Electrophilic Aromatic Substitution Lab

Electrophilic Aromatic Substitution
5. Introduction In this experiment, the directing effects of a bromo substituent was observed in the nitration by an electrophilic aromatic substitution reaction. The nitration was done with the addition of a nitric acid and sulfuric acid solution to bromobenzene, which was an exothermic reaction. When the reaction subsided, the mixture was heated before it was poured on ice and then neutralized to a pH of 8 with sodium carbonate. Liquid-liquid extraction was used to isolate the arene solution before it was analyzed through GC. The relative reactivities of different arenes in electrophilic aromatic bromination was also observed. In this part, five different arenes were reacted with a solution of acetic acid and bromine and the rates of reaction—determined by a change in color—were recorded. These reactions were done with a water bath.
6. Data and Results The retention time of the nitrated arene products were approximately 24.165, and 24.477 minutes. With the bromination, phenol was the first to change color, with the change occurring almost instantly at approximately half a second. The next arene to change was anisole, at approximately 15 seconds. The third was 4-bromophenol at 22 seconds, and then acetanilide at 34 seconds. Last to change color was diphenyl ether, at 340 seconds.
7. Discussion and

Due to steric and inductive effects, the major product would be 1-bromo-2,4-dinitrobenzene and not 1-bromo-2,6-dinitrobenzene. This dinitration is undesired in the reaction and was prevented by performing the experiment below 60 °C. The nitro group already on the arene is strongly deactivating and so the activation energy required to add another nitro group is high. Thus, without a higher heat, the undesired reaction will not occur. Dinitration is also prevented by the precipitation of the para product, so that it is removed from the nitration