Experiment 8- Reaction- Synthesis of t-Pentylchloride by unimolecular nucleophilic substitution PDF

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Hazel Kim Professor Shukla Experiment 8: Reaction: Synthesis of t-Pentylchloride by unimolecular nucleophilic substitution January 27, 2020 Objective The purpose this experiment is to convert t-Pentylchloride using Sn 1 reaction with HCl. Introduction Alcohol can be a useful versatile starting material in organic synthesis. Depending on the reagent they are paired with, they can function as an acid, base, nucleophile, or electrophile. Alkyl halides can be prepared from alcohols by reacting them with a hydrogen halide, HX. We have used Cl- for this experiment. Tertiary alcohol;ls react with hydrogen halides SN1. The SN1 reaction is the reaction that was used and studied in this experiment. SN1 is a type of nucleophilic substitution that is unimolecular, meaning one bond is broken and one bond is formed in more than one step. SN 1 reaction undergoes a two-step process in which the 1st slow step consists of the formation of carbocation by the ionization of the reagent. However, this step can be sped up by including a polar solvent or tertiary alkyl halide. The 2nd step is the nucleophilic attack on either side of the alpha carbon. Furthermore, the rate law states that this substitution reaction is sensitive to only the substrate concentration. In this experiment, the tertiary alcohol (t-pentyl alcohol) will be treated with strong hydrogen halide (HCl). The chloride ion from HCl, reacts with the carbocation in the final step of the reaction to give the tertiary chloride as the product of the reaction. Materials  Deionized water  Separatory funnel  Beaker  Erlenmeyer flask Distillation Setup Materials: 1. Round bottom flasks 2. 10 mL Graduated cylinder 3. Receiver distilling still 4. Condenser 5. Thermometer 6. 2 Capillary tubes 7. Heat Mantle Chemicals: 3 mL of t-Pentylchloride 7mL concentrated HCl 3 mL NaHCO3 3 mL NaCl AgNO3 Procedure There are two parts to the experiment

Part 1: Separation -Obtain 3 mL of t-Pentylchloride into a Erlenmeyer flask -Slowly add 7mL concentrated HCl and stir the mixture -Transfer the mix into a separatory funnel -Wait until visible separation of layers are shown - Drain the lower layer into a beaker -add 3 mL deionized water into the separatory funnel, mix and repeat drainage for the lower layer -Repeat this procedure by adding 3 mL NaCl, 3 mL NaHCO3 mix and repeat drainage for the lower layer Part 2: Distillation -Set up the distillation -Transfer the upper layer into a distillation flask -distill at 84-95 ℃ and collect the distillate -Test the product with AgNO3 solution Reaction: The compound was proved to be pure as when it was reacted with AgNO 3 solution, it gave a white ppt. Discussion Tert-pentyl chloride was synthesized using SN 1 mechanism using it’s starting molecule tert-pentyl alcohol. More stable carbocations are formed with SN 1. Therefore, tertiary alcohols favor SN 1 reactions. Hydrochloric acid (HCl) was also present in the synthesis of tert-Pentyl chloride. This was used because HCl provides an acidic medium that will protonate the hydroxyl group, allowing it to leave as a molecule of water. After adding concentrated HCl, two layeres formed, which was then separated. After distillation and addition of AgNO3 solution, a white precipitate formed. The formation of a precipitate is a positive test for alkyl halides. The white precipitate forms after the addition of AgNO3 because the tert-Pentyl Chloride undergoes a rapid SN1 mechanism to form a precipitate of silver chloride. This is why the white precipitate was seen so quickly. Some of the limitation to this experiment that can potentially cause discrepancy can be due to the apparatus itself, inconsistent judgement in monitoring the temperature or the external pressure of the environment where it was conducted. Conclusion In conclusion, when we convert an alcohol to an alkyl halide, we perform the reaction in the presence of acid, halide ions and not at elevated temperatures. Halide ions are good nucleophiles. They are much stronger nucleophiles than water. Moreover, because halide ions are present in a high concentration, most of the carbocations react with an electron pair of a halide ion to form a more stable species, the alkyl halide product. The overall result is a Sn1 reaction. Furthermore, the silver nitrate test is used to confirm the presence of t-Pentyl chloride due to its rapid reaction with silver nitrate via SN1 mechanism to produce a whitish precipitate, silver chloride. One of the main objectives of this experiment was to synthesize tert-Pentyl Chloride from tert-Pentanol, it was successful as precipitate formed after the addition of AgNO3. Overall, this lab accomplished what it set out to do. New skills and techniques

were learned when synthesizing tert-Butyl Chloride from tert-Butanol.Overall, this lab accomplished what it set out to do. New skills and techniques were learned when synthesizing tert-Pentyl Chloride from tert-Pentanol. Result (Photo)

Picture 1: Separation after adding 3 mL of t-Pentylchloride and HCl Picture 2: Separation after adding 3 mL D.I water Picture 3: Separation after adding 3 mL NaCl Picture 4: Separation after adding 3 mL NaHCO3 Picture 5: white precipitate formation after adding AgNO3 solution. Questions 1. Why is the t-pentyl chloride phase the upper layer? The compound in the upper layer has lower density than the compound in the lower layer. For example, t-pentyl chloride has lower density than the compound in the lower layer. 2. NaHCO3 solution was used to wash the crude t-pentyl chloride, -What was the purpose of this wash? Give equations. Aqueous sodium bicarbonate wash is to neutralize the trace amounts and present in solution due to hydrolysis of alkyl halide. The bicarbonate is a weak base that will react and neutralize the HCl. The equation is HCL + NaHCO3  H2CO3 + NaCl -Why is it undesirable to wash the crude halide with aqueous NaOH? Sodium hydroxide solution is very undesirable because it's very polar and will act as a base by giving an elimination product or a nucleophile by giving substitution reaction 3. How was the unreacted t-pentyl alcohol removed in this experiment? The unreacted t-pentyl alcohol was removed by washing the crude t-pentyl chloride twice withdistilled water. 4. Explain why some 2-methyl-l-butene can be formed in this experiment. 2-methyl but-1-ene is formed due to elimination reaction...