Protonating Reagent Research Articles

Electrochemical ammonium-cation-assisted pyridylation of inert N-heterocycles via dual-proton-coupled electron transfer

SummaryA straightforward and practical strategy for pyridylation of inert N-heterocycles, enabled by ammonium cation and electrochemical, has been described. This protocol gives access to various N-fused heterocycles and bidentate nitrogen ligand compounds, through dual-proton-coupled electron transfer (PCET) and radical cross-coupling in the absence of exogenous metal and redox reagent. It features broad substrate scope, wide functional group tolerance, and easy gram-scale synthesis. Various experiments and density functional theory (DFT) calculation results show the mechanism of dual PCET followed by radical cross-coupling is the preferred pathway. Moreover, ammonium salt plays the dual role of protonation reagent and electrolyte in this conversion, and the resulting product 9-(pyridin-4-yl)acridine compound can be used for fluorescence recognition of Fe2+ and Pd2+ with high sensitivity.

Protonated NH2-MIL-125 via HCl vapor to introduce the moiety with charge and ample hydrogen as a novel bifunctional photocatalyst: Enhanced photocatalytic H2 production and NO purification

• A novel bifunctional protonated NH 2 -MIL-125 photocatalyst was prepared facilely. • Using HCl vapor to protonate MOFs was first proposed. • The catalyst can enhance the activity of photocatalytic H 2 production and NO removal. • The favorable effect can be explained via the moiety with charge and ample hydrogen (–NH 3 + Cl - group) • The in-situ DRIFTS spectra were used to analyze intermediates during the NO removal. A novel protonated NH 2 -MIL-125 was fabricated to introduce the moiety with charge and ample hydrogen (–NH 3 + Cl - group) into NH 2 -MIL-125 using HCl vapor obtained by natural volatilization of hydrochloric acid as a protonating reagent, which could exhibit excellent photocatalytic activity in both hydrogen production and NO purification under visible light irradiation. The hydrogen production and NO purification rate of the best protonated NH 2 -MIL-125 were 6762.80 μmol g −1 and 49.17%, respectively, which were 20.53 and 1.84 times as that of the original NH 2 -MIL-125. A series of characterizations, such as Mott-Schottky, PL, FT-IR and in situ DRIFTS, etc. were used to characterize the photoelectrochemical properties of the optimal catalyst, which demonstrated the protonation effect can not only enhance the electron migration rate, but also effectively accelerate photo-generated electron-hole pairs separation in the photocatalytic reaction process. This research believed that using HCl vapor as a facile protonation reagent to introduce the moiety with charge and ample hydrogen (–NH 3 + Cl - ) was a very effective method to decorate MOFs for hydrogen evolution and NO removal.

HFIP as Protonation Reagent and Solvent for Regioselective Alkylation of Indoles with All-Carbon Centers

The regio- and chemoselective construction of indole bearing an all-carbon center at the C3-position, a versatile bioactive building block, by C(sp2)-C(sp3) formation with olefins has been achieved through utilization of hexafluoroisopropanol (HFIP) as the protonation reagent and solvent. The catalytic reactions are operationally simple and green compared with previous reports utilizing elaborated olefins and catalysts. This protocol allows for alkylation of a variety of substituted indoles with diverse of styrene type alkenes in excellent yields and with high selectivity. Application of this protocol to the synthesis of drug was pursued and with an improved yield in contrast to previous art. Catalytic kinetics and deuterium-labeling experiments suggest that the rate-determining step involves the protonation of olefin by HFIP to generate carbocation, followed by electrophilic addition to indole derivative.

Electrochemical Ammonium Cation‐Assisted Hydropyridylation of Ketone‐Activated Alkenes: Experimental and Computational Mechanistic Studies

AbstractThis work describes an electrochemical ammonium cation enabled hydropyridylation of ketone‐activated alkenes under metal‐ and exogenous reductant free conditions giving access to β‐pyridyl ketones, through dual proton‐coupled electron transfer and radical cross‐coupling. It features a broad substrate scope and allows a gram‐scale synthesis. Ammonium chloride plays various roles in this transformation such as the hydrogen donor, the protonation reagent, and electrolyte. In particular, various experiments and density functional theory (DFT) calculation results show the mechanism of dual proton‐coupled electron transfer followed by radical cross‐coupling is the preferred pathway.magnified image

2-Isopropylbenzimidazole and 2-methylbenzimidazole as bulky proton sources: Stereoselective protonation and application to the synthesis of γ- and δ-lactones

2-Isopropylbenzimidazole and 2-methylbenzimidazole have been found to be effective bulky proton sources for stereoselective protonation of chiral enolate anions. 2-Isopropylbenzimidazole worked in the stereoselective protonation of the Birch reduction of chiral α,β-unsaturated imides. On the other hand, 2-methylbenzimidazole was found to be the best protonation reagent in the isomerization reaction of α,β-unsaturated imide into β,γ-unsaturated imide. The Birch reduction using 2-isopropylbenzimidazole realized a concise and stereoselective synthesis of δ-lactone 14, a sex pheromone of Macrocentrus grandii, while the isomerization reaction using 2-methylbenzimidazole was employed in the highly stereoselective synthesis of the γ-lactone intermediate in the synthesis of depsipeptide antibiotics. These bulky proton sources would be powerful tools to achieve a concise synthesis of natural products.

From ascorbic acid to furan derivatives: the gas phase acid catalyzed degradation of vitamin C.

Furan derivatives, potentially carcinogenic to humans, can be formed, in addition to carbohydrates and other sources, from the degradation of ascorbic acid (AA). At present, the mechanisms involved in the ascorbic acid degradation are not yet fully understood. In this study, we reported a gas-phase investigation, performed using Triple Quadrupole (TQ/MS) and Ion Trap Mass Spectrometry (QIT/MS) together with quantum mechanical calculations at the B3LYP/6-31+G(d,p) level of theory, on the non-oxidative degradation mechanism of l-ascorbic acid (AA) to furan derivatives. Gaseous protonated ascorbic acid ions, the AAH+ ionic reagents, were generated by Electrospray Ionization (ESI) of an aqueous AA solution added with a mild protonation reagent. The Collisionally Induced Dissociation (CID) mass spectra of the AAH+ ions displayed gaseous fragment ions corresponding to the degradation intermediates and reaction products, which were structurally characterized and identified. Precise mechanistic insights were achieved by using l-[1-13C]-AA. On the basis of experimental and computational results, the gas phase non-oxidative acid catalyzed degradation mechanism of ascorbic acid is proposed, a benchmark point for the comprehension of the mechanism in the condensed phase.

Liquid Marbles Stabilized by Charged Polymer Latexes: How Does the Drying of the Latex Particles Affect the Properties of Liquid Marbles?

The coating of solid particles on the surface of liquid in air makes liquid marbles a promising approach in the transportation of a small amount of liquid. The stabilization of liquid marbles by polymeric latex particles imparts extra triggers such as pH and temperature, leading to the remote manipulation of droplets for many potential applications. Because the functionalized polymeric latexes can exist either as colloidally stable latex or as flocculated latex in a dispersion, the drying of latex dispersions under different conditions may play a significant role in the stabilization of subsequent liquid marbles. This article presents the investigation of liquid marbles stabilized by poly(styrene-co-methacrylic acid) (PS-co-MAA) particles drying under varied conditions. Protonation of the particles before freeze drying makes the particles excellent liquid marble stabilizers, but it is hard to stabilize liquid marbles for particles dried in their deprotonated states. The static properties of liquid marbles with increasing concentrations of protonating reagent revealed that the liquid marbles are gradually undermined by protonating the stabilizers. Furthermore, the liquid marbles stabilized by different particles showed distinct behaviors in separation and merging manipulated by tweezers. This study shows that the initial state of the particles should be carefully taken into account in formulating liquid marbles.

Controlled fabrication of PANI/CNF hybrid films: Molecular interaction induced various micromorphologies and electrochemical properties

In this paper, a facile and efficient method is reported to prepare polyaniline/carbon nanofiber (PANI/CNF) hybrid films by in situ chemical polymerization of aniline. The various morphologies and microstructures of PANI/CNF hybrid films can be controlled by adjusting the concentration of aniline and different acids as the protonation reagent, and the formation mechanism is illustrated in this study. The surface morphologies and chemical structure of the PANI/CNF hybrid films are characterized by scanning electron microscope (SEM), transmission electron microscope (TEM), water contact angle (CA), FT-IR, Raman, and UV–vis spectrophotometers. The different morphology of uniformly coated, twist-tangled, and needle-like PANI built on CNF films are obtained by using HCl, H2SO4, and HClO4 as protonation reagent and the obtained hybrid films are labeled as PANI/CNF-f1, PANI/CNF-f2, and PANI/CNF-f3, respectively. We demonstrated that the different protonation reagent has the determined effect on the surface properties of the obtained hybrid films that can transfer from hydrophilic to hydrophobic. Besides, the various morphologies of PANI play an important role in their electrochemical properties. PANI/CNF-f3 exhibits higher specific capacitance and better stability than that of the PANI/CNF-f1 and PANI/CNF-f2. Considering its unique needle-like structure, this work is a proof of concept that micro-structure and morphology can determine the macro-properties. And this study supplies a facile method to fabricate PANI/CNF hybrid films that can be used as electrode materials in supercapacitors.

Highly controlling selectivity of copper(I)-catalyzed azide/alkyne cycloaddition (CuAAC) between sulfonyl azids and normal alkynes or propynoates

In this article, a combination of Cu(OAc) 2·H 2O/2-aminophenol was developed as a highly efficient and controlling catalytic system for sulfonyl azids involved CuAAC. By using this catalytic system, sulfonyl azids reacted with normal alkynes or propynoates to selectively give the ring products or the chain products, respectively, in excellent yields within minutes. HOAc in situ produced in the reaction has been proved to be a super protonation reagent, by which the unstable intermediate 5-cuprated 1,2,3-triazole was protonated efficiently to yield ring-product 1-sulfonyl 1,2,3-trizoles. The control experiments also proved that 2-aminophenol played dual roles as both ligand and reductant, which led to the cheap and chemically stable Cu(OAc) 2·H 2O being an efficient copper source for our purpose.

Fabrication and charge/energy-transfer study of 4,7-bis(4-triphenylamino)benzo- 2,1,3-thiadiazole/CuPc composite films

Composite films of 4,7-bis(4-triphenylamino)benzo-2,1,3-thiadiazole (TBT) and copper phthalocyanine (CuPc) are fabricated via protonation-coelectrophoretic deposition from nitromethane solutions of TBT/CuPc mixture in the presence of trifluoroacetic acid as a protonation reagent. A nanospheres–nanowires interpenetrating network structure is obtained when the molar percentage of TBT is 70%. Furthermore, the existence of TBT makes α-phased CuPc be partly transformed into the β-phase, and simultaneously, CuPc disorganizes the TBT unit cells. The blue shift on the absorption edge of TBT and the significant fluorescence quenching in the composite films indicate energy/charge transfer and donor–acceptor (D–A) heterojunction formation. Then these results are proved from another point of view: the mutual overlap of absorption and emission spectra of TBT and CuPc lead to a bidirectional Förster resonance energy transfer at the interface; the molecular energy levels calculated from the results of cyclic voltammetry theoretically determine that there exist a D–A heterojunction and charge transfer from TBT to CuPc. Finally, from the investigation of the field-induced surface photovoltage spectra, it can be concluded that this charge transfer results in efficient dissociation of the photoinduced excitons in the composite films, followed by the generation of a strong photovoltage response.

Gas-Phase Reactions of Laser-Desorbed Molecules with Ions from Electrospray

Gas-phase reactions of neutral molecules delivered by laser desorption with ions introduced via an electrospray interface have been observed. To maximize the production of neutrals while keeping laser ionization products negligible, the laser fluence has been adjusted only slightly above the ionization threshold fluence. The reactions have been performed in the entrance to an ion funnel operated at 3–4 mbar. Both the laser desorption assembly and the electrospray interface belong to an electrospray ionization to matrix-assisted laser desorption/ionization switchable combination ion source attached to a Fourier transform ion cyclotron resonance mass spectrometer. The reaction products of molecular species of 1-aza[6]-helicene, 1,8-dihydroxy-9-anthrone (dithranol) and 2-mercaptobenzothiazole with protonating reagent ions and silver cations from electrospray were detected. The products were identified by their accurate mass, proton/deuterium isotopic exchange and by resolving the corresponding peaks of isotopolog ions.

Regioselectivity of the protonation of captodative enamines bearing a CF 3 group

Capodative enamines bearing a CF 3 group are protonated at the N- or β-C-atom depending on the structure of the initial base and the nature of protonating reagent.

Catalytic reactions of oxetanes with protonic reagents and aprotic reagents leading to novel polymers

AbstractThis paper reports new addition reactions of oxetanes with certain protonic reagents such as carboxylic acid, phenol, and thiol, and with certain aprotic reagents such as acyl chloride, thioester, phosphonyl dichloride, silyl chloride, and chloroformate using quaternary onium salts as catalysts. The kinetic study of the addition reactions of oxetanes was also investigated. These new addition reactions were applicable to the synthesis of new polymers. These polyaddition systems could also construct both polymer main chains and reactive side chains. The alternating copolymerization of oxetanes with carboxylic anhydride was performed. Furthermore, it was found that anionic ring‐opening polymerization of oxetanes containing hydroxy groups proceeded to afford the hyperbranched polymer (HBP) with an oxetanyl group and many hydroxy groups at the ends of the polymer chains. Alkali developable photofunctional HBPs were synthesized by the polyaddition of bis(oxetane)s or tris(oxetane)s, and their patterning properties were examined, too. The photo‐induced cationic polymerization of the polymers with pendant oxetanyl groups and the thermal curing reactions of polyfunctional oxetanes (oxetane resins) were also examined to give the crosslinking materials quantitatively. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 709–726, 2007

06/02030 Flameless incineration of pyrene under sub-critical and supercritical water conditions: Onwudili, J. A. and Williams, P. T. Fuel, 2006, 85, (1), 75–83.

Anhydrous ammonia, methanol, and other protonic reagents have been utilized for the chemical comminution of coal. In this investigation, subbituminous, low-volatile bituminous and high-volatile bituminouscoals have been comminuted readily by trifluoroacetic acid. Approximately 5% of the original coal dissolves during the trifluoroacetic acid treatment leaving a material which has a high calorific value. The pyritic and organic sulphur contents and the ash yields are greatly reduced. Micrographs after treatment show the layered structure of the coal.

06/02028 Preferences for domestic fuel: analysis with socio–economic factors and rankings in Kolkata, India: Gupta, G. and Köhlin, G. Ecological Economic, 2006, 57, (1), 107–121.

Anhydrous ammonia, methanol, and other protonic reagents have been utilized for the chemical comminution of coal. In this investigation, subbituminous, low-volatile bituminous and high-volatile bituminouscoals have been comminuted readily by trifluoroacetic acid. Approximately 5% of the original coal dissolves during the trifluoroacetic acid treatment leaving a material which has a high calorific value. The pyritic and organic sulphur contents and the ash yields are greatly reduced. Micrographs after treatment show the layered structure of the coal.

Amino Acid Derivatives of Cholesterol as “Latent” Organogelators with Hydrogen Chloride as a Protonation Reagent

A series of low molecular weight organic gelator (LMOG) gel systems sensitive to alkaline/acidic stimuli was established by employing amino acid derivatives of cholesterol as "latent" gelators, which are cholesteryl glycinate (1), cholesteryl L-alaninate, cholesteryl D-alaninate, cholesteryl L-phenyl alaninate, and cholesteryl D-phenyl alaninate. The hydrochloric salts are denoted as 2, 3, 4, 5, and 6, respectively. For the 18 solvents tested, one proved to be a weak gelator and gels only two of the solvents. Its gelation ability, however, was greatly improved by bubbling HCl gas, which was produced by reaction of concentrated sulfuric acid with NaCl, through its solution owing to protonation of its amino group. It was demonstrated that the protonated form of it gelled 14 of the solvents tested. Further investigation revealed that the gels changed into solution with addition of any of the amines, including triethylamine (TEA), diethylamine, ethylenediamine, and NH3. The phase transition could be reversed by further introduction of the acidic gas. SEM measurements showed that 1 self-assembled into different supramolecular structures in different gels. Salt effect studies proved that electrostatic interaction is one of the driving forces for formation of the gels.

Mass spectrometry as an emerging tool for systems biology.

Completion of the human genome project has created a blueprint of the genes and proteins necessary to construct and maintain a complex organism. Understanding how the molecular entities of human cells and tissues function will require sophisticated experiments to decipher how these molecules interact as a system. Beyond genes and proteins, metabolites encompass another important level of the system. To understand cellular systems, high-throughput strategies to investigate the functions of proteins and metabolites within the context of the system are necessary. Thus, understanding gene function (and ultimately biological systems) will require methods to broadly and quickly determine how the amounts and forms of various molecules are changing (Figure 1). Three considerations are relevant: (i) broad and unbiased measurement tools; (ii) comprehensive separation techniques; and (iii) informatics to analyze the data. This article will discuss mass spectrometry for the measurement of proteins and metabolites.

Proton induced P–H and Mo–H bond activation at the phosphide bridged dimolybdenum complexes [Mo2Cp2(µ-H)(µ-PHR)(CO)4] (R = Cy, 2,4,6-C6H2R′3; R′ = H, Me,tBu)

The new hydride complexes [Mo2Cp2(mu-H)(mu-PHR)(CO)4] having bulky substituents (R = 2,4,6-C(6)H2tBu3= Mes*, R = 2,4,6-C6H2Me3= Mes) have been prepared in good yield by addition of Li[PHR] to the triply bonded [Mo2Cp2(CO)4] and further protonation of the resulting anionic phosphide complex [Mo2Cp2(mu-PHR)(CO)4]-. Protonation of the Mes* compound with either [H(OEt2)2][B{3,5-C6H3(CF3)2}4] or HBF4.OEt2 gives the cationic phosphinidene complex [Mo2Cp2(mu-H)(mu-PMes*)(CO)4]+ in high yield. In contrast, protonation of the analogous hydride compounds with Mes or Cy substituents on phosphorus give the corresponding unsaturated tetracarbonyls [Mo2Cp2(mu-PHR)(CO)4]+, which are unstable at room temperature and display a cis geometry. Decomposition of the latter give the electron-precise pentacarbonyls [Mo2Cp2(mu-PHR)(mu-CO)(CO)4]+, also displaying a cis arrangement of the metal fragments. In the presence of BF4- as external anion, fluoride abstraction competes with carbonylation to yield the neutral fluorophosphide hydrides [Mo2Cp2(mu-H)(mu-PFR)(CO)4]. Similar results were obtained in the protonation reactions of the hydride compounds having a Ph substituent on phosphorus. In that case, using HCl as protonation reagent gave the chloro-complex [Mo2ClCp2(mu-PHPh)(CO)4] in good yield. The structures and dynamic behaviour of the new compounds are analyzed on the basis of solution IR and 1H, 31P, 19F and 13C NMR data as well as the X-ray studies carried out on [Mo2Cp2(mu-H)(mu-PHMes)(CO)4](cis isomer), [Mo2Cp2(mu-H)(mu-PFMes)(CO)4](trans isomer), [Mo2Cp2(mu-PHCy)(mu-CO)(CO)4](BF4) and [Mo2ClCp2(mu-PHPh)(CO)4].

The Crystallographic Structure of a Lewis Acid Assisted Chiral Broensted Acid as an Enantioselective Protonation Reagent for Silyl Enol Ethers.

AbstractFor Abstract see ChemInform Abstract in Full Text.

The crystallographic structure of a Lewis acid-assisted chiral Brønsted acid as an enantioselective protonation reagent for silyl enol ethers.

It is difficult to control the enantioselectivity in the protonation of silyl enol ethers with simple chiral Brønsted acids, mainly due to bond flexibility between the proton and its chiral counterion, the orientational flexibility of the proton, and the fact that the proton sources available are limited to acidic compounds such as chiral carboxylic acids. To overcome these difficulties, we have developed a Lewis acid-assisted chiral Brønsted acid (LBA) system. The coordination of Lewis acids with Brønsted acids restricts the orientation of protons and increases their acidity. Optically active binaphthol (BINOL) derivative.SnCl4 complexes are very effective as enantioselective protonation reagents for silyl enol ethers. However, their exact structures have not yet been determined. We describe here optically active 1,2-diarylethane-1,2-diol derivative.SnCl4 as a new type of LBA for the enantioselective protonation as well as its crystallographic structure. A variety of optically active 1,2-diarylethane-1,2-diols could be readily prepared by asymmetric syn-dihydroxylation. This is a great advantage over BINOL for the flexible design of a new LBA. The most significant finding is that we were able to specify the conformational direction of the H-O bond of LBA, which has some asymmetric inductivity, by X-ray diffraction analysis. The stereochemical course in the enantioselective protonation of silyl enol ethers using LBA would be controlled by a linear OH/pi interaction with an initial step. The absolute stereopreference in enantioselective reactions using BINOL.SnCl4 can also be explained in terms of this uniformly mechanistic interpretation.