Novel synthesis of -caprolactam from cyclohexanone-oxime via Beckmann rearrangement over mesoporous molecular sieves MCM-48

Vapor-phase synthesis of -caprolactam (-C) from cyclohexanone-oxime (CHO) has been studied at 1 atm and 300–400 °C using SiMCM-48 and AlMCM-48(X) with Si/Al molar ratios X in a fixed-bed, continuous flow reactor. The catalysts were characterized with ICP-AES, XRD, TEM, FT-IR, N₂-adsorption, ²⁷Al and ²⁹Si MAS NMR and TPD of ammonia. An increase of X value in AlMCM-48(X) enhances both the BET surface area and the unit cell parameter but diminishes the acid amount. In the reaction of CHO, benzene, toluene, ethanol and 1-hexanol were utilized as solvents. The CHO conversion increases with the reaction temperature, whereas the -C selectivity exhibits the opposite trend due to side reactions. The catalyst stability is greatly enhanced by using ethanol and 1-hexanol as the solvents due to their production of water vapor via dehydration. Excellent catalytic performance of AlMCM-48(10) is attained at 1 atm, 350 °C and W/Fc 74.6 g h/mol by using 1-hexanol in the feed; the CHO conversion and the -C selectivity exhibit higher than 99% and 90%, respectively, during at least 130 h process time.     

Living/controlled hex-1-ene polymerization initiated by nickel diimine complexes activated by non-MAO cocatalysts: Kinetic and UV-vis study

Living/controlled polymerization of hex-1-ene initiated by nickel diimine catalysts of general form [ArN=C(1,8-naphthalenediyl)C=NAr]NiBr₂ activated by simple organoaluminium compounds was investigated. Polyhexenes with a very narrow molar mass distribution and molar mass controlled by the monomer/initiator ratio were prepared using diethylaluminiumchloride, ethylaluminiumdichloride and methylaluminiumdichloride as cocatalysts for nickel complexes 1 (Ar = 2,6-iPr₂C₆H₃) and 2 (Ar = 2-tBuC₆H₄). Nickel complexes with smaller aryl substituents (3, Ar = 2,6-Me₂C₆H₃; 4 Ar = 2,4,6-Me₃C₆H₂; 5, Ar = 2,6-Et₂C₆H₃) undergo transfer reactions significantly. For the most bulky complex 1 activated by ethylaluminiumdichloride living hex-1-ene polymerization was achieved, proved by the reinitiation of polymer growth upon the addition of fresh monomer. The effect of Al/Ni ratio on the activity of the catalytic systems was studied by dilatometry. The catalytic systems were investigated by UV-vis spectrometry and a new interpretation of their absorption spectra was suggested.     

Synthesis of tadpole-shaped copolyesters based on living macrocyclic poly(-caprolactone)

Synthesis of an asymmetric tadpole-shaped aliphatic copolyester consisting of a poly(-caprolactone) ring and two poly(l-lactide) tails was reported for the first time. First, a high molecular weight cyclic PCL macroinitiator (M_n = 31,000) was prepared by intramolecular photocross-linking of “living” chains. Polymerization of l-lactide was resumed by the tin dialkoxide containing macrocycles, thus making the targeted tadpole-shaped copolyester available. A preliminary investigation of the crystallization of these copolyesters was carried out by differential scanning calorimetry and polarized optical microscopy.     

A novel route to α,ω-telechelic poly(-caprolactone) diols, precursors of biodegradable polyurethanes, using catalysis by decamolybdate anion

A new convenient route for the synthesis of poly(-caprolactone) (PCL) with α,ω-telechelic diols' end-groups is presented. Synthesis of α,ω-telechelic PCL diols (HOPCLOH) was achieved by ring-opening polymerization (ROP) of -caprolactone (CL) catalyzed with ammonium decamolybdate (NH₄)₈[Mo₁₀O₃₄] and using diethylene glycol (DEG) as initiator. Obtained HOPCLOH was characterized by ¹H and ¹³C NMR, FT-IR, GPC and MALDI-TOF. Comparative studies demonstrate that ammonium decamolybdate (NH₄)₈[Mo₁₀O₃₄] is better catalyst than Sn-octanoate (SnOct₂) toward CL polymerization in presence of DEG, under the conditions tested. A biodegradable poly(ester-urethane-urea) derivative was efficiently prepared from synthesized HOPCLOH. Obtained polymer shows minor differences with respect to the properties recorded for a poly(ester-urethane-urea) obtained from commercial HOPCLOH.     

Enzymatic degradation of poly(propylene carbonate) and poly(propylene carbonate-co--caprolactone) synthesized via CO2 fixation

Poly(propylene carbonate) (PPC) and poly(propylene carbonate-co--caprolactone) (PPCCL) were synthesized via the zinc glutarate catalyzed copolymerization of carbon dioxide (CO₂) and propylene oxide (PO) without and with -caprolactone (CL), respectively. In addition, poly(-caprolactone) (PCL) was prepared via the homopolymerization of CL with the aid of methyl triflate catalyst. The polymer products were characterized in terms of their chemical compositions, molecular weights, and thermal properties. Films of these polymers were tested with a series of enzymes (four different families and a total of 18 enzymes) in a phosphate buffer in order to characterize their enzymatic degradabilities. This is the first report demonstrating that PPC films exhibit positive enzymatic degradability with Rhizopus arrhizus lipase, esterase/lipase ColoneZyme A, and Proteinase K. Moreover, PPCCL films exhibited positive enzymatic degradability with most of the enzymes utilized in our study, and thus PPCCL has an enzymatic degradability comparable to that of PCL. In particular, the PPCCL films exhibit excellent enzymatic degradability with Pseudomonas lipase, Rhizopus arrhizus lipase, and esterase/lipase ColoneZyme A. Considering its excellent enzymatic degradability, the PPCCL terpolymer has potential biomedical applications. In conclusion, ZnGA-catalyzed copolymerizations of CO₂ and PO with or without CL are chemical fixation processes of CO₂ that can be used to produce enzyme-degradable aliphatic polymers.     

Preparation of poly(-caprolactone) grafted titanate nanotubes

This work reported for the first time the surface functionalization of titanate nanotubes (TNTs) with biodegradable poly(-caprolactone) (PCL). A “grafting from” approach based on in situ ring-opening polymerization of -caprolactone from TNTs with a special surface modification was adopted to prepare the PCL-g-TNTs. The thickness of the grafted PCL shell can be controlled by increasing reaction time. After grafted with PCL, both the dissolubility and flexibility of the tubes were greatly improved. The obtained PCL-g-TNTs can easily disperse in several organic solvents, and the dispersal stability depends on solvent polarity and PCL shell thickness. Furthermore, the PCL immobilized on the surface of TNTs still possessed a good biodegradable capacity and could be completely decomposed in the presence of Pseudomonas (PS) lipase. The PCL-g-TNTs reported here are promising in biotechnology applications due to good dissolubility, flexibility, biocompatibility and the tubular nano-structure.     

Fischer-Tropsch Synthesis: Catalyst activation of low alpha iron catalyst

Activation with three different gases (H₂, CO and synthesis gas) over an Fe100/K1.4/Si4.6/Cu2.0 catalyst was conducted to investigate the effects of pretreatment gas on Fischer-Tropsch Synthesis (FTS) activity and selectivity. Catalyst slurry was withdrawn from the reactor at increasing time intervals of FTS for Mössbauer spectroscopic analysis. Activation with CO produced the highest syngas conversion while H₂ generated the lowest; syngas activation produced a slightly lower conversion than CO activation. CO activation transformed the majority of the iron into χ-Fe₅C₂ and Magnetite with only 12% -Fe_2.2C being detected. Unlike the CO activated catalyst, the syngas activated iron catalyst resulted in a lower amount of χ-Fe₅C₂ than -Fe_2.2C. The initial high (64%) content of -Fe_2.2C decreased gradually to below 30% while CO conversion decreased from 83% to 55%. During this period, χ-Fe₅C₂ increased from initial 10% to 33%. Magnetite changed little during the process while the form of carbides interchanged. Hydrogen activation yielded a low CO conversion of 50% and only 8% χ-Fe₅C₂ and 16% -Fe_2.2C was formed while Magnetite was as high as 75% after the FTS reaction rate became constant. Although activation gas type had a significant effect on syngas conversion, hydrogen, syngas and CO activations produced similar H₂ to CO usage ratio, hydrocarbon product distribution, olefin fraction, alpha value and CO₂ selectivity.     

Drastic ligand electronic effect on anilido-imino nickel catalysts toward ethylene polymerization

A novel nitro-anilido-imino nickel complex (Ar¹NCHC₆H₃(-5-NO₂)NAr²)NiBr (Ar¹ = Ar² = 2,6-dimethylphenyl) was designed, synthesized, and characterized to investigate ligand electronic effect on late transition metal olefin polymerization catalysts. As a catalyst for ethylene polymerization, neutral anilido-imino nickel complex with an electron-withdrawing nitro group showed good activity (442.1 kg (mol Ni h)⁻¹) with MAO as cocatalyst. The catalytic activity and molecular weight of the obtained products were significantly affected by electronic effect of the anilido-imine ligand. Theoretical calculations suggested that ligand electronic effect led to different charge distribution on the nickel metal atom, and the catalytic activity predominantly increased with an increase in electrophilicity of the nickel metal center.     

Synthesis and characterization of trichlorotitanium 2-(2-pyridinyliminomethyl)phenolates and their ethylene (co-)polymerization behavior

The series of trichlorotitanium 2-(2-pyridinyliminomethyl)phenolates, [4,6-tBu₂C₆H₂O-2-CHNC₅R^1-4N]TiCl₃ (R^1-4 = H (1); R^1,3,4 = H, R² = Me (2); R^1,2,4 = H, R³ = Me (3); R^2,4 = H, R^1,3 = Me (4); R^1,3 = H, R² = CF₃, R⁴ = Cl (5)), were synthesized and characterized by elemental analysis and ¹H/¹³C NMR spectroscopy. The molecular structures of the representative complexes 2 and 4 were confirmed by single-crystal X-ray diffraction, and revealed distorted octahedral geometry at titanium. In the presence of MAO, all titanium pro-catalysts showed good activities for ethylene polymerization with good thermal stability at the optimum temperature of 50 °C. In comparison with the ethylene polymerization results, the activity observed for the co-polymerization of ethylene/1-hexene was far lower, but the polymers produced were of high molecular weight. For the co-polymerization of ethylene/1-octene, enhanced catalytic activity was observed, with 1-octene incorporation of up to 3.83 mol%.     

Different hydrolytic stabilities of some C,N-chelated germanium alkoxides

C,N-intramolecularly coordinated germanium(IV) methoxides Ar₃GeOMe (1) and (Ar′)₂Ge(OMe)₂ (2) [where Ar = [2-(Me₂NCH₂)C₆H₄]⁻, Ar′ = [2-(DipN = CH)C₆H₄]⁻, Dip = 2,6-(i-Pr)₂C₆H₃] were prepared by the reaction of the lithium precursors ArLi and Ar′Li with Ge(OMe)₄ in appropriate molar ratio. While the diorganogermanium(IV) compound 2 is air-stable specie, triorganogermanium(IV) compound is surprisingly smoothly hydrolyzed by air-moisture to corresponding triorganogermanol Ar₃GeOH (3). Studied compounds were characterized by the help of multinuclear NMR spectroscopy and in the case of 2 and 3 using single-crystal X-ray diffraction analysis.     

Lithium-mediated ring opening of 1,4-dioxane and structural characterization of a Li12O12 truncated octahedron

The equimolar reaction of ^tBuLi with 4-Cl-2,6-Me₂-C₆H₂OH (ArOH) in 1,4-dioxane led to the unexpected formation of the mixed-anion, 1D polymer [(ArO)₂(RO)₄Li₆ · (diox)]_∞, 1 (where RO = H₂CC(H)OCH₂CH₂O⁻). Incorporation of the alkoxy vinyl ether is due to cleavage of 1,4-dioxane by ^tBuLi. Compound 1 can also be prepared rationally by the reaction of ⁿBuLi with ethylene glycol vinyl ether and ArOH in 1,4-dioxane solution. Direct lithiation of ethylene glycol vinyl ether results in the formation of the alkoxide [ROLi]₁₂, 2. The crystal structure of 2 reveals an unusual truncated octahedral arrangement in the solid state, where each metal is chelated by a vinyl ether subunit.     

Fabrication, biomolecular binding, in vitro drug release behavior of sugar-installed nanoparticles from star poly(-caprolactone)/glycopolymer biohybrid with a dendrimer core

Star poly(amido amine)-b-poly(-caprolactone)-b-poly(d-gluconamidoethyl methacrylate) (PAMAM–PCL–PGAMA) block copolymers with a dendrimer core were synthesized from the ring-opening polymerization of -caprolactone using a hydroxyl-terminated dendrimer poly(amido amine) initiator followed by the direct atom transfer radical polymerization of unprotected glycomonomer. The self-assembly and the biomolecular binding of PAMAM–PCL–PGAMA with Concanavalin A (Con A) were investigated by NMR, UV–vis, dynamic light scattering, and transmission electron microscopy, respectively. Multivalent sugar-installed vesicles and large compound aggregates were self-assembled from these dendritic copolymers in aqueous solution, demonstrating thermodynamically more stable than those self-assembled from linear counterpart. Moreover, these copolymers presented specific biomolecular binding with Con A lectin compared with bovine serum albumin, while both the lower mobility and the higher spatial hindrance within dendritic copolymers, to some extent, limited the clustering between sugar and Con A. Furthermore, these star copolymer nanoparticles showed a higher drug-loading efficiency and less burst release compared with linear counterpart. This work provides a method not only for the synthesis of star PCL/glycopolymer biohybrid with a dendrimer core but also for the fabrication of sugar-installed nanoparticles with tunable clustering ability, good drug-loading efficiency, and controlled drug-release profile useful for targeted drug delivery system.     

A new type of supramolecular assembly consisting of crown ether complex cation and a polyoxometalate anion: Synthesis and crystal structure of [Na(C20H24O6)(CH3CN)2]2[Mo6O19] · 4CH3CN

A novel supramolecular assembly consisting of sodium-dibenzo-18-crown-6(DB18C6) complex cation [Na(C₂₀H₂₄O₆)(CH₃CN)₂]²⁺ and isopolyanion [Mo₆O₁₉]²⁻ has been demonstrated in the 3D structure of [Na(C₂₀H₂₄O₆)(CH₃CN)₂]₂[Mo₆O₁₉] · 4CH₃CN (1). Weak intermolecular forces (C–HO hydrogen bonds) between isopolyanion and crown ether play a significant role in the construction of supramolecular framework in the crystal structure of 1. Compound 1 has been characterized in the solid state by single crystal X-ray diffraction, IR, CHN analysis, and TGA.     

Dielectric properties and microstructures of CaSiO3 ceramics with B2O3 addition

The effects of B₂O₃ additives on the sintering behavior, microstructure and dielectric properties of CaSiO₃ ceramics have been investigated. The B₂O₃ addition resulted in the emergence of CaO–B₂O₃–SiO₂ glass phase, which was advantageous to lower the synthesis temperature of CaSiO₃ crystal phase, and could effectively lower the densification temperature of CaSiO₃ ceramic to as low as 1100 °C. The 6 wt% B₂O₃-doped CaSiO₃ ceramic sintered at 1100 °C possessed good dielectric properties: _r = 6.84 and tan δ = 6.9 × 10⁻⁴ (1 MHz).     

MoV-based catalysts in ethane oxidation to acetic acid: Influence of additives on redox chemistry

The formation of acetic acid and/or ethylene by oxidation of ethane is strongly dependent on X additives or Y promotor added to MoVO-based catalysts. MoV_0.4X_0.12YO_z (X = Nb; Y = Pd;  = 10⁻⁴) catalysts were prepared by the slurry method and their structural properties were studied by in situ (redox conditions) XRD, Raman and XPS techniques. The reactivity during reduction and reoxidation was analysed by thermal analysis (TGA/DSC). The oxidation of ethane was carried out in a conventional fixed bed microreactor with on line analysis by gas chromatography. Results show that Nb exerts mainly a structural effect as it is responsible for the stabilisation of molybdenum (VI) by formation of solid solutions with V, and that Pd modifies the rate of reduction of the solid catalysts. The increase of selectivity to acetic acid observed by Pd promotion is likely due to the transformation of ethylene to acetic acid occurring on neighboring Pd–V active sites.     

Highly active and selective ethylene oligomerization catalysts: Asymmetric 2,6-bis(imino)pyridyl iron (II) complexes with alkyl and halogen substitutients

A series of asymmetric 2,6-bis(arylimino)pyridines with alkyl and halogen substitutients on different iminoaryl rings and corresponding iron (II) complexes ([2-(Ar₁N = CCH₃)-6-(Ar₂N = CCH₃)C₅H₃N]FeCl₂, 3a–3j) are synthesized and characterized. These Fe(II) complexes are highly active for ethylene oligomerization with high selectivity for linear α-olefins. The oligomer distributions can be tuned by the synergism of alkyl-steric effect and halogen electronic effect, and the production of C₆–C₁₆ can reach more than 80% with the highest selectivity being 87.5% for 3 g (Ar₁ = 2-ethylphenyl, Ar₂ = 2-fluorophenyl), which is 15–30% higher than that catalyzed by their methyl or fluoro-substituted symmetric counterparts.     

Magnetic behavior within a new Ni(mnt)2-based molecular solid containing 1-(2′-fluorobenzyl)isoquinolinium

A novel molecular solid, [OFBzIQl][Ni(mnt)₂] (1), where [OFBzIQl]⁺ = 1-(2′-fluorobenzyl)isoquinolinium and mnt²⁻ = maleonitriledithiolate, forms 1D column of alternating between cations and anions via ππ stacking interaction between Ni(mnt)₂ plane and isoquinoline ring, and the Ni(mnt)₂ anions between the adjacent columns exist short CN interaction. The extensive hydrogen bonds between anions and cations in the crystal generate a 2D network structure. Magnetic susceptibility measurement for 1 in the temperature range 2.0–300 K shows that 1 exhibits a magnetic constant transition from ferromagnetic to antiferromagnetic around 35 K as the temperature is lowered.     

Effect of carbonization time on the structure and electromagnetic parameters of porous-hollow carbon fibres

A series of polyacrylonitrile-based porous-hollow carbon fibres (PAN-PHCFs) were prepared by carbonizing PAN porous-hollow cured fibres at 1073 K for different times in nitrogen. The effects of carbonization time on the structure, electrical volume conductivity and electromagnetic parameters were investigated. Results indicate that the degree of graphitization increases as carbonization time increases. The electrical volume conductivity increases as the degree of graphitization and carbonization time increase. The real and imaginary parts of the complex permittivity (′ and ″) increase with carbonization time increasing. The values of ′ and ″ of composites of PAN-PHCFs and paraffin are 13.76 and 10.09 when the carbonization time is 240 min, and the electrical volume conductivity of PAN-PHCFs is 190.47 Ω⁻¹ m⁻¹.     

Cs exchanged phosphotungstic acid as an efficient catalyst for liquid-phase Beckmann rearrangement of oximes

Cs exchanged phosphotungstic acid is a highly efficient and environmentally benign solid acid catalyst for the liquid-phase Beckmann rearrangement of ketoximes to the corresponding amides. The catalysts Cs_xH_3−xPW₁₂O₄₀ (x = 1.5, 2, 2.5 and 3) were prepared by a titration method. The characterization results indicated that the primary Keggin structure remained intact after exchanging the protons with Cs ions. Moreover, the Cs exchanged catalysts were insoluble and exhibited larger BET surface area than the parent acid. The catalysts exhibited high reactivity and selectivity for the formation of -caprolactam, the precursor of Nylon 6, from cyclohexanone oxime. The catalyst can be recovered after reaction without any structural transformation.