scholarly journals Silica gel and microwave-promoted synthesis of dihydropyrrolizines and tetrahydroindolizines from enaminones

2021 ◽  
Vol 17 ◽  
pp. 2543-2552
Author(s):  
Robin Klintworth ◽  
Garreth L Morgans ◽  
Stefania M Scalzullo ◽  
Charles B de Koning ◽  
Willem A L van Otterlo ◽  
...  
Keyword(s):  
Microwave Heating ◽  
Carbonyl Group ◽  
Silica Gel ◽  
Microwave Power ◽  
Pyrrole Ring ◽  
Microwave Assisted ◽  
Nonpolar Solvents ◽  
Wide Range ◽  
Lower Temperature ◽  
Sulfide Contraction

A wide range of N-(ethoxycarbonylmethyl)enaminones, prepared by the Eschenmoser sulfide contraction between N-(ethoxycarbonylmethyl)pyrrolidine-2-thione and various bromomethyl aryl and heteroaryl ketones, underwent cyclization in the presence of silica gel to give ethyl 6-(hetero)aryl-2,3-dihydro-1H-pyrrolizine-5-carboxylates within minutes upon microwave heating in xylene at 150 °C. Instead of functioning as a nucleophile, the enaminone acted as an electrophile at its carbonyl group during the cyclization. Yields of the bicyclic products were generally above 75%. The analogous microwave-assisted reaction to produce ethyl 2-aryl-5,6,7,8-tetrahydroindolizine-3-carboxylates from (E)-ethyl 2-[2-(2-oxo-2-arylethylidene)piperidin-1-yl]acetates failed in nonpolar solvents, but occurred in ethanol at lower temperature and microwave power, although requiring much longer time. A possible mechanism for the cyclization is presented, and further functionalization of the newly created pyrrole ring in the dihydropyrrolizine core is described.

Dielectric Relaxation Process and Microwave Heating Mechanism in ε-Caprolactone as a Function of Frequency and Temperature

2014 ◽  
Vol 931-932 ◽  
pp. 205-209 ◽  
Author(s):  
Mohd Johari Kamaruddin ◽  
Anwar Johari ◽  
Ramli Mat ◽  
Tuan Amran Tuan Abdullah ◽  
Siti Hamidah Mohd Setapar ◽  
...  
Keyword(s):  
Dielectric Properties ◽  
Microwave Heating ◽  
Processing System ◽  
Debye Model ◽  
Microwave Energy ◽  
Dielectric Relaxation Process ◽  
Microwave Assisted ◽  
Heating Mechanism ◽  
Wide Range ◽  
Properties Of Materials

Dielectric properties of materials play a significant role in design of microwave assisted processing system. This paper is focused on the dielectric properties of ε-caprolactone (ε-cap) which is the monomer for the biodegradable polymer, Poly (ε-caprolactone) (PCL). The dielectric properties of ε-cap were measured across a wide range of frequencies (0.1 GHz5.0 GHz) and temperatures (20-150oC). Then the measured dielectric properties data was modelled using Debye model in order to relate quantitatively the dielectric properties to microwave heating mechanisms. The analysis carried out gives a clear picture of interaction of ε-cap with microwave energy and its heating mechanism in microwave assisted polymerisation process. This study concluded that microwave heating mechanism of the ε-cap in the measured range may be dominated by the dipole reorientation.

Microwave-Assisted Chemistry: a Closer Look at Heating Efficiency

2009 ◽  
Vol 62 (3) ◽  
pp. 236 ◽  
Author(s):  
Richard Hoogenboom ◽  
Tom F. A. Wilms ◽  
Tina Erdmenger ◽  
Ulrich S. Schubert
Keyword(s):  
Microwave Heating ◽  
Microwave Power ◽  
Large Scale ◽  
Small Scale ◽  
Passive Heating ◽  
Conductive Heating ◽  
Heating Efficiency ◽  
Medium Scale ◽  
Microwave Assisted ◽  
Demineralized Water

Nowadays, microwave heating has evolved into a common tool for chemists based on its numerous advantages over conventional conductive heating. Surprisingly, the efficiency of microwave-assisted heating is still rather unexplored. In this contribution, we report our investigations concerning the heating efficiency of a variety of solvents including polar and apolar substances. Moreover, the effects of adding salt or passive heating elements on the microwave heating efficiency will be addressed. Finally, the heating efficiency of demineralized water is discussed at different volumes and with different microwave power levels in both monomode and multimode microwave synthesizers, demonstrating maximum average heating efficiencies of 10% for small-scale vessels (5 mL), 20% for medium-scale (50 mL), and 30% for large-scale microwave heating (400 mL).

scholarly journals Microwave assisted ignition to achieve combustion synthesis

2001 ◽  
Vol 5 (3) ◽  
pp. 151-164 ◽  
Author(s):  
E. Balakrishnan ◽  
M. I. Nelson ◽  
X. D. Chen
Keyword(s):  
Mathematical Model ◽  
Combustion Synthesis ◽  
Microwave Heating ◽  
Microwave Power ◽  
Simple Mathematical Model ◽  
Combustion Kinetics ◽  
Temperature Dependent ◽  
First Order ◽  
Microwave Assisted ◽  
Dependent Absorption

The use of microwave heating to initiate combustion synthesis has been increasingly investigated in recent years because of its advantages over traditional methods. A simple mathematical model is used to model these experiments. The microwave power absorption term is modelled as the product of an Arrhenius reaction term with a function that decays exponentially with distance. The former represents the temperature-dependent absorption of the microwaves whereas the latter describes the penetration of the material by the microwaves. Combustion kinetics are modelled as a first-order Arrhenius reaction.

scholarly journals Optimization of Microwave-Assisted Extraction Process of Callicarpa candicans (Burm. f.) Hochr Essential Oil and Its Inhibitory Properties against Some Bacteria and Cancer Cell Lines

Processes ◽  
2020 ◽  
Vol 8 (2) ◽  
pp. 173 ◽  
Author(s):  
Quoc Toan Tran ◽  
Thu Le Vu Thi ◽  
Tien Lam Do ◽  
Hong Minh Pham Thi ◽  
Bich Hoang Thi ◽  
...  
Keyword(s):  
Essential Oil ◽  
Cell Lines ◽  
Cancer Cell ◽  
Microwave Power ◽  
Cancer Cell Lines ◽  
Extraction Process ◽  
Raw Material ◽  
Extraction Time ◽  
Microwave Assisted ◽  
Wide Range

Callicarpa candicans (Burm. f.) Hochr. (Callicarpa cana L.) is a medicinal plant that is distributed mainly in the tropics and subtropics of Asia and finds a wide range of uses in traditional medicine. In this study, we attempted and optimized the microwave-assisted hydro-distillation (MAHD) process to obtain essential oil from the leaves of C. candicans. In addition, the obtained oil was analyzed for volatile composition by gas chromatography–mass spectrometry (GC-MS) and assayed for bioactivity against several bacteria and cancer cell lines. To optimize the extraction process, response surface methodology (RSM) in combination with central composite design (CCD) was adopted. Experimental design and optimization were carried out with respect to three experimental factors including the ratio of water to raw material, extraction time, and microwave power. The optimal extraction conditions were obtained as follows: water to raw material ratio of 6/1 (v/w), extraction time 42 min, and microwave power 440 W. Composition determination of the obtained C. candicans essential oil indicated the presence of predominant components including caryophyllene <b-> (10.45%), cadinene <d-> (10.28%), gurjunene <a-> (8.95%), muurolene <g-> (8.92%), selinene <a-> (7.06%), selinene <b-> (5.59%), and copaene <a-> (5.40%). In comparison with the essential oils obtained via traditional hydro-distillation method, the essential oil extracted by MAHD exhibited superior anti-proliferative activity on all tested cancer cell lines. Current results imply that the MAHD is capable of recovering biologically-active natural products of greater quantity than that recovered by the conventional distillation.

scholarly journals CONTINUOUS INDUSTRIAL-SCALE MICROWAVE-ASSISTED EXTRACTION OF HIGH-VALUE INGREDIENTS FROM NATURAL BIOMASS

2019 ◽  
Author(s):  
Steven Splinter ◽  
Marilena Radoiu
Keyword(s):  
Energy Transfer ◽  
Residence Time ◽  
Microwave Power ◽  
Continuous Flow ◽  
Microwave Energy ◽  
Industrial Scale ◽  
Innovative Technology ◽  
Microwave Assisted ◽  
Assisted Extraction ◽  
Wide Range

An innovative technology for the continuous extraction of bioactive compounds from a wide range of biological materials has been developed, scaled up and successfully demonstrated at commercially-relevant scales. The technology, known as MAPTM, or “Microwave-Assisted Process”, robustly transfers from laboratory to continuous, industrial scale operation.  In wide-ranging trials, MAPTM has comprehensively demonstrated its ability to outperform many KPIs of conventional extraction processes, while offering biomass throughput, product consistency and low operational costs not attainable by other emerging technologies. Radient’s proprietary continuous-flow MAPTM extractor, Figure 1, was designed for continuous processing of up to 200 kg/h of biomass material. Verification of the mechanical integrity of the system was confirmed by flow testing of biomass / solvent slurries. Testing and verification of the efficiency of microwave energy transfer to the extractor cavity was completed at various microwave power settings using flowing water at 870 kg/h.  The microwave energy transfer to the system was verified to be &gt;95 % in each case. As an example of performance, continuous flow MAPTM extraction of the antioxidant SDG from flax biomass was performed using 70 % ethanol / water as the solvent at two different conditions: -          75 kg/h flax / 5 L/kg solvent / 15 kW microwave power / extractor residence time 24 min; -          110 kg/h flax / 5 L/kg solvent / 20 kW microwave power / extractor residence time 16 min. The industrial-scale conditions for these runs were determined by extrapolating from optimized conditions previously obtained from batch lab-scale MAPTM experiments. The continuous flow approach eliminates the requirement for having geometric similarity between scales, i.e the equipment shape and dimensions do not have to scale proportionately.

Microwave-assisted preparation of polyphosphoric acid in a continuous-flow reactor

2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Jinghua Ye ◽  
Chun Zhang ◽  
Taotao Gao ◽  
Huacheng Zhu
Keyword(s):  
Microwave Heating ◽  
Microwave Power ◽  
Continuous Flow ◽  
Polyphosphoric Acid ◽  
Orthophosphoric Acid ◽  
High Energy ◽  
Dehydration Process ◽  
Reduced Pressure ◽  
Inlet Flow ◽  
Microwave Assisted

Abstract Polyphosphoric acid (PPA) is widely used in inorganic salt production, petrochemical industry, electronic material preparation and other manufacturing industries. Conventional preparation methods of PPA has disadvantages of pollution, high energy consumption and long production time. To address this problem, microwave continuous-flow preparation may be a desirable way due to its advantages of environmentally-friendly, rapidity and high efficiency. Therefore, to explore the process of preparing PPA by microwave continuous-flow method, a continuous-flow microwave reactor was designed for the dehydration process of orthophosphoric acid to prepare PPA in this paper. The microwave-assisted dehydration process was studied in comparison with the conventional dehydration process and the “closed” microwave-assisted dehydration process in terms of energy efficiency, process times and treatment capacity. The effect of input microwave power, reduced pressure and inlet flow velocity of orthophosphoric acid on the performance of the dehydration process was studied. The results showed that the influence of the microwave power on the temperature rise process during dehydration is greater than that of the reduced pressure. Moreover, the inlet flow rate has a great impact on the treatment capacity and product quality of the dehydration process. Bedsides, the comparison with the other two methods showed that microwave heating can effectively shorten the dehydration time, and the continuous-flow treatment can effectively improve the treatment capacity of microwave heating. The perspectives of the process scale-up by continuous-flow microwave heating method is also discussed.

scholarly journals Preparation and application of carbon and hollow TiO2 microspheres by microwave heating at a low temperature

e-Polymers ◽  
2021 ◽  
Vol 21 (1) ◽  
pp. 200-209
Author(s):  
Caiyun Zhang ◽  
Chunhong Li ◽  
Bolin Ji ◽  
Zhaohui Jiang
Keyword(s):  
Low Temperature ◽  
Microwave Heating ◽  
Raw Material ◽  
Carbon Microspheres ◽  
Microwave Assisted ◽  
The Core ◽  
Good Crystallinity ◽  
Carbon Core ◽  
Microwave Assisted Method ◽  
Uniform Particle Size

Abstract A fast, simple, and energy-saving microwave-assisted approach was successfully developed to prepare carbon microspheres. The carbon microspheres with a uniform particle size and good dispersity were prepared using glucose as the raw material and HCl as the dehydrating agent at low temperature (90°C) in an open system with the assistance of microwave heating. The carbon microspheres were characterized by elemental analysis, XRD, SEM, FTIR, TG, and Raman. The results showed that the carbon microspheres prepared under the condition of 18.5% (v/v) HCl and heating for 30 min by microwave had a narrow size distribution. The core–shell structure of the carbon core and TiO2 shell was prepared with (NH4)2TiF6, H3BO3 using the microwave-assisted method. The hollow TiO2 microspheres with good crystallinity and high photocatalytic properties were successfully prepared by sacrificing the carbon microspheres.

scholarly journals Effect of Microwave Power on Performance of Microwave-Assisted Spark Ignition under CO2-Diluted Condition

2021 ◽  
Vol 692 (2) ◽  
pp. 022001
Author(s):  
Xinhua Zhang ◽  
Zhaowen Wang ◽  
Huimin Wu ◽  
Chaohui Liu ◽  
Zhihao Wang ◽  
...  
Keyword(s):  
Microwave Power ◽  
Spark Ignition ◽  
Microwave Assisted

Behavior of Microwave Heating of 316 Stainless Steel Green Body

2014 ◽  
Vol 936 ◽  
pp. 1694-1700
Author(s):  
Zhi Wei Li ◽  
Kai Yong Jiang ◽  
Fei Wang ◽  
Ji Liang Zhang
Keyword(s):  
Particle Size ◽  
Stainless Steel ◽  
Microwave Heating ◽  
Powder Particle ◽  
Microwave Power ◽  
Arc Discharge ◽  
Steel Powder ◽  
Powder Particle Size ◽  
Auxiliary Heating ◽  
316 Stainless Steel

This paper mainly introduces the mechanism of microwave heating: electric conduction loss, eddy current loss and arc discharge. The microwave heating behavior of 316 stainless steel powder body which made by gel casting was investigated in the paper. Experiments on different microwave power, powder particle size, and the content of auxiliary heating material showed that the smaller the powder particle size, the larger microwave power and auxiliary heating materials help 316 stainless steel body for sintering.

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