Aromatic Nitration

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Experiment #1 – Aromatic Nitration

The purpose of this lab is to convert toluene to nitrotoluene through the process of aromatic nitration. This is done by electrophilic aromatic substitution. The aromatic organic compound, toluene, is reacted under mild conditions with an electrophile, the nitronium ion, resulting in a product of nitrotoluene. Failure to use mild conditions may result in polynitration. Different reaction conditions were studied to understand the effect of nitrating agent concentrations on the results.

Initially, toluene is combined with a mixture of nitric acid and sulfuric acid. Both of these must be reduced to ice-cold temperatures prior to mixing because the reaction is exothermic. Failure to maintain low temperatures may result in polynitration of the toluene to trinitrotoluene. The nitric acid is combined with sulfuric acid to create the nitronium ion that is to be reacted with toluene (see mechanism below).

The nitronium ion is then reacted with toluene to create a combination of ortho, meta, and para-nitrotoluene (see mechanism below). As expected, the resulted indicated 51.8% ortho, 37.91% para and only 2.97% meta.

The mixture had to be warmed to room temperature and then heated for ten minutes at a temperature less than 50° C in order for the reaction to take place. Trinitrotoluene would result at temperatures greater than 50° C. Our results displayed 5.70% 2,4-dinitrotoluene and 1.53% 2,6-dinitrotoluene.

The compound is mixed with diethyl ether to isolate the organic products. This resulted in a light yellow mixture. It was then washed twice with 5% Na2CO3 because it is an ionic solution (more ionic than water) and will bond to the H+ ions. This resulted in a bright yellow mixture. Anhydrous CaSO4 is used as a drying agent. It absorbs all of the H2O in the mixture. If H2O is present, then the product cannot be analyzed by gas chromatography.

Gas chromatography is used to determine the amount of...
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