Transreactions of PET and PEN melt‐mixed in a twin‐screw extruder are investigated. The extruder is modeled and characterized in the frame of a tubular system of closed type. The kinetic modeling is based on a modified second‐order reversible reaction equation, which allows the dispersion equation to be solved analytically. The analysis shows a good agreement between the model and experiment. The axial dispersion model is employed to predict the extent of transesterification reactions (X) and degree of randomness (RD). 1H NMR measurements are performed to estimate X and RD. Theoretical and experimental data are in good agreement. The model can thus be exploited to describe the effects of processing parameters, mixing time, mixing temperature, and blend composition on X and RD.
In this study, a new sample vial has been designed for the extraction and determination of methyl tert-butyl ether (MTBE) in water samples by headspace solid-phase microextraction method. The special feature of this new vial is cooling the HS above the aqueous sample by cold water stream for maximum analyte absorption on SPME fiber coating. The analysis was by a gas chromatograph equipped with flame ionization detector and a capillary column (CP-sil 13 CB). Some significant variables affecting the extraction procedure were optimized. By use of divinylbenzene/carboxen/polydimethylsiloxane fiber, a sample volume of 10 mL, stirring rate of 1,000 rpm, salt concentration of 24%, extraction time of 15 min and extraction temperature of 83 °C, detection limit of 0.022 μg L?1 and a good linearity (R2 = 0.998) in a calibration range of 0.1–400 μg L?1 were achieved. The relative standard deviation for triplicate runs ranged between 6 and 8%. The method could be applied to the analysis of trace levels of MTBE in various water samples. 相似文献
The role of vitamin B1 as a catalyst is investigated for the quinoxaline ring condensation under various mild reaction conditions. The results revealed
that the combination of vitamin B1 and ultrasonic irradiation promotes the reaction more efficiently. The salient features of this environmentally benign method
are fast conversions, excellent yields for a wide range of substrates, and the use of a low-cost, readily available, nontoxic,
and metal-ion-free natural catalyst. The wide range of turnover frequency values (6–400 h−1) shows that the reaction rate is highly dependent on the nature of the functional groups on the aromatic ring of substrates.
Moreover, a plausible mechanism for the catalytic action of vitamin B1 has been introduced. 相似文献
Water has been found for the first time as a useful solvent in the Willgerodt-Kindler (WK) reaction for the synthesis of benzothiomorpholides in high yield at 80°C for 3 h. This novel approach confronts the WK protocol with a new situation in which water not only is not regarded as a serious disadvantage but also is applied in this
case as a useful solvent in the reaction. The basis of this finding is the presence of a methylene chain in the carbonyl substrates,
which leads to the high reaction selectivity of benzaldehydes over acetophenones. 相似文献
Summary. Water has been found for the first time as a useful solvent in the Willgerodt-Kindler (WK) reaction for the synthesis of benzothiomorpholides in high yield at 80°C for 3 h. This novel approach confronts the WK protocol with a new situation in which water not only is not regarded as a serious disadvantage but also is applied in this
case as a useful solvent in the reaction. The basis of this finding is the presence of a methylene chain in the carbonyl substrates,
which leads to the high reaction selectivity of benzaldehydes over acetophenones. 相似文献