Ryan Xu
10/29/2024
Alkene Addition
Purpose:
The purpose of this lab is to perform an alkene addition reaction on the terpene limonene,
forming a bis-bromohydrin product through the addition of water and N-bromosuccinimide (NBS) across
the two alkenes in limonene. This will be the first step in a two-part reaction designed to achieve a greater
understanding of halohydrin alkene addition reactions, including predicting regio- and stereochemistry,
and using liquid–liquid extraction and rotary evaporation for product isolation. We will also use TLC to
monitor the reaction progress and visualize the formation of product.
Safety:
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Limonene: Flammable; may cause skin and eye irritation and is a suspected reproductive and
aspiration toxin. Avoid inhalation.
N-bromosuccinimide (NBS): Oxidizing solid; may cause skin and eye irritation
Ethyl Acetate: Highly flammable; vapors can cause eye irritation, drowsiness, and dizziness. Use
in a fume hood.
Hexanes: Highly flammable; can cause serious eye and skin irritation and is toxic upon
inhalation or ingestion. Use in a fume hood.
TLC Plates: Fragile; silica gel may flake off and cause respiratory irritation. Use in a fume hood.
Iodine (I₂): Toxic and corrosive; can cause skin and eye irritation. Avoid direct contact.
General Lab Safety: Wear goggles, gloves, and appropriate lab attire always.
Waste and Clean up:
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Place organic solvents in the organic waste container.
Place aqueous solvents in the aqueous waste container
Dispose of used Pasteur pipettes, TLC spotters, and TLC plates in the solid waste or broken
glass container as appropriate
Protocol:
1. Reaction Set-Up
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Add Limonene to Flask:
o Use a syringe to measure 1.0 mL of (+)-limonene and transfer it to a
50-mL round-bottom flask containing a stir bar
o Clamp the flask to the fume hood’s monkey bars so it hovers above a stir plate
Add Solvents:
o Carefully add 9 mL of reagent-grade acetone and 8 mL of reverse-osmosis (RO) water to the flask
o Cover the flask with a septum and stir the mixture at room temperature for 10 minutes
Prepare TLC Plate:
o Prepare a TLC plate with three lanes: one for an NBS standard,
one for a limonene standard, and one for your reaction mixture (post-liquid–liquid extraction)
Add NBS:
o After 10 minutes, stop stirring and let the solution settle
o Gradually add 2.75 g of N-bromosuccinimide (NBS) portion-wise
over 2–3 minutes, replacing the septum between each addition.
o Leave the septum on after the final addition
Stir the Reaction:
Notes:
Ryan Xu
10/29/2024
Alkene Addition
o Stir the mixture at room temperature for 15 minutes
o Prepare NBS and Limonene TLC Standards:
o dip a clean Pasteur pipette into the reagent bottle so some solid sticks to it
o Place the pipette tip into a clean vial and add a small amount of ethyl acetate to dissolve the NBS sample
o Spot this solution in lane 1 of the TLC plate using a TLC spotter
o For the limonene standard, follow the same process and spot in lane 2
2. Liquid-Liquid Extraction
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Set Up Separatory Funnel:
o Secure a 125-mL separatory funnel to the fume hood’s monkey bars with a ring clamp
o Ensure the stopcock is closed and place a funnel in the top
Transfer Reaction Mixture:
o Carefully pour the reaction mixture into the separatory funnel
o Rinse the flask with ~5 mL of ethyl acetate three times, adding each rinse to the funnel
Add Brine Solution:
o Add ~2 mL of brine (saturated NaCl) to the separatory funnel
Separate Layers:
o Drain the aqueous layer (bottom layer) into a clean, labeled 100-mL beaker
o Pour the organic layer (top layer) into another labeled beaker
o Return the aqueous layer to the separatory funnel, add 15 mL of fresh ethyl acetate, shake, and drain again
o Combine all organic layers and return to the separatory funnel
Wash with Brine:
o Add 15 mL of brine to the combined organic layers in the separatory funnel
o Drain the aqueous layer and pour the organic layer into a labeled 100-mL beaker
Dry the Organic Layer:
o Add a small scoop of anhydrous sodium sulfate to the organic layer
o Swirl the solution and let it sit for 5 minutes
3. Product Isolation
o Weigh Round-Bottom Flask:
o Record the mass of a clean 100-mL round-bottom flask
o Transfer Organic Layer:
o Carefully decant the organic layer into the round-bottom flask, avoiding any sodium sulfate
o Prepare TLC Sample:
o Dip a clean TLC spotter into the organic layer and spot lane 3 of the TLC plate
o Rotary Evaporation:
o Use a rotary evaporator (rotavap) to remove the organic solvent.
4. Thin-Layer Chromatography (TLC) Analysis
o Develop TLC Plate:
o Run the TLC plate in a 50/50 ethyl acetate/hexanes solvent mixture
o Allow the plate to dry for 5 minutes
o Visualize TLC Spots:
o Place the dried TLC plate in an iodine chamber, cap it, and let it sit for 2–3 minutes
o Remove the plate and tap off excess iodine. Quickly circle any visible spots with a pencil
o Calculate Rf Values:
o Measure and record the Rf values for each spot
5. Final Steps
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Determine Product Mass:
After rotavap, obtain the crude mass of the product.
Calculate the theoretical yield and percent yield
Submit Sample for GC–MS
o The stockroom team will perform GC–MS on your sample, and data will be available on Canvas
Ryan Xu
10/29/2024
Alkene Addition
6. Waste Disposal
o Discard organic solvents in the organic waste container
o Discard aqueous solvents in the aqueous waste container
o Place used Pasteur pipettes, TLC spotters, and TLC plates in
the solid waste or broken glass container, as appropriate
Results/Analysis: