Synthesis Of 1-Bromobutane

Experiment # 13- Synthesis of 1-Bromobutane: An SN2 Reaction

Jasio-Dane Bispott

February 3, 2012

Michon Jackson

James Rolling

Tierra Rossin

Omikunle Bradley

Chandra Browning

Monique Noel

Christina Philip

Britanny Henry

Introduction

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.

Abstract

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.

Purpose

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.

Materials, Reagents

1-Butanol (C4H90H)

Sodium Bromide (NaBr)*powdered*

Concentrated Sulfuric Acid (H2SO4)

Round Flask

Ice-water Bath

Boiling Chips

Reflux Condenser

Thermometer

Seperatory Funnel

Erlenmeyer flask

Physical Properties

Compound Density (g/cm3)

Molecular Weight(g/mol) Structure Boiling Point˚ C

Water

(H2O) 1.0g/cm3 18.01g/mol 100˚C

1-Butanol

(C4H9OH) 0.81g/cm3 74.12g/mol 118˚C

1-Bromobutane

(C4H9Br) 1.27g/cm3 137.02g/mol 101.6˚C

Sulfuric Acid

(H2SO4) 1.84g/cm3 98.07g/mol 327˚C

Procedure

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

...