Scaling Helicene Synthesis via Photochemical Oxidation─ A Comparison between Batch and Flow Reactors

Helicenes, a class of helically chiral aromatic molecules often functionalized for various applications due to their axial chirality, are typically synthesized under high dilution conditions to prevent undesirable side reactions, requiring large volumes of solvent and thus making scale-up challenging. The challenges of scaling helicene syntheses are discussed in this study, and facile strategies to address some of these challenges are offered. The increased interest in using helicenes for materials, sensing, and electronic applications necessitates the development of strategies for their effective scaling with high purity. It is well-known that more reproducible, scalable, safe, and efficient options for chemical synthesis are facilitated by flow chemistry, which is valued in both academic and industrial settings due to the precise control it allows over reaction conditions such as stoichiometry, mixing, temperature, and reaction time, leading to greater yields and better selectivity across various reaction classes. Three reactor systems—1L-batch, 5L-batch, and flow reactors—were evaluated towards the synthesis of a [5]-helicene tetraester (5HLTE) using quantitative 1H-NMR and isolated yields of the desired product and notable side products. After initial optimization, the optimal conditions were applied to demonstrate scalability, providing a throughput of approximately 5 g/day in a 5 mL reactor flow system, with linear scaling relative to reactor volume. Discrete control of purity was found to be vital for these applications, as impurities may lead to incorrect structure-property conclusions when applied to organic electronics and polymer mechanical properties.

• Hewitt, P
• Dunlap, J
• Varshney, V
• Baldwin, L
• Simone, D

• AeroVironment Inc

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