Date of Experiment:19th March 2005, Group: B1
Title:Preparation of 1-bromobutane from 1-butanol by SN2 reaction Objective:
1. To study the preparation of 1-bromobutane from 1-butanol by an SN2 reaction 2. To study the method of purification of an organic compound by simple extraction 3. To study the test of identification of alkyl halide
Chemicals and Apparatus:
~18.0 g 1-butanol, ~20.0 g sodium bromide, 15 ml of concentrated sulfuric acid, anhydrous magnesium sulfate, ~10 ml of 5% aqueous sodium bicarbonate, ~1 ml of sodium iodide – acetone reagent, 1 ml of bromine in chloroform, 1 piece of 100 cm3 round-bottomed flask, 1 piece of 50 cm3 of beaker, 1 piece of 50 cm3 of conical flask, 1 piece of 250 cm3 of separating funnel, 1 piece of 10 cm3 of measuring cylinder, 1 piece of electronic hot plate, oil bath, several pieces of anti-bumping granules, ice, filter paper and filter funnel.
Nucleophilic substitution is an important class of organic reaction. In the experiment, 1-bromobutane was synthesized through the second order mechanism in the present of concentrated sulphuric acid and sodium bromide. The nucleophile in the experiment is bromide ion (Br-) while the leaving group is water.
Purification of the product was then obtained by extraction. The principle of extraction as a purification method was based on the difference in solubility between impurities and product.
Identify of the product (1-bromobutane) can be confirmed by carrying out sodium iodide in acetone test. The test involves displacement of bromide by iodide. Since iodide is strong nucleophile which can displace the bromide ion from attached carbon. The reaction was carried out in acetone since acetone dissolved NaI, but not the products NaBr. So the appearance of precipitate and the time it takes to form is the basis for a qualitative test for alkyl halides. Procedures:
The experiment was divided into three parts and worked in pairs.
A) Preparation of 1-bromobutane from 1-butanol
1. 18.0 mL of 1-butanol was weighed into a 50 cm3 beaker. The exact amount of 1-butanol used was being marked. 2. The 1-butanol was transferred into a 100 cm3 round-bottomed flask. 3. The beaker was rinsed with 15 mL deioned water and the rinse was put into the round-bottomed flask. 4. 20 gram of sodium bromide was added into the round-bottomed flask. 5. The mixture was cooled in a ice water bath.
6. To the flask in the ice bath, 15 mL of concentrated sulphuric acid was added gently. The flask was swirled to mix the content and a few anti-bumping granules were added. 7. The flask was fitted with the apparatus for reflux on a hot plat with an oil bath; a condenser was placed with tubing connected on top of the round-bottomed flask as shown in figure 1 of the laboratory menu and the join was wrapped with grease. 8. Checked that water was flowing through the condenser, and then the mixture was heated to reflux. 9. The mixture was allowed to reflux for 45 minutes, during which time mark the observation of the reaction mixture. 10. After the reflux period, the heat was removed and the mixture was allowed to cool at room temperature.
B) Purification of 1-bromobutane by extraction
1. The cool mixture was decanted into a 250-mL separatory funnel. 2. The round-bottomed flask was rinsed with small amount of water and the rinse was put into the separatory funnel. 3. The two layers were allowed to separate and the aqueous later was drained off. 4. The organic later was washed in the separatory funnel successively with 10 mL water, 10 mL of 5 % aqueous sodium bicarbonate and 10 mL of water. 5. The funnel was shaken well in each case. The gas pressure was released regularly during the shaking. 6. The aqueous layer was discarded down the drain.
7. The organic later was collected into a 50 mL conical flask. 8. To the organic later, about 1 gram of anhydrous magnesium sulphate was added. The conical...