Phosphonium Ion Research Articles

Distinct π-Bonding Capability between Phosphinidene and Phosphonium Ion: A Computational Study

The heavy dipnictenes (RE=ER, where E=P, As, Sb, and Bi with the substituent R) have essentially planar geometry and appreciable strength in pi-bonding, unlike related heavier main group 14 analogues of alkenes as concluded recently by Power. This work demonstrated that the protonated pnictenes behave more like the heavy carbene for their weak pi-bonding character from the computational study with the B3LYP/6-311++G** method. For example, although both phosphinidene (HP) and the phosphonium ion (H2P+) are isoelectronic to silylenes, the pi-bonding tendency of the former is rather strong and it forms a planar adduct with both the stable carbene and stable silylene ((HCNH)2E, where E=C and Si). In contrast, the latter forms trans-bent adducts with the two species. These results can be interpreted in terms of the Carter-Goddard-Malrieu-Trinquier (CGMT) model, and the fact that the value of DeltaEST [E(triplet)-E(singlet)] of the HP fragment increases significantly after protonation. All other heavy pnictenes resemble the phosphinidene. In contrast, nitrene (HN) and nitrenium (H2N+) have a ground triplet state, thus both have strong pi-bonding character similar to that of carbene.

Gas phase FT ICR investigation of the production of phosphoranides and ion chemistry of tris(trifluoromethyl)phosphine

In a long cylindrical ion cyclotron resonance (ICR) cell the ion chemistry of tris(trifluoromethyl)phosphine has been investigated. The only major negative primary ion, produced by dissociative electron attachment is the phosphide ion (CF 3) 2P −, which reacts at elevated kinetic energy with the neutral molecules at 2 × 10 −7 mbar to produce three phosphoranides: CF 3PF 3 −, (CF 3) 2PF 2 −, and (CF 3) 3PF −. Simultaneously, three minor ions CF 3 −, F −, and C 2F 3 − are formed by self-collision-induced dissociation. Ion–molecule reactions between CF 3 − and (CF 3) 3P have also been investigated. Positive ions form phosphonium ions and a diphosphonium product ion, (CF 3) 2P–P(CF 3) 3 +, whereas no P–P bond is observed with negative ions. All the structures and reaction pathways have been investigated theoretically with the aid of DFT calculations. The results are in excellent agreement with the experiments. The electron affinity of tris(trifluoromethyl)phosphine as EA((CF 3) 3P) = 22.6 kcal/mol has been calculated.

Effect of π-donating substituents on the dative or covalent character of adducts of some simple “enium” ions with PMe 3 and NMe 3

The charge distribution, molecular structure and bond cleavage of formal donor adducts of phosphenium, arsenium, and the isolobal selenenyl cations with trimethylphosphane and trimethylamine have been explored by quantum chemical methods on Hartree–Fock, DFT and MP2 level. According to our results, adducts of methyl substituted cations are mainly covalent and therefore should be better described as phosphonium or ammonium ions. Switching from methyl substituted “enium” ions to their π-donor substituted analogs increases the dative character of the central bond to an extent for which a description as donor adducts of phosphenium or arsenium ions appears appropriate, while their selenium congener still remains preferentially covalent.

A Simple One‐Pot Entry to Cyclic Ethers of Varied Ring Sizes from Diols via Phosphonium Ion Induced Iodination and Base Catalyzed Williamson Etherification.

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Preparation and Characterization of Epoxy/Clay Nanocomposites

Epoxy/clay nanocomposites have been prepared using montmorillonite (MMT) ionexchanged with various organic cations ; hexadecyltributyl phosphonium ion, octadecyltrimethyl ammonium ion, methyl tallow bis-2-hydroxyethyl ammonium ion and dimethyl hydrogenatedtallow (2-ethylhexyl) ammonium ion. The resulting nanocomposites were found to show exfoliated clay structure by using transmission electron microscopy (TEM) and X-ray diffractometry (XRD). The flame retarding property of 5wt% clay/epoxy nanocomposites was found to be enhanced when compared with that of the original epoxy without clay.

Mechanism of the sulfurisation of phosphines and phosphites using 3-amino-1,2,4-dithiazole-5-thione (xanthane hydride)

Contrary to a previous report, the sulfurisation of phosphorus(III) derivatives by 3-amino-1,2,4-dithiazole-5-thione (xanthane hydride) does not yield carbon disulfide and cyanamide as the additional reaction products. The reaction of xanthane hydride with triphenyl phosphine or trimethyl phosphite yields triphenyl phosphine sulfide or trimethyl thiophosphate, respectively, and thiocarbamoyl isothiocyanate which has been trapped with nucleophiles. The reaction pathway involves initial nucleophilic attack of the phosphorus at sulfur next to the thiocarbonyl group of xanthane hydride followed by decomposition of the phosphonium intermediate formed to products. The Hammett rho-values for the sulfurisation of substituted triphenyl phosphines and triphenyl phosphites in acetonitrile are approximately -1.0. The entropies of activation are very negative (-114+/-15 J mol-1 K-1) with little dependence on solvent which is consistent with a bimolecular association step leading to the transition state. The negative values of DeltaS(not equal) and rho values indicate that the rate limiting step of the sulfurisation reaction is formation of the phosphonium ion intermediate which has an early transition state with little covalent bond formation. The site of nucleophilic attack has been also confirmed using computational calculations.

Thermal analysis of montmorillonites modified with quaternary phosphonium and ammonium surfactants

The thermal stability of seven organically modified montmorillonites (‘organoclays’) has been investigated using differential thermal analysis, differential scanning calorimetry, and thermogravimetry in conjunction with X-ray diffractometry. Six organoclays were synthesised by replacing the interlayer inorganic cations, initially present, with quaternary phosphonium and ammonium surfactant cations. The samples modified with tetrabutylphosphonium (TBP), and butyltriphenylphosphonium (BTPP) ions have an appreciably higher thermal stability than the octadecyltrimethylammonium (ODTMA)-modified clays. Thus, in the case of TBP- and BTPP-modified montmorillonites, the onset temperature of decomposition is close to 300 °C. Samples modified with hexadecyltributylphosphonium (HDTBP) ions have a lower onset temperature of decomposition of 225 °C. In comparison, the onset temperature for ODTMA-montmorillonites (obtained at different concentrations of ODTMA-bromide) ranges from 158 to 222 °C, being highest where the concentration of intercalated surfactant is lowest. The onset temperature for a commercial alkylsilane-treated quaternary ammonium-modified organoclay (S-BEN N-400FP) is 207 °C. The basal spacing of the TBP- and BTPP-modified clays is 1.7–1.8 nm, indicating a monolayer arrangement of quaternary phosphonium ions in the interlayer space, while the value of 2.5 nm for HDTBP-montmorillonite indicates a more open structure. The ODTMA-modified samples have basal spacings ranging from 1.9 to 2.1 nm, indicative of a bilayer to pseudo-trilayer arrangement. The exceptionally high basal spacing of 3.4 nm for the S-BEN N-400FP organoclay might be due to interlayer penetration of organosilane hydrolysis products during synthesis. The thermal properties of organoclays are apparently related to the nature of the surfactants and their arrangement in the interlayer space of montmorillonite.

A simple one-pot entry to cyclic ethers of varied ring sizes from diols via phosphonium ion induced iodination and base catalyzed Williamson etherification

A novel and an efficient one-pot cyclization method using triphenylphosphine, iodine and a nitrogenous base has been established for the synthesis of cyclic ethers of various ring sizes. This appears to follow a two-step procedure, which includes preferential substitution of one hydroxyl group by an iodide generated in situ followed by an intramolecular ring closure through the attack of a free hydroxyl group or the more nucleophilic oxide ion.

Density, Viscosity, and Conductivity of Tetraalkyl Phosphonium Ionic Liquids

The density, viscosity and conductivity of nine commercially available tetra-alkyl phosphonium ionic liquids (ILs) are presented. The effect of cation volume and symmetry, anion volume, and temperature are observed. The Vogel-Tamman- Fulcher (VTF) equation is used to calculate the theoretical glass transition temperature (To) and the activation energy of conductivity Ea,Λ. The conductivity of three halo-aluminate ionic liquid systems for mole fractions up to 0.7 AlCl3 is reported.

Reactions of Ph4Se4Br4 with tertiary phosphines. Structural isomerism within a series of R3PSe(Ph)Br compounds

The synthesis and characterisation of Ph(4)Se(4)Br(4) (1) directly from the reaction of Ph(2)Se(2) with dibromine is reported. The solid-state structure of 1 consists of four PhSeBr units linked by weak selenium-selenium bonds [3.004(2)-3.051(2) A] into a Se(4) square, and is structurally analogous to the previously reported Ph(4)Te(4)I(4). The reactions of Ph(4)Se(4)Br(4) with a variety of tertiary phosphines have been undertaken, resulting in the formation of compounds of formula R(3)PSe(Ph)Br. X-Ray crystallographic analysis of three of the compounds reveals different structural isomers. Ph(3)PSe(Ph)Br (2) is a charge-transfer (CT) compound [Se-Br 3.0020(8) A], with an essentially linear P-Se-Br bond angle, 172.15(4) degrees and T-shaped geometry at selenium. Me(3)PSe(Ph)Br (5) also contains the selenium atom in a T-shaped geometry, consistent with a CT formulation, although the Se-Br distance of 3.327(3) A is considerably longer than observed for 2. In contrast, Cy(3)PSe(Ph)Br (6) is an ionic phosphonium salt, [Cy(3)PSePh]Br with no short Se-Br interactions. Geometry at selenium is bent, as expected for an ionic compound. These results are discussed with reference to the previously reported iodo-compounds Ph(3)PSe(Ph)I and [(Me(2)N)(3)PSe(Ph)]I.

Ion/molecule reactions in a miniature RIT mass spectrometer

Ion/molecule reactions were explored in a newly developed miniature mass spectrometer fitted with a rectilinear ion trap (RIT) mass analyzer. The tandem mass spectrometry performance of this instrument is demonstrated using collision induced dissociation (CID) and ion/molecule reactions. The latter includes Eberlin transacetalization reactions and electrophilic additions. Selective detection of the chemical warfare simulant dimethyl methyl phosphonate (DMMP) was achieved through selective Eberlin reactions of its characteristic phosphonium fragment ion CH3OP(+)(O)CH3 (m/z 93), with 1,4-dioxane or 1,3-dioxolane. Efficient adduct formation as a result of electrophilic attack by the phosphonium ion on various nucleophilic reagents, including 1,1,3,3-tetramethyl urea, methanesulfonic acid methyl ester, dimethyl sulfoxide and methyl salicylate, was also observed using the RIT device. The product ions of these reactions were analyzed using CID and the characteristic fragmentation patterns of the ionic addition products were recorded using multiple-stage experiments in the miniature RIT instrument. This study clearly demonstrates that a small, home-built, miniature RIT mass spectrometer can be used to perform analytically useful ion/molecule reactions and also that instruments like this have the potential to provide a portable platform for in situ detection of organophosphorus esters and related compounds with high specificity using tandem mass spectrometry.

A study of NMR chemical shielding in 5-coordinate phosphorus compounds (phosphoranes)

Calculations of the phosphorus NMR chemical shielding in 5-coordinate phosphorus compounds have been carried out using the gauge-including-atomic-orbital (GIAO) 6-311+G(nd,p) basis set at both scaled density functional theory (sDFT) and estimated infinite order Møller–Plesset (EMPI) approaches. Results are generally in accord with previous studies on 3-coordinate phosphorus compounds but fail badly for compounds containing multiple chlorine atoms and indicate a need for a relativistic treatment of these species. We observe that some compounds with reported experimental 31P NMR chemical shifts far downfield of the calculated values are in fact in the range known from experiment and calculation to be in that expected for phosphonium ions; the reported structures need to be reconsidered.

Gas-Phase Synthesis, Characterization, and Reactivity Studies of the Prototype Aromatic Phosphirenylium Ion

The unsubstituted phosphirenylium ion, cyclo-C2H2P+, was generated in the gas phase via an addition−ablation strategy employing a modified quadrupole ion-trap mass spectrometer. The reaction of gas-phase PBr+ with acetylene affords H2C2P+ as the sole product ion. Its structure is that of the phosphirenylium cation (1). Experimental results find support from density functional theory calculations at the B3LYP/6-31G* and G3//B3LYP/6-31G* levels. The reaction of PBr+ with acetylene is predicted to be exothermic with respect to the formation of two isomers, the phosphirenylium cation (1) and the ethenylidenephosphenium cation (2), whereas formation of eight other isomers is endothermic. Reactions of 1 with acetylene and ethylene do not lead to observable products, but 1 does react with 1,3-butadiene as a phosphenium ion via formal 1,4-addition to give the 3-phosphaspiro[2,4]-hepta-1,5-diene phosphonium ion. The formation of this P-spiro adduct is predicted to be a stepwise process. An isotopic labeling experiment supports this structure, which is predicted by computational modeling to be kinetically favored over a lower energy structure that could arise from a Diels-Alder-like reaction of the phosphirenylium ion.

Examination of the Covalent Cationization Method Using Narrow Polydisperse Polystyrene

Four bromine- and phosphonium-terminated polystyrenes were analyzed by matrix-assisted laser desorption/ionization (MALDI) mass spectrometry (MS) using covalent cationization. Bromine-terminated polystyrenes were prepared by atom transfer radical polymerization (ATRP) giving narrow molar mass (MM) distributions with number-average molar mass ranging from 2 to 40 ku. The resultant bromine end group was converted to a phosphonium ion. Precharging the polymer by covalent cationization is an alternative approach to traditional metal cationization for MALDI−MS polymer analysis. MALDI−MS, gel permeation chromatography, and proton nuclear magnetic resonance analyses confirmed ATRP synthesis and end group modification of the polystyrenes. High performance liquid chromatography at the critical point of adsorption was used to determine a phosphonium salt conversion between 37% and 90%. Similar MMs and MM distributions determined by MALDI−MS analysis were observed for Br-terminated polystyrene ionized using traditio...

Does phosphoryl protonation occurs in aqueous phosphoesters solutions

Ionisation of trimethylphosphate (TMP), dimethylphosphate (DMP) and diethylphosphate (DEP) is investigated by acidic titration in water by Raman (R), Fourier transform infrared (FTIR) and nuclear magnetic resonance (NMR) spectroscopies. The vibrational frequencies of the PO 2 − ionic form and the neutral form were found in accord with the literature. While increasing further H + concentration, the P O band disappears in the benefit of new ones. These results, together with deuteration experiments indicate the presence of a new ionic form positively charged with general formula R 1R 2R 3P(OH) + or R 1R 2P(OH) + 2. The p K of this phosphonium entities is lying in the range −2, −4. These results were confirmed by 31P NMR titration. The occurrence of such a phosphonium ion in aqueous solutions might be of crucial importance for biochemical reactions and interactions, owing to the large spread of phosphoryl group in biomolecules and keeping in mind that intracellular compartments are more likely concentrated media with little free water than real aqueous solutions. Furthermore, p K's can be shifted by physical–chemical parameters like dielectric constant and electric field. This may involve at least fractional positive charge apparition that might be important in biochemical regulation by charge–charge and charge–dipole interactions. This finding will gain to be further explored on more complex molecules like phospholipids, nucleic acids and proteins.

Rates and Equilibria of the Reactions of Tertiary Phosphanes and Phosphites with Benzhydrylium Ions

The kinetics of the reactions of benzhydrylium ions and quinone methides with eight tertiary phosphanes and two phosphites were investigated photometrically. The nucleophilicity parameters N and slope parameters s of these nucleophiles were derived according to the equation log k(20 degrees C) = s(N + E). Correlations of the nucleophilicity parameters N with pK(Ha) and sigma(p) values as well as with the rate constants of reactions with other electrophiles are discussed. In some cases, equilibrium constants for the formation of phosphonium ions were measured, which allow one to determine the Marcus intrinsic barriers of DeltaG(0) (not equal) = 58 kJ mol(-1) for the reactions of triarylphosphanes with benzhydrylium ions. The N parameters [5.51 for P(OPh)3, 10.36 for P(OBu)3, 14.33 for PPh3, 15.49 for PBu3, 18.39 for P(4-Me2NC6H4)3] are compared with the reactivities of other classes of nucleophiles (see, www.cup. uni-muenchen.de/oc/mayr).

Gas-phase reactivity of the O?P(OCH3)2+ phosphonium ion towards ?,?-unsaturated esters in a quadrupole ion trap

Ion-molecule reactions between the O=P(OCH3)2 + phosphonium ions and eight alpha,beta-unsaturated esters (methyl acrylate, ethyl acrylate, methyl crotonate, ethyl crotonate, methyl 3,3-dimethylacrylate, ethyl 3,3-dimethylacrylate, methyl methacrylate and ethyl methacrylate) were performed in a quadrupole ion trap mass spectrometer. The O=P(OCH3)2 + phosphonium ions, formed by electron ionization from neutral trimethyl phosphite, were found to react with alpha,beta-unsaturated esters to give an adduct [RR'C=CR''COOR''', O=P(OCH3)2]+, which lose spontaneously a molecule of trimethyl phosphate (R'''=CH3) or dimethyl ethyl phosphate (R'''=C2H5). An ion corresponding to a protonated trialkyl phosphate is also observed when substituent R''=H. To confirm the experimental results, and to elucidate the mechanism for the formation of the ionic species, a theoretical study using the density functional theory (DFT) approach was carried out. The potential energy surface obtained from B3LYP/6-31G(d,p) calculations for the reaction between O=P(OCH3)2 + and methyl acrylate is described.

Meerwein reaction of phosphonium ions with epoxides and thioepoxides in the gas phase

Phosphonium ions are shown to undergo a gas-phase Meerwein reaction in which epoxides (or thioepoxides) undergo three-to-five-membered ring expansion to yield dioxaphospholanium (or oxathiophospholanium) ion products. When the association reaction is followed by collision-induced dissociation (CID), the oxirane (or thiirane) is eliminated, making this ion molecule reaction/CID sequence a good method of net oxygen-by-sulfur replacement in the phosphonium ions. This replacement results in a characteristic mass shift of 16 units and provides evidence for the cyclic nature of the gas-phase Meerwein product ions, while improving selectivity for phosphonium ion detection. This reaction sequence also constitutes a gas-phase route to convert phosphonium ions into their sulfur analogs. Phosphonium and related ions are important targets since they are commonly and readily formed in mass spectrometric analysis upon dissociative electron ionization of organophosphorous esters. The Meerwein reaction should provide a new and very useful method of recognizing compounds that yield these ions, which includes a number of chemical warfare agents. The Meerwein reaction proceeds by phosphonium ion addition to the sulfur or oxygen center, followed by intramolecular nucleophilic attack with ring expansion to yield the 1,3,2-dioxaphospholanium or 1,3,2-oxathiophospholanium ion. Product ion structures were investigated by CID tandem mass spectrometry (MS 2) experiments and corroborated by DFT/HF calculations.

Insights into the reactivity and structure of silylene phosphonium ions.

Experimental evidence for the intermediate occurrence of a so far unknown silylene phosphonium ion is presented and its reactivity and bond situation is discussed on the basis of ab initio calculations.

The Behavior of Zinc Metal in Alkaline Solution Containing Organic Inhibitors : II. Identification of Surface Films Formed on Zinc

Surface analysis obtained with the use of high resolution scanning electron microscopy and in situ atomic force microscopy revealed different morphology characteristics developed at the zinc surface in the presence of polyoxyethylene backbone based organic inhibitors. Fourier transform Infrared spectroscopy data show that polyoxyethylene alkyl phosphate ester acid [GAFAC RA 600] adsorbed on the zinc surface via the phosphonium ion head, while polyethylene glycol is adsorbed on the zinc surface via the alkoxide anion head. It was also established that the preferred organic inhibitor should include a linear polyoxyethylene chain. © 2003 The Electrochemical Society. All rights reserved.