Discovery of unexpectedly complex reaction pathways for the Knorr pyrazole synthesis via transient flow

Kinetic data for reactions between phenyl hydrazine and 1,3-diketones (Knorr pyrazole synthesis) were acquired by using transient flow methods. Supported by further spectroscopic and mass spectrometry data, a microkinetic model was subsequently constructed, which provided new insights into the mechanism, including autocatalysis and the involvement of an unexpected reaction intermediate. During this work, a novel reactant stoichiometry transient flow methodology was demonstrated, allowing the robustness of these models to be asserted.