Fig. 2. Influence of milling time, t_reaction, and milling ball diameter, d_MB, on the yield of the Knoevenagel condensation of vanillin and barbituric acid (equimolar ratio). Left: PBM Fritsch P7 premium line (V_MV = 0.045 L, n = 20 mmol, rpm = 800 min⁻¹). Right: PBM Fritsch P6 (V_MV = 0.25 L, n = 100 mmol, rpm = 650 min⁻¹).⁴⁶.