Continuous flow synthesis of xylidines via biphasic nitration of xylenes and nitro-reduction

Two-Step Synthesis of a Dolutegravir Intermediate DTG-6 in a Microfluidized Bed Cascade System: Route Design and Kinetic Study

In the existing two-step method for the preparation of DTG-6 (i.e., an important intermediate of the anti-HIV drug Dolutegravir (DTG)), a strong base is required to neutralize the homogeneous strong acid catalyst of the first step to make the reaction solution weakly acidic for the DTG-5 cyclization in the second step. The DTG-6 yield in the two-step synthesis is affected by the reaction of the strong base with the carboxyl group on the generated intermediate DTG-5. In this article, a solid acid catalyst, titanium cation-exchanged montmorillonite (Ti4+-mont), was used in the microfluidized bed to catalyze the conversion of DTG-4 to DTG-5. DTG-5 can be directly cyclized with (R)-3-aminobutanol (RABO) to form DTG-6 without the introduction of a strong base into the reaction solution. After the parametric screening on the flow rate, solid acid type, temperature, residence time, and solvent type, the DTG-6 yield increased from 90% (in our previous work) to 95% in the microfluidized bed cascade system. Due to the easy separation of heterogeneous catalyst, the utilization of a microfluidized bed not only simplified operations, but also improved synthetic efficiency. Moreover, the kinetics of the cyclization of unstable intermediate DTG-5 with RABO was investigated and verified by means of experimental data.

Development of a scalable and sustainable continuous-flow microreaction process for mononitration of aromatic compounds with high selectivity and yield

Nitroaromatic compounds are extensively used in industries such as pharmaceuticals, pesticides, and dyes. However, traditional synthesis methods often face challenges, including high safety risks, significant environmental pollution, and poor selectivity in mononitration reactions. In this study, we developed an efficient and safe continuous-flow microreaction process for mononitration, which achieves high yield and excellent selectivity. This process is applicable for the continuous synthesis of various mononitro compounds, including nitro-p-xylene, nitro-o-xylene, nitro-chlorobenzene, and nitro-toluene. Furthermore, the process was successfully applied to the synthesis of a key intermediate in the anticancer drug erlotinib, achieving a yield of 99.3%. The process has also been scaled up for the continuous production of nitro-p-xylene and nitro-o-xylene, with a product output of 800 g h-1. Under the same reaction conditions, the yield and selectivity were consistent with, or even improved over, those obtained in small-scale experiments, demonstrating the scalability and industrial potential of the process. Additionally, the process incorporates a waste acid recycling strategy, which has no significant impact on product yield, thus enhancing economic benefits and reducing environmental pollution. This continuous nitration process not only shows broad application potential but also offers a safe and efficient solution for nitration in the pharmaceutical and chemical industries.

Continuous-Flow Synthesis of Nitro-o-xylenes: Process Optimization, Impurity Study and Extension to Analogues

An efficient continuous-flow nitration process of o-xylene at pilot scale was demonstrated. The effects of parameters such as temperature, ratio of H₂SO₄ to HNO₃, H₂SO₄ concentration, flow rate, and residence time on the reaction were studied. Under the optimal conditions, the yield of products reached 94.1%, with a product throughput of 800 g/h. The main impurities of this continuous-flow nitration process were also studied in detail. Compared with batch process, phenolic impurity decreased from 2% to 0.1%, which enabled the omission of the alkaline solution washing step and thus reduced the wastewater emission. The method was also successfully applied to the nitrification of p-xylene, toluene, and chlorobenzene with good yields.