Crystallisation: An Overview
Crystallisation is a fundamental technique in organic chemistry used primarily for the purification of solid compounds. It works on the principle of differing solubilities of compounds in solvents at varying temperatures. Generally, an impure substance is dissolved in a suitable solvent at elevated temperatures, often while concentrated to create a saturated solution. As the solution cools, the pure compound crystallises out, allowing for the separation of the impurities that remain dissolved in the solution, referred to as the mother liquor.
The process of crystallisation can be enhanced through several methods, including using multiple solvents to exploit differential solubility and employing activated charcoal to remove colored impurities. Repeated crystallisation steps may be necessary if impurities are present at similar solubility levels to the desired compound. Effective crystallisation not only increases the purity of the compound but is a critical step in many laboratory and industrial applications in organic chemistry.