Robotic work station for microscale synthetic chemistry: On-line absorption spectroscopy, quantitative automated thin-layer chromatography, and multiple reactions in parallel

Abstract

A robotic work station has been constructed for automatically initiating and monitoring microscale chemical reactions. The work station consists of a robot with a general-purpose arm and interchangeable special-purpose hands, a carousel of seven reaction vessels, a series of stations for performing quantitative automated thin-layer chromatography (TLC), an on-line multichannel absorption spectrophotometer, sensors for verification, syringes and pumps for sample and solvent delivery, a supervisory computer for real-time data acquisition and process control, and a graphics terminal for data display. The controlling software is menu-driven and contains a scheduling algorithm that permits multiple reactions to be performed simultaneously. The automated TLC process is performed in four stages (plate dispensing, sample application, plate development, and plate densitometry), and samples are moved sequentially among these stations by the robot. The partial autonomy of these separate stations permits distributed sample processing. Four TLC plates are processed simultaneously with interleaving segmented schedules, giving a 160% increase in TLC sample throughput. The workstation can be applied to yield optimizations of synthetic reactions and to the exploration of synthetic reaction spaces. The capabilities of the workstation are demonstrated in the two-step synthesis of tetraphenylporphyrin from benzaldehyde and pyrrole in 1 h at room temperature. Kinetic data are obtained from a single-batch reaction concerning the consumption of benzaldehyde, the side reactions forming dipyrrylmethenes, and the formation of tetraphenylporphyrin.