Transference numbers for anhydrous methanol solutions at 10 and 25°C

Transference numbers are reported for LiCl and NaCl in methanol at 25°C and for NaCl, KCl, and Bu₄NBr in methanol at 10°C. The potentiometric moving-boundary method as developed by Kay and Fratiello was employed to give a precision of about 0.05% and an accuracy of at least 0.1% as indicated by two independent determinations of the conductances of the Cl^– and Br^– ions. The data are extrapolated by the Fuoss-Onsager theory, and the magnitude of the electrophoretic effect is calculated as described by Kay and Dye. The agreement with this theory is quite good at both temperatures, although the å value required in the case of Bu₄NBr is considerably larger than that obtained from conductance data. This agreement contrasts with that obtained for ethanol and acetone solutions where the measured electrophoretic effect is considerably larger than the corresponding calculated values. The importance of this fact in the determination of ion-pair association constants is discussed.     

Second-sphere ligand-field effects in solid solutions of anhydrous transition-metal phosphates

Powders of the solid solutions In1-xCrxPO4 (0 < or = x < or = 1), In1-xCrx(PO3)3 (0 < or = x < or = 1), (In1-xCrx)4(P2O7)3 (0 < or = x < or = 0.7), and In1-xMnx(PO3)3 (0 < or = x < or = 0.8) have been synthesized by solid-state reactions. Depending on the dopant concentration, these materials show striking variations in color [In1-xCrxPO4, light pink to green-brown; (In1-xCrx)4(P2O7)3, light pink to red-brown; In1-xCrx(PO3)3, pale green to green; In1-xMnx(PO3)3, light blue to purple). Powder reflectance spectra of the solid solutions were measured in the UV/vis/NIR region (5500-35000 cm(-1)). Observed d-d electronic transition energies and results of calculations within the framework of the angular overlap model (AOM) for the low-symmetry chromophores [M(III)O6] (M = Cr, Mn) are in good agreement. In the case of the mixed In/Cr phosphates, the observed color changes can be related to second-sphere ligand-field effects. Clear evidence for differences in the pi-bonding of oxygen toward Cr(3+) (d(3) ion) and In(3+) (d(10) ion) are observed. For In1-xMnx(PO3)3, the variation in color is attributed to a slightly increasing elongation of the [Mn(III)O6] chromophore with increasing dopant concentration.     

A new pathway in the reactions of chromones and hydroxylamine in anhydrous solutions

In the nucleophilic reaction of chromone ($\text{1}$) with NH₂OH·HC1 in anhydrous methanol a new compound 2-methoxychromanone ($\text{6}$) appeared as an intermediate in the formation of chromone oxime ($\text{8}$) and 2-methoxychromanone oxine ($\text{7}$).     

Preparation of pure hydrogen peroxide and anhydrous peroxide solutions from crystalline serine perhydrate

Hydrogen peroxide is one of the most versatile oxidation reagents, still it has not fully been exploited by synthetic chemists since anhydrous (let alone pure) hydrogen peroxide requires hazardous preparation protocols. We have recently reported on the crystallization of serine and other amino acid perhydrates, thus paving the way for a new method for laboratory-scale production of anhydrous hydrogen peroxide solutions. Serine is insoluble in most organic solvents (e.g., methanol, ethyl acetate, and methyl acetate) that readily dissolve hydrogen peroxide. Moreover, since the adduct of hydrogen peroxide and serine is unstable in these organic solvents, crystalline serine perhydrate readily decomposes to give anhydrous solutions of hydrogen peroxide and crystalline precipitate of the amino acid. This procedure can then yield an anhydrous hydrogen peroxide solution in a single step. Moreover, filtration of the amino acid, and room temperature evaporation of the volatile solvent (e.g., methyl acetate), yields over 99% hydrogen peroxide.     

Electrochemical study of the methylcyclopentane oxidation in anhydrous hydrogen fluoride and HF−SbF5 superacid solutions

The electrochemical study of methylcyclopentane (MCPH) oxidation in anhydrous hydrogen fluoride and related superacid media leads to determination of the standard potentials of the MCPH redox couples and to the establishment of the potential acidity diagram of MCPH. Fromtthese results the oxidation by H⁺ ion of MCPH into the carbenium ion MCP⁺ is observed in acidic media: pH<6 or R(H)<?21.9 (pH values are reported on the acidity scale in HF, pH=0 for a molar solution of SbF₅, and the acidity levels are referred to H₂O by means of an R(H) function: for pH=0, R(H) is ?27.9). In HF?SbF₅ mixtures, pH<2.3 or R(H) <?25.6, the protonation of MCPH to form the carbonium ion MCPH₂⁺ has to be taken into account and the acidity constant is determined. In basic media, pH>8.1 or R(H)>?19.8, condensation reactions are enhanced through a radical oxidation state; the disproportionation constant of the dimer (MCP)₂ is determined. Moreover, in the most acidic media, pH<2 or R(H)<?25.9, evidence for the cracking of MCPH through the protolysis of a C?C bond is shown.     

Study of monensin complexes with monovalent metal lons in anhydrous methanol solutions

Potentiometric and cyclo-voltammetric studies have been carried out on monensin anion (Mon^–) complexes with the alkali ions as well as with Tl⁺ and Ag⁺ in absolute methanol solutions. The log K_f values obtained for the complexity constants and corrected for the activity effects are: Li⁺, 3.3±0.1; Na⁺, 6.72±0.05; K⁺, 5.18±0.05; Rb⁺, 4.58±0.05; Cs⁺, 3.75±0.05; Tl⁺, 5.31±0.05; Ag⁺, 8.2±0.2. It is seen that for the alkali, the most stable complex is formed with Na⁺. The enthalpy and entropy of complexation with the sodium ion were found to be H^o=–5.47±0.24 kcal-mole^–1 and S^o=+12.4±0.7 e.u. The complex, therefore, is enthalpy and entropy stabilized.     

Thermochemical study of two anhydrous polymorphs of caffeine

The mean values of the standard massic energy of combustion of caffeine in phase I (or alpha) and in phase II (or beta) measured by static-bomb combustion calorimetry in oxygen, at T = 298.15 K, are Δ_cu^° (C₈H₁₀O₂N₄, I) = −(21823.27 ± 0.68) J · g⁻¹ and Δ_cu^° (C₈H₁₀O₂N₄, II) = −(21799.96 ± 1.08) J · g⁻¹, respectively.The standard (p^° = 0.1 MPa) molar enthalpy of formation in condensed phase for each form was derived from the corresponding standard molar enthalpies of combustion as, and .The difference between the standard enthalpy of formation of the two polymorphs in condensed phase was also evaluated by using reaction-solution calorimetry. The obtained result, 2.04 ± 0.25 kJ · mol⁻¹, is in agreement, within the uncertainty, with the difference between the molar enthalpies of formation obtained from combustion experiments (4.5 ± 3.2) kJ · mol⁻¹, which can be considered as an internal test for consistency of the results.A value for the standard enthalpy of formation of caffeine in the gaseous state was proposed: , estimated from the values of the standard enthalpies of formation of both crystalline forms obtained in this work, and the data on standard enthalpies of sublimation collected from the literature.     

A new apparatus for the extraction of organic compounds from aqueous solutions

A new apparatus for the extraction of organic compounds from sea water is described. With this apparatus it is possible to extract 54 standard compounds with high recovery percentages from 9 1 of sea water with 3 ml ofn-hexane. The analysis time (about 1 h) is appreciably lower than those of the extraction methods based on RP-18 and Carbopack-B adsorption (about 15 h). Furthermore, it is possible to analyze samples without filtration. An application of this method to the analysis of Tirreno sea water is reported.     

A new procedure for preparation of anhydrous perchloric acid employing anhydrous magnesium perchlorate

The dehydration of hydrated perchloric acid to yield anhydrous acid is described. Anhydrous (5·5% water content) magnesium perchlorate is employed as desiccant followed by distillation under reduced pressure. The new procedure is less complicated than previously described processes, and is convenient for the preparation of small amounts to be employed in studies of the preparation of anhydrous metallic perchlorates from reactions with suitable selected reagents, and for convenient lecture demonstrations.     

Thermal decomposition of aqueous manganese nitrate solutions and anhydrous manganese nitrate. Part 3. Isothermal kinetics

The kinetics of the thermal decomposition of aqueous manganese nitrate solutions and anhydrous manganese nitrate in air were established from isothermal experiments. By heating the solution, first most of the water evaporates to a composition of equimolar amounts of water and manganese nitrate; this concentrated solution then decomposes to γ-Mn(NO₂, NO₂ and water, usually in two steps. The first step can be described best by the model [?ln(1 ? α)]^{$\text{1}\text{2}$} = 8.9 × 10¹¹ exp(?121000/RT)t, whereas the second step is described equally well by several models. The kinetic parameters of these models are quite similar, the average activation energy being 141 kJ mole^?1.The decomposition of anhydrous Mn(NO₃)₂, which proceeds in a single step, can also be described with several similar models. In this case the average activation energy is about 92 kJ mole^?1.     

Raman and infrared spectroscopic study of the anhydrous carbonate minerals shortite and barytocalcite

The Raman spectra of shortite and barytocalcite complimented with infrared spectra have been used to characterise the structure of these carbonate minerals. The Raman spectrum of barytocalcite shows a single band at 1086cm(-1) attributed to the (CO(3))(2-) symmetric stretching mode, in contrast to shortite where two bands are observed. The observation of two bands for shortite confirms the concept of more than one crystallographically distinct carbonate unit in the unit cell. Multiple bands are observed for the antisymmetric stretching and bending region for these minerals proving that the carbonate unit is distorted in the structure of both shortite and barytocalcite.     

DSC study of phase transition of anhydrous phospholipid DHPC and influence of water content

The phase transition behavior of 1,2-di-n-heptadecanoyl phosphatidylcholme (DHPC)with and without water has been studied by use of differential scanning calorimetry It was found by experiment that the glass transition occurred at first during the first heating of a sample of DHPC without water and then the sample underwent melting as an ordinary crystal.Therefore the sample of DHPC without water was a glassy crystal However,the DHPC sample crystallizing from melt was an ordinary crystal From the relationship between the total melting enthalpy Qf of freezable water and the water content h,it was concluded that the water contained in the DHPC samples might exist in three states recognizable thermodynamically.The water in the first state was an unfreezable water It was the water bound directly with the head groups of the phospholipid,i.e.the primary hydration water Every head group might bind seven such molecules of water.The water in the second state was the secondary hydration water,us melt ing point was     

Heteropolyacid-encapsulated self-assembled materials for anhydrous proton-conducting electrolytes

The composite material of heteropolyacid (12-phosphotungstic acid; PWA) and polystyrene sulfonic acid (PSS) construct the PWA-encapsulated material by the self-assembly of -SO3H onto the PWA surface; as a result, the fast proton transfer occurred at the interface between the PWA and -SO3H, and the encapsulated material indicated the high anhydrous proton conductivity of 1 x 10(-2) S cm(-1) at 180 degrees C. These anhydrous proton-conducting materials without the existence of water molecules are quite different from customary ion-exchange membrane, such as Nafion, and may have advantages as an electrolyte membrane for polymer electrolyte membrane fuel cells operating at intermediate temperatures under anhydrous conditions but also for electrochemical devices including electrochromic displays, chemical sensors, and others.     

Sodium ibuprofen dihydrate and anhydrous

(R,S)-(±)-ibuprofen sodium salt (racemate) dihydrate (SID) was dehydrated and the physicochemical properties of SID and the anhydrous forms (SIA) were compared by different analytical techniques (scanning electron microscopy, helium pychnometry, differential scanning calorimetry, X-ray powder diffractometry). The dehydration of SID, followed by thermogravimetry in isothermal conditions, allowed to calculate the activation energy of the dehydration process and to predict the mechanism of dehydration. Dehydration occurred in one step and the activation energy was rather low, indicating the ease of water removal from the crystal. The mechanism of dehydration followed a three dimensional diffusion (Jander equation). Similarly to the dehydration, the hydration process was followed under isothermal conditions by exposing the anhydrous powder at 64% RH at different temperatures. The mechanism of hydration was governed by a two dimensional diffusion and the energy associated to the process was very low, indicating the ease of crystal hydration. The driving force for the hydration is higher than that for the dehydration. From a thermodynamic point of view this fact may explain why the hydrated form is more stable than the anhydrous one. Solubilities, determined at different temperatures in water and in phosphate buffer (pH 6.8), showed that SID is more soluble in water than SIA for temperatures higher than approximately 283 K. On the contrary, in phosphate buffer SIA is always more soluble than SID in the temperature range considered for the experiments. Drug release reflects the solubility in water and phosphate buffer previously reported.     

On the application of a laser T-jump apparatus for perturbation of ionic micellar solutions

A laser T-jump apparatus which permits the detection of relaxation processes in ionic micellar solutions by conductivity measurements without addition of dyes or electrolytes, is briefly described. The apparatus is used to determine the time constants as well as the relative amplitudes of the slow relaxation process in the system H₂O-NaDS at 15 and 25°C. The time constants are in good agreement with those obtained by other methods. The concentration dependence of the relative amplitudes is well described by the existing theory. The comparison yields, in particular, that at room temperature the mean aggregation number of the NaDS micelles decreases with rising temperature.     

Coordination-network-based ionic plastic crystal for anhydrous proton conductivity

An ionic coordination network consisting of protonated imidazole and anionic one-dimensional chains of Zn(2+) phosphate was synthesized. The compound possesses highly mobile ions in the crystal lattice and behaves as an ionic plastic crystal. The dynamic behavior provides a proton conductivity of 2.6 × 10(-4) S cm(-1) at 130 °C without humidity.