UV-VIS spectroscopic study of interaction and transformation of allyl alcohol on zeolites HZSM-5

Formation of alkenylcarbenium ions has been proved during transformation of allyl alcohol on zeolite HZSM-5.

---

HZSM-5.

     

Some new aspects of a HPLC-method for the determination of traces of formaldehyde in air

Summary A practicable method was developed for the routine determination of formaldehyde in air. Formaldehyde is sampled in small sampling tubes filled with Chromosorb P, coated with 2,4-dinitrophenylhydrazine (= DNPH). The sorbent is extracted with acetonitrile, and the different DNPhydrazones were separated by reversed-phase HPLC. UV-detection at = 345 nm was compared with electrochemical detection. The detection limit was 100 pg for UV- and 50 pg for electrochemical detection with a linear range of more than 3 decades, respectively. For the determination of formaldehyde in air the detection limit is 10 ppb with an average recovery of 99.3% and an estimated relative standard deviation S of 1.5%. This method was compared with the sampling by impingers using the same separation and detection method.

---

Einige neue Aspekte einer HPLC-Methode zur Spurenbestimmung von Formaldehyd in Luft

---

Dedicated to Prof. Dr. G. Tölg on the occasion of his 60th birthday     

Diastereoselective addition of dimethyl phosphite to 3,3′,4,4′-tetramethyl-1,1′-diphosphaferrocene-2-carboxaldehyde

Addition of dimethyl phosphite to racemic 3,3′,4,4′-tetramethyl-1,1′-diphosphaferrocene-2-carboxaldehyde gives almost exclusively one diastereomer of the corresponding α-hydroxyphosphonate (d.r. ?96:4). Its absolute configuration (S, R_p)-(R, S_p) was established by X-ray diffraction.     

Monodisperse thermosensitive particles prepared by emulsifier-free emulsion polymerization with microwave irradiation

The emulsifier-free emulsion polymerization of styrene (St) and N-isopropylacrylamide (NIPAAm) was successfully carried out with microwave irradiation, and the monodisperse thermoresponsive poly(styrene-co-N-isopropylacrylamide) (poly(St-co-NIPAAm)) particles with diameters in the range 100–130 nm were prepared. The morphology, size and size distribution of the poly(St-co-NIPAAm) particles were characterized by transmission electron microscopy, scanning electron microscopy (SEM) and photon correlation spectroscopy (PCS), respectively. The results showed that poly(St-co-NIPAAm) particles had spherical morphology, and the poly(St-co-NIPAAm) particles prepared by emulsifier-free emulsion polymerization with microwave irradiation were smaller, more uniform than those obtained with conventional heating. The hydrodynamic diameters of poly(St-co-NIPAAm) particles were decreased as the temperature increased from 25 °C to 40 °C, and poly(St-co-NIPAAm) particles collapsed remarkably at 32 °C, which is the lower critical solution temperature of the poly(N-isopropylacrylamide). The morphology of the assembled poly(St-co–NIPAAm) particles was observed by SEM, it was found that monodisperse poly(St-co-NIPAAm) particles could assemble to form the two-dimensional order structures.     

Spin crossover studies in tris(N,N′-dialkyldithiocarbamato)iron(III) complexes

A series of fifteen complexes of the type [Fe(RRNCS₂)₃] with symmetric (R=R=n- C₆H₁₃, n-C₈H₁₇, CH₂–CH=;CH₂, C₆H₅, C₆H₁₁ and C₆H₅CH₂), unsymmetric (R = CH₃; R = n-C₄H₉, C₆H₁₁, C₆H₅ and R = C₂H₅; R = n-C₄H₉, C₆H₁₁, C₆H₅ and i-C₃H₇) and ring substituents (RNR=pyrrolidyl and piperidyl) have been synthesized and their magnetic moments and Mössbauer spectra recorded from room temperature (RT) to liquid nitrogen temperature (LNT). Room temperature Mössbauer spectra of all the complexes exhibit an asymmetric doublet, which could be resolved into two doublets, each corresponding to low and high spin states in equilibrium. The crystal structure of tris(N, N-diallyldithiocarbamato)iron(III) shows it to be monoclinic with trigonally distorted octahedral geometry and space group C2/c. Fe–S stretching vibrations in the far i.r. region also show equilibria, HS LS. Depending on the nature of the alkyl group substituent, variable temperature magnetic moment and Mössbauer spectral studies, all the complexes may be divided into three groups; high spin complexes exhibiting spin-crossover (⁶A_1g ²T_2g), high spin complexes exhibiting spin transition (⁶A_1g ⁴T_1g) and intermediate spin complexes showing spin transition (⁴A_1g ²T_2g). On the basis of areas of the two doublets corresponding to high and low spin states, their percent contributions were calculated. Furthermore, magnetic moments of the equilibrium mixture calculated on the basis of respective areas compare well with the experimentally determined _eff values. E_Q values for both high and low spin states show linear decrease with increasing temperature.     

Effect of ionic and non-ionic surfactants on the reduction of water soluble colloidal MnO<Subscript>2</Subscript> by glycolic acid

Kinetics of the redox reaction between colloidal MnO₂ and glycolic acid have been studied spectrophotometrically by monitoring the decay in the absorbance of colloidal MnO₂ in absence and presence of surfactants. Anionic sodium dodecyl sulfate has no effect, non-ionic Triton X-100 catalyzed the reaction and experiments were not possible in presence of cationic cetyltrimethylammonium bromide due to the precipitation of MnO₂.The reaction followed the same type of kinetic behavior, i.e., fractional-, first- and fractional-order dependencies, respectively, in [glycolic acid], [MnO₂] and [H⁺ ] in both the media. Effects of gum arabic and manganese(II) have also been studied and discussed. Mechanisms in accordance with the experimental data are proposed for the reaction.     

Effect of chemical potential on the computer simulation of hydrogen storage in single walled carbon nanotubes

Hydrogen is a kind of clean, sustainable and renewable energy carrier. Of the problems to be solved for the utilization of hydrogen energy, how to store and transport hydrogen has been given high priority on the research agenda. Recently, carbon nanotubes (CNTs) were reported to be very promising candidates for hydrogen uptake[1], which may have possibility to satisfy the benchmark set by the US Department of Energy (DOE) Hydrogen Plan for fuel cell powered vehicles: a gravimetric density …     

Electrochemical Determination of Ascorbic Acid at γ-MnO<Subscript>2</Subscript> Modified Carbon Black Microelectrodes

A carbon black microelectrode modified by -MnO₂ has been prepared. The electrocatalytical oxidation of ascorbic acid (AA) at this microelectrode was investigated. The 2nd-order linear scan voltammograms of AA are recorded from –0.5 to 0.5V (vs. SCE). The relationship between the oxidation peak current of AA and its concentration in the range of 1.0×10^–64.0×10^–3molL^–1 is linear. The detection limit (3) was found to be 6.0×10^–7molL^–1. Also, the determination of AA in samples is evaluated, and the results are satisfactory.     

Polymeric positive-temperature-coefficient materials: dynamic curing effect

The object of this work was to prepare high-density polyethylene (HDPE)/ethylene–propylene–diene terpolymer (EPDM)/conductive carbon black (CB) composites by dynamic curing and to characterize the positive-temperature-coefficient (PTC) performances of the composites.EPDM and dicumyl peroxide were preblended in a research mill. The roll-milled strands were blended with HDPE and CB in a Haake mixer. The sheet resistivity and morphology of the HDPE/EPDM/CB composites with or without the dynamic curing process were investigated. It was concluded that the dynamically cured blends exhibit better PTC performance than the simple blends without dynamic curing. The effects of shear intensity and dicumyl peroxide content during the dynamic curing process were discussed for the PTC characteristics of the HDPE/EPDM/CB composites.     

Fluorescence of tryptophan-containing peptides on paper or silica gel after treatment with formaldehyde, formaldehyde-ozone or formaldehyde-hydrochloric acid.

Sensitive and specific procedures for the chromatographic detection of tryptophan and tryptophan-containing peptides are described. Formaldehyde gas induces strong and characteristic fluorescence from tryptophan and peptides with NH2-terminal tryptophan residues on silica gel. On filter-paper, the detection of small amounts of these compounds requires the additional use of an oxidant, such as ozone. Treatment with formaldehyde-hydrochloric acid was used as a method for inducing fluorescence from tryptophan-containing peptides regardless of the position of the tryptophan residue in the peptide molecule. This reaction is useful for the chromatographic demonstration of small amounts of such peptides on both paper and silica gel. The spectral properties of the fluorophores of such tryptophan-containing peptides are distinctive and serve to distinguish them from all other known biogenic compounds that are capable of giving fluorescence with formaldehyde.