Solving the crystal structure of 4 from SCXRD data (ESI Table ) showed the formation of ammonium carboxylate salt of 1 and 2, but this time with two molecules of 1 and a single molecule of 2 in the asymmetric unit (ESI Fig. ). The structural motif involving hydrogen bonding of ammonium cation with three carboxylate anions is essentially the same as in 3 (Fig. ), but now each molecule of 2 hydrogen bonds to three molecules of 1, i.e., there is no structural disorder of 2. Next, we employed thermo-mechanochemical reaction conditions with simultaneous mechanical and thermal activation to enable amide bond formation. Recently, the latter was shown as a successful strategy to obtain amides and oligopeptides. We used a protocol in which the stainless-steel jar is wrapped with a ring heater and controlled by a proportionalintegral derivative device for a precise temperature control. Encouragingly, after milling equimolar amounts of 1 and 2 for 1 h at 100 °C, 3% of amide 5 was detected by Being aware that removing the water from the reaction mixture in a thermal amidation approach enhances the amide bond formation, we decided to open the jar after milling 1 and 2 for 1 h at 190 °C. We then waited until the milling jar to cool to room temperature and milled the same reaction mixture for an additional 1 h at 190 °C (Table , entry 5). Importantly, this improved the conversion to 5 up to 80%. In another experiment, we lengthened the second milling cycle to 2h, which increased the conversion to 5 up to 89% (Table , entry 6). We used the latter reaction conditions for scaling the reaction to a gram scale. Specifically, we milled 8.5 mmol (1.0 g) of 1 and 8.5 mmol (0.9 g) of 2 under these reaction conditions. Analysis by 1 H NMR spectroscopy showed the 92% conversion to 5 (ESI Fig. ). Finally, after isolation by column chromatography and purification by recrystallisation (details can be found in ESI), we isolated 1.53 g of 5 in 85% yield. 98 Reaction conditions: a mixture of benzoic acid (1) (1 equiv.; 73 mg; 0.6 mmol or 2 equiv.; 147 mg; 1.2 mmol) and p-toluidine (2) (1 equiv.; 64 mg; 0.6 mmol or 2 equiv.; 129 mg; 1.2 mmol) was milled in a 12 mL stainless steel milling jar using two 1.4 g milling balls of the same material. [a] Determined by 1 H NMR spectroscopy. [b] After 1 h the milling jar was opened until cooled to room temperature then the milling was restarted for 1 h. [c] After 1 h the milling jar was opened until cooled to room temperature then the milling was restarted for 2 h. Furthermore, inspired by the crystal structure of salt 4, we performed a milling experiment with 1 and 2 in a 2:1 ratio for 1 h at 190 °C (Table , entry 7). Surprisingly, this resulted in 52% conversion to 5, a higher conversion rate compared to milling equimolar amount of 1 and 2 under the same conditions (Table , entry 3). On the other hand, milling 1 and 2 in a 1:2 ratio favouring an excess of 2 (Table , entry 8) resulted in 11% conversion to 5. Moreover, milling 1 and 2 in a 2:1 ratio for overall 2 h at 190 °C (Table , entry 9) gave almost quantitative conversion to 5. Hence, there was a clear benefit of having an excess of 1 to form amide 5.