Mechanically induced reactions in organic solids: liquid eutectics or solid-state processes?

The solvent-free reaction between o-vanillin and p-toluidine was investigated using NMR, DSC and XRD analyses. At room temperature, o-vanillin and p-toluidine react in a liquid eutectic formed upon grinding, while below 10 degrees C the same materials appear to react without the formation of a liquid phase, which most likely remains hidden behind solid reactants and reaction products.