Bromohexane Lab Report

Under reflux conditions, a bromohexane compound is synthesized from 1-hexene and HBr(aq). The desired product, 2-bromohexane, is analyzed to see if it is produced according to Markovnikov’s rule, which states that when an alkene reacts with a hydrogen halide (HBr) to form an alkyl halide, the H+ is added to the carbon with a greater number of hydrogen substituents to form a more stable carbocation and the halogen (Br-) is added to the carbon with fewer hydrogen substituents. A heterogeneous mixture of 0.5mL of 1-hexane, 2 mL of 48% aqueous hydrobromic acid, and 150 mg of tetrabutylammonium bromide is heated under reflux. The organic chemicals that are used are volatile and can evaporate and get lost; therefore we heat the reaction mixture
The separatory funnel in the first extraction contains petroleum ether and 1-hexene in the organic layer and water and HBr in the aqueous layer. Between both layers, the catalyst, tetrabutylammonium bromide exists. Alkenes are immiscible with concentrated HBr and if the reaction is not mixed efficiently then the reaction is slow. HBr is a strong acid so it ionizes into H+ and Br – and protonates water into H3O+. H3O+ is a weaker acid than HBr, thus it is incapable of protonating the alkene quickly. Furthermore, the existence of H2O presents the opportunity of competing acid-catalyzed addition of water to the
In the organic layer, the HBr becomes more reactive toward the alkene by dehydrating it and the addition becomes likely. The rate of the reaction is determined by the efficiency of dividing the reagents and reactants to increase the surface area. Thus, the reaction mixture must be vigorously agitated by stirring allowing the formation of immiscible tiny droplets to form. After removing the aqueous layer and adding aqueous sodium bicarbonate solution to the organic layer an extraction is performed again. The second extraction should mainly consist of 2-bromohexane in the organic layer and water and the catalyst in the organic layer. The 2-bromohexane is dried using anhydrous sodium sulfate and then filtered to obtain 2-bromohexane. The product does not only contain 2-bromohexane, but there is still some 1-Hexene and petroleum ether present. To access the degree of the alkyl halide formed (1° or 2° halide) and to determine whether Markovnikov’s addition occurred, two qualitative tests can be used: (a) reaction with alcoholic silver nitrate solution and (b) reaction with sodium iodide in acetone. For the silver nitrate test, one drop of alkyl halide is added to 2 mL of 0.1 M solution of silver nitrate in