Reactions of diazoles with manganese and iron carbonyls

The compounds of two types were isolated in the reactions of dimanganese decacarbonyl with diazoles. The compounds with an unaltered oxidation state of the metal were formed as a result of nucleophilic substitution of a carbonyl ligand of Mn₂(CO)₁₀. The compounds with an altered oxidation state of the central atom were produced in redox-transformations of Mn₂(CO)₁₀. The substances were characterized by the data of mass-, IR-, ¹H-NMR-spectra. The EPR-data were obtained for paramagnetic Mn²⁺ salts. The reactions of Mn₂(CO)₁₀ with diazoles are compared with those of iron carbonyls.     

Screening of anti-inflammatory and antioxidant potential of functionalized tetrahydrocarbazole linked 1,2-diazoles and their docking studies

Inflammatory diseases are associated with life-threatening syndromes like hepatitis, cancer, and trauma injury while some decrease the quality of life such as rheumatism, arthritis, and tuberculosis. 1,2-Diazoles (pyrazolines) play a vital role in COX-2 inhibition thus dinitro-tetrahydrocarbazole linked pyrazolines have been synthesized and endeavor to screen for anti-inflammatory, antioxidant and molecular docking studies. For this purpose, 6,8-dinitro-acetyl-2,3,4,9-tetrahydrocarbazole (I), aromatic aldehydes (IIa-e) and hydrazines (IIIa-b) were combined via multicomponent reaction approach under the influence of microwave irradiations to afford pyrazolines (1–10). All new molecules were screened for in vitro anti-inflammatory activity by human red blood cells membrane stabilization, antioxidant potential by2,2-diphenyl-1-picrylhydrazyl,2,2´-azinobis (3-ethylbenzo thiazoline)-6-sulphonic acid, lipid peroxidation, and total antioxidant capacity assays along with cytotoxicity by brine shrimp lethality assay. Molecular docking was performed by using the Auto Dock program. Both disubstituted and trisubstituted diazoles showed excellent membrane stabilizing effects, (91.89 % and 77 %, respectively). The presence of phenol, furan, thiocarbamide, and chloro-moieties have the most prominent effect. Toxicity results indicated that compounds were less toxic at the tested dose (0.1 mg/ml). The antioxidant study showed that compound 2 was more active showing low IC₅₀ values (32.2 and 39.2 µg/ml) in DPPH and total phenolic contents assays respectively. Compound 3 (44.0 µg/ml) showed the highest potential assay in ABTS radical neutralization assay while compound 7 (65.0 µg/ml) showed maximum potential in lipid peroxidation. All diazoles (1–10) were screened for in vitro anti-inflammatory potential where disubstituted diazoles were found better than trisubstituted analogs and exhibited significant antioxidant potential. Molecular docking of diazoles showed a good correlation of their anti-inflammatory activity with p38α MAPK, COX-2, and 5-LOX enzymes that are molecular therapeutic targets of inflammation.     

Proton-transfer reactions in azoles

The kinetics of proton transfer in solutions of diazoles were investigated by ¹H and ¹³C NMR spectroscopy. The kinetic data are explained by means of quantummechanical representations of the elementary act of proton transfer. It is concluded that proton transfer has substantial collective character. It was established that a small number of coordination centers (transition metal ions) have a dramatic effect on proton transfer owing to extraspheral complexing.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 781–786, June, 1977.     

Copper-catalyzed N-arylation of diazoles with aryl bromides using KF/Al2O3: an improved protocol

Copper-catalyzed N-arylation of diazoles can be accomplished using air-stable CuI as a copper source and 1,10-phenanthroline in the presence of KF/Al₂O₃ as a base. This is a simple and efficient method for the coupling of aryl bromide with diazoles. Different functionalized aryl bromides were coupled with diazoles using this system.     

NMR investigation of chlorophosphorylation products of N‐vinylazoles

The structure of novel phosphorus‐containing N‐vinylazoles prepared by action of phosphorus pentachloride has been studied by multinuclear ¹H, ¹³C, ¹⁵N, ³¹P and two‐dimensional (2D) NMR spectroscopy. N‐vinyl‐substituted 1,2‐diazoles and 1,2,3‐triazoles have undergone phosphorylation, exclusively, on double bond. N‐vinylazoles‐based hexa‐coordinated phosphorus compounds have been synthesized for the first time. ³¹P NMR spectroscopy provides the most convenient and unambiguous method for the investigation of E—Z‐isomeric structures of phosphorylated enamines. Copyright © 2008 John Wiley & Sons, Ltd.     

Ethylene glycol,an efficient and recoverable medium for copper-catalyzed N-arylation of diazoles under microwave irradiation

Ethylene glycol was used as an efficient and recoverable medium for the reaction of diazoles with aryl iodides and aryl bromides in the presence of CuCl₂ as the catalyst and K₂CO₃ as the base. Consequently, imidazole, benzimidazole, and pyrazole reacted readily under microwave irradiation to give good to excellent yields of their corresponding N-arylated products in relatively short time periods. Apparently, ethylene glycol plays a dual role by activating the catalyst and also providing a homogenous medium for the processes. The reaction medium consisting of the solvent, the base, and the copper salt was recovered and reused successfully in the next several reactions.     

Dimethylheptyl [3-(N-hetaryl)propyl]silanes: Synthesis,antimicrobial and antiblastic activity

The alkylation of monoazoles, diazoles, triazoles and tetrazoles with dimethylheptyl(3-iodopropyl)silane using liquid/liquid phase-transfer catalysis affords the corresponding [3-(N-azolyl)propyl]silanes in high yield, by which means the nonsymmetric ambident heterocycles 1,2,4-triazole and tetrazole undergo alkylation regiospecifically in position 1 and 2, respectively. Dimethylheptyl[3-(N-imidazolyl)propyl]silane demonstrated high fungistatic activity with respect to S. cerevisiae and T.rubrum in combination with high cytotoxicity.     

Unusual course of diazolees silylation and N-siloxycarbonylation

The N-siloxycarbonylation and transamination reactions were studied by an example of diazoles. We found that because of insufficient nucleophilicity of the nitrogen atoms in the first case only the sililylation process occurs, in the second case the low-boiling amine is replaced by the higher boiling one and the process is completed by the formation of O-silyluretans.     

Kinetics and Mechanism of Catalytic Reduction of U(VI) with Hydrazine on Platinum Catalysts in Nitric Acid Media

The kinetics of U(IV) produced by hydrazine reduction of U(VI) with platinum as a catalyst in nitric acid media was studied to reveal the reaction mechanism and optimize the reaction process. Electron spin resonance (ESR) was used to determine the influence of nitric acid oxidation. The effects of nitric acid, hydrazine, U(VI) concentration, catalyst dosage and temperature on the reaction rate were also studied. In addition, the simulation of the reaction process was performed using density functional theory. The results show that the influence of oxidation on the main reaction is limited when the concentration of nitric acid is below 0.5 mol/L. The reaction kinetics equation below the concentration of 0.5 mol/L is found as: -dc(UO₂²⁺)/dt)=kc^0.5323(UO₂²⁺)c^0.2074(N₂H₅⁺)c^-0.2009(H⁺). When the temperature is 50 ℃, and the solid/liquid ratio r is 0.0667 g/mL, the reaction kinetics constant is k=0.00199 (mol/L)^0.4712/min. Between 20 ℃ and 80 ℃, the reaction rate gradually increases with the increase of temperature, and changes from chemically controlled to diffusion-controlled. The simulations of density functional theory give further insight into the influence of various factors on the reaction process, with which the reaction mechanisms are determined according to the reaction kinetics and the simulation results.     

Polar effect in columnar unsymmetric 1,3,4-oxa(thia)diazoles

Three new series of heterocyclic 1,3,4-oxa(thia)diazoles 1a–c were prepared and their mesomorphic behavior studied. All compounds 1a exhibited monotropic columnar phases, which were confirmed by powder XRD diffractometer. Compounds 1b were not mesogenic. The formation of columnar phases was sensitive to the substituent groups attached on the phenyl moiety; those with electron-donating groups (R=H, OCH₃) were not liquid crystals, in contrast, other derivatives with electron-withdrawing groups (R=F, NO₂) formed enantiotropic columnar phases. A N_cell and R_ar value equal to 4.73 and 20.20 Å² of compound 1a (n=16) within a slice of 9.0 Å thick were obtained, indicating that two molecules was correlated to give a supplemental more disc-like molecule within columns. This is the first example, showing that the formation of columnar phases could be controlled by polar groups. The PL spectra of two compounds 1a–c showed one intense peak at λ_max=505–511 nm, and these photoluminescent emissions originated from quinoxaline moiety.     

Kinetics of the reaction of hydroxyl radicals with 2-(dimethylamino)ethanol from 234–364 K

The temperature dependence of the rate of the reaction of OH with 2-(dimethylamino)-ethanol, (CH₃)₂NCH₂CH₂OH (DMAE) was investigated over the temperature range, 234 to 364 K. The reaction was studied using the flash photolysis-resonance fluorescence technique. The room temperature rate constant determined for this reaction was (10.3 ± 2.0) × 10^?11 cm³ molecule^?1 s^?1, with essentially no temperature dependence evident within the uncertainty in the experiments. A value of (9.0 ± 2.0) × 10^?11 cm³ molecule^?1 s^?1 is believed to best describe the reaction over the entire temperature range. The room temperature rate constant is about twice the value reported previously for this reaction. The overall reaction of OH with DMAE was apportioned to the reactivity of OH for abstracting individual H- atoms from different types of C? H bonds and the O? H bond within the molecule. This technique predicts the overall rate constant for the OH-DMAE reaction to within about 15% of the experimental value and makes it possible to estimate the yields of the initial radical products of the OH attack on DMAE. A mechanism is proposed for the subsequent atmospheric reactions that would occur in the photooxidation of DMAE.     

The reaction of the hydroxyl radical with acetylene

The reaction of OH with acetylene was studied in a discharge flow system at room temperature. OH was generated by the reaction of atomic hydrogen with NO₂ and was monitored throughout the reaction using ESR spectroscopy. Mass-spectrometric analysis of the reaction products yielded the following results: (1) less than 3 molecules of OH were consumed, and less than 2 molecules of H₂O were formed for every molecule of acetylene that reacted; (2) CO was identified as the major carbon-containing product; (3) NO, formed in the generation of OH, reacted with a reaction intermediate to give among other products N₂O. These observations placed severe limitations on the choice of a reaction mechanism. A mechanism containing the reaction OH + C₂H₂ → HC₂O + H₂ better accounted for the experimental results than one involving the abstraction reaction OH + C₂H₂ → C₂H + H₂O. The rate constant for the initial reaction was measured as 1.9 ± 0.6 × 10^?13 cm³ molecule^?1 sec^?1.     

Spectroelectrochemical and Voltammetric Studies of L‐DOPA

The electrooxidation of L -dopa at GC electrode was studied by in situ UV-vis spectroelectrochemistry (SEC) and cyclic voltammetry. The mechanism of electrooxidation and some reaction parameters were obtained. The results showed that the whole electrooxidation reaction of L -dopa at glassy carbon (GC) electrode was an irreversible electrochemical process followed by a chemical reaction in neutral solution (EC mechanism). The spectroelectrochemical data were treated by the double logarithm method together with nonlinear regression, from which the formal potential E⁰=228 mV, the apparent electron-transfer number of the electrooxidation reaction αn=0.376 (R=0.99, SD=0.26), the standard electrochemical rate constant k⁰=(3.93±0.12)×10⁻4 cm s⁻¹ (SD=1.02×10⁻²), and the formation equilibrium constant of the following chemical reaction k_c=(5.38±0.34)×10⁻¹ s⁻¹ (SD=1.02×10⁻²) were also obtained.     

Reaction of [Xe-F]+ with HI

The reaction behavior of [XeF][AsF₆] in solution toward hydrogen iodide, HI, was investigated, and Xe, HF, and [I₄][AsF₆]₂ were identified as the final reaction products. The reaction enthalpy of the gas-phase reaction ([XeF]⁺ + HI → [XeI]⁺ (¹Σ) + HF) was calculated at the optimized MP4(SDQ) geometries at the QCISD(TQ) level to be: ΔH0298 [QCISD(TQ)/LANL2DZ//MP4(SDQ)/LANL2DZ] = −63.3 kcal mol⁻¹. The [XeI]⁺ cation is bound only in the ¹Σ singlet state, and the triplet state (³Π) was shown to be essentially unbound at all levels of theory applied and very close in energy to the singlet state at equilibrium structure. According to the ab initio calculations, [XeI]⁺ can react with HI in a thermodynamically and spin-symmetry allowed reaction to yield the [XeI]⁺ (¹Σ) cation that may, after interconversion into the unbound triplet state, immediately dissociate into xenon (¹S) and I⁺ (³P). © 1997 John Wiley & Sons, Inc. Heteroatom Chem 8: 473–478, 1997     

The reaction of O(3P) with OClO

The laser photolysis-long path transient absorption technique was used to study the mechanism and products of the reaction O(³P) + OClO (→^M) Products (3) at 260 K in 100 to 400 torr of He, N₂, and Ar. ClO was not detected as a reaction product, <5% yield, from this reaction at 400 torr and 260 K. A broad UV absorption feature associated with a product of this reaction, with a peak located at 260 nm, was observed. The peak absorption cross section of this species was measured to be (1.72 ± 0.12) × 10⁻¹⁷ cm² molecule⁻¹. The rate coefficient for the appearance of this species was measured to be (1.69 ± 0.46) × 10⁻¹³ cm³ molecule⁻¹ s⁻¹ and was independent of pressure. The rate coefficient for the appearance of the species is ca. 10 times lower than that for the disappearance of O(³P), indicating that the observed species is not a direct product of the reaction of O(³P) with OClO. Mechanistic considerations and the possible identity of the absorber are discussed. © 1997 John Wiley & Sons, Inc.     

Decomposition of meta- and para-phenylphenol during ozonation process

The decomposition of meta-phenylphenol (m-PP) and para-phenylphenol (p-PP) in a heterogeneous gas-liquid system using ozone was investigated. The influence of different reaction parameters such as ozone and PP isomers concentration as well as pH and temperature of the reaction mixture on the PP decay rate was determined. The second-order rate constants for the direct reaction of molecular ozone, determined in a homogeneous system, were (5.85 ± 0.35) × 10² M^?1 s^?1 and (8.90 ± 0.33) × 10² M^?1 s^?1 for m-PP and p-PP, respectively. The rate constants for the reaction of m-PP and p-PP with ozone increased with increasing pH. The reaction rate constants with ozone were found to be (1.75 ± 0.02) × 10⁹ M^?1 s^?1 and (1.86 ± 0.02) × 10⁹ M^?1 s^?1 for m-PP and p-PP anions, respectively.     

Ag(I)‐Catalyzed Chlorination of Linezolid during Water Treatment: Kinetics and Mechanism

The kinetic and mechanistic study of Ag(I)‐catalyzed chlorination of linezolid (LNZ) by free available chlorine (FAC) was investigated at environmentally relevant pH 4.0–9.0. Apparent second‐order rate constants decreased with an increase in pH of the reaction mixture. The apparent second‐order rate constant for uncatalyzed reaction, e.g., k″_app = 8.15 dm³ mol⁻¹ s⁻¹ at pH 4.0 and k″_app. = 0.076 dm³ mol⁻¹ s⁻¹ at pH 9.0 and 25 ± 0.2°C and for Ag(I) catalyzed reaction total apparent second‐order rate constant, e.g., k″_app = 51.50 dm³ mol⁻¹ s⁻¹ at pH 4.0 and k″_app. = 1.03 dm³ mol⁻¹ s⁻¹ at pH 9.0 and 25 ± 0.2°C. The Ag(I) catalyst accelerates the reaction of LNZ with FAC by 10‐fold. A mechanism involving electrophilic halogenation has been proposed based on the kinetic data and LC/ESI/MS spectra. The influence of temperature on the rate of reaction was studied; the rate constants were found to increase with an increase in temperature. The thermodynamic activation parameters E_a, ΔH^#, ΔS^#, and ΔG^# were evaluated for the reaction and discussed. The influence of catalyst, initially added product, dielectric constant, and ionic strength on the rate of reaction was also investigated. The monochlorinated substituted product along with degraded one was formed by the reaction of LNZ with FAC.     

Kinetic Study of the Thermal Polymerization Reactions between Diazide and Internal Diyne

The reaction kinetics between diazide(4,4′‐biphenyl dibenzyl azide) and internal diyne(bis[2‐(phenyl)ethynyl]dimethylsilane) was studied in this study by means of differential scanning calorimetry (DSC) and nuclear magnetic resonance spectra (¹H NMR). DSC was carried out to analyze the reaction in bulk polymerization condition, whereas ¹H NMR for solution reaction polymerization. The apparent activation energy (e_α) calculated by Kissinger's method was 90.83 kJ/mol, which was confirmed by Friedman's method, and 87.67 kJ/mol by ¹H NMR, respectively. The polymerization between the diazide and internal diyne was the second‐order reaction based on calculation from both of DSC and ¹H NMR.     

Determination of the Rate Constant of the Reaction of CCl2 with HCl

The rate constant of the reaction between CCl₂ radicals and HCl was experimentally determined. The CCl₂ radicals were obtained by infrared multiphoton dissociation of CDCl₃. The time dependence of the CCl₂ radicals' concentration in the presence of HCl was determined by laser‐induced fluorescence. The experimental conditions allowed us to associate the decrease in the concentration of radicals to the self‐recombination reaction to form C₂Cl₄ and to the reaction with HCl to form CHCl₃. The rate constant for the self‐recombination reaction was determined to be in the high‐pressure regime. The value obtained at 300 K was (5.7 ± 0.1) × 10^?13 cm³ molecule^?1 s^?1, whereas the value of the rate constant measured for the reaction with HCl was (2.7 ± 0.1) × 10^?14 cm³ molecule^?1 s^?1.     

Taming of the DIBAL Promoted Debenzylation of α-Cyclodextrin. Kinetics,Substituent Effects and Efficient Synthesis of Lings Tetrol**

The kinetics of the reaction of perbenzyl α-cyclodextrin was studied varying the concentration of DIBAL and substrate, and the temperature. The initial debenzylation was found to be 1^st order in substrate and follow the relationship 0.0675+0.179[DIBAL]² with respect to the concentration of DIBAL. The second and the third debenzylation which led to the 3^A,6^A,6^D-triol (Lings triol) were both found to be 1^st order in substrate concentration and zero order in DIBAL concentration. Longer reaction times with DIBAL in high concentration gave further debenzylation to comparatively complex mixtures containing the 2B,3^A,6^A,6^D-tetrol and the 3^A,6^A,6^C,6^D-tetrol. In contrast reaction at 0.1 M DIBAL gave the symmetrical 3^A,6^A,3D,6D-tetrol (Lings tetrol) in 60 % yield. The effect of chlorine or methyl substitution of the phenyl groups of perbenzyl α-cyclodextrin was also investigated. Per 4-chlorobenzyl slowed down the reaction with DIBAL, while 4-methylbenzyl increased the reaction rate, but still gave the corresponding 6 A-monool or 6^A,6^D-diol products. A Hammett reaction constant of −4.9 was found for the first debenzylation showing a high degree of positive charge in the transition state. The per(2,4-dichlorobenzyl)-α-cyclodextrin-derivative was completely resistant to DIBAL, however upon addition of trimethyl aluminium this derivative also reacted to give the 6^A,6^D-diol product.