Tetraalkylammonium Cations Research Articles

Mesoporous ZSM-5 zeolite catalysts prepared by desilication with organic hydroxides and comparison with NaOH leaching

Hierarchical zeolites combining micro- and mesoporosity were prepared by desilication of ZSM-5 (Si/Al = 42) in aqueous solutions of tetraalkylammonium hydroxides (TPAOH, TBAOH). Similarities between the treatment mediated by organic hydroxides and the conventional NaOH leaching comprised (i) the requirement to work with a starting zeolite in the optimal Si/Al window of 25–50 and (ii) the minor influence of the counter-cation (H +, NH 4 +, Na +) on the degree of mesoporosity developed. However, both desilication media presented distinctive kinetic and mechanistic characteristics. The use of organic hydroxides directly produced the protonic form of the mesoporous zeolite upon calcination, simplifying the final ion exchange with NH 4NO 3 characteristic of the NaOH treatment. Silicon dissolution in TPAOH (or TBAOH) was much slower than in NaOH, making the demetallation process highly controllable. The treatment in the organic base was less selective for silicon extraction, i.e. a higher amount of aluminum was leached to the solution compared to the NaOH treatment. The differences in porosity development and chemical composition of the final solid can be assigned to the effect of the bulky tetraalkylammonium cation. The optimal hierarchical ZSM-5 zeolite (treated in 1 M TPAOH at 338 K and 8 h) had a mesopore surface area of 160 m 2 g −1 and the intrinsic zeolite properties were largely preserved. This sample displayed improved catalytic performance in the liquid-phase benzene alkylation with ethylene compared to the parent and NaOH-treated zeolites.

How are Heteroelements (Ga and Ge) Incorporated in Silicate Oligomers?

The properties of microporous solids can be strongly influenced during the first stages of solid-state formation from solution. Furthermore, their properties are directly related to the presence, number, and character of intra- or extraframework heteroelements. In this contribution we studied the influence of the substitution of silicon against heteroelements, such as gallium and germanium. The aqueous prenucleating solutions were obtained by hydrolysis of the silicon and heteroelement sources in the presence of tetraalkylammonium cations. The time-resolved stepwise formation of larger oligomers was studied by using electrospray ionization mass spectrometry (ESI-MS). Furthermore, the structures of the obtained signals were verified by using MS/MS experiments, which led to the conclusion that strong structure-directing effects emerge from the introduction of heteroelements into the solutions.

Formation of cation–radical anion pairs derived from carboxybenzophenone–tetrabutylammonium salts. Pulse radiolysis studies

Pulse radiolysis of acetonitrile solutions of tetra-n-butyl ammonium salts of 2- and 4-carboxybenzophenones [BP-COO−···N+(C4H9)4] were performed in order to generate directly the reduced forms of the benzophenone moieties within pre-formed ion pairs. In earlier studies on photochemical electron transfer reactions, ion pairs containing a tetraalkyl ammonium cation and a benzophenone radical anion were formed in an electron transfer to the triplet BP from a quencher consisting of a tetraalkyl ammonium salt of (phenylthio)acetic acid. In the current work, the [BP•−COO−···N+(C4H9)4] ion pairs were formed by direct reduction of the salts without the complication of a third moiety, i.e., the (phenylthio)acetic anion. The spectra and kinetic parameters of the radiolytically-reduced salts were compared to the behavior of reduced forms of the 2- and 4-COOH substituted benzophenones. The results from the pulse radiolysis and photochemistry were compared and explained in terms of the different structures of the ion pairs.

Properties of Radical Anions of Triptindanones and Indanones: Electronic Communication and Stability of Ion Pairs Containing Lithium Cations

The properties of radical anions and dianions of three related spatial ketones, 9-triptindanone (T1), 9,10-triptindanedione (T2), and 9,10,11-triptindanetrione (T3), in DMF solutions containing tetraalkylammonium and lithium cations were investigated by electrochemical methods and compared with the properties of radical anions of planar 1-indanone (I1), 1,3-indanedione (I2), and 1,2,3-indanetrione (I3). Electronic communication between carbonyl groups in T2 in the presence of tetraethyl and tetrabutyl cations was found to be two times smaller than for I3, but communication decreases substantially in the presence of Li+. Radical anions T1•− and T2•− and dianion T22− that form ion pairs with Li+ cations and corresponding association constants Kass are equal to 493 ± 38, 418 ± 32 and (2.6 ± 0.9) × 107 dm3 mol−1, respectively. The chelating structure of the last ion pair is supported by theoretical calculations of the distribution of the negative charge. A linear relationship between log Kass and maximum valu...

Thermochemical study of the influence of tetraalkylammonium cation sizes on the interaction of their salts with formamide and carbamide in aqueous solutions

Solutions of tetrahexylammonium salts in mixtures of water with additives of hydrophilic substances formamide and carbamide were studied by the thermochemical method at 298.15 K. The enthalpies of solution of tetrahexylammonium perchlorate were measured by the sedimentation method, and the enthalpies of solution of tetrahexylammonium bromide were calculated. The enthalpic coefficients of pair interaction electrolyte—amide in an aqueous solution were determined. The data obtained were compared with those for te tramethyl- tetraethyl- and tetrabutylammonium salts to study the influence of the tetraalkylammonium cation size on its solvation and interaction with amides in an aqueous solution.

Effects of Silica Sources on Nanoporous Organosilicate Films Templated with Tetraalkylammonium Cations

AbstractNanoporous organosilicate films have been recently prepared using tetraalkylammonium cations in acid and basic media, outperforming other materials. Resulting films using basic medium were called zeolite-inspired low-k dielectrics. Here we study the dependence of the properties of these films on the used silica sources: methyltrimethoxy silane (MTMS) and tetraethyl orthosilicate (TEOS). A set of experiments varying the MTMS:TEOS ratio were prepared in acid medium and characterized. A textural, physico-chemical, mechanical, and electrical characterization of this series of experiments is presented.

Low viscosity amino acid ionic liquids with asymmetric tetraalkylammonium cations for fast absorption of CO2

Fifteen novel amino acid ionic liquids (AAILs) were prepared by the combination of several tetraalkylammonium cations with four amino acid anions ([Gly], [L-Ala], [β-Ala] and [Val]).The asymmetry of the tetraalkylammonium cations is shown to have a significant influence on the viscosity of the ionic liquids composed of amino acid anions, especially for the four triethylbutylammonium ([N2224])-based ionic liquids that have viscosities of lower than 60 mPa s, with the lowest being only 29 mPa s. The low viscosity tetraalkylammonium-based AAILs are further demonstrated to improve apparently the reaction and mass transfer rates of CO2 in the ionic liquids.

Studies on dissolution of carbohydrates in ionic liquids and extraction from aqueous phase

An extended study on the solubility of the carbohydrates glucose, fructose, sucrose and lactose in twenty eight different ionic liquids (ILs) was performed. These ILs were based on the combination of tetraalkylammonium, tetraalkylphosphonium, 1-methyl-3-alkylimidazolium and dimethyl-tetraalkylguanidinium cations containing alkyl and ether pendant substituent groups, and anions of chloride, dicyanamide, saccharine, acesulfame, acetate or thiocyanate. It was possible to achieve solubilities, at 35 °C, of each carbohydrate up to 43.9, 49.0, 17.1 and 16.6% (g of carbohydrate per 100 g of IL), respectively. The possibility to extract carbohydrates from an aqueous phase by hydrophobic ILs was also demonstrated. Besides, some selectivity for a mixture of two carbohydrates was also observed.

A Continuous Symmetry Measure of [4Fe−4S]+ Core Distortions and Analysis of Supramolecular Synthons in Crystal Structures of (Et4N)3[Fe4S4Cl4]·Et4NCl at 100 and 295 K

Distortions of the [4Fe-4S](+) cores of synthetic models from T(d) symmetry are analyzed in terms of the continuous symmetry measures (CSM, S(T(d))), and these are related to lattice effects in terms of the supramolecular synthon terminology common to crystal engineering of small molecule structures. The small tetragonal compression to D(2d) from idealized T(d) symmetry observed at low temperature is attributed to environmental factors. New members of the isomorphous series of compositional variations of double salts of the air-sensitive reduced cluster (Et(4)N)(3)[Fe(4)S(4)Cl(4)].Et(4)NCl (1) are prepared in modest yield by treatment of FeCl(2) with NaHS, or (Et(4)N)(2)[FeCl(4)] with Et(4)NSH and a base. The crystals are isomorphous with the corresponding HS(-) ligated cluster. Crystal data: tetragonal, P42(1)c, Z = 2, a = b = 12.2550 (4), c = 16.278 (1) A at 100 K, and a = b = 12.385 (1), c = 16.344 (2) A at 295 K. The crystallographically imposed S(4) symmetry obtained with sterically unincumbering ligands affords a better view of the intrinsic geometry of the core structure. The cocrystallization of the halide ion affords the opportunity to compare three types of weak C-H...X hydrogen bonds, or hydrogen bridges, between tetraalkylammonium cations and anions within the same crystal lattice. The C...Cl(-) distances (3.590 and 3.634 at 100 K increase to 3.616 and 3.655 A, respectively, at 295 K) are virtually temperature independent, indicative of hard hydrogen bridges, whereas the C...Cl-Fe distances are 3.702-3.718 A at 100 K but are 3.753-3.764 A at room temperature, suggesting a softer hydrogen bridge. A similar trend applies to the two sets of C...mu(3)-S distances (3.766-3.788 A and 3.594-3.604 A at 100 K and 3.821-3.848 A and 3.614-3.676 A at room temperature). The longer hydrogen bridges are more linear (170 degrees ) than the shorter ones (134 degrees ). The core distortions are correlated with spatial distribution of cations around the clusters.

Influence of tetralkylammonium cations on the formation of silicoaluminophosphates CAL-2

SAPO molecular sieves were synthesized under hydrothermal conditions from gels containing AlPO-kanemite, silica and a series of four tetralkylammonium (TAA +) salts. The influence of each of the tetralkylammonium cations on the molecular sieve syntheses was studied at constant SiO 2/Al 2O 3 and TAA +/SiO 2 molar ratios of 1.0. The obtained materials were characterized by typical physico-chemical techniques for solid materials such as powder X-ray diffraction (XRD), Fourier transformed infrared spectroscopy (FTIR), thermal analysis (thermogravimetry), elemental analysis (CHN), scanning electron microscopy (SEM) and multinuclear 13C- and 29Si-solid state nuclear magnetic resonance. A theoretical evaluation of the n-butylammonium conformers, energy of interconversion and molecular sizes, was useful to understand the behavior of each system containing different SDA’s. Thus different structures were obtained depending on the TAA + cation used: in the case of tetramethylammonium the sodalite structure was prepared, tetraethylammonium and tetrapropylammonium cations on the other hand, directed the formation of chabazite structures and for the tetrabutylammonium cation the layered structure of the reactant was not changed. The presence of silicon islands is clear and is an important part of this work. 29Si-solid state nuclear magnetic resonance, elemental analysis of C, H and N and energy dispersive spectroscopy (EDS) techniques were all applied to characterize this aspect.

Studying the Thermodynamics and Kinetics of Ion Transfers Across Water-2-nitrophenyloctyl Ether Interface by Means of Organic-solution-modified Electrodes

Transfer reactions across a water-2-nitrophenyloctyl ether (W|NPOE) interface for a series of monovalent inorganic ions and tetraalkylammonium cations are studied by means of square-wave (SWV) and cyclic voltammetry at thin organic-film-modified (TFE) and three-phase electrodes (TPE). Both electrode configurations are assembled using lutetium bis(tetra-tert-butylphthalocyaninato) as the redox probe, whose properties enable assessment of both anion and cation transfer reactions in a single voltammetric experiment. It is demonstrated that TFE can be effectively applied to measure the Gibbs energy of ion transfer reactions when the transferring ion is common to both liquid phases, controlling the Galvani potential difference at the W|NPOE interface. A comparative study of the thermodynamics of ion transfer reactions performed with TFE and TPE reveals that both electrode configurations provide a consistent set of data. Kinetic measurements referring to the transfers of ClO4−, and a series of tetraalkylammoniu...

Thermodynamics of Silica Nanoparticle Self-Assembly in Basic Solutions of Monovalent Cations

Silica nanoparticle formation is studied using microcalorimetry to measure the heats of reaction evolved from the addition of tetraethylorthosilicate (TEOS) to basic aqueous solutions of monovalent cations. This approach tracks a series of reactions, beginning with the formation of soluble species (i.e., monomers/oligomers), followed by the self-assembly of nanoparticles at a critical silica concentration (CAC). Contributions to the net enthalpy arise from three primary reactions: TEOS hydrolysis, silanol dissociation, and silica condensation. Analyses are performed in the presence of tetrapropylammonium (TPA) ion, which serves as a structure-directing agent (SDA) in hydrothermal syntheses of the all-silica zeolite, silicalite-1. Plots of enthalpy versus TEOS concentration exhibit sigmoidal behavior with a 18 ± 3 kJ/mol reduction in the magnitude of enthalpy, which is related to the CAC and is independent of solution alkalinity, but dependent on the identity of the cation. Solutions of Na+ and various tetraalkylammonium (TAA) cations display similar sigmoidal curves with much lower changes in the magnitude of enthalpy at the CAC (∼5 kJ/mol SiO2). Nanoparticle formation may involve endothermic reactions, derived from protonation of negatively charged silica to form neutral species, which participate in condensation, thereby providing an explanation for the previously observed exothermic−endothermic crossover as a function of time during silicalite-1 syntheses.

Pd-Catalyzed ortho Halogenation of C-H Bonds

The study shows a new catalytic method for the ortho halogenation of arylcarboxylic acids without the need for a nitrogen-containing directing group. Tetraalkylammonium cations as well as organic and inorganic bases such as DBU or DABCO are effective in promoting the C-H activation and enhance the monoselectivity of the halogenation.

Multiple functions of ionic liquids in the synthesis of three-dimensional low-connectivity homochiral and achiral frameworks.

Multiple functions of ionic liquids in the synthesis of three-dimensional low-connectivity homochiral and achiral frameworks.

Decomposition pathways of an alkaline fuel cell membrane material component via evolved gas analysis

The mechanism of the thermal decomposition of [NMe4][OH]·5H2O, tetramethyl ammonium hydroxide pentahydrate, was studied using DSC, TG and evolved gas analysis because of the importance of related ions in anion exchange membranes. The products of the reaction are trimethyl amine, methanol and dimethyl ether. The relative ratio of the products is determined by how much water remains in the sample as it is decomposing. Isotopic labeling experiments with D2O show that deprotonation of the tetramethyl ammonium ion by hydroxide establishes a rapid equilibrium between tetramethyl ammonium ion and the nitrogen ylide species and water that scrambles the deuterium with the proton in the methyl groups. The results of this work also suggest that tetraalkyl ammonium cations may be more stable in hydroxide conducting membranes than previously believed.

Tetraalkylammonium Ions in Aqueous and Non-aqueous Solutions

Property data for tetraalkylammonium cations, [H(CH2)n]4N+, are reviewed. They pertain to the isolated cations and their transfer from the gas phase into aqueous solutions. Various properties of these cations in aqueous and non-aqueous solutions and data for their transfer between these are also reviewed. Emphasis is placed on the dependence of data on the length n of the alkyl chains rather than on the absolute values. Most of the data are available only for the first four members of the series.

Temperature and Length Scale Dependence of Tetraalkylammonium Ion−Amide Interaction

We have studied the temperature and length scale dependence of the energetics of the pair interaction of well-established hydrophobic solutes tetraalkylammonium bromides with hydrophilic formamide (FA) and hydrophobic hexamethylphosphoric triamide (HMPT). Our results do indicate the anomalous length scale dependence of the tetraalkylammonium cation-amide interaction in water. As the cation size is increased, the unfavorable enthalpy of interaction is increased rather linearly until the maximum is reached, after which there appears to be a reversal of the trend. We believe that this phenomenon arises from the impossibility of water to maintain its H-bond network near large tetraalkylammonium cations that leads to the formation of a somewhat disordered solute hydration shell. The energetic cost for overlapping this shell with the amide hydration shell in water is noticeably smaller than that for tetraalkylammonium cations of a moderated size.

Enhanced Sorption of Polycyclic Aromatic Hydrocarbons to Tetra-Alkyl Ammonium Modified Smectites via Cation−π Interactions

The objective of this study was to characterize molecular sorptive interactions of polycyclic aromatic hydrocarbons (PAHs) by organoclays modified with quaternary ammonium cations. Three PAHs, naphthalene (NAPH), phenanthrene (PHEN), and pyrene (PYR), and three chlorobenzenes, 1,2-dichlorobenzene (DCB), 1,2,4,5-tetrachlorobenzene (TeCB), and pentachlorobenzene (PtCB), were sorbed from aqueous solution to reference montmorillonite clays (SWy-2) exchanged respectively with tetramethyl ammonium (TMA), tetraethyl ammonium (TEA), tetra-n-butyl ammonium (TBA), and hexadecyltrimethyl ammonium (HDTMA) cations. Solute hydrophobicities are compared between PAHs and chlorobenzenes using the solute n-octanol-water partition coefficient, n-hexadecane-water partition coefficient, and polyethylene-water distribution coefficient. The PAHs show several- to more than 10-fold greater sorption than the chlorobenzenes having close hydrophobicities but fewer delocalized pi electrons (NAPH/DCB, PHEN/TeCB, and PYR/ PtCB) by TEA-, TBA-, and HDTMA-clays. Furthermore, the PAHs show greater trends of solubility enhancement than the compared chlorobenzenes by TMA, TEA, and TBA in aqueous solution. The enhanced sorption and aqueous solubility of PAHs are best described by cation-pi interactions between ammonium cations and PAHs relative to chlorobenzenes that are incapable of such interactions. Cation-pi complexation between PAHs and tetra-alkyl ammonium cations in chloroform was verified by ring-current-induced upfield chemical shifts of the alkyl groups of cations in the 1H NMR spectrum.

Organo-Zintl Clusters Soluble in Conventional Organic Solvents: Setting the Stage for Organo-Zintl Cluster Chemistry

Organo-Zintl cluster ions were synthesized by reactions of alkynes with Ge94- clusters in ethylenediamine. The triple bonds are hydrogenated to double bonds during the process. The resulting dial-kenylated species [RHC=CHGe9CH=CHR]2- have lower charge, their alkali-metal cations can be exchanged for tetralkylammonium cations, and the resulting compounds are soluble in nonpolar solvents. This was demonstrated with [H2C=CHGe9CH=CH2]2-, which was structurally characterized with [K-(18-crown-6)]+, [Me4N]+, and [Pr4N]+ as countercations. The solubility of its salt with [Oc4N]+ in various conventional organic solvents was studied.

Thermal analysis of some organoclays

Thermogravimetric (TG) and differential thermal analysis (DTA) curves of methyltributylammonium smectite (MTBAS), methyltrioctylammonium smectite (MTOAS), and di(hydrogenatedtallow)dimethylammonium smectite (DHTDMAS), and also corresponding sodium smectite (NaS) and tetraalkylammonium chlorides (TAAC) were determined. The TAACs was decomposed exactly by heating up to 500°C. The adsorbed water content of 8.0% in the pure NaS was decreased down to 0.2% depending on the size of the non-polar alkyl groups in the tetraalkylammonium cations (TAA+). The thermal degradation of the organic partition nanophase formed between 2:1 layers of smectite occurs between 250–500°C. Activation energies (E) of the thermal degradations in the MTBAS, MTOAS and DHTDMAS are 13.4, 21.9, and 43.5 kJ mol−1, respectively. The E value increases by increasing of the interlayer spacing along a curve depending on the size of the alkyl groups in the TAA+.