Nitrobenzene Solution Research Articles

Dodecamethoxyorthocyclophane: conformational and dynamic properties studied by proton 2D exchange NMR

A new member of the orthocyclophane series, Le., 3,4,5,10,11,12,17,18,19,24,25,26-dodecamethoxy(l.1.1.1)- orthocyclophane (DCP), has been synthesized and its conformational and dynamic properties studied by ID and 2D proton NMR spectroscopy. Its proton NMR exhibits in solutions two subspectra due to two conformers. Molecular mechanics calculations and NMR chemical shift data indicate that these conformers correspond to the sofa and boat forms, respectively. The equilibrium constant between the two forms was determined at room temperature in a number of solvents. In all cases the ratio (sofa)/(boat) was larger than unity, but in general this ratio decreased with increasing the polarity of the solvent. Two-dimensional exchange NMR experiments were performed in order to investigate the various rearrangement mechanisms involving the two conformers. The results at 30 C in a nitrobenzene solution show that the direct sofa-sofa pseudorotation is most rapid (k, = 6.8 s-l), while pseudorotation of the boat is slow and proceeds mainly indirectly via the sofa form. There are two distinct sofa-boat interconversion processes with comparable rate constants (k, = 4.5 and k, = 4.7 s-'). X-ray diffraction measurements indicate that DCP crystals are monoclinic and belong to the space group Ella. There are two symmetry-related molecules per unit cell located at points of inversion symmetry, with geometry corresponding to that of the sofa conformation.

Comparative reactivities of hydroxylated polybutadienes with isocyanate in nitrobenzene

The rates of reactions between two hydroxylated polybutadienes (R-45M and H-110) and 1,6-hexamethylene diisocyanate (HDI) have been studied in nitrobenzene solution in the temperature range from 30 to 60°C. An analytical method was used to follow the kinetics of the reactions. The second-order rate constants were calculated and it was concluded that the reactivities of the two-NCO groups in HDI are identical. The rate of the R-45M/HDI reaction is slightly higher and its activation energy is lower than that of the H-110/HDI reaction. The R-45M/HDI reaction is slower in nitrobenzene solution than in chlorobenzene solution.

Selectivity coefficients of univalent cations for liquid ion-exchange membrane electrodes based on nitrobenzene

Liquid ion-exchange membrane electrodes, sensitive to potassium, caesium, tetramethyl-, tetraethyl- and tetrabutylammonium cations, were prepared and their response characteristics studied. The membranes of the electrodes were nitrobenzene solutions of tetrakis(4-fluorophenyl)borates of the respective cations. Selectivity coefficients were determined by the modified separate solution method and the reliability of such measurements is discussed. Values of the selectivity coefficients are given for 41 univalent cations in the range of almost 13 orders of magnitude. The values represent constants which are independent of the membrane composition and the activities of both primary and interfering ions in a sample solution. They give comprehensive information not only on the cation interference with the electrode response, but also on the extractability of the cations into nitrobenzene.

Extraction of polyethylene glycols with dicarbolide solutions in nitrobenzene

The extraction of polyethylene glycol of average molecular mass 400 (PEG 400) with dicarbolide solution in nitrobenzene and of longer-chain polyethylene glycol, of average molecular mass 1 500 (PEG 1 500), with chlorinated dicarbolide solution in nitrobenzene was studied. During the extraction of PEG 400, the polyethylene glycol solvates the Horg+ ion in the organic phase giving rise to the HLorg+ species (L is polyethylene glycol). The obtained value of the extraction constant Kex(HLorg+) = 933 is consistent with published data of metal extraction. Extraction of PEG 1 500 was treated applying the simplified assumption that the thermodynamic behaviour of PEG 1 500 is the same as that of n molecules of polyethylene glycol with relative molecular mass 1 500/n, each solvating one cation. For this model, the value of n = 3.2 ± 1.1 and the values of the extraction constants of the HL1/n,org+ and HL2/n,org+ species were obtained by using the adapted program LETAGROP. This value of n is consistent with published extraction data in the presence of polyethylene glycol with a relative molecular mass from 200 to 1 000.

On the anomalous magnetic quenching of positronium in solutions of nitrobenzene in hexane

A new explanation is proposed of the anomalous magnetic quenching of positronium found by others for solutions of nitrobenzene in hexane, but not benzene and cyclohexane. It is assumed that particular “swollen”-Ps-nitrobenzene states occurring during attachment-detachment of Ps on nitrobenzene at higher temperatures, give the effect. Depending on temperature and acceptor structure, the effect is expected for certain other solutions of electron acceptors. The effect is related to a similar effect in solid naphthalene.

The first conducting cationic bis-dithiolene complexes of nickel and gold

[Ni(dddt)2]3(BF4) 2 (I) was obtained as a crystalline solid by the electrochemical oxidation of the neutral complex, Ni(dddt) 2 [3-5] in nitrobenzene solution on a platinum anode applying a constant current of 5 ~A/cm 2 at 50 C. Et4NBF 4 was used as the electrolyte. The unit cell parameters of the monoclinic crystals at 295=K are as follows: a 15.998(2), b = ii.946(I), c 24.281(2) A, ~ 90.161(8) ~ V 4640.6(8) A 3 Z 4(C24H24FsNi3BzS24) space group P21/C. The structure of (I) features regular Ni(dddt) 2 stacks with short intrastack and interstack S..-S contacts of 3.45-3.68 A. Due to the latter, the stacks in the crystals form Ni(dddt) z layers in the bc planes, which alternate along the a-axis with BF 4 anion layers. The conductivity of (I) at -20~ is i ~-1.cm-1. [Au(dddt)2] + salts with BF 4, CI04, and IBr z anions were obtained by the electrochemical oxidation of neutral Au(dddt)2[2 ] . The conductivity of these salts is 10-50 ~-1.cm -I. M(dddt)2 cationic salts hold great interest since they are metal complex analogs of organic superconductors of the BEDT-TTF radicalcation salt family [6].

A nitrate-selective electrode based on bis(triphenylphosphine)iminium salts

A nitrate-sensitive electrode based on the ionic associates between bis(triphenylphosphine)iminium and nitrate ions in nitrobenzene solution is proposed. The electrode can be used for determinations of 10 −5 0.1 M nitrate in aqueous solutions.

Phosphorus-Nitrogen Compounds. I. Reactions of Cl2P(O).N[dbnd]PCl3with an Excess of Pyrrolidine: Isolation of an Acycylic Phosphazene, (H8C4N)2P(O).N[dbnd]P(NC4H8)3, Bis (Pyriolidinophosphinoyl)Amine, [H8C4N)2P(O)]2NH and Amidinium Salt, [CH3(H8C4N)C[dbnd]NH]. HCl

Abstract Reactions of 1-(dichlorophosphinyl)-2,2,2-trichlorophosphazene, Cl2P(O).N[dbnd]PCl3, with an excess of pyrrolidine led to the isolation of the acyclic pyrro-lidino-derivative, (H8C4N)2P(O).N[dbnd]P(NC4H8)3, and bis(pyrrolodinophosphinoyl) ∼ amine, [(H8C4N)2P(O)]2NH. N',N'-tetramethyleneacetamidiniumchloride, [CH3 ∼ (H8C4N)C[dbnd]NH]. HCl, was formed from CH3CN, pyrrolodine and HCl evolved during the reactions in CH3CN. The reactions of N3P3Cl6, N4P4Cl8, and N4P4(NHEt)2Cl6 with an excess of pyrrolidine in CH3CN gave the above mentioned amidinium salt and some known phosphazene derivatives. The phosphazene compounds promote the formation of the amidinium salt. The reaction of N3P3(NH2)2Cl4 with an excess of dimethylamine gives the free base, N3P3(NH2)2(NMe2)4, and its salt, N3P3(NH2)2(NMe2). HCl, but no amidinum salt, [Me(Me2N)C[dbnd]NH]. HCl could be separated as a stable product. The basicities of these phosphazene derivatives in nitrobenzene solution are reported. Possible reaction mechanisms fo...

Anomalous13C Isotropic NMR Shifts in Tetraalkylammonium Tetrahalometallate(II) Ion Pairs. I. Organic Substituent Effects

13C isotropic NMR shifts have been recorded for a number of tetrahalocobaltate(II) salts containing various quaternary ammonium cations in dichloromethane and nitrobenzene solution. The isotropic shifts are a consequence of ion- aggregate formation, and show great sensitivity to changes in the organic substituents about the -onium centre. The 13C shifts appear to be due in large measure to a predominantly Fermi contact (through-bond) mechanism, unlike the more usual shifts encountered in lanthanide-containing systems. The observed shift patterns correlate well with steric effects induced by the presence or absence of bulky substituents near the central cation nitrogen atom.

A General Route to 3-(Hydroxyaryl) Tetrahydro Pyridazines and 1, 2-Diazepines and Derivatives δ

Abstract A three step synthesis of l-acyl-3-(hydroxyaryl) tetrahydro pyridazines and 1, 2-diazepines starting from phenols is described. The hydrolytic lability of some intermediate chloroalkyl aryl ketones and a simple recovery of these ketones from nitrobenzene solution are indicated.

Addition compounds of bis(trifluoromethyl)mercury with tetraphenylphosphonium and tetraphenylarsonium halides and thiocyanates

Addition compounds of Hg(CF 3) 2 with [Ph 4P]X and [Ph 4As]X in the 1:1 ratio for X = Cl, Br, I as well as in the 1:2 ratio for X = SCN, were isolated from aquaeous solution and identified by elemental analysis and infrared spectroscopy. Molar conductance of the thiocyanate compounds in nitrobenzene solution points to its complex-salt nature defined as [Ph 4P] 2[Hg(CF 3) 2(SCN) 2] and [Ph 4As] 2[Hg(CF 3) 2-(SCN) 2], but not for the halide compounds. However, in the monoclinic crystals of the chloride ccompound, as shown by X-ray diffractometry, pairs of [Hg(CF 3) 2 molecules are bridged over by two chlorides in a centro-symmetrical dimer with the CHgC bond angle of 160.5(8)° and the Hg…Cl bond length of 2.823(3) and 2.837(4) Å. The structure was refined to the R factor of 0.053. When X = CN no addition compounds were obtained, the reaction products were HCF 3 and the complex salts [Ph 4P] 2- [Hg(CN)] 4 and [Ph 4As] 2[Hg(CN)] 4, not described so far.

Properties of the nonlinear dielectric effect in critical nitrobenzene in n-alkane solutions in a broad range of temperatures

Measurements of the nonlinear dielectric effect (NDE) have been performed in a broad temperature range, of the order of 100 K wide, for critical solutions of nitrobenzene in n-octane, octadecane and eicosane. A particular case was that of the eicosane solution where the background effect was considerable less than in the other solutions. Even if the background effect is neglected, the experimental data may be described by a power law dependence with an exponent of approximately 0.4.

A new liquid membrane electrode for the selective determination of perrhenate

A new perrhenate ion-selective electrode has been developed, incorporating a nitrobenzene solution of nitron perrhenate as a liquid membrane. The electrode gives near-Nernstian response to 3 × 10 −5-10 −2 M perrhenate over the pH range 3–8. Most common anions (except for periodate and perchlorate) give little interference. The electrode has been satisfactory for direct potentiometric determination of as little as 10 μ/ml rhenium. The average recovery and standard deviation were 99% and 2.1%, respectively. Measurements of the solubility products of some sparingly soluble perrhenates gave results that agreed closely with those recorded in the literature and obtained by other procedures.

Supporting Electrolytes for Voltammetric Study of Ion Transfer at Nitrobenzene/Water Interface

The polarizable potential range was determined by cyclic voltammetry for the interface between an aqueous solution of lithium chloride or magnesium sulfate and a nitrobenzene solution of various electrolytes: tetrabutylammonium salts of tetraphenylborate, tetrakis(4-fluorophenyl)borate, tetrakis(4-chlorophenyl)borate, and tetrakis[3, 5- bis(trifluoromethyl)phenyl]borate, and tetrapentyl- and tetrahexylammonium salts of tetraphenylborate. The anodic and cathodic limits of polarizable potential range were discussed with reference to the standard ion-transfer potentials of the supporting-electrolyte ions.

Critical properties of nitrobenzene +n-alkanes solutions

Abstract Coexistence curves and critical parameters are given for solutions of nitrobenzene with a series of n-alkanes from n-pentane to n-eicosane. By mixing suitable n-alkanes, a pseudosolvent was obtained and the critical properties of the nitrobenzene + pseudo-n-alkane solution were compared with those of the corresponding binary solution.

Stoichiometry Determination of Cation–Macrocyclic Complexes Based on the 1H NMR Chemical Shift of the Cation-Coordinated Water Molecules

Abstract The stoichiometries of alkali and alkaline earth metal complexes with macrocyclic ligands were determined in a water-containing nitrobenzene solution by means of 1H NMR. The chemical shift of the water protons was more sensitive to the complexation than that of the methylene protons of the ligands.

Homogeneous and Electrochemical Electron-Transfer Reaction of Nitrobenzene Anion Radical Dissolved in Nitrobenzene

Abstract Nitrobenzene anion radical was stably prepared by the electrolytic reduction of nitrobenzene solution containing various kinds and amounts of tetraalkylammonium perchlorates. The rate constants of homogeneous electron-transfer reactions of these nitrobenzene anion radicals with nitrobenzene molecules as a solvent were determined by ESR method at various temperatures. These rate constants at 25 °C were about 107 dm3 mol−1 s−1 and comparable with the rate constant of electron-transfer reation between nitrobenzene and its anion radial in N,N-dimethylformamide. The quasi-first order rate constants evaluated from these rate constants were about 108 s−1 and were larger than the rate constants of the intramolecular electron-transfer reactions of the anion radical of bis(p-nitrophenyl) compounds except for bis(p-nitrophenyl)methane. The absorption spectrum of the solution of nitrobenzene anion radical in nitrobenzene containing 0.1 M tetrabutylammonium perchlorate or 0.1 M tetraethylammonium perchlorate showed an additional weak peak at about 800 or 900 nm as well as the ordinary peak. The light energies of these additional peaks were in good agreement with the energy values of the optical electron-transfer reactions evaluated according to the theory of Hush from the activation energies of corresponding thermal electron-transfer reactions. The rate constants of electrochemical electron-transfer reactions and the diffusion coefficients of nitrobenzene anion radical in nitrobenzene were also measured.

SOLVENT EXTRACTION OF CHROMIUM(Vl) BY 3-(4-PYRIDYL)-l,5-DIPHENYL PENTANE

ABSTRACT The distribution equilibrium of Cr(VI) between an aqueous sulfuric acid solution of potassium bichromate and a nitrobenzene solution of 3-(4-pyridyl)-l,5-diphenyl pentane (PDPP or B) has been studied. Hydrogen chromate ion among several ionic species of Cr(VI) in the aqueous solution is extractable in the present system. The chromium concentration in the organic phase is correlated with the concentrations of hydrogen chromate and hydrogen ion in the aqueous phase with PDPP in the organic phase. The interfacial reaction rate is also obtained and it gives the equilibrium relation by equating the extraction rate with the stripping rate. Results of the freezing point depression of the organic solution and the interfacial tension, obtained for the present system, indicate that the Cr(VT)-PDPP complex in the organic phase might be the aggregation of several molecules of chromate acid and PDPP, and that the complex is surface active. A Cr(VI)-PDPP complex adsorbed at the liquid-liquid interface reacts w...

Application of a periodate liquid membrane electrode to the determination of α-diols, carbohydrates and hydrazines

A liquid membrane electrode that is sensitive and reasonably selective for the periodate ion is described. It incorporates a nitrobenzene solution of nitron-periodate as an ion-exchange site. The electrode displays a near-Nernstian response for 10–2–10–5M periodate with an anionic slope of 55 mV (concentration decade)–1. The potential response is fast (<1 min) and almost independent of pH over the range 3–7. Selectivity coefficient data for 30 inorganic and organic anions show negligible interferences from most common anions. The electrode has been used satisfactorily for the direct determination of 0.01–2.5 mg ml–1 of periodate with an average recovery of 98.9% and a mean standard deviation of 1.4%. Some α-diols, reducing carbohydrates and hydrazines at concentrations of 0.05–2.5 mg ml–1 were determined by reaction with periodate under controlled conditions followed by measurement of the excess of the reagent. An average recovery of 98.2% and a mean standard deviation of 1.7% were obtained.

The dielectric behaviour of dipolar mixtures I: chlorobenzene–nitrobenzene mixtures

The dielectric absorption of dilute solutions of nitrobenzene, chlorobenzene, and their mixtures in cyclohexane and Decalin® have been measured in the microwave region at three temperatures between 20 and 40 °C. The relaxation times and thermodynamic parameters are determined. A single relaxation time is found for the mixtures, and the results are discussed.