Notably, under high-temperature milling conditions, the reaction mixture containing 1 and 2 melts and the amide bond formation proceeds in a liquid phase. This was verified by opening the hot jar and by differential scanning calorimetry (DSC) analysis which showed that ammonium carboxylate salts 3 and 4 melt around 53 °C and 54 °C, respectively (ESI Fig. and S9). Additionally, we wondered if the amide-forming reaction was reversible under our mechanochemical conditions. Thus, we performed two milling experiments that included liquid-assisted grinding (LAG) of amide 5 with H2O for 1 h, one at room temperature and the other at 120 °C. However, under these conditions, we have not observed the breakage of the amide bond and crystalline 5 persisted in the mixture (ESI Fig. and).