Two-step continuous flow process of sodium tanshinone IIA sulfonate using a 3D circular cyclone-type microreactor

A sustainable and practical process is presented for the direct synthesis of sodium tanshinone IIA sulfonate (STS). Our approach was inspired by the well-established and industrially applied batch synthetic route for STS production. We constructed a telescoped two-step continuous flow platform. This involved a continuous tanshinone IIA sulfonation and in-line salt formation. For the setup, we constructed a 3D circular cyclone-type microreactor using femtosecond laser micromachining. Compared to the 68% yield for 2 h in batch, the two-step continuous flow had an STS yield of 90%, achieved for a total residence time of < 3.0 min under optimal conditions. The proposed continuous flow method vastly simplified the operation and improved procedural safety, while significantly reducing the required acid content and wastewater production.