Show MoreDiscussion and Conclusion: Preparation of 1-Bromobutane
The purpose of this experiment was to demonstrate the conversion of a primary alcohol, 1-butanol, to a primary bromoalkane, 1-bromobutane, a SN2 reaction.
The conversion of 1-butanol to 1-bromobutane relies on sulfuric acid which plays two important roles. First, it protonates the alcohol of 1-butanol to form an oxonium ion which is a good leaving group. Secondly, it produces the hydrobromic acid, the nucleophile, which attacks 1-butanol causing the oxonium ion to leave and forming 1-bromobutane. However, using sulfuric acid in this experiment has several downsides. First, it poses a huge safety hazard as it can cause severe burns. Secondly, it reacts exothermically, which was…show more content…
The graph is split into a functional group region and a fingerprint region. The functional group region shows the peaks based on the types of bonds present. The infrared spectroscopy of 1-bromobutane should have a large carbon-hydrogen peak which absorbs at approximately 3000 cm-1 and a medium carbon-bromine peak which absorbs at 500 cm-1. However, due to the limitations of the infrared spectroscopy machine, a carbon-bromine peak should not be detected because the machine is not accurate at infrared ranges below 600 cm-1. As a result, relying simply on a carbon-hydrogen peak is not a reliable way to determine if the product is actually 1-bromobutane. This is where the fingerprint region comes in handy. The fingerprint region relies on the fact that the all the bonds affect each other’s absorbency. This means that no two molecules will have the same fingerprint region and any molecule can be compared to known infrared spectroscopies. The infrared spectroscopy produced by the product of this experiment fit the criteria of 1-bromobutane. There was a large peak at approximately 3000 cm-1 which indicated that there were many carbon-hydrogen bonds that 1-bromobutane has. The fingerprint region of the graph also matched a known infrared spectroscopy of 1-bromobutane quite well too. There were peaks of approximately the same length and absorbencies that matched the known 1-bromobutane infrared spectroscopy. The
Experiment # 13- Synthesis of 1-Bromobutane: An SN2 Reaction
February 3, 2012
In this experiment we will use SN2 chemistry to convert 1-butanol to 1-bromobutane .The nucleophile for the reaction are Br- ions. In this lab the nucleophile is produced from an aqueous solution of sodium bromide. The sulfuric acid acts as a catalyst in converting the OH functional group of butanol, to water which is a much better leaving group. As a result, 1-butene, di-n-butyl ether, and the starting alcohol (butanol) were the final products. All by-products are removed by extraction using concentrated sulfuric acid. Thus, the product can be removed from sulfuric acid, since it does not mix with H2SO4 and will remain as a separate layer.
The most common way known to prepare an alkyl halide involves very functional intermediates in syntheses. In this lab it is replacing the OH- group of an alcohol by a halogen. This replacement is a nucleophilic substitution reaction. However, alcohols do not undergo nucleophilic substitution due to the fact that the hydroxide ion is strongly basic and has a very poor leaving group. On the other hand, if the hydroxyl group was activated initially to produce a better leaving group (water), which causes the reaction to be carried out in the presence of a strong acid it would be able to undergo the substitution. In addition, the acid even protonates the alcohol in order to create a more suitable leaving group for the SN2 reaction to occur. In this particular case, sulfuric acid ( H2SO4) is used and is first added to the 1-bromobutane layer to remove any leftover starting material and after the 1-bromobutane layer is isolated sodium hydroxide solution is added to remove any remaining acid. Anhydrous calcium chloride pellets is then used to remove any remaining water in the solution and then the simple distillation process is performed again on the dried 1-bromobutane. It would be hypothesized that the amount of recovered 1-bromobutane will be relatively fair since there are many techniques involved, which allow for many places for error and product loss. Also, the theoretical yield for the experiment is 13.83g, which is relatively fair.
This experiment is to do an SN2 reaction, learn various techniques in order to synthesize, isolate, purify and be able to categorize a specific compound. In this lab some techniques had multiple uses such as distillation. It is useful for isolation/purification and characterization. In this lab in particular, the aim is to prepare 1-Bromobutane. In this experiment, it is necessary to realize that the reaction is a nucleophilic substitution. Thus, the products are tainted. Hence, it is vital that a variety of steps of purification process should be applied so that the result obtained can be reasonably accurate.
Sodium Bromide (NaBr)*powdered*
Concentrated Sulfuric Acid (H2SO4)
Compound Density (g/cm3)
Molecular Weight(g/mol) Structure Boiling Point˚ C
(H2O) 1.0g/cm3 18.01g/mol 100˚C
(C4H9OH) 0.81g/cm3 74.12g/mol 118˚C
(C4H9Br) 1.27g/cm3 137.02g/mol 101.6˚C
(H2SO4) 1.84g/cm3 98.07g/mol 327˚C
A sample of 10.3 g Sodium Bromide (NaBr) was placed on a balance. A sample of 1-butanol (C4H9OH) 7.5 g was placed on a balance. The Sodium Bromide (NaBr) was then placed into a 100mL round bottomed flask. Water was added to the 1-butanol (C4H9 OH).They were both mixed thoroughly by swirling, and then was cooled in ice-water bath. When it was taken out of the ice-water bath, 10mL of sulfuric acid was slowly added to the cold mixture with and was continuously swirled and cooled. The flask was then removed from the ice-water bath and boiling chips were added. A Reflux Condenser was attached, and then the flask was warmed to the point where most of the salts were dissolved. The mixture was gently heated under the reflux for 45 minutes. The flask was prepared for the simple distillation. Distill mixture rapidly in order to collect the distillate. This resulted in 1-bromobutane and water in the ice-cooled receiver. The distillation process was continued until the distillate became clear. The thermometer was then used because the head temperature should be 115˚C.The boiling point was increased because the co-distillation of sulfuric acid and Hydrobromic Acid (HBr) with water. After adding sulfuric acid to the mixture of NaBr, 1-butanol, and water there was a brief yellow stream that appeared and then became clear. The distillate was then transferred to the seperatory funnel with the addition of 10mL of water. The sample was shook gently with venting. Then the layers were separated and were figured as to which was the organic the layer. The organic layer was washed with 4mL of 2M aqueous Sodium hydroxide (NaOH) solution then washed again with about 10mL of saturated sodium chloride (NaCl) solution. The cloudy part of the distillate was the 1-bromobutane, so it was transferred to a 25mL Erlenmeyer flask and was dried over Sodium sulfate (Na2SO4).The flask was swirled occasionally for 10-15 minute periods until the crude 1-bromobutane was clear. Additionally, a small portion of anhydrous sodium sulfate was added if the 1-bromobutane was not completely