Polyarylates. V. The influence of phase transfer agents on the interfacial polycondensation

The effect of various phase transfer agents on the interfacial polycondensation of bisphenol A with isophthaloyl chloride was investigated. It was found that the transfer rate of bisphenolate and, thus, the reaction rate of polycondensation were increased with an increasing lipophilicity of the phase transfer agent, i.e. TBAC > TEBAC > TEAC, whereas the equilibrium of bisphenolate between the organic phase and the aqueous phase was hardly affected. Moreover, experimental evidence indicated that a phase transfer agent of high lipophilicity reduced the hydrolysis of the acid chloride, an important aspect in interfacial polycondensation.     

粗硼砂的氯化铵溶液浸提动力学

研究了反应温度、溶液浓度、固液比、固体粒径大小和搅拌速度对氯化铵溶液浸提粗硼砂(十水四硼酸钠,Na₂B₄O₇·10H₂O)动力学的影响。结果表明反应速率随反应温度、溶液浓度的增加和固体粒径、固液比的减小而增加,但搅拌速度对溶解速率无显著影响。根据均相和多相动反应力学模型研究了粗硼砂的溶解过程。结果表明溶解速率遵从假一级均相反应模型。粗硼砂在氯化铵溶液中溶解的活化能为82.73 kJ·mol^-1。     

Chemoselectivity in the microwave-assisted solvent-free solid-liquid phase benzylation of phenols: O- versus C-alkylation

The outcome of the solvent-free benzylation of phenol and 4-substituted phenols (such as 4-cresol and 4-chlorophenol) under MW irradiation was found to depend on the absence or presence of the base (K₂CO₃) and catalyst (triethylbenzylammonium chloride (TEBAC)). Reaction of benzyl halides at 80-120 °C in the presence of K₂CO₃ and TEBAC resulted in O-alkylation in high (89-96%) chemoselectivities. In the absence of TEBAC, the proportion of C-alkylation was considerable (16-34%). Omitting also K₂CO₃ from the reaction mixture, C-alkylation became predominant. In the case of 4-tert-butylphenol, the presence of TEBAC promoted C-alkylation. The selectivity of the alkylations can be fine-tuned by choosing the appropriate conditions.     

Kinetics of Interfacial Polycondensation of Bisphenols with Isophthaloyl Chloride

Reaction rates of interfacial polycondensation of bisphenol A and chlorobisphenol II with isophthaloyl chloride were investigated. Rate constants and activation energies were determined The reaction rate was found to depend on stirring speed, catalyst, type of bisphenol, and temperature.     

Polyarylates (I): Investigation of the interfacial polycondensation reaction by UV

The interfacial polycondensation of bisphenol A with isophthaloyl chloride and terephthaloyl chloride in dichloromethane with triethylbenzylammonium chloride as the catalyst was described. A well-defined two-phase system had been observed, so the concentration of bisphenolate in the aqueous phase could be determined by UV spectrometer. The conversion was found to increase rapidly with reaction time, but the rate of increase in molecular weight was slow. At the initial stage with conversion up to 95%, the reaction proceeded similarly to that of solution polycon-densation because the synthesized polyarylate could be dissolved in dichloromethane, and a polymer with a low molecular weight resulted. At the final stage of the reaction, the molecular weight was increased to a very high value due to the local concentration effect. The mole ratio of bisphenol A to diacid chlorides was found to affect the molecular weight very much. In the case of a mole ratio less than 1, the reaction remained in the initial stage mostly, and the molecular weight was low. However, for a mole ratio greater than 1, polyarylate with a very high molecular weight could be obtained because the local concentration effect was much more significant owing to the high concentration of bisphenolate that remained in the aqueous phase at the final stage.     

Triphase catalysis. II. Alkylation of phenylacetone with 1-bromobutane catalyzed by aqueous NaOH and polystyrene-supported benzyltriethyl ammonium chloride

Insoluble microporous polystyrene-bound benzyltriethyl ammonium chloride has been used as a catalyst in the alkylation of phenylacetone with 1-bromobutane, and the kinetics of this reaction was investigated under phase-transfer catalytic conditions. The observed reaction rates depend on many experimental parameters, viz., stirring speed, substrate amount, basicity of aqueous NaOH, amount of 1-bromobutane, temperature, order of addition of the reactants and particle size, percent active site, and percent crosslinking of the polymer. The rates are nearly 12 times higher at lower concentrations of base than at higher concentrations and do not vary appreciably with a variation in stirring speed from 200 to 700 rpm. The rate of alkylation increases with a decrease in the particle size of the catalyst and crosslinking of the polymer. Based on the results obtained, a suitable mechanism in which a combination of intraparticle diffusion and intrinsic reactivity limit the reaction rates has been proposed. © 1993 John Wiley & Sons, Inc.     

Study on the extraction kinetics of phenolic compounds from petroleum refinery waste lye

A large amount of waste lye is produced in petroleum refineries during alkali cleaning process, which consists of high concentration of phenols, sulfides, oils and other pollutants. In this study, tributyl phosphate (TBP) was used as extraction agent and the extraction kinetics of phenolic compounds was investigated by the constant interfacial cell method. The effects of stirring speed, temperature and specific area on extraction rate were studied. The experimental results show that the extraction of phenols by TBP is a first-order reaction, and the extraction process may be controlled by diffusion. The effects of stirring speed and specific area on extraction rate are significant.     

Reaction of benzyl chloride with ammonium sulfide under liquid–liquid phase transfer catalysis: Reaction mechanism and kinetics

The reaction between benzyl chloride and aqueous ammonium sulfide was carried out in an organic solvent – toluene, using tetrabutylammonium bromide (TBAB) as phase transfer catalyst (PTC). Two products, namely dibenzyl sulfide (DBS) and benzyl mercaptan (BM), were identified in the reaction mixture. The selectivity of DBS was maximised by changing various parameters such as NH₃/H₂S mole ratio, stirring speed, catalyst loading, concentration of benzyl chloride, volume of aqueous phase, and temperature. The highest selectivity of DBS obtained was about 90% after 445 min of reaction with excess benzyl chloride at 60 °C. Complete conversion of benzyl chloride could be achieved at the cost of very low selectivity of DBS and very high selectivity of BM. The apparent activation energy for the kinetically controlled reaction was found to be 12.3 kcal/mol. From the detailed study of the effects of various parameters on the reaction, a suitable mechanism was established which could explain the course of the reaction.     

Polyarylates. IV. Synthesis of block copolymers via two-step interfacial polycondensation

A new method for preparing block copolyarylates via two-step interfacial polycondensation is proposed. First, oligomers with acid chloride end groups were obtained from interfacial polycondensation with a mole ratio of bisphenol A to diacid chloride(s) less than I. In the second step, two reaction systems containing various oligomers were mixed thoroughly and more bisphenolate was charged into this mixture. The synthesis of the block copolyarylates was justified from the viewpoint of statistics, and of differences in molecular weight between oligomers and block copolymers. These block copolyarylates could be differentiated from polyarylates through crystal-line behavior and solubility in m-cresol analyses.     

无添加剂条件下文石型碳酸钙晶须制备及影响因素研究

在不加任何结晶控制剂或模板条件下,以CaCl2和Na2CO3为原料,利用复分解反应法制备了具有较好形貌和高长径比,且分布均一的文石型碳酸钙晶须,并利用扫描电镜(SEM)、X-射线粉末衍射(PXRD)和傅里叶转换红外光谱图(FT-IR)等手段对其进行了表征。研究了浓度、滴加速度、反应温度、搅拌速度以及滴加方式等因素对碳酸钙晶须的影响。结果表明最佳制备工艺为:CaC12溶液与Na2CO3溶液的浓度为0.05 mol.L-1,溶液滴加速度为1 mL.min-1,反应体系温度为80℃,搅拌速度为250 r.min-1。     

Dissolution kinetics of copper(II) oxide in water saturated by sulphur dioxide

The dissolution and the kinetics of dissolution of cooper(II) oxide in water saturated by sulphur dioxide has been studied. In the experiments, the particle size, the flow rate of the gas, the solid to liquid ratio, and the reaction temperature have been chosen as parameters, while the stirring rate was held constant. As a result of present experiments, it was observed that the decrease of the particle size, the solid to liquid ratio, and an increase of the reaction temperature increased the dissolution rate. It was also observed that the flow rate of sulphur dioxide in the range of its flow rate values did not affect the dissolution rate. The reaction kinetics of copper(II) oxide according to the heterogeneous reaction models was examined and it was found that the dissolution rate was controlled by chemical reaction. The calculated activation energy is 66.50 kJmol^?1. © 1994 John Wiley & Sons, Inc.     

含氟硫酸体系HEH/EHP萃取铈(Ⅳ)的动力学研究

采用层流恒界面池法研究了2-乙基己基膦酸单2-乙基己基酯(HEH/EHP)萃取含氟复杂硫酸体系中铈(Ⅳ)的动力学。考察了搅拌速度、水相金属离子浓度、萃取剂浓度、酸度和温度对萃取速率的影响。试验结果表明:萃取反应为一级反应,萃取反应的正向表观活化能为50.8 kJ·mol-1,属于化学反应控制。试验得到萃取动力学方程为R=k[Ce(HF)(HSO4-)3+]1.05[H2A2]2.07[H+]-2.43,并探讨了反应机制。     

Reaction of difluorocarbene with anions from amides and oximes: Synthesis of N-difluoromethyl substituted amides, O-difluoromethylimidates or O-difluoromethyl substituted oximes under phase-transfer catalysis conditions

N-Aryl substituted amides react with chlorodifluoromethane in the presence of concentrated aqueous sodium hydroxide and benzyltriethylammonium chloride (TEBAC) as a catalyst in benzene (phase-transfer catalysis, PTC), affording mixtures of N- and O-difluoromethyl substituted derivatives. Amide anions are involved in this process. The reaction carried out with oximes gives O-difluoromethyl oxime ethers.     

Kinetics of beta-haematin formation from suspensions of haematin in aqueous benzoic acid

Kinetics of beta-haematin (synthetic malaria pigment) formation from haematin have been studied in the presence of aqueous benzoic acid and derivatives of benzoic acid. Formation of the beta-haematin product is demonstrated by X-ray diffraction and IR spectroscopy. Reactions were followed by determining the fraction of unreacted haematin at various time points during the process via reaction of extracted aliquots with pyridine. The kinetics can be fitted to the Avrami equation, indicating that the process involves nucleation and growth. Reaction kinetics in stirred benzoic acid are similar to those previously observed in acetic acid, except that benzoic acid is far more active in promoting the reaction than acetic acid. The reaction reaches completion within 2 h in the presence of 0.050 M benzoic acid (pH 4.5, 60 degrees C). This compares with 1 h in the presence of 4.5 M acetic acid and 4 h in the presence of 2 M acetic acid. The reaction rate in benzoic acid is not affected if the stirring rate is decreased to zero, but very vigorous stirring appears to disrupt nucleation. The rate constant for beta-haematin formation in benzoic acid has a linear dependence on benzoic acid concentration and follows Arrhenius behaviour with temperature. There is a bell-shaped dependence on pH. This suggests that the haematin species in which one propionate group is protonated and the other is deprotonated is optimal for beta-haematin formation. When the reaction is conducted in para-substituted benzoic acid derivatives, the log of the rate constant increases linearly with the Hammett constant. These findings suggest that the role of the carboxylic acid may be to disrupt hydrogen bonding and pi-stacking in haematin, facilitating conversion to beta-haematin. The large activation energy for conversion of precipitated haematin to beta-haematin suggests that the reaction in vivo most likely involves direct nucleation from solution and probably does not occur in aqueous medium.     

Polymer-supported reagents. II. Kinetics of esterification of acrylic acid with n-butanol using polymer supported titanium tetrachloride as catalyst

Crosslinked poly(4-vinylpyridine-co-styrene) was prepared and functionalized with titanium tetrachloride to afford the corresponding poly(4-vinylpyridine-co-styrene)-titanium tetrachloride complex. This insoluble functionalized polymer-supported catalyst shows good catalytic activity for esterification reactions. In this article, the kinetics of esterification of acrylic acid with n-butanol is reported. The rate of formation of product depends on many experimental parameters, viz., stirring speed, concentration of acrylic acid, catalyst amount, temperature, percent active site, percent crosslinking, and mesh size of the polymer catalyst. The reaction rates were found to increase with increase in the stirring speed, concentration of acrylic acid, catalyst amount, and temperature, and decreases with increasing percentage crosslinking and mesh size of the polymer beads. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 727–733, 1997     

Pressure effects on Friedel-Crafts alkylation reactions in supercritical difluoromethane.

Dielectrometry is used as a novel technique for following the rate of a Friedel-Crafts alkylation reaction in supercritical (sc) difluoromethane. Although the process was not optimized, good product yields were obtained and reaction rates were found to be larger than in CO2 at comparable conditions. The reaction order is determined using the initial rate method and the reaction is shown to be first-order with respect to both anisole and t-butyl chloride. The reaction rate constant is unaffected by pressures above 120 bar but close to the critical pressure the value decreases with increasing pressure. It is also shown that the product distribution for the alkylation of anisole shows significant pressure dependence with substitution at the ortho-position being favored at lower pressures, which is ascribed to hydrogen bonding. This pressure dependency is not observed in sc CO2 or using toluene as a substrate, which supports the idea that hydrogen bonding may be important in the reaction mechanism. The effect of the different reagents and temperature on the rate of the alkylation reaction was also determined.     

Reaction kinetics of malachite in ammonium carbamate solution

The dissolution of malachite particles in ammonium carbamate (AC) solutions was investigated in a batch reactor, using the parameters of temperature, AC concentration, particle size, and stirring speed. The shrinking core model was evaluated for the dissolution rate increased by decreasing particle size and increasing the temperature and AC concentration. No important effect was observed for variations in stirring speed. Dissolution curves were evaluated in order to test shrinking core models for fluid-solid systems. The dissolution rate was determined as being controlled by surface chemical reaction. The activation energy of the leaching process was determined as 46.04 kJ mol^?1.     

Absorption and reaction of CO2 with 2,3-epoxypropyl phenyl ether using aliquat 336 AS catalyst

A kinetic study on the absorption and reaction of carbon dioxide with 2,3-epoxypropyl phenyl ether (phenyl glycidyl ether, PGE) in benzene solution has been carried out at room temperature in the presence of tricaprylylmethyl ammonium chloride (Aliquat 336) as catalyst. A simple method of measuring the absorbed volume of CO₂ was proposed to obtain the reaction rate constant, and it was based on the film theory accompanied by a chemical reaction. The enhancement factor (β-N_CO2/N_CO2 ^o) increased with increasing bulk concentration of PGE and Aliquat 336. The flux of CO₂ was proportional to the agitation speed.     

A study of dissolution kinetics of a Nigerian galena ore in hydrochloric acid

The results of experimental investigation on the study of dissolution kinetics of a Nigerian galena ore in hydrochloric acid solution were discussed. The influence of acid concentration, temperature, particle size, stirring speed and solid/liquid ratio on the extent of dissolution was examined. The elemental analysis by XRF showed that the galena ore is composed mainly of PbS with metals such as Sn, Fe and Zn occurring as minor elements and Mn, Rb, Sr and Nb as traces. The XRD analysis indicated galena as the dominant mineral phase, with the presence of associated minerals, such as α-quartz (SiO₂), sphalerite (ZnS), cassiterite (SnO₂), pyrite (FeS₂) and manganese oxide (MnO₂).Results of leaching studies showed that galena dissolution in HCl solution increases with increasing acid concentration and temperature; while it decreases with particle diameter and solid/liquid ratio at a fixed stirring rate of 450 rpm. The study showed that 94.8% of galena was dissolved by 8.06 M HCl at 80 °C within 120 min with initial solid/liquid ratio of 10 g/L. The corresponding activation energy, E_a was calculated to be 38.74 kJ/mol. Other parameters such as reaction order, Arrhenius constants, reaction and dissociation constants were calculated to be 0.28, 73.69 s^?1, 1.73 ± 0.13 × 10³ and 1.37 ± 0.024 × 10⁴ mol L^?1 s^?1, respectively. The mechanism of dissolution of galena was established to follow the shrinking core model for the diffusion controlled mechanism with surface chemical reaction as the rate controlling step for the dissolution process. Finally, the XRD analysis of the post-leaching residue showed the presence of elemental sulphur, lead chloride and α-quartz.     

硝酸胺溶液浸提硬硼酸钙的动力学研究

对硬硼酸钙在硝酸铵水溶液的溶解在间歇式反应器中就搅拌速度、粒径大小、反应温度、固液比和溶液的浓度等参数的影响进行了研究。结果表明溶解速度随温度、硝酸铵水溶液的浓度以及粒径和固液比的增加而增加,但搅拌速度对溶解速度无重要影响。硬硼酸钙在硝酸铵水溶液中可以高达100%。硬硼酸钙的溶解动力学根据多相和均相反应模型进行了检验。实验数据表明有高的活化能,说明基于多相反应动力学模型的溶解速度可表达为：1-(1-X)^1/3=3.28 ×10⁴·D^{-0.653 7}·C^{1.295 8}·(S/L)^{-0.490 9}·e^-41.40/(RT)·t。反应过程的活化能为41.40 kJ·mol^-1。