Nitration of Naphthalene

Abstract:
The purpose of this experiment was to nitrate naphthalene with nitronium ion, which is formed at low concentration from a reaction of nitric acid and sulfuric acid. The percent yield from the experiment was 54.4% of the product, and the melting point of the possible results were 59 °C for 1-nitronaphthalene, and 78°C for 2-nitronaphthalene.

Introduction:
Polynuclear aromatic hydrocarbons such as naphthalene can be nitrated by the same methods as benzene derivatives, including the well-known “mixed acid” method that utilizes a mixture of nitric acid and sulfuric acid. The electrophile is the nitronium ion, NO2+, which is formed at low concentration by a reaction of the two acids. The mononitration of naphthalene could lead to either one of two products, 1-nitronaphthalene or 2-nitronaphthalene. The purpose of this experiment was to nitrate naphthalene with nitronium ion, which is formed at low concentration from a reaction of nitric acid and sulfuric acid. Reaction:

Reaction mechanism:

Safety Notes:
Sulfuric acid and nitric acid can cause very serious burns, and they react violently with water and other chemicals. Nitric acid produces toxic nitrogen dioxide fumes during the reaction. Use gloves and a hood, avoid contact with the acids, and do not breathe their vapors. The nitro naphthalene is a suspected carcinogen; avoid contact. The mixture of hexanes is very flammable; keep flames away. Procedure:

Into a 5-ml conical vial, 1.0 ml of mixed 1:1 sulfuric acid and nitric acid was added. Approximately, 0.610 g of finely divided naphthalene was added in small portions to the solution while stirring after each addition, and cooling to keep the temperature around 45-50°C. The reaction mixture was then stirred in a 60°C water bath for 20minutes after the addition of naphthalene. When the reaction cooled to room temperature, the solution was transferred to a beaker containing 20 mL of ice-cold water with stirring. Yellow crystals were allowed to form, and then the liquid content was removed with filter-tip pipet.

The solid was then boiled with 10ml of fresh water for 10minutes. The mixture was cooled in ice and the product was collected by vacuum filtration. 0.1 of the crude product was then recrystallized for 5minutes with 5ml of hexane under reflux. The hot solution was filtered using a preheated filtering paper. Crystallization occurred, and then the product was collect by vacuum filtration. The product was dried and the melting and mass were measured of the product, nitro naphthalene.

Discussion:
The percent yield from the experiment was 54.4% of the product, which was low. This low percentage yield might occurred due to loss of the product during transferring or weighing. The melting point of the possible results were 59 °C for 1-nitronaphthalene, and 78°C for 2-nitronaphthalene. Even though there was discrepancy in the results obtained from the experiment, the product is more likely to be 1-nitonaphthalene because its melting point was closer to that of the product obtained. The discrepancy in the result obtained may have been from various sources during the experiment. During vacuum filtering, if not properly performed, some of the product might have been lost, therefore decreasing the amount of the product obtained. Another source might have been from the addition of naphthalene to the 1:1 mixture of nitric acid and sulfuric acid. The reaction probably did not fully react if the naphthalene was added at once without stirring. Again, this might have caused the discrepancy in result. Conclusion:

The purpose of the experiment, which was to synthesize nitro naphthalene, was accomplished through the method implemented in this experiment because of the similarity between the obtained product and the predicted outcome. This experiment can be improved by circumspectly following the procedure, carefully adding the finely divided naphthalene in little amounts in order to facilitate a good reaction between the nitronium ion and naphthalene.

References:

Multiscale operational organic chemistry, by John W. Lehman, custom edition.