SONOMA STATE UNIVERSITY

Chemistry 336-Dale Trowbridge

Bromination of Propene:

Any modern Organic Chemistry text book will give the currently accepted mechanism for the reaction of bromine with an alkene. In preparation for this experiment you should review this mechanism paying particular attention to the potential regioselective (Markonikov addition) and stereoselective (Anti addition) nature of this reaction. In this experiment you will use GLPC to study the products of the reactions of the double bond compound, propene with molecular bromine: 1) in the presence of the nonnucleophilic solvent, carbon tetrachloride; and 2) in the presence of other nucleophilic species including the solvent.

The major emphasis of your laboratory report should be the analysis of the results of your experiment in terms of what you were and were not able to determine about the nature of this reaction. You can improve your report by suggesting other related experiments that could be run to learn more about this reaction, and, in fact, you may wish to actually try one or more of these proposed experiments.

Procedure

A. Bromination of Propene in Carbon Tetrachloride

With gentle swirling pass propene gas into 5 ml of a solution of bromine in carbon tetrachloride in a 25 ml round bottom flask until the red-brown color of the molecular bromine is completely gone. Analyze the product solution by GLPC. Run any appropriate standards that might be useful in interpreting your data.

B. Bromination Reactions of Propene in Acetic Acid

1. With gentle swirling pass propene into 5 ml of a solution of bromine in acetic acid in a 25 ml round bottom flask until the color of the bromine is completely gone. Transfer the mixture to a 250 ml separatory funnel containing 100 ml of deionized water. Extract this mixture with two 15 ml portions of diethyl ether. Wash the combined ether extracts with 20 ml of water, 20 ml of saturated sodium bicarbonate and 20 ml of saturated sodium chloride solution. Dry the ether solution over anhydrous magnesium sulfate and analyze this product solution by GLPC.

2. Add 0.3 g (2 mol equiv.) of solid lithium chloride to 5 ml of a solution of bromine in acetic acid (1 mol equiv.) in a 25 ml round bottom flask. Stopper the flask and shake it until all of the solid lithium chloride has dissolved. Pass propene gas into this solution and treat the resulting product solution as in part B 1 above.

 C. Bromination Reaction of Cyclohexene

With gentle swirling,add cyclohexene dropwise into a solution of bromine in carbon tetrachoride (5 mL) contained in a 25 mL r.b. flask until the red color is completely discharged.. Inject a 0.2 mL sample on the Varian GC with a column temp of 140 C^o. Do a library search on the major peaks and carefully note the full IUPAC name of the product(s).

.