Greener Dye Synthesis: Continuous,Solvent-Free Synthesis of Commodity Perylene Diimides by Twin-Screw Extrusion

A continuous, scalable, and solvent-free method for the synthesis of various naphthalic imides and perylene diimides (PDIs) using twin-screw extrusion (TSE) is reported. Using TSE, naphthalic imides were obtained quantitatively without the need for excess amine reactant or product purification. With good functional-group tolerance, alkyl and benzyl amine derived PDIs (incl. commercial dyes) were obtained in 50–99 % yield. Use of K₂CO₃, enabled synthesis of more difficult aniline-derived PDIs. Furthermore, an automated continuous TSE process for Pigments Black 31 and 32 is demonstrated, with a throughput rate of about 1500 g day⁻¹, corresponding to a space time yield of about 30×10³ kg m⁻³ day⁻¹, which is 1–2 orders of magnitude greater than for solvent-based batch methods. These methods provide substantial waste reductions and improved efficiency compared to conventional solvent-based methods.