The purpose of this experiment was to react 2-methyl-2-butanol with concentrated HCl in order to form 2-chloride-2-methylbutane. The hydrogen for the HCl make the -OH from the 2-methyl-2-butanol into a good leaving group because H2O is formed. The H2O leaves and Cl- is free to bond with the carbocation creating 2-chloride-2-methylbutane.
The materials needed for the lab were an Erlenmeyer flask with a stir bar, the stirring function of the hot plate, an ice bath, a separatory funnel, and an IR machine.
Measured out 5 mL of 2-methyl-2-butanol and 13 mL of HCl, the latter was cooled to approximately 0 . The HCl was slowly added to the 2-methyl-2-butanol and stirred for 15 ℃ minutes. The mixture was then added to the separatory funnel and the aqueous HCl layer removed. The mixture was then washed with 10 mL of H2O, 10 mL of sodium bicarbonate, and 10 mL of NaCl. The product was dried with enough anhydrous sodium sulfate so that there were free floating particles in the solution and allowed to sit for 10 minutes. After the elapsed time the solution was then decanted and distilled. The weight of the distillate was measure and the IR ran.
Data and Calculation:
Crystallization is a technique for purifying solids that contain small amount of impurities. This purification method takes advantage of the differences in solubility between the compound and its impurities. After the weighed 0.5 grams sample went through the purification process, the impurities were removed and it dropped to about 0.257 grams. The melting point of the crude sample was between a range of 140.7 and 141.9 while the pure sample had a melting point range of 141.9 and 142.
Mass of Crude Sample (g)
Mass of Pure Sample(g)
Melting point of Crude Sample(°C)
Melting point of Pure Sample(°C) 0.50 0.26
Percent Recovery = = = 50% Discussion
Most of the impurities will remain dissolved in the cool solvent, allowing them to be removed when the sample is isolated by vacuum filtration. Some of the impurities may not dissolve even in hot solvent, requiring a hot filtration to remove them. Occasionally the crystals may not form as the solution cools. A few steps can be taken to induce crystallization in these cases. It was observed that methanol was used as the solvent because of its partial volatile properties and the solvent did not react with the substance being purified. The advantages of purification by recrystallization is that it removes impurities and it’s an easy process; the disadvantages of purification by recrystallization is that part of the product is lost and it doesn’t remove insoluble impurities and it must always be followed by vacuum and if not done properly, one may run