Benzene and Activating Group

In the mechanism, the alkene in the benzene ring attacks the Br2 group leaving a carbocation intermediate and a bromine anion. The Br2 was in an HBr solution, which used as a catalyst similar to FeBr3. The bromine anion then deprotonated a beta hydrogen, forming HBr and a benzene ring with the activating substituent and bromine. This reaction could be repeated up to two more times based on the strength of the orthro/para directing group. As a result, there were many possible different products when the aromatic compounds underwent bromination. For aniline, the prediction was that the product would be 2,4,6-tribromoaniline because anime was a very strong activating group that reacted strongly with halogenations reactions in general. For phenol, the hydroxy group was also a ring activating and electron donating group. A disubstituted bromine product was predicted because the hydroxy group was not as powerful as the amide. Anisole also had an activating group in a methoxy group and the prediction was from the anisole bromination reaction would be a disubstituted product. Lastly, for acetamide, the amide group was considered to be not a strong activating group compared to the anime, hydroxy, and methoxy groups because of the fact that the electrons were not localized in the amide due to resonance. As a result, this reduced the activation of the benzene ring and the predicted product was 4-bromoacetanilide. Mechanism (for acetanilide): Results: Compound| Melting Tempeature (degrees Celsius)| Product (g)| Anisole| N/A| oil| Aniline| 119-120; 116-117 | 0. 116g; 0. 010g| Phenol| N/A; 36-51| 0. 325; 0. 007| Acetanilide| 166-168; 156-162| 0. 140g; 0. 111g| Calculations are posted at the back Reaction| Limiting Reagant| Actual Yield| Percent Yield:| Acetanilide| Acetanilide| 0. 140g| 65. 4 %| Discussion:The reaction that was done in lab was the bromination of acetamide. Overall, the reaction was pretty efficient as the percent yield of the reaction was 65%. Due to using a 10% v/v bromine solution, there was 0. 15 ml (0. 02 mol) of bromine in 1. 5 ml of the solution. Compared about 0. 135 g of acetamide used (0. 01 mol), there was an excess of bromine to react with the acetamide. As a result, there may have been not enough acetamide to react with bromine. The product also appeared to be somewhat water soluable, which reduced the efficiency. Also, the reactions done by the other groups had similar results or inefficient reactions that had small yields. Based on the melting point measurements in lab, the rankings in terms of reactivity were aniline, phenol, anisole, and acetamide. As predicted before, aniline was ranked as the most reactive because the product was 2,4,6-tribromoaniline, which had a melting point of 119-120 Â °C. The second most reactive aromatic compound was phenol with products 2,4 and 2,6 dibromophenol at 36 to 51 Â °C. The hydroxy group was a good activating group, but not strong enough to activate the benzene ring for a third bromination due to the deactivating effects of the added benzylic bromine. The third most reactive compound was anisole with an oil and possible products for this reaction could be 2 or 4 or 2,6 bromoanisole. Based on this reactivity, the methoxy group had steric bulk and the oxygen in the methoxy preferred to stabilize adjacent bromines. The least reactive compound was acetamide, with a product of 4-bromoacetanilide. The amide group in acetanilide was bulky, so preferring the ortho position would mean a more stable product with less steric interaction. Overall, the predictions in the theory matched besides the anisole. The results make sense because as the reactivity decreases, it was down to factors such as electron delocalization due to resonance, steric bulk, and bromine being a deactivator to the benzene ring. Sources of Errors: Sources of errors may result from not crashing the reaction with enough water and sodium bisulfite and not rinsing the product with water during vacuum filtration. Conclusion: The product obtained in the reaction was 4-bromoacetanilide and the order of reactivity of bromination was determined. Calculations: Mol of Bromine: 10% v/v = (0. 15 mL Br2) x (3. 11 g/mL) x (159. 81 g/mol) = 0. 003 mol Br2 Mol of Acetanilide: (0. 135g acetanilide) x (1 mol/135. 17 g) = 0. 001 mol acetanilide Acetanilide is Limiting Reagant. Theoretical Yield: (0. 135g acetanilide) x (1 mol acetanilide/135. 17 g) x (1 mol 4-bromoacetanilide/1 acetanilide) x (215. 07 g/1 mol 4-bromoacetanilide) = 0. 215g Percent Yield: . 140g/ 0. 215g= 65. 1%