1. Dichloromethane has low solubility to methyl hydrochloride and cannot be completely dissolved.
2 The boiling point of dichloromethane is relatively low, and the evaporation is too fast to form large crystals, and will only appear as crystalline powders.
3. Clean the hydrochloride before recrystallization, (acetone, ether, dry and cold)
4. It is recommended to use - acetone: water, acetone: ethanol, acetone: methanol, ethanol: water, methanol: water, for recrystallization.
Water can slow down evaporation, acetone can reduce solubility, and alcohol can form better crystals.