Acetic Acid Medium Research Articles

Kinetic Study of Oxidation of Thiophene-2-Carbaldehyde by Imidazolium Dichromate Promoted By 1, 10-Phenanthroline

Kinetic study of oxidation of Thiophene-2-carbaldehyde by Imidazolium dichromate in aqueous acetic acid medium using 1,10-phenanthroline have been studied. In the absence of mineral acids, the oxidation kinetics of Thiophene-2-carbaldehyde acid by Imidazolium dichromate shows a first-order dependence on Imidazolium dichromate and fractional order on Thiophene-2-carbaldehyde. The variation of ionic strength, H+ and reaction product have in significant effect on reaction rate. Activation parameters have been studied for the reaction from the Arrhenius plot by studying the reaction at different temperatures.

Influence of growth medium on the species-specific interactions between algae and bacteria.

In this study, we investigated a species-specific algal-bacterial co-culture that has recently attracted worldwide scientific attention as a novel approach to enhancing algal growth rate. We report that the type of interaction between Chlorella vulgaris and bacteria of the genus Delftia is not solely determined by species specificity. Rather, it is a dynamic process of adaptation to the surrounding conditions, where one or the other microorganism dominates (temporally) depending on the growth conditions, in particular the medium. Under laboratory conditions, we found that Delftia sp. had a negative effect on C. vulgaris growth when co-cultured in a TAP medium. However, the co-culture of algae and bacteria under BG-11 and BG-11 + acetic acid resulted in an increase in algal concentration compared to algal cultures without bacteria under the same conditions. Additional chemical analysis revealed that the presence of different carbon (the main organic carbon source-acetic acid in TAP or BG-11 + acetic acid medium and inorganic carbon source-Na2CO3 in BG-11 or BG-11 + acetic acid medium) and nitrogen (NH4Cl in TAP medium and NaNO3 in BG-11 or BG-11 + acetic acid medium) species in the growth medium was one of the main factors driving the shift in interaction type.

Insight into D-galactose Oxidation: Kinetic and Mechanistic Analysis with Imidazolium Fluorochromate

In a 50% (v/v) aqueous acetic acid medium, a study on the oxidation kinetics of D-galactose by imidazolium fluorochromate (IFC) was conducted. The study revealed unit-order dependence on [D-galactose], [IFC], and [perchloric Acid]. The reaction was catalyzed by perchloric acid, and followed a 1:1 stoichiometric ratio. Adding sodium hyperchlorate (VII) salt did not affect the reaction. Polymerization of acrylonitrile was not observed in the oxidation process. The oxidation rates were retarded on adding Mn2+ ions in the mixture, and rates increased as the reaction medium’s dielectric constant (D) decreased. The observed results follow the Amis and Kirkwood plots {log k1 vs. (1/D) and ((D-1/2D+1))}. Several thermodynamic variables were determined by analyzing the kinetic data across a temperature range. Arabinose and formic acid were formed as the products of the reaction. A mechanistic path involving the formation of an ester followed by hydride ion transfer was proposed.

Keratin protein nanofibers from merino wool yarn: a top-down approach for the disintegration of hierarchical wool architecture to extract α-keratin protein nanofibers.

We report the extraction of keratin nanofibers from the medulla of a parent yarn after denaturing the cuticle and cortex microstructures of a merino wool yarn. Controlled alkaline hydrolysis, followed by high-speed blending in acetic acid, allowed for the extraction of keratin protein nanofibers with an average diameter of 25 nm and a length of less than 3 μm. SEM and AFM analyses showed the removal of cuticle cells from the yarn. FT-IR and DSC analyses confirmed the hydrolysis and denaturation of the sheet protein matrix of cuticle cells. XPS analysis provided strong evidence for the gradual removal of the epicuticle, cuticle cells, and cortex of the hierarchical wool structure with an increase in alkaline hydrolysis conditions. It was confirmed that the merino wool yarn subjected to hydrolysis under alkaline conditions exposed its internal fibrillar surface. In an acetic acid medium, these fibrillar surfaces obtained a surface charge, which further supported the defibrillation of the structure into its individual nanofibrils during high-speed blending. The extracted nanostructures constitute mainly α-helical proteins. The morphology of the nanofibers is composed of a uniform circular cross-section based on the images obtained using AFM, TEM, and SEM. The extracted nanofibers were successfully fabricated into transparent sheets that can be used in several applications.

ИЗУЧЕНИЕ ГИДРОДИНАМИЧЕСКИХ СВОЙСТВ ХИТОЗАНА В БИНАРНЫХ РАСТВОРАХ УКСУСНАЯ КИСЛОТА-ВОДА

The hydrodynamic properties of chitosan solutions in the acetic acid-water binary system were studied by viscometry and potentiometry methods. The degree of protonation of chitosan macromolecules was determined. The dependence of the degree of chitosan protonation on its concentration in solution and on the acetic acid-water ratio has been established. The obtained results make it possible to formulate optimal conditions for carrying out graft polymerization of chitosan in acetic acid media.

Molecular interactions in ternary system of K-contin and (2-Aminoacetamido)acetic acid at various temperatures–ultrasonic and viscometric analysis

Ultrasonic techniques are frequently used in organic molecule conformation analysis. Mixtures of ternary liquid complexes are extensively used for comprehending the strength as well as the characteristics of the interactions between molecules. Experimentally, the thermo physical properties of ternary liquid mixtures such as viscosity (η), density (ρ) and velocity (u) of K-contin, (2-Aminoacetamido)acetic acid and non-aqueous medium were determined over temperature ranges of 298.15, 308.15 and 318.15 K. The experimental data were used to ascertain the thermoacoustic parameters such as free volume, internal pressure, adiabatic compressibility, solvation number, specific acoustic impedance and intermolecular free length. These parameters are more useful for predicting and validating molecular interactions.

Micellar Effect on the Oxidation of Anisaldehyde by Quinolinium Dichromate in Aqueous Acidic Media: A Kinetic Study

Aims: Oxidation of p-anisaldehyde by Quinolinium dichromate (QDC) in the aqueous acetic acid medium in the presence of sulphuric acid using surfactants. Background: The oxidation studies of anisaldehyde is very important as the oxidized products are used as a synthetic intermediate for the preparation of a variety of drugs. Quinolinium dichromate (QDC) has emerged as a very useful and versatile oxidant. Micellar medium enhances the reaction rate. Objective: 1. To study the kinetics of the reaction, which includes the determination of order, rate, and activation parameters. 2. Spectral characterization of QDC by NMR and the kinetic study of the reaction mechanism is done through UV – A visible spectrophotometer. 3. Solvent effect for the oxidation of anisaldehyde by QDC. 4. Determination of critical micelle concentration (CMC) of used surfactants (CTAB and SDS). Methods: The reactions were followed at constant temperature and were followed by monitoring the UV – Visible spectrophotometer (Double Beam – 2203) in a quartz cuvette of 1 cm path length by following the absorbance decay of Cr (VI) at 440 nm. Result: KINETIC RESULTS: 1. The reaction follows first-order dependence on panisaldehyde and QDC. 2. The reaction is found to be acid-catalysed. A plot of log [k] versus log [H+] was found to be a straight line with a slope of 1.07. EFFECT OF SOLVENT: The rate of reaction increases with the increase in acetic acid proportion in the medium, which suggests that the reactions were of the ion–dipole type. MICELLAR EFFECT: 1. Experimental results demonstrated that anionic surfactant SDS catalysed and accelerated the study more effectively than CTAB, which is a cationic surfactant, and the rate of reaction increases with an increase in the concentration of the SDS while in the case of CTAB, the rate decreases with an increase in its concentration. 2. CMC values of CTAB and SDS were 3.9 mM and 8.2 mM, respectively. Conclusion: The value of negative ΔS (entropy of activation) and positive ΔH (enthalpy of activation) suggests the formation of more ordered activated complexes, and the transition state is highly solvated. SPECTROSCOPIC ANALYSIS 1.NMR characterisation of synthesised QDC shows a resemblance with pure QDC. 2. Effect of oxidant QDC, panisaldehyde and acid was studied by considering the spectra of the reaction mixture and varying their concentration.

Oxidation of D-Glucose and D-Fructose by N-Bromosaccharin in Aqueous Acetic Acid Medium in Presence of NaLS: A Comparative Study

The oxidation of D-Glucose and D-Fructose was monitored iodometrically by N-Bromosaccharin in the aqueous acetic acid medium in presence of NaLS (Sodium Lauryl Sulphate). Reaction demonstrated that oxidative species HOBr and H2O⊕Br were involved in the acidic oxidation of Carbohydrates. It was established that respective acids of carbohydrates gluconic acid and arabinoic acid were the oxidation products. Respective acids of carbohydrates were the results of reactive HOBr in acidic conditions. The reaction follows first-order kinetics with respect to HOBr, Glucose, Fructose, and [H+] uniformly and is homogeneous. The Effect of varying salt electrolyte concentration was insignificant showing that the molecular species was involved in the rate-determining step. The Reaction was monitored at 600C (±10C) temperature and thermodynamic activation parameters were determined. Binding parameters have been calculated by analyzing the data using the model suggested by Menger Portnoy and Piszkiwicz's model. Kinetic studies, stoichiometry of the reaction and product analysis have been proposed for the oxidation of sugars in the presence of NaLS.

DEVELOPMENT AND VALIDATION OF THE QUANTITATIVE DETERMINATION METHOD FOR A NEW BIOLOGICALLY ACTIVE COMPOUND N-[2-[4-OXO-3(4Н)-QINAZOLINYL]PROPIONYL]-GUANIDINE BY THE METHOD OF TITRATION IN A NON-AQUEOUS MEDIUM

Relevance. Due to the wide spread of diseases of the cardiovascular system, the development and study of drugs aimed at the treatment of diseases of the circulatory system is relevant. A new biologically active compound (BAC) is synthesized at the Department of Pharmaceutical and Toxicological Chemistry of the Volgograd State Medical University – a derivative of quinazoline: N-[2-[4-oxo-3(4H)-quinazolinyl] propionyl]-guanidine (VMA-13-15), which at the stage of preclinical studies confirmed the prospects for use in medical practice as a cardioprotective and neuroprotective drug. The aim of the study is to develop and validate a method for the quantitative determination of N-[2-[4-oxo-3(4H)-quinazolinyl]propionyl]-guanidine (VMA-13-15). Material and methods. The objects of study are laboratory samples of N-[2-[4-oxo-3(4H)-quinazolinyl]propionyl]-guanidine (VMA-13-15, series 2019, 2020 and 2021). A laboratory sample VMA-13-15 twice recrystallized from methanol and dried to constant weight is used as a standard sample (RS). Quantitative determination is carried out by acid-base titration in a non-aqueous medium. The end of the titration is fixed potentiometrically. Results. The ionization constants VMA-13-15 are determined. A procedure is developed for the quantitative determination of N-[2-[4-oxo-3(4H)-quinazolinyl]propionyl]guanidine by acid-base titration in a solvent medium of glacial acetic acid with the establishment of an equivalence point using a potentiometer. The developed method is validated according to the main characteristics: specificity, linearity, correctness, convergence and analytical area. The validation analysis of the developed method confirms that it is suitable for the quantitative determination of the main substance content in the VMA-13-15 substance. Conclusions. A technique for potentiometric titration of N-[2-[4-oxo-3(4H)-quinazolinyl]propionyl]guanidine in a non-aqueous medium is developed and validated.

Synthesis and properties of 6-(2,6-dichlorophenyl)-3- (3-methyl-1H-pyrazol-5-yl)-6,7-dihydro-5H-[1,2,4]triazolo[3,4-b] [1,3,4]thiadiazine-7-carboxylic acid and its salts

Carboxylic acids and their derivatives are an important component of many biological processes. For example, they can be used to create new medicines that can be useful in the fight against various diseases. Additionally, compounds containing a thiazole moiety may possess beneficial properties in practical pharmacy. The incorporation of this heterocyclic structure in molecules can positively impact several biological characteristics, such as anti-inflammatory, antiviral, and antifungal activities. Consequently, exploring novel compounds that combine a thiazole fragment with a carboxyl group holds promise for the advancement of new drugs and diagnostic tools that can contribute significantly to the battle against numerous diseases. The aim of the work was to create a number of organic and inorganic salts of 6-(2,6-dichlorophenyl)-3-(3-methyl-1H-pyrazol-5-yl)-6,7-dihydro-5H-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazine-7-carboxylic acid and study of their properties, as well as selective determination of the biological potential of these compounds. Materials and methods. The synthetic part of the study involved the sequential synthesis of the original compound 4-amino-5-(3-methyl-1H-pyrazol-5-yl)-1,2,4-triazole-3-thiol using a well-established method described in previous articles. The next stage involved the reaction of thiol with 2,3-dichlorobenzaldehyde in a medium of glacial acetic acid. The resulting Schiff base was subsequently reacted with 2-chloroethanoic acid in tetrahydrofuran in the presence of an equimolar amount of sodium hydride. Salts of the corresponding acid were formed during the reaction of 6-(2,6-dichlorophenyl)-3-(3-methyl-1H-pyrazol-5-yl)-6,7-dihydro-5H-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazine-7-carboxylic acid with both organic and inorganic bases in an aqueous-alcohol medium. The structures of all synthesized compounds were determined using 1H NMR spectroscopy and elemental analysis. Additionally, the individuality of each compound was confirmed using high-performance liquid chromatography-mass spectrometry. Results. The study determined the optimal conditions for the formation of both organic and inorganic salts of 6-(2,6-dichlorophenyl)-3-(3-methyl-1H-pyrazol-5-yl)-6,7-dihydro-5H-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazine-7-carboxylic acid. The analysis of pharmacokinetic parameters and physicochemical properties using ADME (absorption, distribution, metabolism, and excretion) allowed for the identification of promising synthesized compounds and the selection of more optimal compounds for further investigation. Conclusions. The structure of 12 compounds was synthesized and confirmed. Physical-chemical and pharmacokinetic analysis of ADME parameters was carried out and promising compounds were selected for more in-depth research.

Domino Reaction for the Synthesis of Pyrazole/Isoxazole Fused Naphthyridine Derivatives Involving Indole Ring Opening and Double Ring Formation

Herein, a hitherto unreported approach for the synthesis of pyrazole/isoxazole-fused naphthyridine derivatives by a three-component domino reaction of arylglyoxal monohydrate, 5-amino pyrazole/isoxazole, and indoles in acetic acid medium has been reported. In this method, four bonds (2 C-C and 2 C-N) form in one-pot with the concomitant formation of two new pyridine rings via indole ring opening and double cyclization reactions. This methodology is also applicable in gram-scale synthesis. The reaction mechanism was studied by isolating and characterizing the reaction intermediates. Along with complete characterization of all the products, the structure of the product 4o was unambiguously confirmed by single crystal X-ray diffraction.

DFT Calculation and MD Simulation Studies on Gemini Surfactant Corrosion Inhibitor in Acetic Acid Media.

Gemini surfactant corrosion inhibitor (CI) is one type of CI mainly used in mitigating corrosion in the complex system of oil/gas production industries. Computer modeling methods such as density functional theory (DFT) calculation and molecular dynamic (MD) simulation are required to develop new CI molecules focusing on their application condition as a prediction or screening process before the physical empirical assessment. In this work, the adsorption inhibition efficiencies of two monomer surfactants (2B and H) and their respective Gemini structures with the addition of different spacers (alkyl, benzene, ester, ether, and ketone) are investigated using DFT calculation and MD simulation method in 3% sodium chloride (NaCl), and 1500 ppm acetic acid solutions. In DFT calculation, 2B-benzene molecules are assumed to have the most promising inhibition efficiency based on their high reactivity and electron-donating ability at their electron-rich benzene ring region based on the lowest bandgap energy (0.765 eV) and highest HOMO energy value (-2.879 eV), respectively. DFT calculation results correlate with the adsorption energy calculated from MD simulation, where 2B-benzene is also assumed to work better as a CI molecule with the most adsorption strength towards Fe (110) metal with the highest negative adsorption energy value (-1837.33 kJ/mol at temperature 323 K). Further, diffusion coefficient and molecular aggregation analysis in different CI concentrations through MD simulation reveals that only a small amount of Gemini surfactant CI is needed in the inhibition application compared to its respective monomer. Computer simulation methods successfully predict and screen the Gemini surfactant CI molecules that can work better as a corrosion inhibitor in acetic acid media. The amount of Gemini surfactant CI that needs to be used is also predicted. The future planning or way forward from this study will be the development of the most promising Gemini surfactant CI based on the results from DFT calculation and MD simulations.

Metal‐Free Synthesis of Pyrimidine and Naphthoquinone‐Fused Pyrroles from Arylglyoxal‐Based Domino Reactions

AbstractHerein we report acid mediated two and three‐component domino reactions of cyclic enamines such as 2‐amino‐1,4‐naphthoquinone, and 6‐amino‐1,3‐dimethyluracil with arylglyoxals for the synthesis of diverse fused pyrroles. The two‐component reaction of arylglyoxal and 2‐amino‐1,4‐naphthoquinone in the acetic acid medium provided substituted naphthoquinone‐fused pyrroles tethered with hydroxyl and aryl substituents. On the other hand, under similar reaction conditions, the reaction of phenylglyoxal with 6‐amino‐1,3‐dimethyluracil provided an unusual bipyrrolopyrimidine with a quaternary carbon center following a domino reaction involving the formation of five new sigma bonds in one‐pot. Interestingly, the reaction of arylglyoxals with 6‐amino‐1,3‐dimethyluracil in ethanol medium in the presence of 10‐mol% PTSA provided a three‐component product having pyrimidine fused pyrrole linked with 6‐aminouracil moiety. We have also developed a three‐component reaction of 2‐amino‐1,4‐naphthoquinone, arylglyoxals, and 4‐hydroxy‐1‐methylquinolin‐2(1H)‐one for the synthesis of naphthoquinone‐fused pyrroles linked with hydroxyquinoline derivatives.

Improved syntheses of doubly naphthalene-bridged diphosphine and its diiminodiphosphorane derivatives linking two Cu(I) centers

An improved method for preparing bis(1,8-naphthalenediyl)diphosphine, 1, was developed. A phosphino-naphthalene unit of a precursor, iPr2NP-peri-bridged naphthalene, was dimerized in an acetic acid medium, while the precursor in a previously reported method was heated in toluene. The reaction time was reduced from 48 h to 1 h, and an increase to the gram scale was achieved. The diphosphine, 1, comprised a unique PP bond, which was clamped by two 1,8-naphthalene units and was used to synthesize the diiminodiphosphorane derivatives. Thereafter, the two imino-donating groups comprising Ph, p-nBu–C6H4, Mes, and 2,6-iPr2–C6H3 were introduced into two phosphorus centers via the Staudinger reaction using the corresponding R−N3 group (R = Ph, p-nBu–C6H4, Mes, and 2,6-iPr2–C6H3). The result revealed that they did not function as a chelating pair to a single metal center; rather, they acted as a bridging ligand that linked the two metal centers, as demonstrated by the formation of dicopper complexes, except for the bulky 2,6-iPr2–C6H3 case. The two rigid naphthalene groups forced the PPC(naphthalene) angles of five-membered rings to be ca. 90°, thereby increasing the P−PN bond angles (ca. 130°). These increased P−PN bond angles forced the two imino nitrogen to trigger each other. This accounted for the bridging and nonchelating functionalities of the synthesized diiminodiphosphoranes. Both iminophosphorane groups of the synthesized diiminodiphosphorane were directly linked; they could facilitate the binding of two neighboring metal units.

INTERACTION OF HAFNIUM(IV) WITH 6,7-DIHYDROXY‑4-CARBOXYL‑2- PHENYLBENZOPYRYLLIUM SALTS IN BINARY SYSTEMS AND IN THE PRESENCE OF CATIONIC SURFACTANTS

In the current study, the peculiarities of the complexation of Hafnium(IV) with 6,7-dihyroxy‑4-carboxyl‑2-phenylbenzopyrylium salts (CDC) in binary systems and in the presence of cationic surfactants (Surf) were studied. The CDC was synthesized by condensation of pyrogallol A with benzoylpyruvic acid in an acetic acid medium in the presence of perchloric acid. To obtain KDC bromide and chloride, the synthesis was carried out in the presence of bromide acid or by sparging of dry hydrogen chloride, respectively. Using classical spectrophotometric methods of molar ratios and Bent-French, it was found that at pH 2.5 in binary system one complex with stoichiometry Hf(IV): CDC1:2 was formed. Molar absorptivity coefficient was calculated for Hf(IV) complex with CDC and it was equal 3,9⸱104. It was shown that in the presence of cetylpyridinium chloride or cetyltrimetrylammonium bromide complexes with a molar ratio of Hf(IV): CDC: Surf = 1:2:2 were formed. It is noted that the complexes were formed within 10–15 minutes, and the absorbance of the solutions remains constant for at least 2 hours. It was established that the nature of the anion, which is part of the reagent, does not significantly affect the characteristics of the analytical form. It is shown that in the presence of cationic surfactants, the optimal pH of complex formation shifts to a more acidic region. In addition, the introduction of cationic surfactants leads to a batachromic shift of the absorption band by 10–15 nm and an increase in the molar absorptivity to 5.8⸱104 and 6.4⸱104 when cetylpyridinium chloride or cetyltrimetrylammonium bromide were used respectively. It is noted that the found analytical forms can be used as a basis for the development of combined spectroscopic methods for determining trace amounts of Hafnium(IV).

The Adjustability of Physicochemical Properties: Comparison of 1-Vinyl-5H-tetrazole and 1-Allyl-5H-tetrazole as Ligands in 3d Metal Energetic Coordination Compounds

Energetic coordination compounds (ECCs) show promising properties to be used as potential substitutes for highly toxic lead-containing primary explosives. The concept is to combine the three building blocks: (i) ligand, (ii) transition metal, and (iii) anion, acting as (i) fuel, (ii) matrix, and (iii) oxidizer (e.g., ClO4-, NO3-, ClO3-) or energetic component (e.g., DN-, N3-, picrate, styphnate, trinitrophloroglucinate). By variation of the ligands, the complexes' properties can be adjusted toward their desired performance and sensitivities. In the present study, 1-vinyl-5H-tetrazole (1-VTZ, 1) and 1-allyl-5H-tetrazole (1-ATZ, 2) were used as nitrogen-rich endothermic ligands to form 3d metal (Mn2+, Fe2+, Cu2+, Zn2+, Co2+, Ni2+)-based ECCs. The influence of the introduction of an unsaturated C-C bond (1-ETZ vs 1-VTZ and 1-PTZ vs 1-ATZ) on the performance and sensitivity of the complexes is discussed, as is the lengthening of the alkenyl chain (1-VTZ vs 1-ATZ). For further insights, the novel complexes were compared to literature-known complexes based on N1-substituted C2- and C3-derived tetrazole ligands, respectively. The ligand 1-VTZ (1) was prepared by elimination of hydrogen chloride from 1-(2-chloroethyl)-5H-tetrazole in methanolic KOH solution. 1-ATZ (2) was obtained by a heterocyclization reaction of allylamine with triethyl orthoformate and sodium azide in an acetic acid medium. All compounds were intensively characterized with analytical methods such as XRD, IR, EA, DTA, TGA, and sensitivity measurements (IS and FS). The energetic performances were visibly evaluated in fast heating experiments. Furthermore, PETN initiation and laser ignition experiments were carried out for promising ECCs.

Influence of Fe<sub>3</sub>O<sub>4</sub> on Physicochemical and Photocatalytic Properties of Nanosized Barium Titanate

A procedure has been proposed for the synthesis of a nanocomposite based on barium titanate modified by adding nanodispersed magnetite using the sol–gel method in an acetic acid medium followed by annealing at 800°C. The physicochemical analysis of the products has shown that the matrix phase after annealing is barium titanate with an admixture of barium carbonate, and, in addition to magnetite, there are minor inclusions of hematite and wustite. The elemental composition of nanosized samples has been determined using energy-dispersive X-ray spectroscopy. It has been demonstrated that the concentration of introduced Fe3O4 affects the morphological and phase composition of the composites. The specific surface area and type of porosity of calcined samples have been determined by the low-temperature nitrogen adsorption/desorption method. The effect of BaTiO3, BaTiO3/Fe3O4-1%, and BaTiO3/Fe3O4-10% powders on the adsorption capacity and photocatalytic activity in the process of decolorization of the dye rhodamine B from an aqueous solution in the dark and under the action of ultraviolet light has been studied. The kinetics of adsorption in the dark and photocatalytic decomposition of rhodamine B under the action of ultraviolet radiation in an aqueous suspension of the obtained composites have been analyzed using pseudo-first and pseudo-second order kinetic models.

C-H functionalization of quinoline N-oxides catalyzed by Pd(II) complexes: a computational study.

Pd(II) catalysts, particularly the acetate salt in acetic acid, tended to favor regioselective C-H activation of quinoline N-oxides (QOs) at the C2 position. However, Pd(II)Cl2 was shown to catalyze their C-H activation at C8 and, in the presence of water, C8-H activation was accompanied by the formation of 2-quinolinones. The aim of the DFT study described in this work was to shed light on the complete mechanism of these competing catalytic reactions, when PdCl2 reacts with QO and benzaldehyde in dichloroethane. C-H activation of QO was the first step of the reaction and involved either a metallacycle, with a CQO-Pd(II) σ-bond and a C(8)-H-Pd(II) agostic bond, or an η3-QO complex, with three carbon atoms of the heteroring of QO binding PdCl2. The first situation led to the unusual C8 activation and the second to C2 activation. The σ-metallacycle undergoes C8-H activation and the energy of the TOF determining the transition state to form the product is ∼17 kcal mol-1, while for the reaction through the π-metallacycle (C2-H activation) the corresponding energy is higher (∼29 kcal mol-1) and thus is not competitive under the same conditions. The reaction proceeding through the σ-complex, activating the C8 position, is preferred, in agreement with experimental results. Both reactions involve oxidation of Pd(II) to Pd(IV) and the catalyst is regenerated. When small amounts of water are added to the reaction mixture, C8-H activation (acylation) results from the same σ-metallacycle with the same barrier, but the simultaneous formation of 2-quinolinones is more complicated. It starts with OH- attack at the C2 position, and is followed by the migration of two hydrogen atoms, and the final reductive elimination step ends with Pd(0). The higher barriers for the migration and reoxidation of Pd(0) are associated with the more demanding reaction conditions. The different reactivity of Pd(II)(OAc)2 under analogous conditions is clarified, as it is only capable of forming the above mentioned π-complex and thus of activating the C2 position of QO. This catalyst can preferentially activate the C8-H bond under rather different conditions, including in particular acetic acid medium, as shown by other authors.

Practical approaches to the application of hygienic criteria for substances that do not need to establish hygienic standards in the air of the working area

Introduction. When new industrial enterprises appear, whose activities are related to the use and/or production of chemicals, pollutants that do not have approved hygiene standards may appear in the air of the working area. We note that the introduction of new chemicals into the production process does not always require the development of a hygienic standard in the air of the working area, since conditions can be met for these compounds, namely compliance with hygienic criteria, under which the development and approval of hygienic standards is not required. The study aims to demonstrate a practical approach to the application of hygienic criteria for substances that do not need to establish hygienic standards in the air of the working area on the example of paraformaldehyde. Materials and methods. The theoretical basis of the work was the methods of substantiating the need to develop hygienic standards: maximum permissible concentration (MPC) and approximate safe level of exposure (ASLE) to harmful substances in the air of the working area. The practical basis of the work was methodological guidelines for measuring mass concentrations of formaldehyde in the air of the working area by a photometric method based on the reaction of formaldehyde with acetylacetone in an ammonium acetic acid medium and subsequent photometric measurement of the optical density of the yellow-colored reaction product. Results. The conducted experiment simulating the processes of formaldehyde emission from paraformaldehyde in various production conditions showed that paraformaldehyde under the influence of temperature releases formaldehyde, while the rate of formaldehyde release increases with increasing temperature. Conclusion. Analysis of the technology of production (application) of paraformaldehyde, toxicological data, as well as an experiment modeling the processes of formaldehyde emission from paraformaldehyde in various production conditions allows us to conclude that the development of a hygienic standard for paraformaldehyde in the air of the working area is impractical, according to paragraph 2.1.1. GN 1.1.701-98 "For substances containing the ingress of which into the air of the working area in the form of vapors and aerosols or a mixture thereof is excluded due to the physico-chemical properties, as well as production and application conditions" and p.2.1.3. GN 1.1.701-98 "For substances that easily hydrolyze in the air with the formation of hydrolysis products, the toxicity of which has been studied and the hygienic standards of which have been established".

Oxidation of Perfumery Secondary Alcohols by Nicotinium Dichromate; A Kinetic Study

Chemical kinetics is mainly concerned with studying the factors that change the reaction rate and the response mechanism. The present paper investigates the rate law for the reaction, order of the reaction of secondary alcohols(menthol) and compares it to other secondary alcohols like Borneol and Isoborneol. Diagnose the product of the oxidation reaction. The kinetics of oxidation of perfumery secondary alcohols [menthol], [Borneol], and [Isoborneol] by NDC have been studied in the aqueous acetic acid medium at 303K. The secondary perfumery alcohols were converted to the corresponding carbonyl compounds. The order concerning [Subs], [Oxi], and [H+] ions concentration is found to be one. The decrease in the dielectric constant of the medium enhances the rate of the reaction. The ionic strength of the medium has no significant effect on the reactivity of the response; it does not induce the polymerization of Acrylonitrile, indicating the absence of free radical pathway. The added Mn2+ ions show the reaction rate was slightly increasing order. The reaction has been studied at four different temperatures Eyring equation is used to calculate the thermodynamic parameters like Gibbs free energy change (ΔG#), entropy change (ΔS#), and enthalpy change (ΔH#). On increase in the temperature of the reaction, the rate of reaction increased abruptly. There was a decrease in entropy (ΔS#) of the system indicated by the value of entropy which showed some restriction in the freedom movement of the molecules. It was observed that the reactivity follows Menthol<Isoborneol<Borneol. Based on steric factors, structure, and isomeric characteristics of the alcohols under investigation.