N-butyl Ammonium Salt Research Articles

Solution-State Anion Recognition, and Structural Studies, of a Series of Electron-Rich meta-Phenylene Bis(phenylurea) Receptors and Their Self-Assembled Structures.

meta-Phenylene bis(phenylurea) receptors 1-4 were designed and synthesized to investigate the association between receptor shape, anion-selective binding and anion-directed self-assembly processes. Solution studies, performed through 1H NMR titrations with a variety of tetra- N-butylammonium salts, demonstrated strong binding of 2 equiv of H2PO4-, AcO-, BzO- anions and comparatively weak binding of Cl-, HSO4-, and SO42- anions. Binding modes and stability constants (log β) were determined by regression analysis of the obtained 1H NMR titration data in DMSO- d6, and the cooperativities of the binding interactions were probed. Host-guest complexes of receptors 1 and 2 were studied in the crystalline phase to further probe the anion-binding behavior of this motif. This included a triple-stranded helicate consisting of three strands of receptor 2 arranged around a mixed-phosphate anionic core, which was characterized by using X-ray crystallography.

Preparation of 1,3-dienyl organotrifluoroborates and their Diels–Alder/cross-coupling reactions

2-BF 3-substituted 1,3-butadienes with potassium and tetrabutyl ammonium counterions have been prepared in gram quantities from chloroprene via a simple synthetic procedure. The potassium salt of this new main group element substituted diene has been characterized by 1H, 13C, 11B, and 19F NMR and the tetra n-butyl ammonium salt was also characterized by X-ray crystallography. Diels–Alder reactions of these dienes with dienophiles such as ethyl acrylate, methyl vinyl ketone, and N-phenylmaleimide are reported as well as subsequent Pd-catalyzed cross-coupling reactions of those Diels–Alder adducts. 4-Phenyl-2-BF 3-substituted 1,3-diene was prepared by magnesium–halogen exchange from the corresponding 2-bromo and iodo dienes. The 4-phenyl-2-bromo-1,3-butadiene was also characterized by X-ray crystallography. 4-Phenyl-2-BF 3-1,3-butadiene was used in Diels–Alder/cross-coupling reactions and the product of a Diels–Alder reaction with N-phenylmaleimide followed by cross-coupling with 4-bromo-benzonitrile was also characterized by X-ray crystallography.

Structural ordering of organovermiculite: Experiments and modeling

The ordering of three different sizes of quaternary ammonium salts (QUATs) has been studied with respect to concentration of guests in the host's interlayer gallery. From the modeling, we could verify that small molecules of n-butylammonium salt build a monolayer structure in the vermiculite gallery without reference to concentration. On the other hand, the larger molecules of dodecyltrimethylammonium and dioctadecyldimethylammonium salts are responsive to the numbers of their molecules in the interlayer space of the host, building mono- or bilayered structures. Supersaturated structure of both QUATs keep an arrangement of alkyl chains nearly perpendicular to silicate layers, while only saturated samples exhibit tilted alkyl chains in the gallery. The ordering changes bring out the calculation of mean crystallite size. Low values of the nonbond energy of supersaturated forms predict that those organovermiculites will readily exfoliate, e.g., in polymer/clay nanocomposite

Polymorphism in tetra-butylammonium salts of Keggin-type polyoxotungstates

Some tetra- n-butylammonium salts of Keggin-type polyoxotungstates, namely α-[PW 11O 39] 7−, α-[PW 11M(H 2O)O 39] 5−, M II=Co, Ni, α-[PW 11CuO 39] 5−, α-[PW 11Fe(H 2O)O 39] 4− and α-[PW 11Fe(OH)O 39] 5−, with the general formula [(C 4H 9) 4N] 4H x [anion]· nH 2O, were studied by powder X-ray diffraction. The salts α-[(C 4H 9) 4N] 4H 3[PW 11O 39] and α-[(C 4H 9) 4N] 4H[PW 11CuO 39] were obtained in two crystalline phases, a behavior that has been scarcely documented in compounds with Keggin polyoxometalates. One of the phases corresponds to a body-centered cubic unit cell ( Im 3 ̄ symmetry) and the other has a body-centered tetragonal unit cell ( I4 1 or I4 122 symmetry). For the compounds with Cu, the cell parameters of the cubic and tetragonal structures were a=17.675(2) and a=18.775(2), c=14.646(2) Å, respectively. The cubic phase was obtained by precipitation from aqueous solution. The tetragonal phase was isolated by crystallization from acetonitrile. The remaining compounds were found to crystallize with one of these two crystal structures. α-[(C 4H 9) 4N] 4H x [PW 11M(H 2O)O 39]· nH 2O, with M=Co, Ni, x=1, and M=Fe, x=0, n=1–2, were found to crystallize with the body-centered cubic structure. The method of synthesis used to prepare α-[(C 4H 9) 4N] 4H[PW 11Fe(OH)O 39] afforded the tetragonal phase. The conversion of the cubic into the tetragonal phase and the stability of each one are discussed.

Alkane oxidation with hydrogen peroxide catalyzed homogeneously by vanadium-containing polyphosphomolybdates

Alkanes (cyclooctane, n-octane, adamantane, ethane) can be efficiently oxidized by hydrogen peroxide in acetonitrile using tetra- n-butylammonium salts of the vanadium-containing polyphosphomolybdates [PMo 11VO 40] 4− and [PMo 6V 5O 39] 12− as catalysts. The oxidation of alkanes gives rise to the corresponding alkyl hydroperoxides as the main products, which slowly decompose in the course of the reaction to produce the corresponding ketones (aldehydes) and alcohols. The reaction in acetic acid and water is much less efficient. The oxidation of cyclooctane at 60°C in acetonitrile gives within 9 h oxygenates with turnover numbers >1000 and yields >30% based on the alkane. Pyrazine-2-carboxylic acid added as co-catalyst accelerates the reaction but does not enhance the product yield. The oxidation of the cis- and trans-isomers of decalin proceeds without retention of configuration. The mechanism assumed involves the reduction of V(V) to V(IV) by a first molecule of hydrogen peroxide, followed by the reaction of V(IV) with a second H 2O 2 molecule to generate hydroxyl radicals. The latter abstract a hydrogen atom from the alkane, RH, leading to alkyl radicals, R , which rapidly react with aerobic oxygen. The alkyl peroxy radicals thus formed are then converted into alkyl hydroperoxides.

Synthesis of PTHF-Grafted PMMA Based on the Reaction of Methyl Esters with Quaternary Ammonium Salts

A new synthetic procedure is proposed to graft polymer chains onto poly(methyl methacrylate) based on the reaction of methyl esters with quaternary ammonium salts (MEQA reaction) under nonprotic conditions. Mechanistic insight into the MEQA reaction has been given by performing model reactions, for example with methyl benzoate and the N-butylammonium salt of 1,4-diazabicyclo[2.2.2]octane. This reaction has been used to graft poly(tetrahydrofuran) with a 1,4-diazabicyclo[2.2.2]octane end group, synthesized from living cationic ring-opening polymerization, on poly(methyl methacrylate) by simply heating the reaction mixture of both components in 1,2-dichlorobenzene as solvent. GPC and NMR analysis demonstrated high grafting yields. The formation of the grafted structures was further evidenced by a comparative DSC study of the crystallization behavior of the starting and end products.

Synthesis and structure of a novel dimeric molybdenum oxyhalide anion

Reaction of [( n-C 4H 9) 4N] 2[Mo 2O 7] with concentrated hydrochloric acid in an aprotic solvent yields a molecular molybdenum oxychloride anion [Mo 2O 5Cl 4] 2− as a tetra- n-butylammonium salt. X-ray structural analysis of [( n-C 4H 9) 4N] 2[Mo 2O 5Cl 4]·1/3(C 2H 5) 2O revealed that the dimeric anion consists of two MoO 3Cl 3 octahedra sharing a common face with a relatively long Mo–Mo distance (3.279 Å). The compound has the highest acidity as a polynuclear molybdate isolated so far.

Synthesis, photochemistry and application of (7-methoxycoumarin-4-yl)methyl-caged 8-bromoadenosine cyclic 3′,5′-monophosphate and 8-bromoguanosine cyclic 3′,5′-monophosphate photolyzed in the nanosecond time region

New caged derivatives of hydrolysis-resistant 8-bromoadenosine cyclic 3′,5′-monophosphate (8-Br-cAMP) and 8-bromoguanosine cyclic 3′,5′-monophosphate (8-Br-cGMP) are described. The compounds are the axial and equatorial isomers of the (7-methoxycoumarin-4-yl)methyl (MCM) esters of cyclic nucleotides. Synthesis is accomplished by treatment of 4-bromomethyl-7-methoxycoumarin with the tetra- n-butylammonium salts of the 8-bromo-substituted cyclic nucleotides or with the free acids of 8-Br-cAMP and 8-Br-cGMP in the presence of silver(I) oxide. MCM-caged 8-Br-cAMP and MCM-caged 8-Br-cGMP liberate 8-Br-cAMP and 8-Br-cGMP during irradiation with ultraviolet light within a few nanoseconds. They show favorable absorption properties and quantum yields and are resistant to hydrolysis in aqueous buffer solutions. The moderate fluorescence properties of the caged compounds in comparison with the strongly fluorescent 4-hydroxymethyl-7-methoxycoumarin (MCM-OH) photoproduct allow the indirect estimation of the amount of photolytically released cyclic nucleotides in aqueous buffer solutions using fluorescence measurements. Their usefulness for physiological studies has been examined in a mammalian cell line expressing the cyclic nucleotide-gated ion channel of bovine olfactory sensory neurons using the patch-clamp technique and confocal laser scanning microscopy. The caged compounds serve as efficient and rapid intracellular sources of 8-Br-cAMP and 8-Br-cGMP. However, at least in HEK 293 cells, fluorescence signals cannot be used to monitor the photolysis of MCM-caged 8-Br-cAMP and 8-Br-cGMP, due to quenching of the fluorescence of MCM-OH.

Keggin-type polyoxotungstates as catalysts in the oxidation of cyclohexane by dilute aqueous hydrogen peroxide

Oxidation of cyclohexane by hydrogen peroxide in the presence of catalytic amounts of the Keggin-type heteropolytungstates [PW 11O 39] 7− and [PW 11M(L)O 39] (7− m)− , M m+ =first row transition metal cation, L=H 2O or CH 3CN, was found to produce cyclohexanol, cyclohexanone and, in certain cases, cyclohexyl hydroperoxide. The presence of the latter was demonstrated by negative chemical ionization GC-MS. The reactions were carried out in acetonitrile, using tetra n-butylammonium salts of the catalysts and aqueous 30% hydrogen peroxide as oxidant. The polyanions [PW 11O 39] 7− and [PW 11Fe(H 2O)O 39] 4− showed higher catalytic activity and different selectivity for the oxidation of cyclohexane than did the corresponding Cu-, Co-, Mn- and Ni-substituted complexes.

Supramolecular Assemblies of Metal Complexes: Light-Induced Electron Transfer in the Galleries of α-Zirconium Phosphate

Rapid photoinduced electron transfer was observed with supramolecular assemblies of donor and acceptor metal complexes at the galleries of n-butylammonium salt of α-zirconium phosphate ((C4H9NH3)2Zr(PO4)2·xH2O, abbreviated as BAZrP). Tris(2,2‘-bipyridyl)ruthenium(II)2+ luminescence, for example, was quenched by tris(2,2‘-bipyridyl)cobalt(III)3+ with rate constants exceeding 1.6 × 1012 m2 mol-1 s-1, when the metal complexes were intercalated in the galleries of BAZrP. The quenching rates were unaffected when the viscosity of the BAZrP suspensions was increased (2:1 mixture of ethylene glycol−water) or when the loading of the donor was increased 10-fold. Even when cooled to 77 K, as a rigid glass, the electron transfer reactions between the donor and the acceptor proceed at essentially the same rate as at room temperature indicating a very low activation energy for the electron transfer reaction. These activation-less rate constants are faster than anticipated for diffusion controlled electron transfer rates at BAZrP galleries, at low temperatures. Excited-state energy migration from donor to donor (antenna effect) followed by electron transfer between the nearest donor−acceptor pairs is one explanation proposed to account for the above observations.

The organometallic ‘molecular tinkertoy’ approach to planar grid polymers

A general approach is outlined for the synthesis of thin-layer materials of arbitrarily configured structure (‘designer solids’), based on confinement to two dimensions. The synthesis of a building module, the tetra- n-butylammonium salt of lanthanum(III)bis[5,10,15,20-tetrakis(4-pyridyl)porphyrinate] ( 1), is described. It is shown by grazing incidence IR spectroscopy that this cross-shaped molecule adheres firmly to a mercury surface, with the porphyrin rings parallel to the surface and the pyridine rings carried by the upper porphyrin ring ready for linear coupling. The proposed surface-confined synthesis of a square grid, which would define a first layer of a designer solid, can now be tested.

Additive effects on ligand activated allylation of aldehydes by allyltrichlorosilane

The rate of allylation of aldehydes using a combination of allyltrichlorosilane and O-donor ligands can be profoundly accelerated by the addition of a range of simple tetra- n-butylammonium salts. Measured t 1 2 values decrease from over 6 hours under defined conditions to less than 5 minutes in favourable cases. These effects are highly relevant to the development of a catalytic asymmetric variant of this reaction and provide insight into the mechanism.

Supramolecular assemblies of ethidium and acridinium ions at the interlayer regions of α-zirconium phosphate

Ethidium bromide (EB), a known DNA intercalating agent and mutagen, binds in the interlayer regions of n-butyl ammonium salt of α-zirconium phosphate (BAZrP). The electronic absorption spectrum of EB changes drastically upon binding to BAZrP. For example, the 478 nm absorption band of the free chromophore is replaced by red shifted (600 nm) and blue shifted (450 nm) bands. The absorption spectrum of the bound chromophore was found to be independent of loading. Binding in the interlayer regions results in the strong quenching of the EB fluorescence accompanied by a large red shift of the spectral maximum. The results observed with acridinium hydrochloride (ACR) are in contrast to those of EB. At low concentrations of ACR, only a small amount of the ligand was bound and the binding is promoted at higher concentrations. The absorption spectra of ACR bound to BAZrP show a new band at 365 nm. The intensity of this band increases with loading and reaches a plateau at ca. 55 μM of ACR. The fluorescence spectra of ACR are blue shifted upon binding to BAZrP, with a strong quenching of the intensity. In both cases (EB and ACR) the average area occupied per molecule in the BAZrP galleries matched well with their footprints. Thus, they bind with their long axes parallel and π planes perpendicular to the ZrP planes. Binding of these cations to BAZrP results in aggregation of the chromophores with strong interchromophore interactions. Such spontaneous organized assembly of chromophores may be of interest in the design of supramolecular assemblies that are capable of promoting bimolecular photoreactions.

Determination of organophosphorus acids by thermospray liquid chromatography-mass spectrometry

The determination of thirteen organophosphorus acids, hydrolysis products of nerve agents and pesticides, by a combination of ion-pair liquid chromatography on a reversed-phase C 18 column and thermospray mass spectrometry was investigated. Ammonium acetate and three tetraalkylammonium salts with different alkyl groups (methyl, ethyl and n-butyl) were applied as ion-pair reagents. All the organophosphorus acids could be eluted using water or water-methanol mixtures. Capacity factors ( k′) were measured for some selected acids using water as eluent. The recorded thermospray mass spectra using ammonium acetate as electrolyte gave the [M + NH 4] + ion as a predominant peak, whereas with the tetraalkylammonium salts cluster ions were found. This difference in ionization mechanism was also reflected in the sensitivity. An amount of 100 pg of dimethylthiophosphoric acid could be detected by selected ion monitoring using ammonium acetate, whereas with tetramethylammonium hydroxide the amount was 5 ng. To obtain lower detection levels preconcentration could be achieved with a Sep-Pak C 18 cartridge pretreated with a tetra- n-butylammonium salt.

Thermodynamic characteristics of solute—solvent interactions in liquid organic salt solvents, studied by gas chromatography

A number of thermodynamic constants were measured for five McReynolds selectivity probes and a series of aromatic selectivity probes on thirteen tetra- n-butylammonium salts and eleven 4-toluenesulfonate salts to elucidate the nature of intermolecular interactions of solute—liquid organic salts by gas chromatography (GC). The molar free energy of solution for a methylene group was used to determine dispersive contributions of individual cations and anions to retention. The partial molar, mole fraction, and molal free energy of solution and partial mole fraction enthalpy and entropy of solution were determined to estimate the contribution of various intermolecular forces to retention and to compare the magnitude of these interactions to those of non-ionic, polar phases. Weak dispersive interactions increasing with the size of the cation, strong orientation interactions of a relatively constant nature, and proton acceptor interactions that varied greatly and correlated with the properties of the anion were observed for the liquid organic salts. The magnitude of the orientation and proton acceptor interactions in several cases were much larger than equivalent interactions for polar, non-ionic phases. The infinite dilution activity coefficient and partial molar excess free energy of solution were determined for the five McReynolds probes on the tetra- n-butylammonium salts. With the exception of butanol the range of values observed were similar to literature values for polar, non-ionic GC phases.

Conductance and ion association in dimethylsulfite

The electrolytic conductances of LiClO4, LiAsF6, NaClO4 and the n-butylammonium salts Bu4NCl, Bu4NClO4, and Bu4NBPh4 (tetraphenylborate) have been determined in dimethylsufite at 25°C. Ion association constants calculated from these data are interpreted in terms of solvent-separated ion pairs (for LiClO4, LiAsF6, and NaClO4), and contact ion pairs (for the n-butyl-ammonium salts). Comparisons are made for analogous electrolytes in acetone, and in which all salts form contact ion pairs.

Variation in the gas chromatographic stationary phase propertiesof tetra- n-butylammonium salts as a function of the anion type

The gas chromatographic stationary phase properties of fifteen tetra- n-butyl-ammonium salts containing chloride, bromide,iodide, nitrate, nitrite, thiocyanate, perchlorate, hexafluorophosphate, tetrabutylborate, tetraphenylborate, picrate, tetrafluoroborate, 4-toluenesulfonate, methanesulfonate, and trifluoromethanesulfonate anions are described. For five of these salts the liquid temperature range exceed 100°C:4-toluenesulfonate (55-200°C), tetrafluoroborate (162-290°C), trifluoromethanesulfonate (112-240°C), picrate (90-200°C), and methanesulfonate (79-180°C). The tetra- n-butylammonium salts exhibit unique solute selectivity, manifested in very weak dispersion and proton donor interactions, accompanied by strong orientation and proton acceptor interactions. For the anions picrate, tetrabutylborate, trifluoromethanesulfonate, 4-toluenesulfonate, nitrate, methanesulfonate, bromide, nitrite, and chloride dipole interactions are fairly constant and change little with the anion type (except for chloride), while the proton acceptor capability of the salts is a strong function of the anion type, increasing in the following order: picrate ≈ trifluoromethanesulfonate < 4-toluenesulfonate < nitrate ≈ methanesulfonate < bromide < nitrite < chloride. The retention of organic solutes on tetra- n-butylammonium 4-toluenesulfonate, trifluoromethanesulfonate, methanesulfonate, picrate, and chloride salts occurs primarily by gas-liquid partition. Gas-liquid adsorption makes a small but significant contribution to the retention of hydrocarbons and to a lesser extent that of pyridine, but in general, does not contribute to the retention of polar solutes. The chromatographic characteristics of the tetra- n-butylammonium salts are illustrated by the separation of some essential oils.

Butylation of inorganic anions for simultaneous determination by gas chromatography

Some aqueous inorganic anions were extracted into the organic layer as their tetra- n-butylammonium salts and then treated with n-butyl p-toluenesulphonate to yield their n-butyl derivatives which were determined by gas chromatography with flame ionization detection. Bromide, iodide, thiocyanate and nitrate were thereby derivatized and determined. The n-butyl derivatives were identified by comparison of the retention times as n-butyl bromide, n-butyl iodide, n-butyl thiocyanate and n-butyl nitrate, respectively. The effects of added base or acid, shaking time and phase-transfer catalyst on the extraction of the anions were discussed. By this method the anions could be determined simultaneously in the concentration range 10–50 m M.

Platinum-195 magnetic resonance spectra of some platinum(II) and platinum(IV) complexes

The 195Pt magnetic resonance spectra of fourteen symmetrical, substitutionally inert octahedral Pt(IV) and square-planar Pt(II) complexes have been measured at 9.75 MHz using Fourier transform techniques. Chemical shifts observed in aqueous solutions of the PtL 6 m complexes cover a range of 6033 ppm and the shielding of the 195Pt nucleus is in the order Cl > 1 2 en > Br > SCN > CN > I. For aqueous solutions of the PtL 4 m complexes, the chemical shifts cover a range of 3876 ppm and the order of shielding is CI > NO 2 > NH 3 > Br > 1 2 en > SCN > CN > I. These results are interpreted in terms of covalency effects in the σ p contribution to shielding. Relaxation times T 1 and T 2 have been measured in several cases where the signal to noise was favorable. In addition the temperature dependence of T 1 has been investigated for H 2PtCl 6 and H 2PtCl 4 in aqueous HCl. The relaxation process for these two complexes appears consistent with a spin-rotation mechanism. The solvent dependence of the 195Pt resonance in PtCl 6 2− and PtCl 4 2− has also been measured for solutions tetra- n-butylammonium salts in a variety of nonaqueous solvents. Some proton and 13C NMR spectra have also been obtained for Pt(en) 3 4+ and Pt(en) 2 2+ in aqueous solution and some 13C spectra for Pt(CN) 6 2− and Pt(CN) 4 2− in D 2O/H 2O. Platinum-195 spin-coupling constants have been determined and some of the factors affecting coupling are discussed.

Polyhedral Clathrate Hydrates. III. Structure of the Tetra n-Butyl Ammonium Benzoate Hydrate

The compound (n-C4H9)4N·C6H5COO·39½H2O forms tetragonal crystals with four molecules in the unit cell. The water structure is a hydrogen-bonded clathrate framework, in the cavities of which are located the tetra alkyl ammonium cations. The oxygen atoms of the benzoate anions are hydrogen-bonded to the water framework and form part of the polyhedral structure. This structure contains 10 pentagonal dodecahedra, 16 tetrakaidecahedra, and four pentakaidecahedra per unit cell. The 20 larger polyhedra are occupied by the 16 alkyl and four benzyl groups with a statistical disorder over two sets of equivalent cation and anion positions. There is evidence of additional hydrogen-bonded water inside some of the dodecahedra which are distorted due to the presence of the ions. The clathrate framework is iso-structural with that of other salts in this series, which have a very similar tetragonal lattice but differ in containing five tetra n-butyl ammonium salt molecules per unit cell.