Wednesday, March 25, 2009

Nitration of Naphthalene

Purpose of experiment:
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. Naphthalene is a house product used... The major product from the reaction is the kinetic product, the one that forms the more stable cabocation intermediate.

Method and procedure:
Into a 5-ml conical vial, 1.0ml of mixed 1:1 sulfuric acid and nitric acid was added. 0.50g 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 25ml of ice-cold was with stirring. Yellow crystals are allowed to form, and then the liquid content is 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 filteration. 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 filteration. Th product was dried and the melting and mass were measured of the product, nitronaphthalene.
The total mass of the product obtained was 0.57g, and the melting point of the product was between 45-50°C.
The theoretical yield of the product is as follows:
Moles of naphthalene = mass of naphthalene / molecular weight of naphthalene
Moles of naphthalene = 0.50g x 1mol/128.17g = 0.00390mole of naphthalene
Because nitronaphthalene and naphthalene are in 1:1 mole ration,
Moles of nitronaphthalene = 0.00390mole
Theoretical weight of nitronaphthalene = 0.00390mole x 173.17g/mol (molecular weight of nitronaphthalene) = 0.676grams
Perencent yield = 0.57/0.676 x 100% = 84.3%

The result obtained from the experiment was 84.3% yield of the product, and the melting point ranged from 45-50°C. The melting point of the possible results are 61°C for 1-nitronaphthalene, and 79°C for 2-nitronaphthalene.
Even though there is discrepancy in the result obtained from the experiment, the product is more likely to be 1-nitonaphthalene because its melting point is closer to that of the product obtained. They also exhibit the same physical and chemical properties.
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 m1:1 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.
The purpose of the experiment, which was to synthesize nitronaphthalene, was accomplished through the method implemente 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.

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