate constants are observed. Using a Grunwald–Winstein (G–W) relationship between these rate constants and the solvent ionizing power (Υ), we determined the sensibility (m) to solvation effects and charge development associated with the transition state (TS) of the rate-determining step (rds). We also determined the Gibbs free energy of activation (∆‡G, at 25 °C) associated with each step, and used it to rationalize the TS character of the rds, considering that in both steps a zwitterionic intermediate is generated and that the addition step is rate limiting. In EtOH/W binary mixtures a non-linear G–W plot was observed, and for 100–95% EtOH/W mixtures the sensibility was m = 1.0 (step 1, ∆‡G = 21.6 to 20.6 kcal mol−1) and 1.1 (step 2, ∆‡G = 23.9 to 23.0 kcal mol−1), indicating full ionization in the TS of the addition step. Smaller Y values in 90–50% EtOH/W reflect a more symmetrical TS, with not as many charges being generated (step 1, m = 0.196, ∆‡G = 20.3 to 19.4 kcal mol−1; step 2, m = 0.30, ∆‡G = 22.6 to 21.7 kcal mol−1). In 100%–70% MeOH/W binary mixtures, with Y values similar to those for 90–50% EtOH/W, m = 0.52 (step 1, ∆‡G = 20.3 to 18.8 kcal mol−1) and 0.27 (step 2, ∆‡G = 21.5 to 20.9 kcal mol−1) were observed. Particularly for step 1 in MeOH/W, the observation of a solvent kinetic isotope effect that varies from inverse (0.63 ± 0.09 in pure MeOH) to normal (1.9 ± 0.3 in 70% MeOH/W) is consistent with the significant participation of the solvent in TS stabilization, resembling general acid catalysis.

Activated complex theory is a classical theory suitable for food science with appropriate use.

Activated complex theory (ACT), apart from Van 't Hoff equation, has long been applying as an alternative tool to connect the kinetics (reaction rate constant, k) and thermodynamics parameters (including standard enthalpy of activation, △H++; standard entropy of activation, △S++; standard Gibbs free energy of activation, △G++). The study mainly focuses on ACT application in food systems, especially oil and fruit juice processing. Considering there are several improper calculations or mistakes often found in papers published recently in 2014-2019, three considerations are presented when applying the ACT, including 1) Understand that the reaction should be a single chemical elementary step; 2) Ensure that the units used should be consistent; 3) Effectively analyze the kinetics and thermodynamic parameters by choosing proper temperatures. This study is expected to further improve the understanding and correct application of this well-known theory in future work.

Electrochemical and Anticorrosive Behavior of Synthesized Diimine-Based Compound on X80 Steel in Acidic Oil and Gas Well Treatment Fluids at Different Temperatures

A green compound, N,N′-bis(2,4,6-trihydroxybenzaldehyde)-2,2-dimethylpropandiimine, was studied as an acid corrosion inhibitor for X80 steel. Aqueous 15% HCl was utilized for simulating the oil well acidizing fluid at various temperatures. The inhibition performance was assessed using the weight loss method, the electrochemical impedance, the polarization, and the scanning electron microscopy. Polarization investigations showed that the studied diimine inhibitor delays both the cathodic and anodic reactions over chemical adsorption and blocks the active corrosion sites. The adsorption procedure was performed physically as best estimated using the Langmuir adsorption isotherm. It was observed that, the adsorption process was spontaneous and exothermic in the direction of a rise in the bulk phase entropy. The efficiency of the inhibitor was reduced by increasing temperature and raised with an increasing amount of the inhibitor. Impedance data indicated that as the inhibitor amount enhanced the charge transfer resistance of steel also increased while the double layer capacitance decreased. Kinetic and thermodynamic factors such as the activation energy, enthalpy, entropy and the Gibbs free energy of activation and adsorption were computed. Scanning electron microscopy was utilized to examine the steel surface in the presence or the absence of the inhibitor, showing excellent surface protection by the studied inhibitor.