CHM 266 Experiment 4

Free Radical Chlorination

Spring 2007

 

 

Procedure

 

Note the hazards listed in the previous section. Also, measure the benzoyl peroxide by carefully pouring onto weighing paper. Do not use a metal spatula or scoopula.

 

Read the notes at the end of the procedure.

 

            Heat a 400 ml beaker on a steam bath to 75° C. (It may be necessary to heat the water on a hot plate with stirring to ~ 65° C and then transfer to the steam bath to save time.) Be sure to insert the thermometer to its immersion line.  Obtain 1 ml of the sulfuryl chloride in carbon tetrachloride solution with a 1 ml pipet (.32g in 1 ml solution) and place it in a clean dry 25 ml round-bottom flask.  To this solution, add by pipet 0.5 ml of 2,4-dimethylpentane with a 0.5 ml pipet   (d = 0.67).  Add 25 mg (0.025 g) of benzoyl peroxide to the mixture.  Add a boiling stone and attach a reflux condenser.  Place a drying tube containing KOH pellets on top of the condenser to exclude moisture and absorb HCl.  Clamp the apparatus in the water bath so that about 1/2 of the flask is submerged.  Heat the bath at such a rate that the temperature remains 75 ± 2 °C for 30 minutes. Transfer the contents to a test tube.  Add 3 ml of water, stir, and then add 1 ml of saturated sodium bicarbonate solution.  Shake or stir the contents well.  Then transfer the carbon tetrachloride layer (CCl4 is more dense than water) to another test tube.  Be sure not to transfer any water.  Add a few grains of anhydrous sodium sulfate to dry the sample.  Remove a portion of this sample without transferring any of the grains of sodium sulfate.  Analyze this mixture by GC.

 

Notes

 

1.      To save time some shortcuts will be made.  If this were a research project on experiments that had never been published, we would probably not take the shortcuts.

  1. We will not use known samples to determine retention times.  The order of elution should of the compounds is (air), 2,4-dimethylpentane, carbon tetrachloride, 2-chloro-2,4-dimethylpentane, 3-chloro-2,4-dimethypentane, and 1-chloro-2,4-dimethylpentane.
  2. Response factors will not be calculated.
  3. The last two peaks in the chromatogram may not be resolved although we will use the data.

 

2.      The proper attenuation will be announced.

3.      Let the sample run for 10 minutes.

4.      Be sure to place the GC conditions, retention times, peak areas, and area % values in your notebook data section.  After the report is returned, staple the chromatogram in your notebook also.

5.      Tiny granules of sodium sulfate that cannot be seen by the naked eye may nonetheless plug the syringe needle.  To avoid this, rinse the syringe with acetone, then water twice, then acetone, and then 2,4-dimethylpentane, and 5 times with your sample before injection.  Finally rinse the syringe with acetone, twice with water, and finally acetone before turning in the syringe.