A Multistep Synthesis of Trioctylphosphine
LAB TECHNIQUE 5: A Multistep Synthesis of Trioctylphosphine
Lab Safety Clearance Form (to be signed and submitted at the start of the lab technique)
- Students must read the experiment and the MSDS (Material Safety Data Sheet) for all the chemicals to be used in this lab technique prior to entering the lab. It is mandatory for everyone who may be exposed to potentially toxic liquid, solid, and/or gaseous compounds to take every precaution needed based on the information pertaining to the safety hazards of each compound, equipment and/or technique.
- Students must fill the Table of safety hazards for each compound used in this lab (listed below or any replacement thereof when necessary):
|#||Name of Substance/Technique/Equipment||Safety Hazards||Potential and Other Concerns||Proper Attire/Covering|
Submitted by……………………………………………………. Date:……………………………
Checked by ………………………………………………………Date:……………………………
Step 1: Synthesis of 1-bromooctane from 1-octanol
- In a clean and dry 100-mL round-bottomed flask (rbf) equipped with a magnetic bar, an addition funnel and a cooling condenser through a Claisen adapter (with two side arms) with both topped by Calcium Chloride drying guards. To the rbf were placed 10g of 1-octanol (how many moles?). The reaction vessel was immersed in an ice-water bath (use a larger beaker to place crushed ice and tap water).
- 1 molar equivalent of phosphorus tribromide (how many moles? And how many grams?) was added (or injected) to 20 mL of DCM (dichloromethane) already placed in the addition funnel which was topped by a Calcium Chloride drying guard.
- Dropwise, add the solution of PBr3 into the reaction flask with vigorous stirring, and let the mixture stir for 30 min before removing the ice-water bath.
- Let the mixture stir at room temperature for another hour.
- Pour the reaction mixture into a beaker of water and crushed ice (100mL) and once the ice has melted, extracted the solution with ethyl acetate (100 mL). Combine the organic layers into a clean and dry Erlenmeyer flask. Add drying agent (Anhydrous Calcium Chloride, 3 full spatula) to the clear organic layer for 20 min.
- Filter off the drying agent (regular filtration), collecting the organic layer in a 250-mL rbf (clean and dry and ALSO weighed while empty for the purpose of determining the % yield of the crude product below) before removing the solvent at the rotary evaporator (see instructor).
- The resulting dry crude product should be analyzed by NMR spectroscopy (see instructor) after it has been weighed (by subtracting the weight of the empty rbf) the following week.
- Submit a sample of the crude product to your instructor once 0g have been saved in a clean vial for step 2.
- In order to prep for step 2, each group of students should thoroughly clean and place in the oven for a week the following items:
– A 100mL rbf,
– A magnetic bar,
– A Claisen adapter,
– An addition funnel (without the plastic stopcock and accessories which would melt otherwise. These need to be saved in a clean and dry bench),
– A reflux condenser.
Step 2: Synthesis of trioctylphosphine by Grignard Reaction
(No trace of water is allowed, No vessel involved in this step should be washed in water, you should avoid contact with water while running this experiment until you need to quench it with water)DO NOT allow air or moisture to enter the reaction once it has started.
- In a clean and oven-dried 100 mL rbfwith a clean and oven-dried magnetic bar inside,was topped with a clean and oven-dried Claisen adapter, which was equipped on one side by an oven-dried addition funnel, and on the other side with an oven-dried reflux condenser topped with a Calcium Chloride drying guard. To the rbf were placed 20 mL of tetrahydrofuran THF (see Instructor), magnesium powder and a grain of iodine (see instructor) under vigorous stirring.
- To the clean and oven-dried addition funnel equipped with a calcium chloride drying guard were placed 20 mL of THF and 5g (how many moles?) of 1-bromooctane synthesized previously.
- The THF solution in the addition funnelwas dropped slowly to the magnesium suspension in THF and stirred for 30 min (formation of a greyish milky layer is a good indication that the Grignard is formed).
- In the meantime, once the addition funnel has emptied, add 10 mL of THF followed by the required amount of PBr3 (a third of mol equivalent of 1-bromooctane, how many grams? And then how many mL since this compound is liquid? Hint: use the density of this compound to find out).
- Before the next step, place an ice-water bath under the reaction mixture to cool it. Then slowly add the THF solution of PBr3 into the Grignard solution while observing the changes. Once the addition is finished, remove the ice-water bath and let the mixture stir at room temperature.
- Start the reflux by turning on the water (the instructor must inspect your set up and ensure that all water is draining properly before you start) and the heat (heating mantle/variac) with vigorous stirring for the next hour.
- After one hour, turn off the heat, and remove the heating mantle/pad while stirring at room temperature for another 10-20 min. Then replace the ice-water bath under the reaction mixture and turning off the water in the cooling condenser.
- Add 20 mL of tap water into the addition funnel and let it drop slowly to the quench the reaction and neutralize all unreacted Grignard reagent. Remove the ice-water bath and stir the mix at room temperature for another 10 min.
- Extract the reaction mixture in a large separatory funnel with ethyl acetate (2 x 100mL). Combine all organic extracts into a clean and dry Erlenmeyer flask. Do not discard the aqueous layer but keep them inside the fumehood until the end of this lab.
- Add 3-5 spatula of the drying agent (Calcium Chloride anhydrous) into the combined organic layer and let it sit for 10-20 min. Filter off the drying agent, collecting the organic layer in a large 500-mL rbf that has been cleaned, dried and weighed.
- Evaporate the solvent at the rotovap (see instructor) to obtain your crude product. This crude product must be further dried by letting it stand in the fumehood overnight.
- Take the weight to calculate the percent yield (how?) and submit a sample for NMR spectroscopy (You + the Instructor).
- Submit your lab Report in a timely manner.