Benzodiazepines possess a wide spectrum of valuable pharmacological effects and are among the leading drugs, commonly prescribed ones for various pathologies. Herein we describe the continuous flow synthesis of six benzodiazepines from aminobenzophenones: diazepam, fludiazepam, nordazepam, nitrazepam, clonazepam, oxazepam.
N-(3-Amino-4-methylphenyl)benzamide (1) is a crucial building blocks of many drug candidates. In this paper, a continuous flow microreactor system was developed to synthesize 1 and determine intrinsic reaction kinetics parameters. By screening the acylating reagents and reaction conditions, 1 was obtained by the selective acylation of 4-methylbenzene-1,3-diamine (2) with benzoic anhydride (3). Since the two amine groups in 2 are in different chemical environments, parallel by-products and serial by-products coexist, which makes the selective monoacylation process relatively complicated. To reveal the reaction process clearly, reaction rate constants and their 95% confidence intervals, activation energies, pre-exponential factors were acquired by kinetics study in microflow system. The established kinetic model can calculate the selectivity and conversion of the acylation reaction, which are in good agreement with the experimental results. Subsequently, the kinetic model was used to optimize reaction conditions, as a result, 1 was synthesized in the microreactor with a yield of 85.7% within 10 min.
The nitration reaction and purification process of 2-Ethyl-1-hexanol is highly hazardous and characterized by severe thermal instability. Therefore, appropriate safety and kinetics studies are needed to promote safe synthesis in chemical production. However, obtaining accurate kinetic data is challenging due to its fast, highly exothermic, and heterogeneous characteristics. In this study, we obtained reaction kinetic parameters of 2-Ethyl-1-hexanol in a capillary-microreactor at different sulfuric acid concentrations and temperatures and calculated the per-exponential factor and activation energy. The thermal stability of 2-Ethylhexyl nitrate in mixed acids was determined by differential scanning calorimetry. Computational Fluid Dynamics was used to simulated the temperature distribution inside the capillary-microreactor for a T-shaped structure based on the kinetic and thermal stability data. The results show that even small-scale reaction tubes produce hot spots in the reactor inlet region in an isothermal environment. Under adiabatic conditions, the temperature inside the capillary is close to the decomposition temperature of the acid mixture. Therefore, the thermal safety of nitration reactions, even in small-scale microreactor systems, cannot be ignored. The results of this study have important implications for the industrial process design and safety for highly-exothermic reactions.
Resveratrol is a natural bioactive non-flavonoid polyphenol that protects from cardiovascular disease, neurodegenerative diseases and various cancers. Unfortunately, the amounts of resveratrol in plants are low and therefore, chemical synthesis is still the main way to obtain this valuable structure. In this work, Wittig reaction was chosen as the synthetic route for the study on technology influence in batch vs. micro- or milliflow reactors during the production of new resveratrol-like compounds. A series of reactions was carried out by batch synthesis, and intensified in a milli- and a microreactor, changing the reaction conditions to increase the efficiency and productivity of the process. Results were compared based on conversion, yield, productivity and trans/cis ratio. Similar yields and conversions were obtained in all reaction systems, but in much shorter time in the milli- and microscale compared to the batch reactor. On the other hand, higher productivities were obtained in the millireactor and microreactor, making them better systems for the proposed reactions of new heterocyclic resveratrol analogues synthesis.
The field of flow chemistry is growing rapidly, drawing attention across different disciplines. Despite its increasing popularity in the industry and research, little attention is given to the teaching of flow chemistry in the educational environment, especially at the undergraduate level. A major challenge with teaching undergraduate flow chemistry is the high cost of flow chemistry equipment. This study reports the development of low-cost, functioning flow chemistry equipment for the teaching of flow chemistry and experimental practicum. This provides the students with hands-on instruction in fabricating flow reaction devices by 3D printing. It also allows undergraduate students to understand the basics of flow chemistry and chemical engineering. An exciting part of this study is the skills acquired by undergraduate students. This is because of the learning experience they are exposed to by training and independently operating fabrication equipment, setting up flow experiments and conducting flow experiments with the fabricated devices. Finally, due to the low cost of the equipment, the set-up is suitable for teaching flow chemistry in a low-resource environment, such as our teaching laboratories in South Africa.
The development of green synthesis route using plant extract as a simple, cost-effective, and eco-friendly method for the synthesis of nanoparticles has become a major focus of researchers in recent years. In the present study, a novel continuous tri-fluid tortuous microfluidic chip (CTTM) was constructed to induce simultaneous mixing, Dean vortices, tortuosity, and repetitive bending in fluid behavior in order to plant-mediated synthesis of zinc selenide (ZnSe) nanoparticles. Additionally, the anti-pathogenic activity of nanoparticles against a human pathogen (E. coli) through the disruption of the cell membrane and the evaluation of the subsequent flow of cellular components such as continuous leakages of K+, nucleic acid, and intracellular protein was examined using the proposed chip. According to the results, by changing the flow rates up to 1.50 mL/min, nanoparticles with narrow size distribution were obtained. It was found that the nanoparticles sterilization effect in the case of α (Vnanoparticles/Vbacteria strain) =2 was obviously better than α = 0.5 under similar concentration and culture conditions. In this case, when the residence time and nanoparticle concentration tended to the maximum values, the release of intracellular components increased. Light microscopy and SEM clearly confirmed the ability of the antibacterial effects of nanoparticles to disrupt the bacteria membrane. Moreover, the inhibitory activity of the fabricated nanoparticles through a protein denaturation test using human serum albumin (HSA) showed an acceptable ability to inhibit protein denaturation compared to the inhibition of diclofenac sodium as a standard anti-inflammatory drug at the same concentration.
A simultaneous determination of the enthalpy of mixing and reaction in a scalable continuous milli-scale flow calorimeter is investigated. As obtained calorimetric data is pivotal for the safety assessment of chemical reactions and processes. The acid-catalysed selective, homogeneous hydrolysis of acetic anhydride with half-lives from a few seconds to a few minutes is investigated as a model reaction. For the enthalpy of mixing 7.2 ± 2.8 kJ/mol and for the enthalpy of reaction −60.8 ± 2.5 kJ/mol were determined. For reactions that show complete conversion in the continuous reactor, a technique is introduced to further improve the accuracy of the reaction enthalpy determination. Thereby, the resolution of the observed temperature profile is increased by measuring the profile at different flow rates. Applying this procedure, the reaction enthalpy of −62.5 kJ/mol was determined which is in good agreement with literature values for this model reaction.
Herein we report a machine-assisted and scaled-up synthesis of propofol, a short-acting drug used in procedural sedation, which is extensively in demand during this COVID-19 pandemic. The continuous-flow protocol proved to be efficient, with great potential for industrial translation, reaching a production up to 71.6 g per day with process intensification (24 h-continuous experiments). We have successfully telescoped a continuous flow approach obtaining 5.74 g of propofol with productivity of 23.0 g/day (6 h-continuous experiment), proving the robustness of the method in both separated and telescoped modes. Substantial progress was also achieved for the in-line workup, which provides greater safety and less waste, also relevant for industrial application. Overall, the synthetic strategy is based on the Friedel-Crafts di-isopropylation of low-cost p-hydroxybenzoic acid, followed by a decarboxylation reaction, giving propofol in up to 84% overall yield and very low by-product formation.
The continuous flow synthesis of propofol 3 is presented as a two-step protocol. The isopropylated intermediate 2 was obtained from 4-hydroxybenzoic acid (1) in up 43.8 g, 85% yield and 30 min residence time. Propofol 3 was then obtained in 71.6 g, 87% yield, and 16 min residence time. A safe and cost-competitive machine-assisted protocol is described with a process intensification demonstration (24 h experiments) and a telescoped process intensification (6 h).
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