Recrystallization Synthesis

The purpose of this experiment was to study the purification of an unknown solution through the process of recrystallization. Recrystallization is a process of the solid organic compound being purified, and impurities soluble at high temperature to form crystals. The identification of an unknown compound was determined through the process of recrystallization. The use of solvent determines the recrystallization process, so the selection of an appropriate solvent is vital for this process since the solubility of the crystals in the hot solvent, is dependent on decreased solubility when the solution is cooling. The solubility test helps in the determination of an appropriate solvent for a specific solute based on whether or not the solute dissolves

The temperature of the water was then recorded to the nearest 0.1⁰C. Then the melting points of phenylacetic acid, o-anisic acid, and benzilic acid were determined by the use of a Mel-Temp. The unknown sample was obtained from the chemical stockroom. A small scale of crystals from unknown was placed in a test tube with the following solvents: cyclohexane, hexane, toluene, diethyl ether, ethyl acetate, isopropyl alcohol, methanol, or water, to determine the appropriate solvent for the unknown. If the solute was wholly dissolved in the solvent before heating, it was recorded as a bad solvent. If the solute dissolved after being warmed in a water bath, it was set aside to cool to allow recrystallization; if their recrystallization occurred or not was recorded. If the crystals did not form previous to heating, the solution was placed in ice bath. After the ice bath, if the recrystallization did not occur then it was seeded. After completion of the solubility tests, the appropriate solvent, cyclohexane, was selected for large-scale recrystallization. The unknown was weighed for the large-scale recrystallization then the same process was repeated to test the solubility. The solute dissolved after adding of about 60 mL of solvent, it was set aside to cool to induce crystal reformation. The solution was then seeded and set alone once more. When the process was complete, the crystals

Some of the factors are thermometer was calibrated to determine its precision. The actual melting points of water, phenylacetic acid, o-anisic acid, and benzilic acid to their observed melting points were determined by calibrated thermometer. Then the solubility tests were run in order to determine the appropriate solvent for the unknown solute (Table 1). After determination of a solute, a vacuum filtration technique was used to determine the pure form of compound. The melting point of the purified sample was determined and compared to the melting points of other known compounds. The determination of the recrystallized compound’s melting point was used so as to have a better understanding of the purity of the recrystallization