High activity of iron containing metal-organic-framework in acylation of p-xylene with benzoyl chloride

Catalytic behavior of metal-organic-frameworks (MOFs) Cu₃(BTC)₂, MIL-100(Fe) and MIL-100(Cr) was investigated in p-xylene acylation with benzoyl chloride and compared with the behavior of large pore zeolites Beta and USY. It has been clearly shown that MIL-100(Fe) exhibit much higher conversion of benzoyl chloride with excellent selectivity in p-xylene acylation. The performance of MIL-100(Fe) catalyst was favorable with those of other conventional heterogeneous catalysts like zeolites. Conversion of benzoyl chloride equal to 100% was achieved over MIL-100(Fe) with 20-30 min under optimized reaction conditions. It is assumed that unsaturated Lewis acid sites associated with the presence of Fe exhibit optimum acid strength for catalyzing this acylation reaction.     

Data mining macrokinetic approach based on ANN and its application to model industrial oxidation of p-xylene to terephthalic acid

Considering that kinetics and thermodynamics are coupled with heat and mass transfer effects being present in the liquid-phase catalytic oxidation of p-xylene to terephthalic acid (OXTA) in an industrial type of continuous stirred tank reactor (CSTR) and that the time evolution of the concentration of all the interest intermediate and final products of OXTA in the industrial CSTR cannot be obtained to estimate macrokinetic parameters, a novel data mining macrokinetic approach based on artificial neural network (ANN) was proposed to develop the macrokinetic model of OXTA in the industrial CSTR, which mines intrinsic kinetics and transport phenomena information from the sample data collected from OXTA in the industrial CSTR. Firstly, the reaction orders of OXTA are estimated by the mass transfer-free experiment data in the laboratory semi-batch stirred tank reactor. The kinetics of OXTA in the industrial CSTR is assumed to be zeroth-order with respect to gaseous reactants, 0.65-order with respect to p-xylene, and first-order with respect to the other liquid reactants, respectively. Secondly, ANN is employed to model the influence of the reaction parameters on the rate constants of OXTA in the industrial CSTR. Based on the sample data collected from OXTA in the industrial CSTR, heuristic differential evolution algorithm is employed to adjust the weights and thresholds of the rate constant ANN in such a way that it minimizes the prediction error of the macrokinetic model, and thus the optimal weights and thresholds are obtained and the macrokinetic model of OXTA in the industrial CSTR is developed. The reliability of the macrokinetic model was investigated and the satisfactory results were obtained. Further, a generalized macrokinetic approach for multi-phase reaction in industrial reactor was suggested too.     

Solution and solid-state polymerizations of substituted p-quinodimethanes and p-quinone methides

This article describes the polymerization behavior of electron-accepting and electron-donating p-quinonoid monomers such as substituted p-quinodimethanes and p-quinone methides in solutions and solid states. In the solution polymerizations, the electron-accepting substituted p-quinodimethanes and p-quinone methides with same substituents such as cyano, ester, and sulfonyl groups at the exocyclic positions are not homopolymerizable, but copolymerizable with donor monomers like styrene in an alternating fashion. Their spontaneous polymerizations with donor monomers have been explained with the bond-forming initiation mechanism. The substituted p-quinodimethanes with ester groups are a first example to show an amphoteric behavior in alternating copolymerizations. Some electron-accepting substituted p-quinodimethanes and p-quinone methides with different substituents such as cyano, ester, acyl, alkylthio, and/or phenyl groups are homopolymerizable, and an anionic polymerization initiated with a butyllithium initiator proceeded in a living manner. Equilibrium polymerization behavior have been found in their radical homopolymerizations, and on the basis of the thermodynamic parameters determined for their polymerizations, it has been concluded that homopolymerizabilities of the electron-accepting substituted p-quinodimethanes and p-quinone methides are determined exclusively by a steric hindrance effect arising from the substituents at the exocyclic positions. A new concept for the radical alternating copolymerization have been proposed on the basis of the change in modes (random and alternating copolymerizations) for their copolymerizations with styrene and the cross-propagation step analysis by linear free energy relationship. The polymerizations of the electron-donating substituted p-quinodimethanes take place only in the presence of oxygen molecules. In the solid-state polymerizations, some electron-accepting substituted p-quinodimethanes with same ester substituents polymerized topochemically in vacuo, and the strict requirements of topochemical polymerization for substituted p-quinodimethane and p-quinone methide monomers have been determined on the basis of their crystallographic data. Topochemical alternating copolymerization with molecular oxygen in solid state was discovered for the first time.     

Competitive electrochemical oxidation of p-chlorophenol and p-nitrophenol on Bi-doped PbO2

The initial stages of oxidation of aqueous solutions of p-chlorophenol (pcp) and p-nitrophenol (pnp) on Bi-doped PbO₂ electrodes have been studied. From deconvolution and analysis of UV-Vis spectra of the solutions obtained during electrochemical oxidation, benzoquinone and aliphatic acids were identified as the primary oxidation intermediates; oxidation of benzoquinone was found to be the slow step during the early stages of the electrochemical combustion process. The effect of competing adsorption of pcp and pnp on Bi-PbO₂ was also examined, and the presence of pnp in solution was found to inhibit the rate of oxidation of pcp during concurrent oxidation of both phenols.     

Study of the oxidation of solutions of p-chlorophenol and p-nitrophenol on Bi-doped PbO2 electrodes by UV-Vis and FTIR in situ spectroscopy

The oxidation of p-chlorophenol (pcp) and p-nitrophenol (pnp) was studied at Bi-doped PbO₂ (Bi-PbO₂) electrodes. The mass balance between solution composition and flowing charge was obtained from deconvolution of UV-Vis spectra recorded during electrolysis at constant potential. It is shown that the time-dependent production of CO₂ is different for the oxidation of pcp and pnp, indicating different reaction mechanisms for the oxidation of each of these compounds. The reaction kinetics was also followed under thin layer conditions by SNIFTIRS; the similarly increasing signals associated to the generation of CO₂ obtained during oxidation of both compounds indicates that under conditions of restricted mass transfer the mineralization rates of pcp and pnp are similar. The results show that benzoquinone (bq) formed from oxidation of phenols desorbs prior to further oxidation to yield maleic acid (ma), in turn oxidizing further to CO₂.     

Radical copolymerization of N-vinylcarbazole and p-bromostyrene: determination of monomer reactivity ratios by SEC-multidetection

N-Vinylcarbazole (A)/p-bromostyrene (B) copolymers were prepared by radical copolymerization. Size exclusion chromatography (SEC) equipped with a refractometer and UV-vis spectrophotometer was found to be a very convenient technique to follow copolymerizations and to determine monomer conversions, copolymer composition, average molecular weights, polydispersity indexes versus time. The monomer reactivity ratios r_A (N-vinylcarbazole) and r_B (p-bromostyrene) were determined by using the Finemann-Ross (FR), the inverted Finemann-Ross (IFR), the Kelen-Tüdos (KT), and the fitting curve graphical methods. The four methods were in good agreement and led to very different values for r_A (0.55) and r_B (12.3) which induces a preference for the incorporation of B in the copolymer structure. Eventually, with these results the influence of initial feed on the microstructure of the copolymer has been predicted.     

Fabrication of tridoped p-ZnO thin film and homojunction by RF magnetron sputtering

Tridoping (Al–As–N) into ZnO has been proposed to realize low resistive and stable p-ZnO thin film for the fabrication of ZnO homojunction by RF magnetron sputtering. The tridoped films have been grown by sputtering the AlN mixed ZnO ceramic targets (0, 0.5, 1 and 2 mol%) on GaAs substrate at 450 °C. Here, Al and N from the target, and As from the GaAs substrate (back diffusion) takes part into tridoping. The grown films have been characterized by Hall measurement, X-ray diffraction, photoluminescence, time-of-flight secondary ion mass spectroscopy and X-ray photoelectron spectroscopy. It has been found that all the films showed p-conductivity except for 2 mol% AlN doped film. The obtained resistivity (8.6×10⁻² Ω cm) and hole concentration (4.7×10²⁰ cm⁻³) for the best tridoped film (1 mol% AlN) is much better than that of monodoped and codoped ZnO films. It has been predicted that [(As_Zn−2V_Zn)+N_O] acceptor complex is responsible for the p-conduction. The homojunction fabricated using the best tridoped ZnO film showed typical rectifying characteristics of a diode. The junction parameters have been determined for the fabricated homojunction by Norde's and Cheung's method.     

Novelties of kinetics and mechanism of liquid-liquid phase transfer catalysed reduction of p-nitroanisole to p-anisidine

Anisidines, which are valuable intermediates in dyestuff industry, are synthesised from nitroanisoles. The reduction of nitroanisoles and other substituted nitroaromatics to the corresponding amines can be affected by aqueous inorganic sulphides and polysulphides and the rates of these biphasic reductions are amenable to intensification under phase transfer catalysis (PTC). The selectivity in the reduction of substituted nitroaromatics is greatly affected by the type and number of phases involved in the PTC process. The kinetics and mechanisms of complex L-L PTC processes are not properly understood. This paper delineates novelties of the kinetics and mechanism of L-L PTC reduction of the model compound p-nitroanisole to p-anisidine wherein the sulphide ions get transformed into bisulphide in the aqueous phase and are extracted as ion pairs in the organic phase. A series of reactions of the bisulphide occur to reduce the nitroaromatic to the corresponding amino compound and the Q⁺HSO₃⁻ ion pair is transferred across the interface to react with S²⁻ leading to the formation of the Q⁺SH⁻ ion pair and S₂O₃²⁻. The effects of different parameters are studied to establish this mechanism. The selectivity to the product is 100%.     

Synthesis and gas permeability of ester substituted poly(p-phenylene)s

Polymerizations of various ester substituted 2,5-dichlorobenzoates [substituent: linear alkyl groups (1a-f), branched alkyl groups (1g-l), cyclohexyl groups (1m-o), phenyl groups (1p-r), and oxyethylene units (1s-v)] were investigated with Ni-catalyzed/Zn-mediated system in 1-methyl-2-pyrrolidone (NMP) at 80 °C. Most of monomers bearing linear and branched alkyl groups successfully polymerized to give relatively high-molecular-weight polymers (M_n = 10,000-20,800). However, the molecular weight of the polymer having eicocyl groups was low because of steric hindrance of long alkyl chain. The polymerizations of cyclohexyl 2,5-dichlorobenzoate and phenyl 2,5-dichlorobenzoate produced low-molecular-weight polymers, while the polymerizations of monomers with alkyl cyclohexyl and alkyl phenyl groups proceeded to afford polymers with relatively high-molecular-weights. The polymers possessing oxyethylene units were obtained, but the molecular weights were low when the oxyethylene chains were long. The gas permeability of membranes of poly(p-phenylene)s with alkyl chains increased as increasing the length of alkyl chain. The membranes of poly(p-phenylene)s with phenyl groups and oxyethylene units exhibited high densities and relatively low gas permeability. However, the CO₂/N₂ separation factor of membrane of poly(p-phenylene) having oxyethylene units was as large as 73.6.     

Solution properties and kinetics of aggregation of an alkyl-substituted poly(p-phenylene)

Freshly prepared solutions of poly(2,5-di-n-dodecyl-1,4-phenylene) (PPP 12) in toluene are metastable at room temperature with regard to a process which leads to the formation of aggregates composed of up to 100 individual macromolecules. This aggregation process has an induction period of more than 10 h at room temperature. The kinetics of aggregation was investigated by making use of a fast capillary membrane osmometer. Aggregation follows an Avrami-Evans type formalism and suggests that clusters of a lyotropic liquid crystalline phase of the polymer are formed of the same type as observed in the melt. The long induction period of aggregate formation in dilute solution in toluene allows to apply conventional techniques of molar mass determination like membrane osmometry and size-exclusion chromatography (SEC). A relationship [η] = 1.94 × 10⁻³ M^0.94 was found for PPP 12 in toluene at 20 °C and a persistence length of 15.6 nm was derived applying the Bohdanecky-formalism. This gives evidence of the worm-like nature of the non-aggregated PPP 12 in dilute solution.     

Polymerization kinetics for the preparation of poly(p-divinylbenzene) via a miniemulsion polymerization process

The polymerization kinetics for the preparation of poly(p-divinylbenzene (p-DVB)) via a miniemulsion polymerization process was studied by the gravimetric analysis and the transmission electron microscopy (TEM) analysis. The influence of the variation of both initiator concentration and polymerization temperature on the polymerization rate was investigated and also the activation energy of p-divinylbenzene was estimated. The evolution of polymer particles was observed by the electronmicrographs and the relatively large size of polymer particles without the formation of coagulum was obtained in the miniemulsion polymerization process.     

Decomposition of NO over Cu-AITS-1 zeolites

H-AITS-1 zeolite with Si/Ti = 50 and Si/Al = 50 was employed in preparing catalyst samples by ion-exchange and impregnation with a copper nitrate solution to obtain 0.24–1.15 wt.% and 1.5, 2 and 2.5 wt.% Cu loading, respectively. The catalytic properties for the NO decomposition were compared with that of Cu-ZSM-5 (Si/Al = 25 with 2 wt.% Cu loading) and similarity was found between the AITS-1 based samples and Cu-ZSM-5. Due to the higher acidity, the activity at 500°C per total copper atoms (an apparent turnover frequency, TOF) was significantly higher over Cu based AITS-1 samples being 2–3 × 10⁻³ s⁻¹ as compared to 1 × 10⁻³ s⁻¹ measured on Cu-ZSM-5. For the ion-exchanged Cu-AITS-1 there was an increase in TOF with increasing copper content, whereas on the impregnated samples a decrease in TOF was found. On all catalysts there was a maximum in the NO conversion at 500–550°C. The amount of NO per copper atom measured by temperature programmed desorption (TPD) was about the same as that on Cu-ZSM-5 and the features of the TPD were also similar. At the first contact of the catalyst at 500°C with the 2 vol% NO/Ar gas a transient N₂O formation and a considerable delay in the O₂ formation was observed. This could, however, be reproduced only on fresh catalyst, while all further transients showed different but reproducible features using the same sample.     

Prediction of the electrochemical oligomerization of p-tert-butyl anisole by analyses of the electrolysed solution

The objective of this paper is the study of the electrochemical oxidation of p-tert-butyl anisole in acetonitrile solution and its subsequent electrodeposition on platinum anode. In dry medium, potentiostatic deposition at potential more anodic than these of the two first overlapped waves, which requires relatively high initial substrate concentration, provided an electroactive film. It is shown that whilst the formation of coated electrode at relatively low concentration is difficult in dry medium, it became possible in the presence of an excess amount of water. In the voltammetric study, we observe that the addition of water to the monomer, in the same concentrations leads to the appearance of several new consecutive redox systems, at potential region more anodic than the two overlapped waves. The number of these processes, which are attributed to oxidation of the products of the two first steps, is found to be increased with the water concentration. Combining cyclic voltammetry along with high performance liquid chromatography (HPLC), the effect of the analytical concentration of the monomer and this of the addition of water, on macroscale electrolyses is discussed. Possible reaction mechanisms as well as probable structures for oligomeric products are proposed.     

Electrosynthesis and characterization of a poly(paraphenylene) deriving from p-fluoroanisole

The electrochemical oxidation of p-fluoroanisole (p-FA) in the solvent acetonitrile leads to oligomers and polymers of poly(paraphenylene) type. The electropolymerization process involves coupling reactions of the cation radicals intermediates. The obtained polymers are separated according to their chain length by selective precipitation in cyclohexane and ether. The corresponding structures are characterized by NMR, MS, FTIR, UV and XR diffraction. A preliminary physical study shows that the polymers are photoluminescent with a maximum emission in the near infrared.     

Direct fluorination of various poly(p-phenylene): Effects of the polymer synthesis and thermal post-treatment

In order to complete a preliminary work about the direct fluorination of poly(p-phenylene) (PPP), the main parameters of the process were investigated. The molecular (chain length and crystallinity) and morphological effects (B.E.T. surface, granulometry) were studied. So, two new starting samples were studied in addition to PPP synthesized by the Kovacic's method (i) a commercial PPP (Polysciences) and (ii) a pyrolyzed PPP, which is similar to an amorphous hydrogenated carbon. Moreover, an annealed PPP (Kovacic's synthesis and post-treatment at 400 °C for 36 h) was compared to the as-synthesized polymer. The reactions with F₂ gas differ significantly in accordance with the synthesis way and the post-treatment (annealing or pyrolysis). Investigations about the direct fluorination of PPPs were carried out for a better understanding of their behavior with respect to molecular fluorine. An extensive characterization was performed by complementary techniques (¹⁹F and ¹³C NMR, FT-IR, and EPR). The fluorine content in the fluorinated PPPs is evaluated by these methods and a reaction mechanism is proposed.     

Packing mode and conformational transition of alkyl side chains in N-alkylated poly(p-benzamide) comb-like polymer

A series of rigid-rod poly(p-benzamide) polymers (PBA) with different length of flexible alkyl side chains, denoted as PBA(n)Cs, have been prepared by N-alkylation method. The alkyl side chain lengths varied from decyl (n=10) to octadecyl (n=18), with an interval of two carbon atoms. The packing mode and conformational transition of the alkyl side chains of the prepared PBA derivatives were characterized by wide-angle X-ray diffraction (WAXD), differential scanning calorimertry (DSC), and Fourier transform infrared spectroscopy (FTIR). WAXD results revealed that the derivatives form layered structure in which the distance between the backbones depends on the length of alkyl side chains. DSC studies indicated that melting transition temperature of PBA(n)Cs increases accordingly with increasing the alkyl chain length of the substituents. Meanwhile, DSC results proved that as the carbon atom number of the side group exceeds 14, alkyl side chains in PBA(n)Cs tend to crystallize FTIR spectroscopic investigation showed that the all-trans zigzag conformation is the most stable state for the alkyl side chain in PBA18C comb-like polymer. Temperature variation caused the reversible transition between trans and gauche conformational states of the side octadecyl group, and in turn made the molecular chain packing mode of PBA18C comb-like polymer undergo an reversible transformation from ordered packing to disordered packing.     

Considerations of polymerization method and molecular weight for proton-conducting poly(p-phenylene) derivatives

Ni(0)-catalyzed coupling polymerization of 2,5-dichloro-4′-phenoxybenzophenone was investigated by varying the ligand and coligand, temperature, reaction time, and solvent. The weight-average molecular weight (M_w) of poly(4-phenoxybenzoyl-1,4-phenylene)s (PPBPs) could be controlled by the polymerization conditions and reached a maximum of 4.4 × 10⁵ g mol⁻¹. Sulfonated PPBPs (S-PPBPs) with various M_ws were prepared with sulfuric acid to study the effect of molecular weight on the chemical and electrical properties of PPBP-based electrolytes. The strong molecular interactions in S-PPBP provided an ion exchange capacity of 2.9 meq g⁻¹ without loss of high mechanical properties. High molecular weight S-PPBPs had more desirable properties for fuel cell applications. While the swelling ratios and hydration numbers of S-PPBPs decreased with increasing molecular weight, the mechanical strength, proton conductivity, and fuel cell performance increased. S-PPBP also showed anisotropic behavior in the swelling and proton conductivity; such behavior is caused by the rigid-rod nature and the liquid-crystal structure.     

Electrochemical regeneration of activated carbon loaded with p-nitrophenol in a fluidized electrochemical reactor

This paper described a novel electrochemical process for the regeneration of activated carbon (AC) loaded with p-nitrophenol (PNP), aiming to reduce regeneration time and improve cost-effectiveness of the process by adoption of a novel non-active anode of modified lead dioxide and operation of AC in a fluidized mode. The regeneration parameters such as current density, liquid flow rate, NaCl concentration, pH of the solution and regeneration time were systematically investigated. Under the optimum conditions, the regeneration efficiency of AC could reach 90% in 1.5 h, and no significant declination was observed after five-times continuous adsorption-regeneration cycles, confirming the reuse feasibility of the regenerated AC. The adsorption of organic pollutants was confirmed occurring in the micropore of AC, and AC regeneration was mainly due to the decomposition of organics by the attack of active species such as hydroxyl radical that were generated by electrochemical oxidation. The time-space production for AC regeneration has been greatly improved in the present modified process, indicating this regeneration process is much more potentially cost-effective for application.     

Preparation and characterization of three-dimensionally ordered macroporous syndiotactic poly(p-methylstyrene)

Three-dimensionally ordered macroporous(3DOM) syndiotactic poly(p-methylstyrene) (sPPMS) with pore size 170 nm was fabricated by means of silica templates using (dbm)₂Ti(OPh)₂/MAO catalytic system. The resulting polymers were characterized by SEM, ¹³C NMR, DSC and GPC. The results indicated that the 3DOM sPPMS were highly syndiotactic. GPC curves showed that the 3DOM sPPMS possessed lower Mn and broader MWD compared with bulk one. Meanwhile, DSC results revealed that three 3DOM sPPMS exhibited crystalline form II, and bulk sPPMS form III.     

t-Butylation of 1,2-dihydroxybenzene over acidic zeolites

t-Butylation of 1,2-dihydroxybenzene (DHB) with isobutene as alkylating agent was carried out over various acidic zeolites such as USH-Y, H-beta, and H-ZSM-5. USH-Y zeolite exhibits the highest catalytic activity and considerable selectivity of 4-t-butylcatechol (4-TBC). The selectivity of 4-TBC is increased in the order of H-ZSM-5>USH-YH-beta. 3-t-Butylcatechol (3-TBC) is well produced over catalyst with high SiO₂/Al₂O₃ ratio and large pore aperture. 3,5-Di-t-butylcatechol (3,5-DTBC) selectivity is maximum in zeolite which contains strong acidity and large pore channel. The influences of various reaction parameters such as reaction temperature, space velocity, reactant molar ratio are discussed. In order to improve 4-TBC formation and decrease in 3,5-DTBC selectivity simultaneously, USH-Y zeolite was silylated by tetraethylorthosilicate (TEOS) resulting in the decrease of 3,5-DTBC selectivity over modified catalysts by about 25%. USH-Y zeolite shows high stability in the t-butylation for at least 350 h. The coke formed during the reaction was identified by FT-IR and the USH-Y zeolite could be regenerated through oxidative thermal treatment.