Lewis Acidic Aluminum Research Articles

Mesoporous Zeolite as a New Catalyst for Polymerization of Lactones

Polymerization of lactones such as δ-valerolactone (VL) and ε-caprolactone (CL) with protic compounds proceeded in the presence of an aluminosilicate mesoporous zeolite Al-MCM-41 (pore diameter of 27 Å, surface area = 1,010 m2 g−1), to give polyesters with narrow molecular weight distribution. The polymerization is likely to proceed via the activated monomer mechanism by the cooperative function of Lewis acidic aluminum and Brønsted acidic silanol functionalities on the interior wall. With titanate-mounted MCM-41 (Ti-MCM-41), the polymerization of VL gave a polymer containing an extremely high molecular weight fraction.

Electrodeposition of Copper and Copper‐Aluminum Alloys from a Room‐Temperature Chloroaluminate Molten Salt

The electrodeposition of copper and copper‐aluminum alloys was investigated in the Lewis acidic aluminum chloride‐1‐methyl‐3‐ethylimidazolium chloride (60.0–40.0 mol %) molten salt containing electrogenerated Cu(I) at 40 ± 1°C. Sampled current and rotating ring‐disk electrode voltammetry experiments indicated that it was possible to produce Cu‐Al alloy deposits at potentials positive of that corresponding to the electrodeposition of bulk aluminum (∼0 V). For a solution of Cu(I), the onset of the aluminum codeposition process was found to occur at around 0.30 V vs. the Al(III)/Al couple; however, a limiting current for the reduction of Cu(I) to pure copper metal can be observed in the 0.60–0.30 V potential interval in this solution. The Cu‐Al alloy composition was found to be independent of the Cu(I) concentration, reaching a maximum value of 43 percent atomic fraction aluminum at 0 V. The surface morphology of bulk Cu‐Al alloy electrodeposits was highly dependent on the aluminum content; pure copper deposits had a dense, nodular appearance, whereas deposits containing appreciable amounts of aluminum consisted of fragile dendrites. X‐ray diffraction studies indicated that Cu‐Al deposits containing about 7.2 percenter atomic fraction Al retained the face‐centered cubic (fcc) copper structure; however, deposits containing 12.8 percent atomic fraction Al were two‐phase with the second phase tentatively identified as martensitic . This phase appears to form before fcc copper becomes saturated with aluminum.

Electrodeposition of Cobalt and Cobalt‐Aluminum Alloys from a Room Temperature Chloroaluminate Molten Salt

The electrodeposition of magnetic cobalt‐aluminum alloys was investigated in the Lewis acidic aluminum chloride‐ 1‐methyl‐3‐ethylimidazolium chloride [60.0–40.0 mole percent (m/o)] molten salt containing electrogenerated Co(II) at 25°C. Rotating disk electrode voltammetry indicated that it is possible to produce alloy deposits containing up to 62 atomic (a/o) aluminum at potentials positive of that for the bulk deposition of aluminum. The onset of the underpotential‐driven aluminum codeposition process occurred at around 0.40 V vs. the Al/Al(III) couple in a 5.00 mmol liter−1 Co(II) solution but decreased as the Co(II) concentration increased. The Co‐Al alloy composition displayed an inverse dependence on the Co(II) concentration but tended to become independent of concentration as the potential was decreased to 0 V. A rotating ring‐disk electrode voltammetry technique was developed to analyze the composition and structure of the Co‐Al alloy deposits. This technique takes advantage of the fact that the mass‐transport‐limited reduction of cobalt(II) occurs at potentials considerably more positive than that at which aluminum codeposition occurs. Scanning electron microscopy and energy dispersive x‐ray analysis of bulk electrodeposits revealed that deposit morphology depends strongly upon aluminum content/deposition potential; deposits produced at 0.40 V from 50.0 mmol liter−1 Co(II) solutions consisted of 10 to 20 μm diam multifaceted nodules of pure hcp cobalt, whereas those obtained at 0.20 V were dense and fine grained, containing about 4 a/o Al. Deposits produced at 0 V had the visual appearance of a loosely adherent black powder. X‐ray diffraction measurements revealed a lattice expansion and a decrease in grain size as the hcp cobalt was alloyed with increasing amounts of aluminum.

Electrodeposition of Cobalt-Aluminum Alloys From the Aluminum Chloride-1-Methyl-3-Ethylimidazolium Chloride Room-Temperature Molten Salt

The electrodeposition of magnetic cobalt-aluminum alloys was investigated in the Lewis acidic aluminum chloride-1-methyl-3-ethylimidazolium chloride (60.0–40.0 mole %) molten salt containing electrogenerated Co(II) at 25 °C. Alloy deposits containing up to 62 atomic % aluminum were produced at potentials positive of that for the bulk deposition of aluminum. The onset of the underpotential driven aluminum co-deposition process occurred at around 0.40 V versus the A1/A1(III) couple. The Co-Al alloy composition displayed an inverse dependence on the Co(II) concentration, but tended to become independent of concentration as the potential was decreased. A RRDE voltammetry technique was developed to analyze the composition and structure of the Co-Al alloy deposits. SEM-EDS analysis of bulk electrodeposits revealed that the deposit morphology depends strongly upon the aluminum content/deposition potential; deposits produced at 0.40 V consisted of 10 – 20 μm diameter multifaceted nodules of pure hcp cobalt whereas those obtained at 0.20 V were dense and fine grained, containing about 4 atomic % Al. Deposits produced at 0 V had the visual appearance a of loosely adherent black powder. XRD diffraction measurements revealed a lattice expansion and a decrease in grain size as the hcp cobalt was alloyed with increasing amounts of aluminum.

Densities, Viscosities, and Conductivities of Mixtures of Benzene with the Lewis Acidic Aluminum Chloride + 1-Methyl-3-ethylimidazolium Chloride Molten Salt

The densities, kinematic viscosities, and specific conductances of mixtures of benzene with the Lewis acidic room-temperature chloroaluminate molten salt aluminum chloride + 1-methyl-3-ethylimidazolium chloride (AlCl3 + MeEtimCl) were determined at 298.2 K. Benzene was added to melts containing 51.00, 60.00, and 66.67 mol % AlCl3. Simple polynomial equations were fitted to the experimental results as a function of the mass fraction of benzene. The addition of small amounts of benzene resulted in a decrease in the kinematic viscosity and an increase in the specific conductance of the mixture. However, the addition of benzene beyond 35 mass % caused the specific conductance to decrease due to a decrease in the concentration of charge-carrying ions.

Lewis acid coordination complexes of polymers: 3. Poly(benzobisimidazobenzophenanthroline) ladder and semiladder polymers

The structures, solution properties and solid state properties of complexes of poly(benzobisimidazobenzophenanthroline) ladder (BBL) and its semiladder analogue (BBB) with the Lewis acid aluminium(III) chloride (AlCl 3) and gallium(III) chloride (GaCl 3) are reported. At a 4:1 mole ratio of Lewis acid to polymer (BBB or BBL) repeat unit, electron donor-acceptor complexes of Lewis acid-base type, which are highly soluble in organic solvents, are formed. A detailed spectroscopic investigation shows that complexation of both polymers involves coordination of the Lewis acids to the electron-rich carbonyl oxygens and the imine nitrogens in the polymer backbones. The complexes of BBL exhibit the characteristic rigid-rod behaviour of the pristine ladder polymer. BBL complexes have rigid, rod-like chain conformations in dilute solution as evidenced by their solvent independent intrinsic viscosities. The complexes form liquid crystalline solutions above 8 wt% BBL in AlCl 3 nitromethane and above 9–9.5 wt% in GaCl 3 nitromethane . The solid complexes of BBL have slightly smaller optical absorption edges than BBL and ∼50% larger absorption coefficients at λ max. D.s.c. revealed a glass transition ( T g) of the 4:1 GaCl 3:BBL complex at 15°C. Dynamic mechanical experiments indicated the T g, measured at the loss tangent peak, was in the range 29–37°C depending on frequency, with an activation energy of 448 kJ mol −1. The complexes of BBB by contrast exhibit flexible-coil behaviour due to the polymer topology. In solution, BBB complexes have intrinsic viscosities which depend on the solvent and Lewis acid used, due to differing degrees of coil expansion in different solvent media. Coil expansion in solution leads to improved conjugation of BBB complexes as evidenced by comparison of the electronic absorption spectra with those of BBL. BBB complexes, like the pure polymer, are apparently not liquid crystalline at high concentrations in solution. The solid 4:1 GaCl 3:BBB complex has a T g at 30°C, and a dynamic mechanical analysis T g in the range 12–24°C. The T g activation energy, at 293 kJ mol −1, is lower than that of the BBL GaCl 3 complex. The overall results of the present studies provide a basis for understanding the structure and properties of these polymers in terms of intermolecular interactions and also have implications for the processing of the polymers for diverse applications.

The donor strength of a series of substituted pyridines towards the Lewis acid aluminium tribromide

The condensed phase heats of complex formation have been determined for the 1:1 complexes formed between aluminium bromide and the following substituted pyridines: α, β, γ-picolines and 2:6 — lutidine. Steric interactions, which occur in complexes with ligands containing α-substituents, are evaluated. For non-hindered ligands the condensed phase heats of complex formation fall in the range 33·3 ± 0·7 kcal. mole −1, and show little variation with the base strength ( pk a ) of the ligand. The results are compared with similar known systems.