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exp3 - Experiment 3 Preparation of tert-Butyl Chloride The...

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Experiment 3 Preparation of tert - Butyl Chloride The purpose of this experiment is to prepare tert -butyl chloride (2-chloro-2- methylpropane) from tert -butyl alcohol ( tert -butanol) using an acid catalyzed dehydration reaction. (Note: the correct IUPAC name for this compound is 2-methyl-2-propanol). We will also learn how to use a separatory funnel, the use and purpose of a drying agent and the technique of distillation. The reaction is shown in Figure 3.1 CH 3 C CH 3 CH 3 OH + H Cl CH 3 C H 3 C CH 3 O H H H 2 O CH 3 C CH 3 CH 3 H O H + Cl - Cl CH 3 C CH 3 CH 3 Cl t -butanol (2-methyl-2-propanol) hydrochloric acid t -butyl chloride (2-methyl-2-chloropropane) Figure 3.1 Preparation of t -Butyl Chloride carbocation + The first step of the overall reaction is an acid-base reaction between the t -butanol and the hydrochloric acid. The t -butanol is a weak base and the hydrochloric acid is a strong acid. The alcoholic oxygen becomes fully protonated and so the equilibrium lies far to the right. In the second step we have the slow loss of water to form a carbocation intermediate. This species is very reactive and is immediately attacked by the chloride ion liberated in the first step to form the final product. This is an example of an S N 1 reaction (Substitution N ucleophilic U nimolecular). Physical Constants Compound Mol. Wt (g/mol) Density (g/mL) b.p. (°C) m.p. (°C) 2-Methyl-2-propanol 74.12 0.775 83 25 - 26 2-Chloro-2-methylpropane 92.57 0.85 51 - 52 -25 Proper Use of the Separatory Funnel Set up the separatory funnel as shown in Figure 3.2. Use a small iron ring stand to hold the funnel. You can also use a metal clamp attached to the top neck of the separatory funnel but the iron ring is more convenient. ALWAYS KEEP A BEAKER UNDERNEATH THE SEPARATORY FUNNEL TO CATCH ANY SPILLS. When the handle of the stopcock is parallel to the separatory funnel (see shown in Fig. 3.2), the stopcock is in the open position. When the handle is perpendicular to the length of the funnel it is closed.
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With the stopcock in the closed position, pour in your solution into the top of the funnel. Insert the glass stopper. Hold the funnel in one hand by grasping the top around the glass stopper. Lift it from the iron ring and SLOWLY invert the funnel, holding it with your other hand. When it is now upside down, the glass stopper should be in the palm of one hand, holding it securely. IMMEDIATELY VENT the funnel by opening the stopcock and pointing the end of the funnel AWAY from your lab neighbor. CAUTION : always vent the separatory funnel immediately when you invert it. Pressure can build up and the contents of the funnel can shoot out uncontrollably. Once you have vented the separatory funnel, close the stopcock and shake it GENTLY AT FIRST 2-3 times. Then VENT the funnel again. Now you can shake it more vigorously several times. Then vent it again. You may hear the sound of escaping gases when you open the stopcock to vent. Once this subsides then it is safe to shake the separatory funnel vigorously for 2-3 minutes. It is very important to shake the funnel very thoroughly to ensure intimate mixing of the two layers.
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