Assessment of Lewis-Acidic Surface Sites Using Tetrahydrofuran as a Suitable and Smart Probe Molecule

Measuring the Lewis-acidic surface sites in catalysis is problematic when the material‘s surface area is very low (S_BET ≤1 m² ⋅ g⁻¹). For the first time, a quantitative assessment of total acidic surface sites of very small surface area catalysts (MoO₃ as pure and mixed with 5–30 % CdO (wt/wt), as well as CdO for comparison) was performed using a smart new probe molecule, tetrahydrofuran (THF). The results were nearly identical compared to using another commonly used probe molecule, pyridine. This audition is based on the limited values of the surface area of these samples that likely require a relatively moderate basic molecule as THF with pK_b=16.08, rather than strong basic molecules such as NH₃ (pK_b=4.75) or pyridine (pK_b=8.77). We propose mechanisms for the interaction of vapour phase molecules of THF with the Lewis-cationic Mo and Cd atoms of these catalysts. Besides, dehydration of isopropyl alcohol was used as a probe reaction to investigate the catalytic activity of these catalysts to further support our findings in the case of THF in a temperature range of 175–300 °C. A good agreement between the obtained data of sample MoO₃-10 % CdO, which is characterised by the highest surface area value, the population of Lewis-acidic sites and % selectivity of propylene at all the applied reaction temperatures was found.     

A possible ethanol-catalyzed rearrangement of vitamin K(1) detected by gas chromatography/mass spectrometry

We studied vitamin K(1)(20), vitamin K(1)(25), and vitamin K(1) epoxide in n-hexane and ethanol solutions by gas chromatography/mass spectrometry (GC/MS) utilizing a DB-5 MS fused-silica capillary column. In ethanol solutions of K(1), we observed an extra peak eluting from the GC column with somewhat longer retention time than K(1)(20). A similar peak following K(1)(25) was also found. These peaks were not found in n-hexane solutions of K(1). A close examination of the mass spectra of these peaks indicated that they were vitamin K(1) variants containing a base peak at m/z 225 characteristic of the methylnaphthoquinone ring with a four-carbon side chain. In addition, they contained the molecular ions of K(1)(20) and K(1)(25), respectively. We conclude that K(1)(20) and K(1)(25), but not K(1) epoxide, might undergo rearrangements in ethanol involving an intramolecular proton transfer and a shift of the beta,gamma-double bond on the phytyl side chain toward the ring. The conjugation of the phytyl double bond with the quinone ring is probably the driving force of the rearrangement. We emphasize, however, that our conclusion is based only on mass spectral analysis and would require further investigation by other spectroscopic methods.     

Palladium complexes with bis(diphenylphosphinomethyl)amino ligands and their application as catalysts for the Heck reaction

Aminomethylphosphine (P–C–N) type ligands, (Ph₂PCH₂)₂NR R = –(CH₂)₃Si(OEt₃)₃ or –CH₂CH₂OH, and their Pd(II) complexes have been synthesized. All the compounds were characterized by ¹H-, ³¹P-NMR, and elemental analysis. The complexes are proposed to have a square planar geometry. They were investigated as catalysts for the Heck reaction of aryl halides (I, Br, Cl) with methyl acrylate. Both complexes showed high activity to give methyl cinnamate in good yields, with the best turnover numbers found for [PdCl₂(Ph₂PCH₂)₂N(CH₂)₃Si(OEt)₃].     

Adsorption and inhibitive properties of aminobiphenyl and its Schiff base on mild steel corrosion in 0.5 M HCl medium

Electrochemical measurements were performed to investigate the effectiveness and adsorption behaviour of aminobiphenyl (Aph) and 2-(3-hydroxybenzylideneamino)biphenyl (Aph-S), as corrosion inhibitors for mild steel (MS) in 0.5 M HCl solution. Potentiodynamic polarization, linear polarization resistance (LP) and electrochemical impedance spectroscopy (EIS) techniques were applied to study the metal corrosion behaviour in the absence and presence of different concentrations of Aph and Aph-S. In order to gain more information about adsorption mechanism the AC impedance technique was used to evaluate the potential of zero charge (PZC) from polarization resistance (R_p) versus voltage (E) plot. Potentiodynamic polarization measurements showed that Aph act as cathodic type inhibitor where as Aph-S act mixed type. The inhibition efficiency (IE%) increases with increasing concentration of compounds and reached 92.6% for Aph and 97.2% for Aph-S at 5 × 10⁻³ M. Double layer capacitance (C_dl) and polarization resistance (R_p) values are derived from Nyquist plots obtained from AC impedance studies. The experimental data fit Langmuir isotherm for both Aph and Aph-S, and from the adsorption isotherm some thermodynamic data for the adsorption processes are calculated and discussed. The effect of exposure time on the corrosion behaviour of mild steel in the absence and presence of inhibitor over 168 h was also studied.     

Gold(I)-dithioether supramolecular polymers: synthesis, characterization, and luminescence

A series of discrete compounds and supramolecular polymers were synthesized by self-assembly of dithioether building blocks and HAuCl4.3H2O. In complexes 1 {[AuL(1-Me)Cl], where L(1-Me) is bis(methylthio)methane} and 2 {[Au2L(2-Ph)Cl2], where L(2-Ph) is 1,2-bis(phenylthio)ethane}, adjacent units are connected via aurophilic interactions. Complex 1, a one-dimensional (1D) supramolecular polymer, and complex 2, a two-dimensional supramolecular network, both feature nearly linear [Au-Au-](infinity) chains. Complexes 4a, 4b, and 4c, all of which contain 1,3-bis(phenylthio)propane (L(3-Ph)), are polymorphs having the composition [Au2L(3-Ph)Cl2]. Complex 3 {[Au2L(1-Ph)Cl2], where L(1-Ph) is bis(phenylthio)methane}and complexes 4a and 4b consist of nearly identical 1D supramolecular polymers formed through Au-Au interactions. The third polymorph, 4c, is a molecular complex, as it does not have metal-metal interactions. Complex 5 {[Au2L(4-Ph)Cl2], where L(4-Ph) is 1,4-bis(phenylthio)butane} is also molecular. UV-vis spectra showed that the absorption bands of these complexes are allowed ligand-centered transitions between 230 and 260 nm. Complexes 1, 2, and 6 {[AuL(3-Me)Cl], where L(3-Me) is 1,3-bis(methylthio)propane} exhibited solid-state luminescence at 5 K with vibronic progressions and band maxima at approximately 570 nm. It is suggested that complex 6 contains [Au-Au-](infinity) chains.     

A μ‐chloro‐bridged dinuclear ruthenium complex with 9H‐carbazole: the formation of one‐dimensional linear chains of star‐shaped edge‐fused rings

The title complex, di‐μ‐chloro‐bis­[chloro­(η⁶‐p‐cymene)ruthenium(II)]–9H‐carbazole (1/2), [Ru₂Cl₄(C₁₀H₁₄)₂]·2C₁₂H₉N, is composed of one [RuCl₂(η⁶‐p‐cymene)]₂ and two 9H‐carbazole mol­ecules. There are one‐half of a dinuclear complex and one 9H‐carbazole mol­ecule per asymmetric unit. In the dinuclear complex, each of the two crystallographically equivalent Ru atoms is in a pseudo‐tetra­hedral environment, coordinated by a terminal Cl atom, two bridging Cl atoms and the aromatic hydro­carbon, which is linked in a η⁶ manner; the Ru⋯Ru separation is 3.688 (3) Å. The title complex has a crystallographic centre of symmetry located at the mid‐point of the Ru⋯Ru line. Inter­molecular N—H⋯Cl and π–π stacking inter­actions are observed. These inter­actions form a four‐pointed star‐shaped ring and one‐dimensional linear chains of edge‐fused rings running parallel to the [100] direction, which stabilize the crystal packing.     

Product and Mechanism of Gas‐phase Pyrolysis of 2‐arylidinehydrazinopyrimidines: Interesting Route to Condensed Heterocycles[1]

Gas‐phase pyrolysis of N‐arylidine‐N′‐pyrimidin‐2‐yl‐hydrazine derivatives 1a , 1b , 1c , 1d , 1e gave the corresponding arylnitriles 2a , 2b , 2c , 2d , 2e , 2‐aminopyrimidine 3 , 3‐phenyl‐1,2,4‐triazolo[4,3‐a]pyrimidines 4 , 2‐phenyl‐1,2,4‐triazolo[1,5‐a]pyrimidines 5 , 2,4,5‐triphenyl‐1H‐imidazole 6 , and 2,3‐diphenylquinoline 7 . The analyses of the reaction products are reported and used to elucidate the mechanism of the pyrolytic process.     

Synthesis and characterizations of N,N,N′,N′-tetrakis (diphenylphosphino)ethylendiamine derivatives: Use of palladium(II) complex as pre-catalyst in Suzuki coupling and Heck reactions

Oxidation of N,N,N′,N′-tetrakis(diphenylphosphino)ethylendiamine (1) with elemental sulfur and selenium gives the corresponding sulfide and selenide, respectively, [(Ph₂P(E))₂NCH₂CH₂N(P(E)Ph₂)₂] (E: S 1a, Se 1b). Complexes of 1 [(M₂Cl₄){(Ph₂P)₂NCH₂CH₂N(PPh₂)₂}] (M: Ni(II) 1c, Pd(II) 1d, Pt(II) 1e) were prepared by the reaction of 1 with NiCl₂ or [MCl₂(COD)] (M = Pd, Pt). The new compounds were characterized by NMR, IR spectroscopy and elemental analysis. The catalytic activity of Pd(II) complex 1d was tested in the Suzuki coupling reaction and Heck reaction. The palladium complex 1d catalyses the Heck reaction between styrene and aryl bromides as well as Suzuki coupling reaction between phenylboronic acid and arylbromides affording stilbenes and biphenyls in high yield, respectively.     

Assesment of dimethyl phthalate removal from aqueous phase using barium hexaferrite containing magnetic beads

The barium hexaferrite (BaFe(12)O(19)) containing magnetic poly (ethylene glycol dimethacrylate-vinyl pyridine; mag-poly [EGDMA-VP]) beads (average diameter=53-212 μm) were synthesized and characterized. Their use as an adsorbent in the removal of dimethyl phthalate (DMP) from an aqueous solution was investigated. The mag-poly (EGDMA-VP) beads were prepared by copolymerizing of 4-vinyl pyridine (VP) with ethylene glycol dimethacrylate (EGDMA). The mag-poly (EGDMA-VP) beads were characterized by N(2) adsorption/desorption isotherms (BET), vibrating sample magnetometer (VSM), X-ray powder diffraction (XRD), elemental analysis, scanning electron microscope (SEM), and swelling studies. At a fixed solid/solution ratio, the various factors affecting the adsorption of DMP from aqueous solutions such as pH, initial concentration, contact time, and temperature were analyzed. The maximum DMP adsorption capacity of the mag-poly (EGDMA-VP) beads was determined as 96.2 mg/g at pH 3.0, 25 °C. All the isotherm data can be fitted with both the Langmuir and the Dubinin-Radushkevich isotherm models. The pseudo-first-order, pseudo-second-order, Ritch-second-order, and intraparticle diffusion models were used to describe the adsorption kinetics. The thermodynamic parameters obtained indicated the exothermic nature of the adsorption. The DMP adsorption capacity did not change after 10 batch successive reactions, demonstrating the usefulness of the magnetic beads in applications.