Analysis of biodiesel conversion using thin layer chromatography and nonlinear calibration curves

Biodiesel (BD) is a fuel produced by the (trans)esterification reaction between the components of vegetable oil (or animal fat) and an alcohol. The presence of several substrates complicates analytical separation of the mixture, yet understanding of the complex reaction kinetics requires acquisition of a large body of data. The two well-established methods of gas chromatography (GC) and HPLC are time consuming and expensive when analyzing multiple samples. Additionally, it is not always possible to record all the reactants on one elution profile. We examined applicability of thin layer chromatography (TLC) for this purpose, where the detection was based on either flame ionization detector (FID) or a modified staining procedure. The suggested staining method gave no background and appeared well suited for quantitative analysis. The relevant calibrations are presented, and the general principles of analysis of nonlinear responses are discussed. Several experimental samples were produced by enzymatic conversion of rapeseed oil to BD. One reaction step resulted in 85-95% conversion (6h). The second step (after removal of glycerol and water) increased the yield to 97-98%. All components of the mixtures were separated and quantified. Relation of the BD contents measured by TLC and GC gave the values of 1.03±0.07 (TLC-staining) and 0.95±0.04 (TLC-FID), indicating applicability of the TLC-methods.     

The geometry of intermolecular interactions in some crystalline fluorine-containing organic compounds

The propensity of C-F groups to form C-F H-C interactions with C-H groups on other molecules has been analyzed. Crystal structures of molecules containing only carbon, hydrogen, and fluorine, but no oxygen, nitrogen, or other hydrogen-bond-forming elements, were chosen for an initial study in which the intermolecular interactions in crystal-structure determinations of polycyclic aromatic hydrocarbons and their analogous fluoro derivatives were analyzed. It is found that C-F H-C interactions occur, but they are weak, as judged by the intermolecular distances and the angles involved. In a study of crystal structures of molecules containing other elements in addition to carbon, hydrogen, and fluorine, it was found that when an oxygen atom is in a neighboring position on an interacting molecule, a C-O group is more likely than a C-F group to form a linear interaction to the hydrogen atom of a C-H group. Thus, in spite of the high electronegativity of the fluorine atom, a C-F group competes unfavorably with a C-O^–, C-OH, or C=O group to form a hydrogen bond to an O-H, N-H, or C-H group. It is found, however, particularly for polycyclic aromatic hydrocarbons with substituted CF₃ groups that, in the absence of other functional groups that can form stronger interactions, C-F H-C interactions may serve to align molecules and give a different crystal packing from that in the pure hydrocarbon (where fluorine is replaced by hydrogen). Thus, C-F H-X (X = C, N, O) interactions are very weak, much weaker than C=O H-X interactions, but they cannot be ignored in predictions of modes of molecular packing in complexes and in crystals.     

Conductivities of 1∶1 salts in 2-cyanopyridine

Electrolytic conductivities of eight simple 11 electrolytes have been measured in dilute solutions of 2-cyanopyridine (2CNP) at 30°. Infinite dilution mobilities and association constants were calculated using the Fuoss-Hsia equation. With the exception of LiCF₃SO₃ all salts show very little association, consistent with the very high dielectric constant of 2CNP. The weak association which does occur is attributed to weak ion-solvent interactions. No evidence was found for triple ion formation. Conductivities of concentrated solutions of LiAsF₆ in 2CNP increase slowly with concentration reaching a maximum at a concentration of around 0.65 mol-dm^–3. These conductances are slightly lower than those in propylene carbonate which has a lower dielectric constant and a higher viscosity. Conductivities of concentrated LiAsF₆ solutions in 2CNP mixtures with acetonitrile vary monotonically, consistent with solution viscosities, and show no sign of the maximum commonly observed in mixed organic solvents.     

Separation of natural product using columns packed with Fused‐Core particles

Three HPLC columns packed with 3 μm, sub‐2 μm, and 2.7 μm Fused‐Core (superficially porous) particles were compared in separation performance using two natural product mixtures containing 15 structurally related components. The Ascentis Express^TM C18 column packed with Fused‐Core particles showed an 18% increase in column efficiency (theoretical plates), a 76% increase in plate number per meter, a 65% enhancement in separation speed and a 19% increase in back pressure compared to the Atlantis T3^TM C18 column packed with 3 μm particles. Column lot‐to‐lot variability for critical pairs in the natural product mixture was observed with both columns, with the Atlantis T3 column exhibiting a higher degree of variability. The Ascentis Express column was also compared with the Acquity^TM BEH column packed with sub‐2 μm particles. Although the peak efficiencies obtained by the Ascentis Express column were only about 74% of those obtained by the Acquity BEH column, the 50% lower back pressure and comparable separation speed allowed high‐efficiency and high‐speed separation to be performed using conventional HPLC instrumentation.     

Capillary electrophoretic enantioseparation of m‐nisoldipine using two different β‐cyclodextrins

The methods for the enantioseparation of m‐nisoldipine, a new 1,4‐dihydropyridine calcium ion antagonist, were developed. The elaborated methods of m‐nisoldipine enantiomers separation were successfully performed using an anionic CD–sulfobutyl ether‐β‐CD (SBE‐β‐CD) or carboxymethyl‐β‐CD as chiral selector. However, the results indicated that SBE‐β‐CD was a better chiral selector for enantioseparation of the neutral m‐nisoldipine. Furthermore, comparing the two SBE‐β‐CDs, the derivative with a higher degree of substitution (DS) of 7.0 induced better enantioresolution than the one with low DS (4.0). In addition, possible chiral recognition mechanisms of dihydropyridines were discussed.     

Syntheses,Structures, and Photoluminescence of Two Three‐dimensional Cadmium Coordination Polymers with Benzene­dicarboxylate Ligands

Two cadmium(II) coordination polymers, namely, [Cd₃(m‐phth)₂(atz)₂]_n ( 1 ) (m‐phth = m‐phthalate and atz = 3‐amino‐1,2,4‐triazolate) and [Cd(atphth)(H₂O)]_n ( 2 ) (atphth = 2‐aminoterephthalate), were synthesized and structurally characterized. Compound 1 features a three‐dimensional (3D) pillared framework based on two‐dimensional (2D) cadmium‐benzenedicarboxylate ladders pillared by the triazolate ligands. Compound 2 has a 3D framework constructed from 2D cadmium‐benzenedicarboxylate layers, which are further linked by Cd–N bonds between the cadmium ions and amino groups of the atphth^2– ligands of the adjacent layers to form the final 3D structure. Compounds 1 and 2 exhibit solid‐state photoluminescence with emission maxima at 448 and 470 nm, respectively.     

Neues vom P4Se4

New Results on P₄Se₄ Preparation of P₄Se₄ from the elements yields always the β-modification of P₄Se₄. α-P₄Se₄ is obtained only with selenium deficient samples. However, it is also observed, when P₄Se₃ is annealed and then extracted with CS₂. The insoluble part has the X-ray pattern of α-P₄Se₄. A reversible α-β transition is not observed. MAS-³¹P-NMR investigations on solid P₄Se₄ by Eckert et al. [2] reveal P₂Se_4/2 building units, which are, in view of our results, not dimer but linked to a polymeric network. Well-crystallized samples of β-P₄Se₄ are obtained only at measuring temperatures above 573 K. The structure is of monoclinic symmetry with the space group P2₁/n (a = 114.9, b = 729.0, c = 1211.0 pm, β = 120.80°). The reaction of α-P₄Se₃I₂ with bis-(trimethyltin)selenide in CS₂ at low temperature yields molecular α-P₄Se₄, which can be detected in solution by ³¹P-NMR spectroscopy. α-P₄Se₄ has D_2d-symmetry like α-P₄S₄. It polymerizes at higher temperature. α-P₄Se₃I(SeSnMe₃) and α-P₄Se₃(SeSnMe₃)₂ were observed in the course of this reaction, too. The analogous reaction of α-P₄Se₃I₂ with bis-(trimethyltin)sulfide leads to comparable results.     

Darstellung und spektroskopische Charakterisierung von Di(acido)phthalocyaninatorhodaten(III)

Preparation and Spectroscopical Characterization of Di(acido)phthalocyaninatorhodates(III) Triethylendiaminorhodiumiodide reacts quickly and completely with boiling phthalodinitrile precipitating ?rhodiumphthalocyanine”?, which is purified and dissolved in alkaline media as di(hydroxo)phthalocyaninatorhodate(III). Acidification in the presence of halides or pseudohalides yields less soluble acidophthalocyaninatorhodium reacting with tetra-n-butyl-ammonium(pseudo)halide to give (blue)green tetra-n-butyl-ammoniumdi(acido)phthalocyaninatorhodate(III), (ⁿBu₄N)[Rh(X)₂Pc^2?] (X = Cl, Br, I, N₃, CN, NCO, SCN, SeCN). The asym. Rh? X-stretching vibration (v_as(RhX)) is observed in the f.i.r. at 290 (X = Cl), 233 (Br), 205 (I), 366 (N₃), 347 (CN), 351 (NCO), 257 (SCN) and 214 cm^?1 (SeCN). v_s(RhI) is the only sym. Rh? X-stretching vibration excited at 131 cm^?1 in the Raman spectrum. The m.i.r. and resonance Raman spectra are typical for hexacoordinated phthalocyaninatometalates(III). The influence of the axial ligands is very small. The frequency of the stretching vibrations of the pseudohalo-ligands are as expected (in the case of the ambident ligands the bonding atom is named first): v_as(NN) at 2006 and v_s(NN) at 1270 cm^?1 (N₃); v_as(CN) at 2126 (CN), 2153 (NCO), 2110 (SCN) and 2116 cm^?1 (SeCN). The characteristic π–π*-transitions of the Pc^2?-ligand dominate the UV-vis spectra. The splitting of the Q and N region is discussed and the weak absorbance at ca. 22 kK is assigned to a n–π*-transition.     

Über die Phasenbreite von V2O5 im Temperaturbereich von 450°C bis 620°C

About the Homogeneity Range of V₂O₅ in the Temperature Range of 450°C to 620°C The influence of the deposition temperature T₁ on the homogeneity range of V₂O₅-crystalls was investigated by using a solid electrolyte cell. The deviation x in V₂O_5–x from the stoichiometric composition was obtained with: x = 0.0066 at T₁ = 450°C up to x = 0.0326 at T₁ = 620°C.     

Physicochemical properties of α, ω-type bolaform surfactant in aqueous solution. Eicosane-1,20-bis(triethylammonium bromide)

The physicochemical properties of the, - type (bolaform) surfactant, eicosane-1, 20-bis(triethylammonium bromide) (C₂₀Et₆), in aqueous solution have been investigated by means of surface tension, electrical conductivity, dye solubilization, and time-resolved fluorescence quenching (determination of average micelle aggregation number). Using electrical conductivity, the critical micelle concentration of C₂₀Et₆ was found to be 6.0×10^–3 mol dm^–3 and the ionization degree of C²⁰Et₆ micelle was found to be 0.42. From surface tension measurments, the molecular area of C₂₀Et₆ at the air-water interface was about twice that of normal type surfactants such as dodecyltrimethylammonium bromide (DTAB). The solubilizing power of micellar solution of C₂₀Et₆ toward Orange OT was 1.0×10^–2 mole of dye per mole of surfactant, i. e., slightly smaller than that of DTAB. The micelle aggregation number,N, was found to be 17±2 by time-resolved fluorescence quenching. C₂₀Et₆ showed a very small temperature dependence ofN, much less than for normal surfactants.