Pyridinium Bromide Research Articles

Electronic Communication in Confined Space Coronas of Shell-by-Shell Structured Al2 O3 Nanoparticle Hybrids Containing Two Layers of Functional Organic Ligands.

A first series of examples for confined space interactions of electron-rich and electron-poor molecules organized in an internal corona of shell-by-shell (SbS)-structured Al2 O3 nanoparticle (NP) hybrids is reported. The assembly concept of the corresponding hierarchical architectures relies on both covalent grafting of phosphonic acids on the NPs surface (SAMs formation; SAM=self-assembled monolayer) and exohedral interdigitation of orthogonal amphiphiles as the second ligand layer driven by solvophobic interactions. The electronic communication between the chromophores of different electron demand, such as pyrenes, perylenediimides (PDIs; with and without pyridinium bromide headgroups) and fullerenes was promoted at the layer interface. In this work, it is demonstrated that the efficient construction principle of the bilayer hybrids assembled around the electronically "innocent" Al2 O3 core is robust enough to achieve control over electronic communication between electron-donors and -acceptors in the interlayer region. The electronic interactions between the electron-accepting and electron-donating moieties approaching each other at the layer interface were monitored by fluorescence measurements.

New pyridinium bromide mono-cationic surfactant as corrosion inhibitor for carbon steel during chemical cleaning: Experimental and theoretical studies

New pyridinium bromide mono-cationic surfactant namely: 1-dodecyl-3-(hydroxymethyl) pyridin-1-ium bromide (DHPB) was prepared, 1H NMR and FTIR spectroscopy are used to confirm its chemical structure. The surface-active characteristics of DHPB were determined via surface tension measurements. The efficiency of the DHPB as corrosion inhibitors for carbon steel (CS) in 2 M HCl solution evaluated by chemical and electrochemical techniques. The high inhibition efficiencies for CS in the acidic medium have been improved by raising DHPB concentration and with raising the temperature. Quantum chemical calculations (QM) and molecular dynamics simulation (MD) show the effect of the chemical structure of the DHPB on its inhibition efficiency. Moreover, the surface morphology of CS in 2 M HCl solution before and after DHPB addition using scanning electron microscope (SEM) and atomic force microscopy (AFM) confirms the protection of CS surface via the protective layer of adsorbed DHPB.

Synthesis of 2,3-Dihydro-1H-imidazo[1,2-a]pyridinium Systems by Halocyclization of 1-Alkenyl(propargyl)-2-aminopyridinium Halides

Reaction of 2-aminopyridine with allyl bromide, methallyl chloride, 2-bromoallyl bromide, and propargyl bromide in acetone furnished 2-amino-1-allyl-, methallyl-, (2-bromoallyl)-, and propargylpyridinium halides. 2-Amino-1-allyl(methallyl)pyridinium halides reacted with bromine and iodine to form 2-halomethyl-2,3-dihydro-1H-imidazo[1,2-a]pyridinium systems. 2-Amino-1-(2-bromoallyl)pyridinium bromide underwent heterocyclization under the action of bromine, and did not react with iodine. 2-Amino-1-propargylpyridinium bromide reacted with bromine and iodine to form 2-halomemylene-2,3-dihydro-1H-imidazo[1,2-a]pyridinium systems.

Synthesis and Characterization of Poly[N-(3-butynyl)-2-ethynylpyridinium bromide

A new conjugated polyelectrolyte with the N-(3-butynyl)pyridinium bromide was synthesized via the non-catalyst polymerization of 2-ethynylpyridine by using 4-bromo-1-butyne. The polymerization proceeded well to give the resulting poly[N-(3-butynyl)-2-ethynylpyridium bromide] in 75% yield. The chemical structure of poly[N-(3-butynyl)-2-ethynylpyridium bromide] was characterized by such instrumental methods as IR, NMR, and UV-visible spectroscopies to have the conjugated backbone system with the designed substituents. The electro-optical and electrochemical properties of polymer were measured and discussed. Comparing absorption spectrum and cyclic voltammetry data, this polymer had the HOMO and LUMO values of 5.33 and 3.35 eV, which means the band gap of 1.98 eV.

Preparation of porous uranium oxide hollow nanospheres with peroxidase mimicking activity: application to the colorimetric determination of tin(II).

Porous uranium oxide hollow sphere nanoparticles were synthesized in ionic liquids under hydrothermal conditions. Various precipitating agents and ionic liquids were investigated to determine their respective impact on the resultant uranium oxide morphologies. Using hydrazine hydrate as precipitating agent and N-butyl pyridinium bromide as templating agent, aporous-hollow structure was created with a surface area of 1958 m2.g-1 and an average pore diameter of 30nm. The nanoparticles revealed high peroxidase-mimicking activity. This was evaluated by using the peroxidase substrate 3,3',5,5'-tetramethylbenzidine (TMB) that is catalytically oxidized by H2O2 to give oxidized TMB (oxTMB) which is blue (with an absorption peak at 652nm). The material was used as a nanozyme for colorimetric detection of Sn2+. Meanwhile, it is found that BSA strongly improves the catalytic activity of the nanozyme, while Sn(II) inhibits its activity. Thus, a colorimetric method for Sn2+ detection was designed. The method works in the 0.5-100μM Sn(II) concentration range and has a lower detection limit of 0.36μM (at S/N = 3). Graphical abstract The catalytic activity of porous-hollow nano-UO2 toward the oxidation of 3,3',5,5'-tetramethylbenzidine by H2O2 is remarkably improved in the presence of bovine serum albumin, while tin(II) inhibits its activity. This finding has been applied to design a method for colorimetric quantification of tin(II) in water samples.

Pyridinium bromide as a new mediator for electrochemical transformations involving CH-acids

Pyridinium bromide has been tested as a new mediator for electrochemical synthesis of functionalized cyclopropane from alkylidenemalononitriles and CH-acids. The process was performed in an undivided cell with the use of substoichiometric amount of PyHBr that serves both as a mediator and a supporting electrolyte, and MeOH or MeCN as the solvents.

(Vapor + liquid) phase equilibria of an aqueous solution of bromide-based ionic liquids – measurements, correlations and application to absorption cycles

In this work, thermodynamic and physicochemical properties including (vapor + liquid) equilibria (VLE), density and dynamic viscosity of binary mixtures composed of bromide-based ionic liquid (IL) and water were measured as a function of IL mole fraction in a wide range of temperature. The aqueous solution of the following ILs: 1-ethyl-1-methylpiperidinium bromide, ethylpyridinium bromide, 1-(2-hydroxyethyl)pyridinium bromide, 1-ethyl-1-methyl-morpholinium bromide, 1-hydroxyethyl-1-methylmorpholinium bromide, and N-ethyl-N,N-dimethyl-N-hydroxyethylammonium bromide have been tested for potential applications as working fluids in absorption refrigeration technology. The isothermal VLE has been measured by an ebulliometric method within a temperature range from T = (338.15–368.15) K and pressure up to 85 kPa and correlated using Redlich-Kwong equation of state. This work is a continuation of our systematic investigation of an aqueous solution of ionic liquids as a potential working fluid in absorption refrigeration technology. The summary of this research is the modeling of the theoretical cycles using working fluids proposed in this paper. The calculated values of the coefficient of performance (COP) were compared to other ILs from available literature and {LiBr + water} system, conventionally used on the industrial scale in absorption refrigeration technology.

Bromination of bis-(pyridin-2-yl) diselenide in methyl-ene chloride: the reaction mechanism and crystal structures of 1H-pyridine-2-selenenyl dibromide and its cyclo-adduct with cyclo-pentene (3aSR,9aRS)-2,3,3a,9a-tetra-hydro-1H-cyclo-penta-[4,5][1,3]selenazolo[3,2-a]pyridinium bromide.

1H-Pyridine-2-selenenyl dibromide, C5H5NSeBr2, 1, is a product of the bromination of bis-(pyridin-2-yl) diselenide in methyl-ene chloride recrystallization from methanol. Compound 1 is essentially zwitterionic: the negative charge resides on the SeBr2 moiety and the positive charge is delocalized over the pyridinium fragment. The C-Se distance of 1.927 (3) Å is typical of a single bond. The virtually linear Br-Se-Br moiety of 178.428 (15)° has symmetrical geometry, with Se-Br bonds of 2.5761 (4) and 2.5920 (4) Å, and is twisted by 63.79 (8)° relative to the pyridinium plane. The Se atom forms an inter-molecular Se⋯Br contact of 3.4326 (4) Å, adopting a distorted square-planar coordination. In the crystal, mol-ecules of 1 are linked by inter-molecular N-H⋯Br and C-H⋯Br hydrogen bonds, as well as by non-covalent Se⋯Br inter-actions, into a three-dimensional framework. (3aSR,(9aRS)-2,3,3a,9a-Tetra-hydro-1H-cyclo-penta[4,5][1,3]selenazolo[3,2-a]pyridinium-9 bromide, C10H12NSe+·Br-, 2, is a product of the cyclo-addition reaction of 1 with cyclo-pentene. Compound 2 is a salt containing a selenazolopyridinium cation and a bromide anion. Both five-membered rings of the cation adopt envelope conformations. The dihedral angle between the basal planes of these rings is 62.45 (11)°. The Se atom of the cation forms two additional non-covalent inter-actions with the bromide anions at distances of 3.2715 (4) and 3.5683 (3) Å, attaining a distorted square-planar coordination. In the crystal, the cations and anions of 2 form centrosymmetric dimers by non-covalent Se⋯Br inter-actions. The dimers are linked by weak C-H⋯Br hydrogen bonds into double layers parallel to (001).

Rapid sequential detection of Hg2+ and biothiols by a probe DNA—MOF hybrid sensory system

A one-dimensional (1D) metal–organic framework (MOF) of [Cu(Cdcbp)(H2O)2·2H2O]n (1, H3CdcbpBr = 3-carboxyl-(3,5-dicarboxybenzyl)-pyridinium bromide) has been synthesized and characterized. MOF 1 features a cationic Cu2+ center, conjugated tricarboxylate ligand bearing positively charged pyridinium and uncoordinated carboxylate groups within its skeleton. These features enable MOF 1 to tightly adsorb thymine rich (T-rich) single-stranded DNA (ss-DNA) probe labeled with carboxyfluorescein (FAM) (denote as P-DNA) through π-stacking, electrostatic interactions and/or hydrogen bonding to give a hybrid complex (denote as P-DNA@1), and quenches its fluorescence via a photo-induced electron transfer (PET) process. The formed P-DNA@1 hybrid can thus function as a sensing platform for the detection of Hg2+, driven by the formation of hairpin-like double-stranded DNA (ds-DNA@Hg2+) with a T-Hg-T coordination motif, and subsequently dissociated into the solution due to its more rigid nature than ss-DNA, leading to the recovery of FAM fluorescence. In the presence of biothiols, including cysteine (Cys), homocysteine (Hcy) and glutathione (GSH), the strong coordination interaction between Hg2+ and the mercapto function serves to sequestrate the Hg2+ from the ds-DNA@Hg2+ duplex. The released ss-DNA, in turn, are re-adsorbed by MOF 1, leading to the formation of the initial P-DNA@1 state with fluorescence quenching. As such, P-DNA@1 detects Hg2+ and biothiols Cys/Hcy/GSH in sequence with detection limits of (2.3 ± 0.8) nM and (29.6 ± 0.1) nM/(19.8 ± 0.5) nM/(10.2 ± 0.1) nM. The sensing process is efficient and selective with instantaneous response time. The detection mechanism was further validated by circular dichroism (CD), and simulation studies using Molecular Operating Environment (MOE) package.

Experimental and computational investigation of a DNA-shielded 3D metal-organic framework for the prompt dual sensing of Ag+ and S2.

We herein report an efficient Ag+ and S2− dual sensing scenario by a three-dimensional (3D) Cu-based metal–organic framework [Cu(Cdcbp)(bpea)]n (MOF 1, H3CdcbpBr = 3-carboxyl-(3,5-dicarboxybenzyl)-pyridinium bromide, bpea = 1,2-di(4-pyridinyl)ethane) shielded with a 5-carboxytetramethylrhodamine (TAMRA)-labeled C-rich single-stranded DNA (ss-probe DNA, P-DNA) as a fluorescent probe. The formed MOF-DNA probe, denoted as P-DNA@1, is able to sequentially detect Ag+ and S2− in one pot, with detection limits of 3.8 nM (for Ag+) and 5.5 nM (for S2−), which are much more lower than the allowable Ag+ (0.5 μM) and S2− (0.6 μM) concentration in drinking water as regulated by World Health Organization (WHO). The detection method has been successfully applied to sense Ag+ and S2− in domestic, lake, and mineral water with satisfactory recoveries ranging from 98.2 to 107.3%. The detection mechanism was further confirmed by molecular simulation studies.

Synthesis and characterization of new hydrolytic-resistant dental resin adhesive monomer HMTAF

ABSTRACTHydrolytic and enzymatic degradation of resin adhesives over time has been mainly attributed to secondary caries formation of methacrylate-based tooth-colored resin-based composite restorations. Ability of resin adhesive monomers to infiltrate into demineralized dentin forming stiff polymer matrix and potentially bonding to tooth structure is also a crucial property. The only commercially available antibacterial monomer, 12-methacryloyloxydodecyl pyridinium bromide (MDPB), is a quaternary ammonium methacrylate. This methacrylate monomer undergoes hydrolytic degradation, and could not bond to tooth structure. In this study, a new hydrolytic resistant monomer HMTAF was synthesized. It is methacrylamide-based monomer that, unlike methacrylate, is highly resistant to hydrolysis. Its molecular structure has particular functional groups; quaternary ammonium fluoride salt with potential antibacterial fluoride-releasing activity, hydroxyl and amide group with hydrogen bonding potential to dentin collagen. Hydroxyl group also increases monomer hydrophilicity for better penetration into water-saturated dentin and sufficient resin-dentin bond. The synthesized HMTAF and its polymer showed no hydrolytic degradation in acidic environment, while MDPB and its polymer were partially decomposed under this challenge. The conversion of monomer HMTAF to polymer was illustrated by FT-IR. The results indicated that HMTAF is highly resistant to hydrolysis, polymerizable and non-cytotoxic to Vero cell lines. It is a potential monomer to be incorporated into resin adhesives for improving hydrolytic and enzymatic resistance.

Micellization of selenium-containing cationic surfactants with different headgroups in aqueous solution

Redox-responsive surfactant based on selenium atom has recently attracted considerable interests. Herein, we have designed and synthesized three selenium-containing cationic surfactants with different headgroups, including N-(benzylselanyl-undecyl)-N,N,N-trimethyl ammonium bromide (BSeTAB)/pyridinium bromide (BSePyB)/methylpyrrolidinium bromide (BSeMPB). Their micellization in dilute solution was investigated by surface tension and conductivity, and was related to redox-induced change in molecular structure. Both 1H NMR and ESI-MS spectra demonstrated that selenide in the reduced form is transformed into selenoxide after oxidation with H2O2, whatever the headgroup is. The formation of selenoxide not only increases the hydrophilicity of surfactant, resulting in a more negative $$ \Delta {G}_{\mathrm{ads}}^o $$ , larger cmc, cmc/C20 ratio, and Gmin, compared to the reduced forms, but also provides a new polar headgroup, making it behave like bola-type structure and enhancing the hydrophilicity. The relatively smaller cmc, larger cmc/C20 ratio, and more negative $$ \Delta {G}_m^o $$ value all revealed that the pyridinium or pyrrolidinium polar headgroup is more favorable for the micelle formation than the trimethylammonium group. The thermodynamic parameters showed that the micellization is transformed from entropy-driven mode to enthalpy-driven mode with increasing temperature and the transition temperature at which $$ \Delta {H}_m^o $$ equals to $$ -\mathrm{T}\Delta {S}_m^o $$ is lowest for BSeMPB, and highest for BSePyB.

Synthesis and Characterization of 1‐(Carboxymethyl)Pyridinium Bromide [CMPy]Br Molten Salt: Application as a Novel Nanocatalyst for the Synthesis of Bis‐Naphthodipyrans

AbstractHerein, a convenient method for the synthesis of bis‐naphthodipyrans from the condensation of naphthalene‐2,3‐diol, malononitrile and various aromatic aldehydes using acetic acid functionalized pyridinium salt 1‐(carboxymethyl)pyridinium bromide [CMPy]Br as a novel, efficient, reusable and nanocatalyst is described. The synthesized catalyst was fully characterized by using various techniques such as single crystal X‐ray diffraction (SCXRD), 1H NMR, 13C NMR, Fourier transform infrared spectroscopy (FT‐IR), mass spectra, scanning electron microscope (SEM), transmission electron microscopy (TEM), X‐ray diffraction analysis (XRD) and Differential thermal analysis (TG/DTG). The major advantages of the convenient method are high yields, short reaction time, and reusability of the catalyst.

Bidentate Iminophosphorane-NHC Ligand Derived from the Imidazo[1,5-a]pyridin-3-ylidene Scaffold

The synthesis of the bifunctional iminophosphorane-NHC (1) based on the imidazo[1,5-a]pyridin-3-ylidene (IPy) platform is reported. Its imidazo[1,5-a]pyridinium salt precursor [1·H](X) was readily obtained by an efficient three-component coupling reaction between 5-bromoimidazo[1,5-a]pyridinium bromide, sodium azide, and triphenylphosphine according to a SNAr/Staudinger reaction sequence. The stable free carbene 1 was generated by deprotonation of [1·H](X) with potassium bis(trimethylsilyl)amide, and its coordination ability toward various transition-metals was evaluated, either upon direct metalation of the free carbene or by transmetalation from a silver(I) NHC complex. While the ligand 1 is singly bounded through the carbene carbon atom in the latter complex, it behaves as a chelating bidentate ligand in all other complexes that were prepared, including the cationic and neutral palladium(II) complexes [Pd(allyl)(κ2C,N -1)](OTf) ([5](OTf)) and [PdCl2(κ2C,N -1)] (7), and the cationic rhodium(I) complexes...

The influence of cholesterol on the generation of radicals in mixed reverse micelles of cationic surfactants with hydroperoxides

Cationic surfactants (S+) and acetylcholine (ACh), the most important neurotransmitter playing an essential role in the neuromuscular and cognitive activity of living beings, form mixed reverse micelles with hydroperoxides (ROOH) in organic media, where ROOH decay into free radicals is catalytically accelerated. Adding cholesterol (Chol, 30 mol.%) to pyridinium (СРВ) and cetyltimethylammonioum (СТАВ) bromides, reduces the radical generation rate in ROOH catalytic decay several times. However, a higher radical initiation rate is observed in the case of less ordered and larger ACh–ROOH reverse micelles. A Chol additive does not essentially affect the size of СТАВ and СРВ micelles with hydroperoxides but results in their decrease in the case of ACh–ROOH.

Chemical Combination of 4-(4-Hydroxybut-2-ynyl) Pyridine and 3-Methylbenzenamine to Construct an Effective Inhibitor: Theoretical and Practical Investigation

A new inhibitor, N-m-benzylamine-4-(4-hydroxybut-2-ynyl) pyridinium bromide (designated as BAP) was designed and synthesized. Quantum chemical calculation and molecular dynamics (MD) simulations manifested that BAP, a compound by covalent combination of 4-(4-hydroxybut-2-ynyl) pyridine (HYP) and 3-methyl benzenamine (MBA), functioned better than did the two moieties (HYP and MBA) for X70 steel corrosion inhibition. The corrosion inhibition investigation revealed that the experiment outcome was in good consistency with the theoretical calculation. The inhibition efficiency of BAP was 95.72% for X70 steel in 5 M HCl at 90 0C. BAP adsorbed on X70 steel surface, obeyed Langmuir isotherm, retarded both the metal dissolution and the hydrogen evolution, and enhanced greatly the acid corrosion resistance of X70 steel. Comparative test demonstrated that the inhibition efficiency of BAP was about 10 times of that for MAB and 8 times of that for HYP albeit the concentration of BAP was tenth of that of HYP and MBA. The experimental investigation backs up the theoretical calculation and manifests intramolecular synergism of the structure moieties being beneficial to design of high effective inhibitors.

Growth inhibition and oxidative stress caused by four ionic liquids in Scenedesmus obliquus: Role of cations and anions

Ionic liquids (ILs) are widely used in various industrial applications. However, they are considered potential toxins in aquatic environments because of their physical stability and solubility. The growth inhibition and oxidative stress induced by four ionic liquids with different cations and anions on the green algae Scenedesmus obliquus was investigated in this study. The order of growth inhibition was 1‑hexyl‑3‑methylimidazolium nitrate ([HMIM]NO3) > 1‑hexyl‑3‑methylimidazolium chloride ([HMIM]Cl) > N‑hexyl‑3‑metylpyridinium bromide ([HMPy]Br) > N‑hexyl‑3‑metylpyridinium chloride ([HMPy]Cl). Imidazolium IL had a higher growth inhibition effect than pyridinium IL, nitrate IL and bromide IL had a higher effect than chloride IL. Reactive oxygen species (ROS) level in S. obliquus increased with increasing IL concentrations. Green fluorescence in [HMIM]Cl treated algae showed increased brightness compared to the [HMPy]Cl treatment, and [HMIM]NO3 treatment produced increased brightness compared to the [HMPy]Br treatment, suggesting that higher ROS levels were induced by [HMIM]Cl and [HMIM]NO3. Soluble protein, catalase (CAT), and superoxide dismutase (SOD) activities were stimulated at lower concentrations but were inhibited at higher concentrations. Regression analysis suggested that ROS level is the main index responsible for oxidative stress induced by the four ILs. The ILs induced oxidative damage on S. obliquus, and ROS in high concentration treatments could not be effectively removed by the antioxidant system, leading to oxidative damage and ultimately resulting in growth inhibition and cell death.

Hybrid polysaccharide beads for enhancing adsorption of Cr(VI) ions

Alginate (Alg) beads were modified by the adsorption of poly(4-vinyl-N-pentyl pyridinium bromide (QVPV) polycation, aiming towards the adsorption of Cr(VI) ions from aqueous solution. The adsorption isotherm of QPVP onto Alg beads fitted well the Langmuir adsorption model, yielding maximum adsorption capacity (qmax) of 91 mg g−1 and high constant affinity of 7.53 × 107 L mol−1. X-ray photoelectron spectroscopy and elemental analysis indicated that the QPVP chains were mainly on the Alg beads surface. The adsorption of Cr(VI) in the dilute range (0.5 mg L−1 to 10 mg L−1) on Alg-QPVP beads in batch system was investigated by means of flame atomic absorption spectrometry. Under optimal adsorption conditions (HNO3, pH 2, 6 mg of dried beads, 15 mL of solution, 30 min contact time) the nonlinear fitting with Langmuir model yielded qmax of 18 mg g−1 and constant affinity of 124 L mol−1, whereas the qmax of 156 mg g−1 and adsorption energy of 9.8 kJ mol−1 were obtained from linear fitting with Dubinin-Radushkevitch model. The breakthrough curves obtained for Cr(VI) at 100 mg L−1 in the fixed bed column system were fitted to the Adams-Bohart and Thomas models. Fitting parameters indicated a fast dynamic adsorption process, which takes place mainly on the beads surface. The reduction of adsorbed Cr(VI) ions to Cr(III) by ascorbic acid, a non-toxic biological reductant, allowed the fast and complete recycling of the Alg-QPVP beads for at least 20 times without losing performance. Novel Alg-QPVP beads presented attractive features for dynamic process, such as quickness (k > 1 × 10−3 L mg−1 min−1) and high adsorption capacity in the dilute range, low cost and recycling possibility.

Preparation and Evaluation of some polyaniline/ cycloadductcomposites for their biocidalactivity against some biofouling-causing organisms

Cycloadducts of 3-Hydroxy-1-phenacyl pyridinium bromide (1) and 3-Hydroxy-1-(4-nitrobenzyl) pyridinium chloride (2) with vinyl trimethylsilane, methyl sulfonyl chloride and vinyl triphenylphosphonium bromide were prepared. Six novel polyaniline/ cycloadduct (PANI/CY) composites were prepared by the polymerization of aniline in the presence of different weight percentages of cycloadduct were characterized using Fourier transform infrared (FTIR) spectroscopy, Mass spectrum (MS) and Nuclear magnetic resonance (NMR),Transmission electron microscopy (TEM). Their potential as antibiofouling agents was evaluated. Antimicrobial /macrobial fouling activity were conventional using inhibition zone, serial tube dilution methods and mortality tests respectively.

Nano γ-Fe2O3-Quinuclidine-Based Catalyst as a Recyclable Organic Base for the Diastereoselective Synthesis of Trans-2,3-Dihydrofuro[3,2-C]Coumarins

A nano γ-Fe2O3-quinuclidine-based catalyst as a new, magnetically recyclable heterogeneous organic base was synthesised and used in the efficient synthesis of a series of 11 trans-3-aroyl-2-(4-halobenzoyl)-2,3-dihydro-4H-furo[3,2-c]chromen-4-ones by the reaction of N-(2-(4-halobenzoyl)-2-oxoethyl)pyridinium bromide with 4-hydroxycoumarin and an aryl glyoxal. The catalyst was easily isolated from the reaction mixture using a magnetic bar and reused at least 10 times without significant decrease in its activity.