The purpose of this two-part experiment was to convert an alkene to alkyne. This is difficult to accomplish in one step, thus a multi-step process was used to produce the alkyne. First, bromination of stilbene through the electrophilic addition of bromine to the double bond was performed through an SN2 reaction, as outlined in Figure 3. Pyridinium tribromide, the source of bromine, since elemental bromine is too corrosive and hazardous, was generated in situ (Figure 1). The bromine was added across the double bond and attacked through the backside, anti-relative to the other bromide. This mechanism produced meso-1,2-dibromo-1,2-diphenylethane as the sole products. Although, cis-1,2-dibromo-1,2-diphenylethane can be generated the substituent groups are too sterically hindered and the molecule too unstable to be a viable product in this reaction (Figure 2). This is evident in the notably different melting points of the isomers, cis-1,2-dibromo-1,2-diphenylethane has a melting point of 113°C while the melting point of meso-1,2-dibromo-1,2-diphenylethane is about 238°C (University of Windsor, 2015).
Figure 1: Pyridinium tribromide generated in situ
Figure 2: Isomers of 1,2-dibromo-1,2-diphenylethane
vicinal dibromide
Figure 3: Bromination Reaction Mechanism
trans-stilbene
vicinal dibromide …show more content…
Silver nitrate test was used in an additional step to verify the final product of the bromination reaction. TLC was performed on a sheet of glass coated with a thin layer of silica gel. On this layer of adsorbent, known as the stationary phase, the solvent mixture, the mobile phase, was added. The solvent mixture moved up the plate via capillary action. Considering different analytes ascend the TLC plate at different rates, due to their varying abilities to hydrogen bond with the stationary phase, the identity of the final products were distinguished (Clark,
Figure 1: Pyridinium tribromide generated in situ
Figure 2: Isomers of 1,2-dibromo-1,2-diphenylethane
vicinal dibromide
Figure 3: Bromination Reaction Mechanism
trans-stilbene
vicinal dibromide …show more content…
Silver nitrate test was used in an additional step to verify the final product of the bromination reaction. TLC was performed on a sheet of glass coated with a thin layer of silica gel. On this layer of adsorbent, known as the stationary phase, the solvent mixture, the mobile phase, was added. The solvent mixture moved up the plate via capillary action. Considering different analytes ascend the TLC plate at different rates, due to their varying abilities to hydrogen bond with the stationary phase, the identity of the final products were distinguished (Clark,