In: Chemistry
Why are cold solvents preferred during recrystallization and when is recrystallization selected vs other purification techniques?
The choosing of solvent is an important part and the bigger the difference between hot solubility and cold solubility, the more product recoverable from recrystallization.
The rate of cooling determines the size and quality of the crystals: rapid cooling favors small crystals, and slow cooling favors the growth of large and generally purer crystals.
The rate of recrystallization is usually greatest at about 50 °C below the melting point of the substance; the maximum formation of crystals occurs at about 100 °C below the melting point. This is why cold solvents are preferred.
Recrystallization selected vs other purification techniques when we want to isolate both the pure product and the impurities as well in their purest form. In this technique, by dissolving both impurities and a compound in an appropriate solvent, either the desired compound or impurities can be removed from the solution, leaving the other behind.