Quaternary Onium Research Articles

Proton conduction in tetra-n-butylammonium bromide semiclathrate hydrate

Clathrate hydrate as well as ice has been spotlighted as promising materials to investigate the properties of hydrogen-bonded networks formed by the water molecules. In the semiclathrate hydrate (SCH, a kind of clathrate hydrate) consisting of host water molecules and guest quaternary onium salts, the anion takes part in the hydrogen-bonded networks with the water molecules. In the present study, we measured the electrical conductivity and electrical relaxation time in the single-crystalline tetra-n-butylammonium bromide (TBAB) SCH by electrochemical impedance spectroscopy. The results clearly revealed that the conduction carrier was proton. The electrical relaxation time of proton conduction in TBAB SCH was similar to the reorientation time of the water molecules in TBAB SCH estimated by the results of nuclear magnetic resonance.

Design of Thermoplastic Polyurethanes with Conferred Antibacterial, Mechanical, and Cytotoxic Properties for Catheter Application.

Thermoplastic polyurethanes (TPUs) are proposed as suitable solution for the fabrication of biocompatible catheters with appropriate mechanical parameters and confirmed antibacterial and cytocompatible properties. For this purpose, a series of quaternary ammonium salts (QASs) and quaternary phosphonium salts (QPSs) based monomers were prepared followed by the determination of their minimal inhibitory concentrations (MICs) against Gram-positive Staphylococcus aureus (S. aureus) and Gram-negative Pseudomonas aeruginosa (P. aeruginosa). A combination of the most active ammonium (QAS-C14) and phosphonium (QPS-TOP) salts led to a MIC down to 2.4 μg/mL against S. aureus and 9 μg/mL against P. aeruginosa, corroborating the existence of a synergistic effect. These quaternary onium salt (QOS) units were successfully incorporated along the polymer chain, as part of a two-step synthesis approach. The resulting TPU-QOS materials were subsequently characterized through thermal, mechanical, and surface analyses. TPU-Mix (combining the most active QAS-C14 and QPS-TOP units) showed the highest antibacterial efficiency, confirming the synergistic effect between both QOS groups. Finally, an MTT assay on the SiHa cell line revealed the low cytotoxicity level of these polymeric films, making these materials suitable for biomedical application. To go one step further in the preindustrialization approach, proof of concept regarding the catheter prototype fabrication based on TPU-QAS/QPS was validated by extrusion.

(Digital Presentation) Phosphonium Salts As Potential Guest Substances for Ionic Semiclathrate Hydrates

Semiclathrate hydrates (SCHs) are ionic crystalline compounds consisting of an organic guest cation in several cages formed by hydrogen bonding of water1. SCHs have recently been considered for application to air conditioning systems and refrigeration systems since desirable equilibrium temperatures and the considerable decomposition enthalpies are observed in the solid-liquid equillibria2. Ionic guest substances of SCHs include quaternary onium compounds such as tetrabutylammonium2 and tetrabutylphosphonium based salts3. We report here the preparation and thermodynamic properties of SCHs based on quaternary phosphonium bromides containing an unsaturated carbon-carbon double bond, as shown in Fig. 1, in comparison with the conventional saturated phosphonium salt, such as tetrabutylphosphonium bromide (P4444-Br).The unsaturated phosphonium bromides (P444(1All)-Br and P444(2All)-Br) were synthesized by quaternarization reaction of tributylphosphine with alkenyl bromides in a nitrogen atmosphere. The aqueous solutions were prepared from 5 to 50 w/w %. After thorough stirring, the aqueous solutions were cooled in a freezer to form SCHs. The SCHs were immersed into a thermostatic bath at 268 K for at least 1 day. The temperature in the thermostatic bath was raised from 268 K at a rate of 0.1 K/step (1 step: more than 5 h). The equilibrium temperatures were defined as the temperature at which SCHs were completely dissolved. The ionic crystal structure was analyzed by a powder X-ray diffraction (PXRD) technique, the dissociation enthalpy was measured by a micro differential scanning calorimeter (μDSC).Fig. 2 depicts the solid-liquid phase equilibrium diagram representing the phase equilibrium temperatures of SCHs. The equilibrium temperature of P444(1All)-Br SCH was higher than P4444-Br SCH. These results might be due to the steric effect of alkenyl group. As shown in Fig. 3, the ionic crystal structure of both P444(1All)-Br and P444(All)-Br SCHs were orthorhombic. The dissociation enthalpy of P444(1All)-Br SCHs and P444(2All)-Br SCHs were 188 J/g and 199 J/g, respectively. The unsaturated phosphonium bromides would be regarded as potential guest substances used for latent heat storage materials in air conditioning systems.References M. Oshima, et al, J. Chem. Thermodynamics, 90, 277 (2015).H. Oyama, et al, Fluid Phase Equilibria, 234, 131 (2005).J. Shimada, et al, Chem. Eng. Sci., 236, 116514 (2021). Figure 1

Intermolecular Interaction of Tetrabutylammonium and Tetrabutylphosphonium Salt Hydrates by Low-Frequency Raman Observation.

Semi-clathrate hydrates are attractive heat storage materials because the equilibrium temperatures, located above 0 °C in most cases, can be changed by selecting guest cations and anions. The equilibrium temperatures are influenced by the size and hydrophilicity of guest ions, hydration number, crystal structure, and so on. This indicates that intermolecular and/or interionic interaction in the semi-clathrate hydrates may be related to the variation of the equilibrium temperatures. Therefore, intermolecular and/or interionic interaction in semi-clathrate hydrates with quaternary onium salts was directly observed using low-frequency Raman spectroscopy, a type of terahertz spectroscopy. The results show that Raman peak positions were mostly correlated with the equilibrium temperatures: in the semi-clathrate hydrates with higher equilibrium temperatures, Raman peaks around 65 cm−1 appeared at a higher wavenumber and the other Raman peaks at around 200 cm−1 appeared at a lower wavenumber. Low-frequency Raman observation is a valuable tool with which to study the equilibrium temperatures in semi-clathrate hydrates.

2-3-3 テトラヒドロフランに第四級オニウム塩を混合したクラスレートハイドレートの熱力学的安定性

2-3-3 テトラヒドロフランに第四級オニウム塩を混合したクラスレートハイドレートの熱力学的安定性

Biocidal Polymers: Synthesis, Characterization and Antimicrobial Activity of Bis-Quaternary Onium Salts of Poly(aspartate-co-succinimide)

Microbial multidrug resistance presents a real problem to human health. Therefore, water-soluble polymers based on poly(aspartate-co-succinimide) were synthesized via reaction of poly(aspartate-co-succinimide) with bis-quaternary ammonium or quaternary salts. The resultant copolymers were characterized by various techniques such as FTIR, TGA, 1HNMR, 13CNMR and elemental microanalysis. Antimicrobial activities of the new onium salts were investigated against Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, and Salmonella typhi, and the fungi; Candida albicans, Aspergillus niger, Cryptococcus neoformans and Aspergillus flavus by agar diffusion method. Antimicrobial activity was studied in terms of inhibition zone diameters, in addition to the estimation of minimal inhibitory concentration (MIC) of the prepared compounds. A. niger and E. coli were the most affected microorganisms among the tested microorganisms with an inhibition zone of 19–21 (mm) in case of biocides, (V) and (VII). The obtained results showed that the quaternary onium salts have higher activity compared to the aspartate copolymer with MIC concentrations of 25 mg/mL for (VII) and (V) and 50 mg/mL for (VI) and (IV).

Water soluble bifunctional complex of tetrapyridino porphyrazinato zinc(II) as highly efficient catalyst for CO2 insertion into epoxide cycles

Abstract The highly active water soluble bifunctional catalyst of porphyrazinato zinc(II) ([Zn(2,3-tmtppa)](MeSO4)4) in which tmtppa stands for tetramethylated tetrapyridino porphyrazine was applied for cycloaddition reaction of CO2 into epoxides to obtain cyclic carbonates. It seems that our catalyst can act as an efficient phase transfer agent because of the presence of tetra positive groups in its structure which increased catalyst solubility in water. Accordingly, the CO2 fixation reaction was performed in water utilizing cheap, simple and commercially available potassium iodide co-catalyst instead of expensive quaternary onium salts (as co-catalyst) because of having the quaternized parts in the porphyrazine skeleton. The mentioned homogeneous catalytic system was adaptable to CO2 insertion into aliphatic, aromatic and functional epoxides efficiently and selectively under mild reaction conditions. Furthermore, our catalyst system was easily recovered and reused in at least three cycles without any decrease of catalytic activity.

Synthesis and characterization of aliphatic polysulfides by interfacial polycondensation of sodium tetrasulfide with dichloroalkanes in the presence of quaternary onium salts

Poly(alkylenetetrasulfide) [poly(R-S4-R)] polymers with R = Me, Et, or Bu are prepared from alkylene dichloride and sodium tetrasulfide by an interfacial polycondensation technique using two quarternary ammonium salts as phase transfer catalysts. FT-IR, X-ray, and elemental analysis have characterized the synthesized polymers. Thermal properties were measured by thermogravimetric analysis and calorimetric differential scanning. Swelling procedure was used to investigate the solvent resistance of the polymers.

Electrochemical Behavior of Selenophene in Quaternary Ammonium and Phosphonium Based Ionic Liquids

Room-temperature ionic liquids (RTILs) have been regarded as potential electrolytic media for electropolymerization processes.1 Many kinds of RTILs have been investigated for the electropolymerizations. For example, we have reported that a bis(fluorosulfonyl)amide (FSA) anion based imidazolium ionic liquid promoted the electropolymerization reaction of pyrrole and the anion doping into the polymerized film, improving the conductivity of the film.2 We also have applied the phosphonium based RTILs to the electropolymerization of pyrrole and thiophene, investigating the influence of the phosphonium RTILs on the polymerized film properties.3 However, electrosynthesis of polyselenophene in phosphonium RTILs has not been examined. In this work, we report the electropolymerization of selenophene in triethylpentylphosphonium FSA (P2225-FSA) (Fig. 1) and the effect of the phosphonium RTIL on the polyselenophene film properties. P2225-FSA was prepared according to the procedure we have previously reported,4 and dried under high vacuum at 80°C for 6 h before use. The electropolymerization of selenophene in P2225-FSA was carried out by cyclic voltammetry (CV) method using a three-electrode cell equipped with a working electrode of platinum or transparent glass electrode and an IL-based Ag/Ag+ reference electrode. Figure 2 showed the cyclic voltammograms for the electropolymerization of selenophene in P2225-FSA. In the first cycle, the oxidation peak current value of about 0.2 mA was shown around +1.7 V vs Ag/Ag+, and the current decayed with each cycle. This closely resembles the electrochemical behavior observed in CVs using π-conjugated aromatic compounds such as pyrrole and thiophene as substrates. 3 After 10 cycles, a black thin film was grown on the surface of the working electrode, and the oxidation current observed in this CV seems to be due to the electropolymerization reaction of selenophene. Furthermore, we will discuss the comparison between the behaviors in various quaternary onium based ionic liquids from the viewpoint of the morphology of the polymer film grown on the working electrode. References K. Sekiguchi, et al, J. Electroanal. Chem. , 1, 557 (2003).K. Tsunashima, et al, ECS Electrochem. Lett., 3, G1 (2014).K. Nishihata, et al, ECS Trans., 75, 99 (2016).K. Tsunashima, et al, Electro cheml. Commun. , 13, 178 (2011). Figure 1

Thermodynamic properties of tetra-n-butylammonium 2-ethylbutyrate semiclathrate hydrate for latent heat storage

The quaternary onium salt-based semiclathrate hydrates have been investigated in many kinds of fields such as latent heat storage materials and gas separation media. In the present study, equilibrium (temperature−composition) relations in the tetra-n-butylammonium 2-ethylbutyrate (TBA-2 EB) semiclathrate hydrate system have been measured. In addition, thermodynamic and spectroscopic properties of TBA-2 EB semiclathrate hydrate were analyzed. The maximal equilibrium temperature and stoichiometric concentration of TBA-2 EB semiclathrate hydrate was 283.22 ± 0.05 K and x1 = 0.0281 ± 0.0007, respectively. The crystal lattice of TBA-2 EB semiclathrate hydrate, determined by the single crystal X-ray diffraction, was tetragonal. Other properties, not only Raman spectrum but also the maximum allowable degree of supercooling, in the TBA-2 EB semiclathrate hydrate system were similar to those in the tetra-n-butylammonium bromide (TBAB) hydrate. The TBA-2 EB semiclathrate hydrate would be an alternative to TBAB hydrate as a halogen-free semiclathrate hydrate system.

Bifunctional phase-transfer catalysts for fixation of CO2 with epoxides under ambient pressure

A series of bifunctional phase-transfer catalysts with a quaternary onium center and a hydrogen-bonding donor group were prepared for the fixation of CO2 with epoxides under mild conditions by using a CO2 balloon (1 atm) to produce cyclic carbonates up to 95% yields.

Macrocyclic Hosts in Asymmetric Phase-Transfer Catalyzed Reactions

The introduction and development of neutral macrocyclic hosts capable of complexing ions within their pre-organized cavity, has been of utmost importance in supramolecular chemistry. Their ability to form stable organic-soluble metal–macrocycle complexes opened up the way to their application in phase-transfer catalysis (PTC) as a viable alternative to quaternary onium salts. In particular, their conformationally rigid preorganized backbone, accommodating organic substrates in defined orientations, promotes highly efficient stereoselective reactions. This short review summarizes the applications of neutral macrocyclic hosts in stereoselective PTC, highlighting the difference and possible complementarity with quaternary ammonium salts.1 Introduction2 Crown Ethers and Related Coronands2.1 Enantioselective PTC with Chiral Macrocyclic Coronands2.2 Enantioselective PTC Reactions Catalyzed by Chiral Quaternary Ammonium Salts with Achiral Crown Ether Co-catalysts3 Cyclic Peptoids4 Miscellaneous Chiral Macrocyclic Hosts5 Summary and Outlook

Highly Active Organic Lewis Pairs for the Copolymerization of Epoxides with Cyclic Anhydrides: Metal-Free Access to Well-Defined Aliphatic Polyesters

Polyester synthesis from the alternating copolymerization of epoxides with cyclic anhydrides via a metal-free route remains a key challenge. This work reports the development of a highly active organocatalytic route for the copolymerization of a spectrum of epoxides and cyclic anhydrides. Fully alternating polyesters were synthesized by a variety of organic Lewis acid–base pairs including organoboranes and quaternary onium salts. The effect of the acidity, type, and size of Lewis pairs on the catalytic activity and selectivity of the copolymerization is presented. The undesirable transesterification and etherification were effectively suppressed even in the case of complete conversion of the cyclic anhydride. This could be ascribed to the formation of a unique tetracoordinate bond-carboxylate (or alkoxide) anion. The Lewis pairs are highly active, with a turnover frequency of 102 and 303 h–1 for the copolymerization of propylene oxide with maleic anhydride and phthalic anhydride, respectively, at 80 °C. B...

Highly Efficient One-Pot Synthesis of COS-Based Block Copolymers by Using Organic Lewis Pairs.

A one-pot synthesis of block copolymer with regioregular poly(monothiocarbonate) block is described via metal-free catalysis. Lewis bases such as guanidine, quaternary onium salts, and Lewis acid triethyl borane (TEB) were equivalently combined and used as the catalysts. By using polyethylene glycol (PEG) as the macromolecular chain transfer agent (CTA), narrow polydispersity block copolymers were obtained from the copolymerization of carbonyl sulfide (COS) and propylene oxide (PO). The block copolymers had a poly(monothiocarbonate) block with perfect alternating degree and regioregularity. Unexpectedly, the addition of CTA to COS/PO copolymerization system could dramatically improve the turnover frequency (TOF) of PO (up to 240 h−1), higher than that of the copolymerization without CTA. In addition, the conversion of CTA could be up to 100% in most cases, as revealed by 1H NMR spectra. Of consequence, the number-average molecular weights (Mns) of the resultant block copolymers could be regulated by varying the feed ratio of CTA to PO. Oxygen-sulfur exchange reaction (O/S ER), which can generate randomly distributed thiocarbonate and carbonate units, was effectively suppressed in all of the cases in the presence of CTA, even at 80 °C. This work presents a versatile method for synthesizing sulfur-containing block copolymers through a metal-free route, providing an array of new block copolymers.

Solvate and protic ionic liquids from aza-crown ethers: synthesis, thermal properties, and LCST behavior.

In recent years, solvate and protic ionic liquids (ILs) have attracted much attention. We synthesized both types of ILs from alkyl aza-crown ethers (L = N-propyl-1-aza-15-crown-5 (L1) and N-C6F13C2H4-1-aza-15-crown-5 (L2)). The solvate ILs [ML][Tf2N] (M = Na+, K+) were solids (Tm = 58-68 °C), whereas the solvate ILs [ML][Tf2N] (M = Li+, Ag+) and protic ILs [HL][Tf2N] were liquids with low glass transition temperatures. The ILs containing Na ions were more crystalline and exhibited higher melting points than the other ILs. The decomposition temperatures of the protic ILs were higher than those of the solvate ILs. A protic IL with a paramagnetic anion, [HL1][FeCl4] (Tm = 70.5 °C), was also synthesized and its crystal structure was determined. The solvate ILs [NaL2][X] (X = Cl-, CF3CO2-, TsO-, PhSO3-) exhibited a lower critical solution temperature (LCST)-type behavior in water. The effects of salt addition on the LCST of L2 were also investigated. The LCST of these ILs generally increased with increasing hydrophilicity or basicity of the counter anion. This tendency, which is nearly opposite to that of ILs with quaternary onium cations, is ascribed to the amphiphilic nature of the cation. The corresponding protic ILs did not exhibit LCST behavior.

Perfectly Alternating and Regioselective Copolymerization of Carbonyl Sulfide and Epoxides by Metal‐Free Lewis Pairs

AbstractThe preparation of perfectly alternating and regioslective copolymers derived from the copolymerization of carbonyl sulfide (COS) and epoxides by metal‐free Lewis pair catalysts composed of a Lewis base (amidine, guanidine, or quaternary onium salts) and a Lewis acid (triethyl borane) is described. Colorless and highly transparent copolymers of poly(monothiocarbonate) were successfully obtained with over 99 % tail‐to‐head content and high molecular weight (up to 92.5 kg mol−1). In most instances, oxygen–sulfur exchange reactions (O/S ERs), which would generate random thiocarbonate and carbonate units, were effectively suppressed. The turnover frequencies (TOF) of these Lewis pair catalyzed processes were as high as 119 h−1 at ambient temperature.

Perfectly Alternating and Regioselective Copolymerization of Carbonyl Sulfide and Epoxides by Metal-Free Lewis Pairs.

The preparation of perfectly alternating and regioslective copolymers derived from the copolymerization of carbonyl sulfide (COS) and epoxides by metal-free Lewis pair catalysts composed of a Lewis base (amidine, guanidine, or quaternary onium salts) and a Lewis acid (triethyl borane) is described. Colorless and highly transparent copolymers of poly(monothiocarbonate) were successfully obtained with over 99 % tail-to-head content and high molecular weight (up to 92.5 kg mol-1 ). In most instances, oxygen-sulfur exchange reactions (O/S ERs), which would generate random thiocarbonate and carbonate units, were effectively suppressed. The turnover frequencies (TOF) of these Lewis pair catalyzed processes were as high as 119 h-1 at ambient temperature.

Phase-Transfer and Ion-Pairing Catalysis of Pentanidiums and Bisguanidiniums.

Catalysts accelerate biological processes and organic reactions in a controlled and selective fashion. There are continuing efforts in asymmetric catalysis to develop efficient catalysts with broad reaction scope and industrial practicability. Among the various modes of asymmetric catalysis, phase-transfer catalysis has attracted intense interest due to its facile scale up and low catalyst loading. Chiral quaternary ammonium and phosphonium salts are well-studied classes of chiral phase-transfer catalysts, and they are typically composed of sp3-hybridized quaternary onium salts. In this Account, we describe our recent attempts to develop N-sp2-hybridized guanidinium-type salts as efficient phase-transfer catalysts as well as ion-pair catalysis based on N-sp2 hybridized bisguanidinium-type salts. The sp2-quaternized ammonium salts, pentanidiums, which contain five nitrogen atoms in conjugation, displayed remarkable phase-transfer catalytic efficiency. We have shown that pentanidium can catalyze Michael additions of tert-butyl glycinate-benzophenone Schiff bases with various α,β-unsaturated acceptors, such as vinyl ketones, acrylates, and chalcones, in high enantioselectivities. The structurally amendable pentanidium phase-transfer catalysts supply diverse reactivity and selectivity to various other organic transformations, such as α-hydroxylation of 3-substituted-2-oxindoles, Michael addition of 3-alkyloxindoles with vinyl sulfone, and alkylation reactions of sulfenate anions and dihydrocoumarins. Pentanidium salts are applicable to enantioselective transformations on a preparative scale at low catalyst loading, allowing for the synthesis of a broad range of enantiopure compounds. From computational and experimental results, we also proposed that the halogenated pentanidium catalysts participated in halogen bonding and that this contributed to the excellent stereocontrol in alkylation reactions. Subsequently, we determined that chiral cations can direct functional anions besides basic anions in traditional Brønsted basic phase-transfer reactions, including metal-centered anions. We identified dicationic bisguanidinium as an excellent ion-pairing catalyst, first demonstrating that bisguanidinium formed an ion pair with permanganate and directed the anion in enantioselective dihydroxylation and oxohydroxylation of a,β-unsaturated esters. This initial success led us to explore chiral cationic ion-pairing catalysis as a general mode of catalysis. This mode of catalysis is at the interphase between organocatalysis, phase-transfer catalysis and organometallic catalysis. We then identified bisguanidinium diphosphatobisperoxotungstate and bisguanidinium dinuclear oxodiperoxomolybdosulfate ion pairs as the active catalysts in enantioselective sulfoxidations using aqueous H2O2 as the oxidant. The structure of the bisguanidinium dinuclear oxodiperoxomolybdosulfate ion pair was elucidated using single-crystal X-ray analysis. Bisguanidinium-catalyzed sulfoxidations emerged as a practical methodology for the synthesis of enantioenriched sulfoxides including armodafinil and lansoprazole, which are commercial drugs. Finally, we are also able to show that pentanidium and bisguanidinium hypervalent silicates are intermediates in enantioselective alkylations using silylamide as a Brønsted probase.

Quaternary onium modified SalenCoXY catalysts for alternating copolymerization of CO2 and propylene oxide: A kinetic study

Quaternary onium modulated SalenCoXY (X=Cl, Br, NO3; Y=phenoxy, benzene-1,4-bisoxy, benzene-1,3,5-trisoxy) catalysts incorporating the N,N′-bis(salicylidene)ethylene diaminato(Salen) ligand and quaternary onium units were designed, synthesized and applied to the copolymerization of CO2 and propylene oxide. The impact factors of the axial anion X, the counter anion Y and the property of quaternary onium group evidently affected PPC selectivity and degree of polymerization. Detailed kinetic investigations and mechanisms of the cycloaddition and copolymerization were documented and discussed. A second order of catalyst was restrainedly proposed for polymerization.

ChemInform Abstract: Asymmetric Phase‐Transfer Reactions under Base‐Free Neutral Conditions

AbstractReview: [17 refs.