Growth of 1:1 Cocrystal in Acetone. Having explored the aspects of this system, the kinetic processes involved in formation of the 1:1 cocrystal are shown in Figure 5. Optical micrographs were taken of a caffeine/maleic acid/acetone mixture having a starting composition of 5.81%
caffeine, 24.3% maleic acid, and 69.89% acetone lying in region 4 of the phase diagram. The higher solubility of maleic acid leads to its rapid dissolution so that Figure 6a shows mostly particles of caffeine with only a few residual maleic acid crystals. In Figure 6b, taken 10 min later, the needle-like 1:1 cocrystal forms very rapidly (actually with stirring it forms in only 5 min). In this solution-mediated process, as the cocrystals grow larger so the caffeine dissolves. After 44 min, the transformation to pure 1:1 cocrystal is complete as seen in Figure 6f.