Experiment 5 - carvone epoxidation

pdf

School

University of Oregon *

*We aren’t endorsed by this school

Course

348

Subject

Chemistry

Date

Feb 20, 2024

Type

pdf

Pages

Uploaded by ElderTigerPerson699

CH 348 Winter 2024 1 Experiment 5. Epoxidations of Carvone In this lab we will oxidize carvone, using two different oxidizing agents, and will determine the regioselectivity of both reactions. Both reactions are known to convert alkenes to epoxides. You will be given the 1 H NMR spectrum of carvone (posted on Canvas) and will need to run both reactions and determine the relative amounts of the three possible epoxidation products shown below by 1 H NMR spectroscopy. The oxidizing reagents we will be using in this lab are m-chloroperoxybenzoic acid (mCPBA), and hydrogen peroxide in base. The mCPBA oxidation will be set up in one lab period and worked up in the second lab period. The reaction requires > 4 hrs at room temperature to go to completion. The hydrogen peroxide oxidation will be set up and worked up in the first lab period; this reaction only requires ~30 minutes. For both reactions we will isolate the crude product using an aqueous work up and submit the crude product for 1 H NMR analysis to determine the regioselectivity. Pre-Lab Follow the Lab Notebook Guidelines. Include a reagent table for both reactions. Procedure Hydrogen peroxide oxidation:  To a scintillation vial, add carvone (500 mg) and methanol (6 mL). Add a small stir bar  Cool in an ice-bath. Stir.  Add an aqueous solution of hydrogen peroxide (30%, 1.2 mL)  Add 6M NaOH (0.7 mL) dropwise.  After 15 minutes let the reaction warm to room temperature.  Stir for 30 minutes.  Transfer the reaction mixture to a separatory funnel and add ~20 mL of ether.  Wash with water (2 x 15 mL)  Wash with brine (15 mL)

CH 348 Winter 2024 2  Dry (Na 2 SO 4 ), filter and rotovap to obtain the crude product.  Submit a sample for 1 H NMR spectroscopy.  TLC your crude product vs carvone (10% EtOAc / hex; UV / I 2 stain). You will need to make a dilute solution of your crude product (1 ~ 10 mg / mL) for spotting on the TLC plate. You can use any volatile solvent that the product is soluble in (CH 2 Cl 2 , acetone, ether…). mCPBA oxidation:  To a scintillation vial, add carvone (500 mg) and CH 2 Cl 2 (12 mL). Add a small stir bar.  Cool in an ice-bath. Stir.  Slowly add mCPBA* (842 mg). Most of the reagent should dissolve. Make sure that the stir bar continues to stir the reaction mixture throughout the addition.  After a few minutes let the reaction warm to room temperature. Continue stirring until near the end of the lab period.  Near the end of the lab period, cap and label the vial, and keep in your lab drawer until next lab period.  Vacuum filter the reaction mixture, washing with a minimal amount of CH 2 Cl 2 (2 x 1 mL). The solid is m-chlorobenzoic acid, which is waste.  Transfer the filtrate to a separatory funnel and add ~30 mL of ether.  Wash with 5 x 15 mL 0.6 M NaHCO 3 (if the organic layer ends up on the bottom of the sep funnel, add more ether). Be very careful here. Sodium bicarbonate and acid produces carbon dioxide which can cause the pressure in the separatory funnel to build up. Vent frequently!!!  Wash with brine (15 mL).  Dry (Na 2 SO 4 ), filter and rotovap to obtain the crude product.  Submit a sample for 1 H NMR spectroscopy.  TLC your crude product vs carvone (10% EtOAc / hex; UV / I 2 stain). You will need to make a dilute solution of your crude product (1 ~ 10 mg / mL) for spotting on the TLC plate. You can use any volatile solvent that the product is soluble in (CH 2 Cl 2 , acetone, ether…). *mCPBA is ~75% pure; the remainder is m-chlorobenzoic acid Waste disposal: All aqueous solutions can go into the aqueous waste containers. All solutions where an organic solvent is the main component must go into the organic waste container.

CH 348 Winter 2024 3 Submitting Samples for NMR Spectroscopy  Normally you would need to check for solubility in CHCl 3 . If soluble, you would use CDCl 3 to prepare the NMR sample. If it’s not solube, then you would test the protonated version of other common NMR solvents until you find one that works (other commonly used NMR solvents: d6-DMSO, d6-acetone, D 2 O). You do not need to do that for this lab, we will be using CDCl 3 .  Place ~ 15 mg of the product in a clean scintillation vial (do not submit the sample you used to check solubility!!). If you need to transfer the material in solution, be sure to evaporate the solvent before submitting the sample.  Fill in the next available line on the NMR sign up sheet and properly label samples!!**  Record the Compound ID from the sign up sheet in your notebook.  NMR data (FID) will be posted on Canvas using the filename (Compound ID) on the sign up sheet.  Download the file and rename it according to your notebook reference.  Process the data using Mestrenova. ** You will fill out the NMR labels in duplicate – one label affixed around the vial; the other to the cap (there is a sample vial in the lab). The Compound ID is listed on the sign up sheet.

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

CH 348 Winter 2024 4 Post-Lab Report 1. For the reaction with mCPBA: Why is the reaction washed multiple times with aqueous sodium bicarbonate? [5 points] 2. For both aqueous workups, the reaction mixture was diluted with diethyl ether then washed with various aqueous solutions. Why was the mixture diluted with diethyl ether instead of dichloromethane (the workup does work equally well if you use dichloromethane instead of diethyl ether)? What would be different if we used dichloromethane instead of diethyl ether? [5 points] 3. Explain how TLC can be used to follow the progress of a reaction. How many products are indicated for each reaction by TLC? Does your TLC for each reaction show any evidence of starting material? [10 points] 4. Determine the regioselectivity of both reactions. Clearly show how you arrived at your answer. Include appropriate figures to aid your explanation. You will be graded not only on your answer, but also on how clearly you present the data. [40 points] 5. Write complete curved arrow mechanisms for both reactions. [20 points] 6. Provide a cogent explanation for the observed regioselectivities. [20 points] --------------------- [100 points]