Chem 230L williamson ether synthesis

pdf

School

Chapman University *

*We aren’t endorsed by this school

Course

230L

Subject

Chemistry

Date

Jan 9, 2024

Type

pdf

Pages

Uploaded by ProfMorningMouse32

CHEM 230L: Chapman University Experiment 8: Synthesis of 2-butoxynaphthalene via the Williamson Ether Synthesis (an S N 2 Reaction) Intended Learning Outcomes By completing this lab, students will: • Understand the theory of how to potentially synthesize compounds using S N 2 reactions. • Learn how to set up a reaction under reflux. • Learn how to monitor reaction progress by using TLC. • Synthesize and isolate an organic product (2-butoxynaphthalene) using a reaction that was learned in lecture (Williamson Ether Synthesis). Introduction This week in lab you use one of the reactions you have learned about in lecture (S N 2 reaction) to synthesize the ether 2-butoxynaphthalene, which has a fruity raspberry/strawberry taste and is used as a flavoring agent in the food industry. The general reaction scheme for this is shown below. First, an acid-base reaction will occur to help generate a strong nucleophile that will then attack the substrate. This experiment will also use a substrate different than alkyl halides that can undergo substitution reactions as a tosylate (R-OTs) instead of an alkyl halide is used. In addition, TLC will be used to monitor the progress of the reaction and we will learn how to set up a reaction under reflux. For monitoring the reaction by TLC, you will spot the reaction mixture on a TLC plate at its start and then at later time intervals. Development of the TLC plate will then allow you to assess whether there is evidence of product formation (a new spot is present) and whether there is evidence that the reaction has completed (the spot that corresponds to the limiting reactant has disappeared because it has been consumed during the reaction). During reflux, a solution is boiled and continually recondensed so that no reagents are lost during the heating process. This is useful for increasing the rate of a reaction without losing any reagents or solvents. At the end of the reaction, you will collect the product to determine the % yield and take the melting point to determine purity.

CHEM 230L: Chapman University Pre-Lab Reading The reading below needs to be completed before the start of lab. 1. Lecture textbook (Klein, 3 trd edition): Sections 7.3 and 7.4, pages 276-287. Section 7.12 (tosylates only), pages323-324. 2. Lab textbook (Pavia, 6 th edition): Technique 7, part 2 – heating under reflux, pages 649 – 651. 3. Carefully read the procedure for the lab experiment below to ensure that you understand the purpose of each step. Pre-Lab Assignment (20 points) Answer the following questions: 1. What is the nucleophile in the reaction and why is the sodium hydroxide present? (2 pts.) The nucleophile is the product of Na+ deprotonating the oxygen in 2-napthol; the sodium hydroxide is present because it is the base in the initial acid-base reaction to deprotonate the oxygen, making the nucleophile. 2. What is the electrophile and what is the leaving group in the reaction? (2 pts.) The electrophile is the carbocation formed below as a result of a nucleophilic attack and a loss of a leaving group – OTs 3. Draw a reasonable mechanism for the reaction? If there are multiple steps, then draw all of them. (4 pts.)

CHEM 230L: Chapman University 4. Determine how many moles of 2-naphthol (MW = 144.17 g/mol) and butyl p- toluenesulfonate (MW = 228.31 g/mol) are used in the reaction and determine which is the limiting reagent. (6 pts.) 1 mol 2-napthol, 1 mol butyl p-toluenesulfonate; 2-napthol is the limiting reagent because it needs to react with NaOH first to become a suitable nucleophile. If there is a limited amount of 2-napthol, then there will be a limited amount of nucleophile available for the further reaction to occur. 5. Determine the molar mass of the desired products (2-butoxynaphthalene) and then determine the theoretical yield of 2-butoxynaphthalene that could be produced in this lab. ( 6 pts.) 2-butoxynaphthalene – C14H16O – 200.28 g/mol 0.60 g 2-Naphthol x 1 mol/144.17 g x 1 mol butyl p-toluenesulfonate/1 mol 2-naphthol = 0.00416 mol 2-butoxynaphthalene Procedure Safety: 2-Naphthol is harmful if swallowed or inhaled and causes serious eye irritation. Butyl p- toluenesulfonate is harmful if swallowed or inhaled, causes skin irritation, and causes serious eye irritation. Sodium hydroxide is corrosive. Wear eye protection, lab coat, and gloves, and work in a hood at all times. 1.To a 25-mL round bottom flask equipped with a stir bar, add 12 mL of 0.5M NaOH in ethanol followed by 0.60 g of 2-naphthol. Place the flask in the heating block on the hotplate stirrer and clamp it in place. Stir the mixture at room temperature until all the 2-naphthol has dissolved (about 5 minutes). Record any observations such as color or appearance of the reaction. 2. While waiting, set up three TLC plates. Set up two (one of these will be aback-up TLC plate in case something goes wrong with developing the first one) to each have 3 spots for your time of reaction monitoring for 0, 20, and 40 minutes. Set up the other TLC plate to compare the starting materials (2-naphthol and butyl p-toluenesulfonate) and the product. Prepare several TLC spotters to use during the reaction. 3.Using a micropipette, add 0.80 mL of butyl p-toluenesulfonate to the reaction mixture. Rinse any droplets adhering to the neck of the flask into the solution with about 1 mL of ethanol. Spot the reaction mixture at this point on the two time monitoring TLC plates as the time zero spot.

Your preview ends here

Eager to read complete document? Join bartleby learn and gain access to the full version

Access to all documents
Unlimited textbook solutions
24/7 expert homework help

CHEM 230L: Chapman University 4.Connect a condensing tube to the flask (it will be upright) and connect a water inlet hose to the bottom inlet of the tube and the water outlet hose to the top inlet with the other end in the sink. Turn on the water and set the hotplate to about 120 o C. Continue stirring for the entire reaction. 5. Continue the reaction under reflux (you should see liquid from the reaction recondensing and falling back down into flask either directly down from the condensing tube or down the sides of the flask) for 40 minutes. After 20 minutes, spot the reaction mixture for the 20 minute mark on both time monitoring TLC plates. To collect a TLC sample during reflux: Open the joint between the round bottomed flask and the condenser and quickly insert a 6-in glass pipet with no rubber bulb into the reaction mixture. A small amount of the reaction mixture will be drawn into the tip of the pipet. Quickly remove the pipet and reclose the joint. Insert a TLC micro spotter capillary into the pipet tip to load the capillary with the solution for spotting. Ask your instructor for help if needed. Record any observations such as color or appearance of the reaction. 6. After 40 min of refluxing, remove the heat source and ensure that the solution has stopped boiling and spot the reaction for the 40 minute mark on the TLC plates. Record any observations such as color or appearance of the reaction. 7. Carefully pour the reaction mixture over ~40 mL of ice in a 250-mL beaker. Allow the mixture to stand with occasional gentle swirling until all of the ice has melted. 8. Collect the product by vacuum filtration using a vacuum flack and Hirsch funnel filter. As you are transferring the mixture to the Hirsh funnel, you may need to stir the mixture to help the liquid get drawn through the filter and into the flask. Wash the product twice with ~3 mL of ice-cold water and then draw air through the product for 15 minutes to help ensure removal of water. 9. Get and record the mass of the recovered final product and record observations on its appearance. Get the melting point for the final product and record it. 10. Make a solution of the final product using a little bit of the solid and about 1 mL of ethanol. Spot this on a TLC plate along with a spot each of the starting materials (2-naphthol and butyl p- toluenesulfonate). Develop this TLC plate and the reaction time TLC plate. The TLC plate(s) can be developed with 60:40 hexanes:ethyl acetate. Be sure to set your TLC developing chamber correctly. Record and take a picture of the TLC plates Post-Lab For this lab you will be writing a full lab report (60 points total). It will need to include the following sections and include everything that should be in those sections as described and practiced in your lab report section write up assignments. Be sure to address everything else noted in the sections below as well. 1. Title and Name (5 points)

CHEM 230L: Chapman University 2. Abstract (5 points) 3. Introduction (including reaction equation and mechanism, when applicable) (10 points) Include the general reaction scheme and reaction mechanism in your introduction. These must be generated in chem draw and be your own work. Do not copy and the reaction scheme from the lab document or mechanism from another source. 4. Materials (Physical data table for compounds & information for instruments and equipment (5 points) 5. Procedure / Methods (5 points) Remember that this must be written in your own words and be in past tense. 6. Data and Observations (5 points) Be sure to include images of TLC plates. Include all quantitative data and qualitative observations. 7. Data Analysis, Calculations, and Discussion. (20 points) Calculate % yield for the reaction and Rf values for the TLC plates and assign what spot on the TLC plates are for which compounds in the reaction. Comment of the purity of the final product and how you came to this determination. Determine a time (or window of time) at which the reaction was complete and explain how you know. Comment generally on the success of the reaction and if you accomplished the intended learning outcomes of the lab. 8. References (5 points)