Double Elimination Reaction Was Performed On Meso-Stilbene Dibromide

Experiment 12: Dehydrobromination
Discussion
In this experiment, a double elimination reaction was performed on meso-stilbene dibromide, to form diphenylacetylene by eliminating two hydrogen and two bromine atoms in he presence of potassium hydroxide. The product was filtered and identified by comparing melting point data, and percent yield was calculated.
Since an E2 reaction was performed in this experiment, the ideal conformation for the hydrogen and bromine would have been anticoplanar. However, since the phenyl groups were bulky and the atom was not symmetric, the hydrogen and bromine could at best be antiperiplanar. For an E2 reaction to occur, the two groups being removed had t be anti to each other. This was easily accomplished in

In order to overcome this issue, the reaction could have been performed in a regular solvent heated to 190C under extremely high pressure to prevent boiling. However, the lab was not equipped to safely deal with high pressure situations, so instead a solvent with an extremely high boiling point had to be used. In this case, triethylene glycol, which has a boiling point of 260℃, was used. This boiling point is significantly higher than the 190℃ that this reaction was performed at, and the solvent would hence not boil away, even under standard pressure

Melting point data was used to confirm the identity of the product as diphenylacetylene. The expected melting point of diphenylacetylene is 59-61℃, according to its MSDS sheet. While there was a discrepancy in this temperature range and the melting point range observed, the melting point was significantly lower than that of meso-stilbene dibromide, which is 241℃. The data hence confirms the formation of diphenylacetylene. The error could have been caused due to impurities in the diphenylacetylene crystals, such as leftover ethanol, or triethylene glycol, which would destabilize the lattice structure of the crystal, making it melt at a lower temperature than expected.
The percent yield for this experiment, calculated as described in the discussion, was 61.7%. This was an excellent percent yield, especially considering the fact that this has been a historically difficult experiment to get good yield in. This high yield most likely occurred due to successfully building a good aluminum tent, which conducted the heat towards the reaction, allowing the relatively inefficient hot plates to heat the reaction to the high temperature necessary. The reaction was also stopped exactly at 5 minutes, which likely resulted in very little product burning