Microwave Synthesis of Phosphorous Salts

Chemistry 123L

Reading: Review filtration and the Sn2 reaction in the textbook:

Objectives: To prepare a phosphorus salt.

Overview of the experiment: In this experiment you will mix triphenylphosphine and an alkyl halide in acetonitrile. The product is a salt which is insoluble in most organic solvents.

Procedure:

Obtain a microwave vessel from your TA or PBJ. Mix triphenylphosphine and an alkyl halide in 5 mL of acetonitrile in the vessel. Your TA will provide the amount of triphenylphosphine and the amount and identity of alkyl halide. PBJ will stopper the vessel. Shake the mixture until it is homogenous. Bring the solution to PBJ who will take you to the microwave for heating.

Upon receiving the vessel after the reaction, pour the mixture into an Erlenmeyer flask and add 15mL toluene. Swirl the flask gently for a few minutes and then place on an ice-bath for 10 minutes. Collect the solid by vacuum filtration and wash with three 15 mL portions of petroleum ether or hexane. Allow the solid to air dry on the filter paper (while drawing air through it with the vacuum) for 15 minutes. Measure your yield.

Is the solid soluble in water?

Report your conditions and yield to the TA.

PPh3 PhCH2Cl 1-bromobutane 1-chlorobutane 2-bromobutane NaI

A 262 mg 0.25 mL

B 262 mg 0.5 mL

C 524 mg 0.25 mL

D 262 mg 0.25 mL 10 mg

E 262 mg 0.25 mL

F 262 mg 0.11 mL

G 262 mg 0.25 mL

Lab Questions 1. Calculate the average % yield for your reaction. Remember that you must determine a limiting reagent and calculate the yield using moles product / moles limiting reagent.

2. Report your % yield to the TA.

Post-lab questions

1. Fill in % yield in the table above (replace amounts with yields).

a) Is the data consistent with an Sn1 or Sn2 mechanism? Explain.

b) How might NaI act to catalyze the reaction?

2. What primary advantage does using the microwave confer over conventional reflux conditions?