Untested

ELECTROPHILIC ADDITION OF  HYDROGEN CHLORIDE TO CYCLOHEXENE

Tested

Torsha S. White, e-mail address, torshawhite@hotmail.com

Background

An electrophilic addition is a reaction that is triggered by the attack of an electrophile on the p electrons of the carbon-carbon double bond.

In many addition reactions the attacking reagent, unlike H₂, is a polar molecule or one that is easily polarizable.  Hydrogen halides, which are polarized, are among the simplest examples of polar substances that add to alkenes.  Addition occurs rapidly in a variety of solvents, including pentane, benzene, dicholoromethane, choloroform, and acetic acid.  The reactivity of the hydrogen halides reflects their ability to donate a proton.  Hydrogen iodide is the strongest acid of the hydrogen halides and reacts with alkenes at the fastest rate.  The product for this particular reaction is 1-chloro-cyclohexane.

Pre-Lab Preparation

1.  Make a table of the densities of: a) concentrated HCl, b) cyclohexene, and c) pentane.  Describe how these densities will be used to identify which layer is which in the separatory funnel in order to separate the layers out.
2.  Record the boiling point for cyclohexene and pentane.  This will help to determine the relative positions of the peaks on the chromatogram.

Procedure

The solvent for this reaction is pentane. The reaction is the electrophilic addition of hydrogen chloride to cyclohexene.
1.  Place approximately 25 ml of cyclohexene in a separatory funnel with 10ml of pentane, which makes the reaction proceed rapidly.
2.  Add 60 ml of concentrated hydrochloric acid that has been cooled in an ice bath.
3.  Shake the mixture occassionally.
4.  Periodically vent the pressure of any evolved gases by holding the ground glass stopper tightly in the flask, invert the flask so that the stem is pointing up, and then carefully and slowly open the stopcock and reclose it.
5.  Allow the mixture to stand in a ring stand until the layers have separated.
6.  Separate and discard the bottom layer, HCl.

Purification

Wash the product by adding 10ml water into the separatory funnel.  Shake the funnel, venting occassionally.  Remove the aqueous layer.  Then wash the product with 10ml of aqueous sodium bicarbonate solution.  Dry the product over anhydrous calcium chloride.

Precautions

Refer to the MSDS sheets for precautionary measures to use when handling hydrocholoric acid, pentane, and cyclohexene.

Analysis

There are several ways to test to see if the reaction was successful.  A chromatograph is one method that is used.  It is a graph of the signal from the detector as a function of time.  The number of peaks in a chromotagraph will indicate the minimum number of compounds in the sample.  Inject cyclohexene and then also inject the product (using the same temperature and pressure conditions).  After the first injection of cyclohexene, clean the syringe with methylene chloride before putting the product into the syringe.  You may or may not observe two peaks in the graph.  Compare the results to determine whether cyclohexene is present in the product.

References

Organic Chemistry, The McGraw-Hill Companies, Inc., New York, 1996.  Francis A. Carey.

Acknowledgements

I would first of all like to thank God, and I would also like to thank my Organic Chemistry classmates and Organic Chemistry instructor Dr. Delphia Harris.
 
 
 
 

About the Author Torsha White is a junior majoring in Biology.