The goal of this experiment is to synthesize a bromohexane compound from the addition of 1-hexene and HBr(aq) under reflux conditions. The product is then isolated and the regiochemistry is analyzed using chemical tests and known standards (1 Br, 2 Br) in order to determine if Markovnikov’s rule is followed. In general, Alkenes are able to undergo addition reactions due to the strength of their C-C -bond (60-65 kcal/mol) which is lower than the strength of a typical -bond (80-100 kcal/mol) between Carbon and other atoms. Adding a reagent across the double bond results in an exothermic reaction because one -bond is replaced by two higher energy -bonds. Accordingly, the addition of HBr(aq) to 1-Hexene involves the protonation of 1-hexene and is expected to produce a secondary carbocation, 2-bromohexane.
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Furthermore, HBr(aq) is a strong acid that protonates water to give the H3O+ ion. Since H3O+ is weaker than undissociated HBr(aq), it is unable to protonate the alkene quickly if not efficiently mixed. The presence of water in the reaction mixture also introduces the possibility of competing acid-catalyzed addition of water to the alkene (Gilbert, Martin). The addition of 150 mg of Tetrabutylammonium bromide which partitions between the aqueous and organic layers, solves many of these issues. This is due to its lipophilic (nonpolar-loving) and hydrophilic (polar-loving) properties, due to the alkyl groups and ionic ammonium function, respectively. The salt also extracts the HBr(aq) from the aqueous phase and transports it into the organic phase where it comes in contact with the alkene. This dehydrates the acid and makes it more reactive toward the alkene, thus, making the addition reaction possible. To complete the process, the salt then repartitions into the aqueous
Furthermore, HBr(aq) is a strong acid that protonates water to give the H3O+ ion. Since H3O+ is weaker than undissociated HBr(aq), it is unable to protonate the alkene quickly if not efficiently mixed. The presence of water in the reaction mixture also introduces the possibility of competing acid-catalyzed addition of water to the alkene (Gilbert, Martin). The addition of 150 mg of Tetrabutylammonium bromide which partitions between the aqueous and organic layers, solves many of these issues. This is due to its lipophilic (nonpolar-loving) and hydrophilic (polar-loving) properties, due to the alkyl groups and ionic ammonium function, respectively. The salt also extracts the HBr(aq) from the aqueous phase and transports it into the organic phase where it comes in contact with the alkene. This dehydrates the acid and makes it more reactive toward the alkene, thus, making the addition reaction possible. To complete the process, the salt then repartitions into the aqueous