3.1.2. Effect of DMC and BDMC on CUR Solubility in the Selected Process Solvents

Before designing seeded cooling crystallizations, the solubility behavior of CUR was evaluated in presence of the main impurities DMC and BDMC in acetone, 50/50 acetone/2-propanol, 50/50 acetone/acetonitrile and acetonitrile. In Figure 6, the resulting solubility data are compared with the solubility values of pure CUR in the respective solvents.

**Figure 5.** Effect of anti-solvents methanol, ethanol, 2-propanol and acetonitrile on the solubility of CUR in acetone at 30 ◦C. Symbols represent experimental data, curves are just guide to the eyes. Dashed curves originate from experimentally determined solubility values in the respective 50/50 (wt/wt) acetone/anti-solvent mixtures. Thin solid lines represent ideal linear solubility behaviors.

**Figure 6.** Comparison of solubility curves determined for pure CUR (empty circles, grey curves), and CUR in presence of the main impurities (solid circles, colored curves). Symbols represent experimental data, fitted curves serve as guide to the eyes.

As seen the solubilities of CUR in presence of DMC and BDMC slightly exceed those of pure CUR in the four solvents. Moreover, comparison of the CUR solubility in 50/50 acetone/2-propanol and 50/50 acetone/acetonitrile shows that with the use of acetonitrile as anti-solvent, a higher supersaturation of CUR in the solution can be obtained resulting in a higher product yield. This observation confirms the behavior of pure CUR in the binary solvents discussed in Figure 5.
