Acetonitrile Solution Research Articles

Probing Isolated Water Molecules in Aqueous Acetonitrile Solutions Using Oxygen K-Edge X-ray Absorption Spectroscopy.

Oxygen K-edge X-ray absorption spectroscopy (XAS) of an aqueous acetonitrile solution exhibited a sharp peak at approximately 537 eV, which was similar to that of water vapor and was not observed in liquid water. The inner-shell spectra of isolated water molecules and water clusters of different sizes surrounded by acetonitrile molecules were obtained by extracting these water structures from the liquid structures of aqueous acetonitrile solutions, as calculated using molecular dynamics simulations. The sharp peak profiles of the O K-edge XAS spectra were derived not from water clusters but from isolated water molecules surrounded by acetonitrile molecules. The present study proposes that isolated water molecules are easily formed in aqueous acetonitrile solutions and that the electronic structures of the isolated water molecules can be analyzed using O K-edge XAS spectra, which separates the contributions of small water clusters.

Double difunctionalization of vinyl ether tethered nucleophile with electron-deficient alkene in two-molecule photoredox system.

Double difunctionalization of a vinyl ether tethered hydroxy or carbamoyl group with electron-deficient alkenes such as acrylonitrile or acrylic esters was achieved by visible-light irradiation in a two-molecule photoredox system. Use of anhydrous acetonitrile solution as a solvent promoted both dimerization of the radical cation of electron-rich alkene with electron-rich alkene and intramolecular nucleophilic addition to generate an electron-rich radical that was added to electron-deficient alkene to furnish the double difunctionalized product. A variety of electronically differentiated rich and deficient alkenes were used in the photoreaction; a simple construction of a complex carbon framework containing acetal from simple alkenes was successful under mild conditions.

Analytical and Bioanalytical Methods for the Determination of Dipeptidyl Peptidase-4 Inhibitors in Various Matrices: A Comprehensive Review.

DPP-4 inhibitors, or gliptins, are new oral antidiabetic drugs for type 2 diabetes. They help to regulate insulin and glucagon. These drugs have the advantage of a lower risk of hypoglycemia compared to some other diabetes medications and are typically prescribed when metformin and sulphonylureas have become less effective. This review analyses a range of analytical and bioanalytical methods for DPP-4 inhibitors, that use spectroscopic techniques, chromatographic, and hyphenated techniques for analysis. So far, no review comprising all DPP-4 inhibitors has been presented. The primary objective of this review is to present the analysts with various analytical and bioanalytical methods for the quantification and estimation of DPP-4 inhibitors in different matrices. To improve understanding, a review was carried out by creating a database of pre-existing research from digital sources such as ScienceDirect, and PubMed. The methodology is shown in the flowchart of the literature selection process. The comprehensive assessment of methods for analysing DPP-4 inhibitors can be a valuable resource for researchers and healthcare practitioners. Hitherto, no review encompassing all DPP-4 inhibitors has been presented. Therefore, gaps in the data available on a particular subject, need to be required to collect data on a particular construct. The review suggests that chromatographic techniques were majorly used for analysis wherein solvents like acetonitrile, methanol, and buffer solutions were used as mobile phases that can deteriorate HPLC columns and equipment. So, scientists could investigate new methods for the assessment of DPP-4 inhibitors using more eco-friendly solvents.

Photochemistry of Ru(II) Triazole Complexes with 6-Membered Chelate Ligands: Detection and Reactivity of Ligand-Loss Intermediates.

Photochemical ligand release from metal complexes may be exploited in the development of novel photoactivated chemotherapy agents for the treatment of cancer and other diseases. Highly intriguing photochemical behavior is reported for two ruthenium(II) complexes bearing conformationally flexible 1,2,3-triazole-based ligands incorporating a methylene spacer to form 6-membered chelate rings. [Ru(bpy)2(pictz)]2+ (1) and [Ru(bpy)2(btzm)]2+ (2) (bpy = 2,2'-bipyridyl; pictz = 1-(picolyl)-4-phenyl-1,2,3-triazole; btzm = bis(4-phenyl-1,2,3-triazol-4-yl)methane) exhibit coordination by the triazole ring through the less basic N2 atom as a consequence of chelation and readily undergo photochemical release of the pictz and btzm ligands (ϕ = 0.079 and 0.091, respectively) in acetonitrile solution to form cis-[Ru(bpy)2(NCMe)2]2+ (3) in both cases. Ligand-loss intermediates of the form [Ru(bpy)2(κ1-pictz or κ1-btzm)(NCCD3)]2+ are detected by 1H NMR spectroscopy and mass spectrometry. Photolysis of 1 yields three ligand-loss intermediates with monodentate pictz ligands, two of which form through simple decoordination of either the pyridine or triazole donor with subsequent solvent coordination (4-tz(N2) and 4-py, respectively). The third intermediate, shown to be able to form photochemically directly from 1, arises through linkage isomerism in which the monodentate pictz ligand is coordinated by the triazole N3 atom (4-tz(N3)) with a comparable ligand-loss intermediate with an N3-bound κ1-btzm ligand also observed for 2.

Magnetic molecularly imprinted polymers are used to selectively extract cephalosporins from milk samples and analyze by LC-MS/MS

Cephalosporins were extracted from milk samples by using magnetic molecularly imprinted polymers (MMIP). To characterize the physical properties of MMIP, an experiment was conducted involving both static and dynamic adsorption. Samples were analyzed with LC-MS/MS to identify cephalosporin residues. The quantitative technique employed was the use of an isotope as an internal standard. Analysis was conducted using an Ascentis C8 column with a mobile phase consisting of a 0.1% aqueous solution of formic acid and acetonitrile. The determination coefficients varied between 0.9945 and 0.9995, as indicated by the linear equations. Cephalosporins exhibited a diverse spectrum of recovery rates, varying between 80.7% and 118.3%, accompanied by a range of relative standard deviations spanning from 3.8% to 13.5%. The detection limits for 9 kinds of cephalosporins in milk samples varied from 1 μg kg−1 to 20 μg kg−1, while the quantification limits ranged from 3 μg kg−1 to 60 μg kg−1. The successful implementation of the validated technique has been applied to detect 9 different kinds of cephalosporins in real milk products.

A Non‐Macrocycle Thiolate‐Based Cobalt Catalyst for Selective O2 Reduction into H2O

AbstractThe reduction of dioxygen to produce selectively H2O2 or H2O is crucial in various fields. While platinum‐based materials excel in 4H+/4e− oxygen reduction reaction (ORR) catalysis, cost and resource limitations drive the search for cost‐effective and abundant transition metal catalysts. It is thus of great importance to understand how the selectivity and efficiency of 3d‐metal ORR catalysts can be tuned. In this context, we report on a Co complex supported by a bisthiolate N2S2‐donor ligand acting as a homogeneous ORR catalyst in acetonitrile solutions both in the presence of a one‐electron reducing agent (selectivity for H2O of 93 % and TOFi=3 000 h−1) and under electrochemically‐assisted conditions (0.81 V <η<1.10 V, selectivity for H2O between 85 % and 95 %). Interestingly, such a predominant 4H+/4e− pathway for Co‐based ORR catalysts is rare, highlighting the key role of the thiolate donor ligand. Besides, the selectivity of this Co catalyst under chemical ORR conditions is inverse with respect to the Mn and Fe catalysts supported by the same ligand, which evidences the impact of the nature of the metal ion on the ORR selectivity.

Scandium Ion-Promoted Electron-Transfer Disproportionation of 2-Phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl 3-Oxide (PTIO•) in Acetonitrile and Its Regeneration Induced by Water.

2-Phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl 3-oxide (PTIO•), a persistent nitronyl nitroxide radical, has been used for the detection and trapping of nitric oxide, as a redox mediator for batteries, for the activity estimation of antioxidants, and so on. However, there is no report on the reactivity of PTIO• in the presence of redox-inactive metal ions. In this study, it is demonstrated that the addition of scandium triflate, Sc(OTf)3 (OTf = OSO2CF3), to an acetonitrile (MeCN) solution of PTIO• resulted in an electron-transfer disproportionation to generate the corresponding cation (PTIO+) and anion (PTIO-), the latter of which is suggested to be stabilized by Sc3+ to form [(PTIO)Sc]2+. The decay of the absorption band at 361 nm due to PTIO•, monitored using a stopped-flow technique, obeyed second-order kinetics. The second-order rate constant for the disproportionation, thus determined, increased with increasing the Sc(OTf)3 concentration to reach a constant value. A drastic change in the cyclic voltammogram recorded for PTIO• in deaerated MeCN containing 0.10 M Bu4NClO4 was also observed upon addition of Sc(OTf)3, suggesting that the large positive shift of the one-electron reduction potential of PTIO• (equivalent to the one-electron oxidation potential of PTIO-) in the presence of Sc(OTf)3 may result in the disproportionation. When H2O was added to the PTIO•-Sc(OTf)3 system in deaerated MeCN, PTIO• was completely regenerated. It is suggested that the complex formation of Sc3+ with H2O may weaken the interaction between PTIO- and Sc3+, leading to electron-transfer comproportionation to regenerate PTIO•. The reversible disproportionation of PTIO• was also confirmed by electron paramagnetic resonance (EPR) spectroscopy.

Synthesis and Application of 1,8-Naphthalimide Derivatives Fluorescent Probe for Sequential Recognition of Cu2+ and H2PO4.

A naphthalimide Schiff base fluorescent probe (BSS) was designed and synthesized from 4-bromo-1,8-naphthalic anhydride, and its structure was characterized by 1HNMR, 13CNMR, FTIR, and MS. Fluorescence emission spectra showed that probe BSS could realize the "turn-off" detection of Cu2+ in acetonitrile solution, detection process with strong specificity and excellent anti-interference of other metal ions. In the fluorescence titration experiments, fluorescence intensity of BSS showed a good linear relationship with the Cu2+ concentration (0-10 µmol/L), and the detection limit was up to 7.0 × 10- 8 mol/L. Meanwhile, BSS and Cu2+ could form a 1:1 complex (BSS-Cu2+) during the reaction process. Under the same detection conditions, complex BSS-Cu2+ had specific fluorescence recovery properties for H2PO4- and the whole process was not only fast (6s) but also free of interference from other anions, with a detection limit was as low as 5.7 × 10- 8 mol/L. In addition, complex BSS-Cu2+ could be successfully applied to the detection of H2PO4- in actual water samples, which with excellent application prospects.

Silver(i) Perfluoroalcoholates: Synthesis, Structure, and their Use as Transfer Reagents.

Herein we report a general access to silver(i) perfluoroalcoholates, their structure in the solid state and in solution, and their use as transfer reagents. The silver(i) perfluoroalcoholates are prepared by the reaction of AgF with the corresponding perfluorinated carbonyl compounds in acetonitrile and are stable for a prolonged time at -18 °C. X-Ray analysis of single crystals of perfluoroalcoholate species showed that two Ag(i) centers are bridged by the alcoholate ligands. In acetonitrile solution, Ag[OCF3] forms different structures as indicated by IR spectroscopy. Furthermore, the silver(i) perfluoroalcoholates can be used as easy-to-handle transfer reagents for the synthesis of Cu[OCF3], Cu[OC2F5], [PPh4][Au(CF3)3(OCF3)], and fluorinated alkyl ethers.

Synthesis, structural characterization and antitumor activities of manganese and cobalt isothiocyanate complexes with 2,2’-bipyridine

[Mn(SCN)2(2,2′-bipy)2] (1) and [Co(SCN)2(2,2′-bipy)2] (2) were synthesized at ambient temperature by adding aqueous solutions of manganese(II) or cobalt(II) chloride hydrate to aqueous acetonitrile solutions of 2,2′-bipyridine (2,2′-bipy) and potassium thiocyanate. Elemental analyses, FT-IR and UV–vis spectra were used to characterize 1 and 2. Single crystal X-ray diffraction was used to analyze the crystal structures of 1 and 2, revealing that the two are structurally similar. The molecular structures of 1 and 2 consist of Mn or Co ion chelated by two molecules of 2,2′-bipy through four nitrogen atoms and two NCS anions, giving distorted octahedral geometries. The isothiocyanate group is not bridging, instead, two ligands coordinate in a cis arrangement to the manganese or cobalt center by their nitrogen atoms while the sulfur atoms are free. Through hydrogen bonding and π–π stacking interactions, the discrete units of 1 and 2 extend to 3D supramolecular networks with flower and fishbone-like structures. The luminescence behavior of 2,2′-bipy, 1 and 2 were investigated. On HepG2 (liver) and MCF-7 (breast) cancer cells, the anticancer effects of 1 and 2 were evaluated. The activity of 1 and 2 on MCF-7 is more significant than that of HepG2. The IC50 of 1 was lower in HepG2 and MCF-7 cells than for 2.

A Co(III)-peroxo-arylboronate complex formed by nucleophilic reaction of a Co(III)-peroxo species

In this work, we report the generation and characterization of two new Co(III)-peroxo complexes 2 and 3. 2 is best described as a mononuclear CoIII-(O2) complex that exhibits an 18O-isotope sensitive OO bond stretching vibration at 845(−49) cm−1, indicating a relatively weak peroxo moiety compared to those of other CoIII-(O2) complexes reported previously. Complex 3 is a CoIII-peroxo-arylboronate species having a rare {CoIIIOOBO} five-membered metallocycle, which is structurally characterized using X-ray crystallography. Investigations of the reaction mechanism using density functional theory calculations show that 2 likely undergoes a nucleophilic attack to an arylboronic acid, which is generated by hydrolysis of the BPh4− anion in wet acetonitrile solution, to first form a CoIII-peroxo-arylboronic acid adduct, followed by the loss of one benzene molecule to generate the five-membered metallocycle. The entire reaction is thermodynamically favorable. Taken together, the conversion of 2 to 3 represents the discovery of a novel nucleophilic reactivity that can be carried out by mononuclear Co(III)-peroxo complexes.

Simultaneous determination of 31 banned veterinary drugs during egg-laying period in poultry eggs by ultra performance liquid chromatography-tandem mass spectrometry

The consumption of poultry eggs has increased in recent years owing to the abundance of production and improvements in living standards. Thus, the safety requirements of poultry eggs have gradually increased. At present, few reports on analytical methods to determine banned veterinary drugs during egg-laying period in poultry eggs have been published. Therefore, establishing high-throughput and efficient screening methods to monitor banned veterinary drugs during egg-laying period is imperative. In this study, an analytical method based on ultra performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) combined with QuEChERS-based techniques was developed for the simultaneous determination of 31 banned veterinary drugs encompassing nine drug classes (macrolides, antipyretic and analgesic drugs, sulfonamides, antibacterial synergists, anticoccidials, antinematodes, quinolones, tetracyclines, amphenicols) in different types of poultry eggs. The main factors affecting the response, recovery, and sensitivity of the method, such as the extraction solvent, purification adsorbent, LC separation conditions, and MS/MS parameters, were optimized during sample pretreatment and instrumental analysis. The 31 veterinary drug residues in 2.00 g eggs were extracted with 2 mL of 0.1 mol/L ethylene diamine tetraacetic acid disodium solution and 8 mL 3% acetic acid acetonitrile solution, and salted out with 2 g of sodium chloride. After centrifugation, 5 mL of the supernatant was cleaned-up using the QuEChERS method with 100 mg of octadecylsilane-bonded silica gel (C18), 50 mg of N-propylethylenediamine (PSA), and 50 mg of NH2-based sorbents. After nitrogen blowing and redissolution, the 31 target analytes were separated on a Waters CORTECS UPLC C18 analytical chromatographic column (150 mm×2.1 mm, 1.8 μm) at a flow rate, column temperature, and injection volume of 0.4 mL/min, 30 ℃, and 5 μL, respectively. Among these analytes, 26 analytes were acquired in dynamic multiple reaction monitoring (MRM) mode under positive electrospray ionization (ESI+) conditions using (A) 5 mmol/L ammonium acetate (pH 4.5) and (B) acetonitrile as mobile phases. The gradient elution program was as follows: 0-2.0 min, 12%B-30%B; 2.0-7.5 min, 30%B-50%B; 7.5-10.0 min, 50%B; 10.0-10.1 min, 50%B-100%B; 10.1-12.0 min, 100%B; 12.0-12.1 min, 100%B-12%B; The five other target analytes were acquired in MRM mode under negative electrospray ionization (ESI-) conditions using (A) H2O and (B) acetonitrile as mobile phases. The gradient elution program was as follows: 0-2.0 min, 12%B-40%B; 2.0-6.0 min, 40%B-80%B; 6.0-6.1 min, 80%B-100%B; 6.1-8.0 min, 100%B; 8.0-8.1 min, 100%B-12%B. Matrix-matched external standard calibration was used for quantification. The results showed that all the compounds had good linear relationships within their respective ranges, with correlation coefficients of >0.99. The limits of detection (LODs) and quantitation (LOQs) were 0.3-3.0 μg/kg and 1.0-10.0 μg/kg, respectively. The average recoveries of the 31 banned veterinary drugs spiked at three levels (LOQ, maximum residue limit (MRL), and 2MRL) in poultry eggs ranged from 61.2% to 105.7%, and the relative standard deviations (RSDs) ranged from 1.8% to 17.6%. The developed method was used to detect and analyze banned veterinary drugs in 30 commercial poultry egg samples, including 20 eggs, 5 duck eggs, and 5 goose eggs. Enrofloxacin was detected in one egg with a content of 12.3 μg/kg. The proposed method is simple, economical, practical, and capable of the simultaneous determination of multiple classes of banned veterinary drugs in poultry eggs.

Unraveling the Ultrafast Photochemical Dynamics of Nitrobenzene in Aqueous Solution.

Nitroaromatic compounds are major constituents of the brown carbon aerosol particles in the troposphere that absorb near-ultraviolet (UV) and visible solar radiation and have a profound effect on the Earth's climate. The primary sources of brown carbon include biomass burning, forest fires, and residential burning of biofuels, and an important secondary source is photochemistry in aqueous cloud and fog droplets. Nitrobenzene is the smallest nitroaromatic molecule and a model for the photochemical behavior of larger nitroaromatic compounds. Despite the obvious importance of its droplet photochemistry to the atmospheric environment, there have not been any detailed studies of the ultrafast photochemical dynamics of nitrobenzene in aqueous solution. Here, we combine femtosecond transient absorption spectroscopy, time-resolved infrared spectroscopy, and quantum chemistry calculations to investigate the primary steps following the near-UV (λ ≥ 340 nm) photoexcitation of aqueous nitrobenzene. To understand the role of the surrounding water molecules in the photochemical dynamics of nitrobenzene, we compare the results of these investigations with analogous measurements in solutions of methanol, acetonitrile, and cyclohexane. We find that vibrational energy transfer to the aqueous environment quenches internal excitation, and therefore, unlike the gas phase, we do not observe any evidence for formation of photoproducts on timescales up to 500 ns. We also find that hydrogen bonding between nitrobenzene and surrounding water molecules slows the S1/S0 internal conversion process.

Evaluation of some sulfonamide antibiotics residues in chicken meat samples using in-syringe counter current homogenous liquid–liquid extraction and magnetic deep eutectic solvent-based dispersive liquid–liquid microextraction and HPLC–DAD

A sample pretreatment method based on the combination of counter current salting-out homogenous liquid–liquid extraction and magnetic deep eutectic solvent-based dispersive liquid–liquid microextraction was developed and employed for the extraction of some sulfonamide antibiotics from chicken meat samples. For this purpose, first, a homogenous solution of acetonitrile and deionized water was passed through a syringe barrel filled sodium chloride and chicken meat sample. By doing so, the fine droplets of acetonitrile were produced and collected on the surface of solution. In the following, this phase containing the extracted analytes was taken and injected into deionized water after mixing with [Choline: 4-chlorophenol]+[FeCl4]- magnetic deep eutectic solvent. Then, the magnetic deep eutectic solvent droplets were separated in the presence of an external magnetic field and injected into high performance liquid chromatography-diode array detector for quantitative analysis. Based on the validation results, low limits of detection (0.15–0.24 ng g−1) and quantification (0.51–0.80 ng g−1), high extraction recovery (67–78 %), and good precision (relative standard deviations ≤ 5.7 %) were obtainable by using the offered method. Finally, the suggested method was employed for the quantification of the studied sulfonamide antibiotics in various chicken meat samples

Electrochemical behavior of a flat gold electrode in an acetonitrile solution of 1,2,4,5-tetraoxane

Electrochemical behavior of a flat gold electrode in an acetonitrile solution of 1,2,4,5-tetraoxane

An Efficient Supported Cu(I) Catalyst for the Amination of Aryl Halides with Sodium Azide

We present the synthesis and characterization of a new Cu(I) complex supported on SBA‐15 as a catalyst for preparing anilines from the reaction of aryl halides with sodium azide. The SBA‐15 support was modified by treating it sequentially with (3‐aminopropyl) triethoxysilane (APTES), cyanuric chloride, and 2‐aminothiazole (AT). The modified mesoporous silica, SBA‐15@BAT, was then treated with a CuI solution in acetonitrile to give SBA‐15@BAT‐Cu(I). The catalyst underwent thorough characterization using conventional methods. X‐Ray photoelectron spectroscopy (XPS) analysis corroborated the presence of copper in the +1 oxidation state in the catalyst. The supported Cu(I) complex sufficiently catalyzed the amination reaction of iodo‐, bromo‐, and chloroarenes with NaN3. The catalyst was centrifuged, washed, and applied in the subsequent run. We investigated the effects of various reaction components and parameters to determine the optimal conditions for the reaction. The heterogeneous catalyst exhibited noticeable stability and was reused over seven runs with slight deactivation.

A simple and efficient pyrazole based colorimetric chemosensor for sensing Hg2+, Zn2+, Cu2+ ions and a selective sensing of Hg2+ ions in the presence of Zn2+and Cu2+ ions and its application in real samples

A simple colorimetric chemosensor (E)-4((4-diethylamino)-2-hydroxybenzylidene)amino)-1,5-dimethyl-2-phenyl-1,2, dihydro-3H-pyrazole-3-one (M2) was synthesized and characterized by NMR, Mass spectra, IR and UV spectra, along with solvatochromism. The synthesized compound showed colorimetric sensing towards Hg2+ ion with high selectivity and sensitivity. The UV–Vis absorption spectra studies demonstrated that the proposed sensor could detect Hg2+ directly in acetonitrile solution over other metal ions. In the presence of Hg2+ ion, the probe exhibits instantaneous color change from colorless to yellow as a naked-eye detection. The binding ratio of the probe with metal has been identified to be of 1:1 using Job’s Plot and the obtained limit of detection is 8.83 × 10−8 M. The binding interaction of probe with the Hg2+ is confirmed using 1H NMR titration, ESI mass, and DFT calculation.

Reduction of CO to Methanol with Recyclable Organic Hydrides.

The reaction steps for the selective conversion of a transition metal carbonyl complex to a hydroxymethyl complex that releases methanol upon irradiation with visible light have been successfully quantified in acetonitrile solution with dihydrobenzimidazole organic hydride reductants. Dihydrobenzimidazole reductants have been shown to be inactive toward H2 generation in the presence of a wide range of proton sources and have been regenerated electrochemically or photochemically. Specifically, the reaction of cis-[Ru(bpy)2(CO)2]2+ (bpy = 2,2'-bipyridine) with one equivalent of a dihydrobenzimidazole quantitatively yields a formyl complex, cis-[Ru(bpy)2(CO)(CHO)]+, and the corresponding benzimidazolium on a seconds time scale. Kinetic experiments revealed a first-order dependence on the benzimidazole hydride concentration and an unusually large kinetic isotope effect, inconsistent with direct hydride transfer and more likely to occur by an electron transfer-proton-coupled electron transfer (EΤ-PCET) or related mechanism. Further reduction/protonation of cis-[Ru(bpy)2(CO)(CHO)]+ with two equivalents of the organic hydride yields the hydroxymethyl complex cis-[Ru(bpy)2(CO)(CH2OH)]+. Visible light excitation of cis-[Ru(bpy)2(CO)(CH2OH)]+ in the presence of excess organic hydride was shown to yield free methanol. Identification and quantification of methanol as the sole CO reduction product was confirmed by 1H NMR spectroscopy and gas chromatography. The high selectivity and mild reaction conditions suggest a viable approach for methanol production from CO, and from CO2 through cascade catalysis, with renewable organic hydrides that bear similarities to Nature's NADPH/NADP+.

Modeling the alkylation of amines with alkyl bromides: explaining the low selectivity due to multiple alkylation.

Nucleophilic substitution reactions of aliphatic amines with alkyl halides represent a simple and direct mechanism for obtaining higher-order aliphatic amines. However, it is well known that these reactions suffer from low selectivity due to multiple alkylations, which is attributed to the higher reactivity of the newly formed amine. In order to provide a detailed explanation for this kind of system, we have investigated the reactivity of primary and secondary amines with 1-bromopropane and 2-bromopropane. The free energy profile in acetonitrile solution was obtained and a detailed microkinetic analysis was needed to analyze this complex reaction system. We have found that the product of the first alkylation is an ion pair corresponding to the protonated secondary amine and the bromide ion, which can transfer the proton to the reactant primary amine. Then, the newly formed secondary amine can also react, leading to a second alkylation to produce a tertiary protonated amine. Our modeling points out that both the proton transfer equilibria and the similar reactivity of the primary and secondary amines produce reduced selectivity. The proton transfer equilibria also contribute to slowing down the kinetics of the first alkylation. The exploration of the mechanism was done by geometry optimization using the CPCM/X3LYP/ma-def2-SVP method, followed by harmonic frequency calculation at this same level of theory. A composite approach was used to obtain the free energy profile, using the more accurate ωB97X-D3/ma-def2-TZVPP level of theory for electronic energy and the SMD model for the solvation free energy. These calculations were performed with the ORCA 4 program. The detailed microkinetic analysis was done using the Kintecus program.

Metal-Free Homogeneous O2 Reduction by an Iminium-Based Electrocatalyst.

The oxygen reduction reaction (ORR) is important for alternative energy and industrial oxidation processes. Herein, an iminium-based organoelectrocatalyst (im+) for the ORR with trifluoroacetic acid as a proton source in acetonitrile solution under both electrochemical and spectrochemical conditions using decamethylferrocene as a chemical reductant is reported. Under spectrochemical conditions, H2O2 is the primary reaction product, while under electrochemical conditions H2O is produced. This difference in selectivity is attributed to the interception of the free superoxide intermediate under electrochemical conditions by the reduced catalyst, accessing an alternate inner-sphere pathway.