@fffaizzarul

     ORGANIC CHEMISTRY    

OBJECTIVE 

1) To prepare1-bromobutane
2) To find the percentage yield calculation of 1-bromobutane
3) To observe the boiling point and literature boiling point of 1-bromobutane

    INTRODUCTION
       In this experiment, nucleophilic substitutions are one of the most useful of synthetic organic reactions.     It introduces the class of reaction which is second order nucleophilic substitution.
     The class of reactions requires three things consist of a nucleophiles, an electrophile and free radical   group. In order for the reaction to proceed via substitution mechanism, the nucleophile should be in goodrange so that an electrophile must be unhindered (methyl or 1^o), and the leaving group should also in the good range. This is the reaction that refer to that criteria where water is the leaving group in acid. We can see that the first two are satisfied where bromide ion is an excellent nucleophile and the electrophile is a 1o alkyl group and the hydroxide ion is a poor leaving group.


                         CH₃CH₂CH₂CH₂-OH^- + Br^- --->  CH₃CH₂CH₂CH₂-Br + H₂O 

     We will carry out a reaction with the specific purpose of making a new compound which is it is a synthetic reaction. It is our responsibility to read the procedure and technique that required when conduct this experiment. We must understand the procedure well enough to be able to go to then lab, get set up and execute the necessary steps quickly, efficient and accurately. In this experiment, sodium bromide and 1-butanol are dissolved in water. Sulfuric acid is added cautiously which generates hydrobromic acid which in turn reacts with the alcohol upon heating to make 1-bromobutane.

MATERIALS
100 mL round-bottom flask
25 mL round bottom flask
Pasteur pipets
Ice bath
Boiling stones
Distillation setup
Reflux apparatus and trap
125 mL separatory funnel
125 mL Erlenmeyer flask
Weighing flask

APPARATUS
17.0 g sodium bromide, NaBr
10.0 mL of n-butyl alcohol (1-butanol, molecular weight= 74.1 g mol^-1, density= 0.81 g mL^-1
17.0 mL distilled water
14.0 mL of concentrated sulfuric acid, H₂SO₄
14.0 mL of 9 M H₂SO₄
14.0 mL distilled water
14.0 mL saturated aquoues sodium bicarbonate, NaHCO₃
1.0 g anhydrous calcium chloride, CaCl₂

PROCEDURE
Safety Consideration
1-butanol and 1-bromobutane are both flammable liquids and irritants where no flame cannot be conduct within this week experiment. We had to wear mask and gloves while handling it. Concentrated sulfuric acid is strongly corrosive and toxic while sodium bromide, sodium bisulfite and calcium chloride are all irritants.
17.0 g of sodium bromide, 17.0 mL of water and 10.0 mL of 1- butanol were placed into the 100 mL round-bottom flask. That round-bottom flask was swirled and place in the ice-water bath. Then, 14.0 mL of concentrated sulfuric acid to the reactants of the flask and swirl gently to mix the contents after each addition.
     The flask was assembled into a reflux apparatus using the condenser tube attached to the flask. A trap is attached to the top opening of the condenser to trap HBr gas which is produced during the reaction. The trap consists of a filter funnel connected to a rubber hose and attached to the top opening of the condenser. The filter funnel is clammed upside down at the stem so that its mouth just touches the surface of the water contained in a beaker. A boiling chip was added to avoid bumping.
     The mixture was refluxed for 1 hour. The heat was turned off when the reflux is over and allow the condensate in the condenser to drain back into the flask. The mixture was transferred to a separatory funnel after the reflux setup is cooled. Two layered was formed and the lower layer was discarded. 14 mL of 9 M H₂SO₄ was added to the funnel and shake that funnel. The lower layer was drained into the beaker after two layered is formed for second time. The lower layer inside the beaker was transferred into the empty separatory funnel. After that, 14 mL of saturated sodium bicarbonate solution was added and shaked for 1 minutes. The lower layer was drained into an Erlenmeyer flask. The product was dried woth 1.0 g anhydrous calcium chloride to remove the cloudiness and removes water moisture. The flask was swirled until the liquid is clear.
     The 1-bromobutane was purified using simple distillation. The liquid was pipetted into a 50 mL round-bottom flask and be careful to not let it any solid crystal inside the distillation flask. A few boiling stone were added and the distillation was started. The sample that distills above 90-95^oC was collected while any forerun was discarded. Collect the 1-bromobutane up to its boiling point about 101^oC. That distillate was weighed and measured to get the mass and volume of the product.

DATA/ RESULT:
Mass of 100 mL of empty round-bottom flask= 56.3478 g
Mass of sodium bromide= 17.0047 g
Mass of anhydrous CaCl₂= 1.0063 g
Mass of 1-bromobutane= (Mass of 100 mL of empty round-bottom flask + 1-bromobutane) -                 
                     Mass of 100 mL of empty round-bottom flask
                   = 56.3478 g – 54.3770 g = 1.9708 g
Melting point = 99^oC
Molecular Mass 1-butanol= 74.1224 g mol^-1
Molecular Mass 1-bromobutane= 137.0191 g mol^-1
Number of mol of 1-butanol= 17.0047 g/ 137.0191 g mol^-1 = 0.1241 mol
CH₃CH₂CH₂CH₂-OH^- + Br^-    CH₃CH₂CH₂CH₂-Br + H₂O
1 mol of 1-butanol ≡ 1 mol of Br^-
0.1241 mol of 1-butanol ≡ 0.1241 mol of 1-butanol
Theoretical yield= 0.1241 mol * 137.0191g mol^-1= 17.0041 g
Actual Yield= 1.9708 g
Percent Yield(%) = (Experimental Yield/ Theorertical Yield) x 100
=  1.9708 g  x 100 = 11.5901 %
  17.0041 g

DISCUSSION
CH₃CH₂CH₂CH₂-OH^- + Br^-    CH₃CH₂CH₂CH₂-Br + H₂O
SN₂ mechanisms was shown as above. SN₂ reaction always occur in with inversion configuration at the substrate carbon. The nucleophile approaches the substrate carbon from the back side with respect to the leaving group. In this experiment we are using water as a solvent because it has a hydrogen atom which it attached to a strongly to electronegative element. Hydrogen bonding encumbers a nucleophile and hinders its reactivity in a substitution reaction. The boiling point of our product is 99˚C, so the boiling point is nearly to 1-bromobutane which has 101˚C as it boiling point. As we know alcohol do not undergo nucleophilic substitution reactions because hydroxide ion is strongly basic and poor leaving group. The leaving group is a group of atom which depart with the electron pair used to bond them with the substrate. However, alcohols readily undergo SN₂ because the sulfuric acid was added which protonate the hydroxyl group in the presence of the bromide ion which changes the leaving group from hydroxide to water and allows bromide ions to react with it in the same mixture.
           
     The sulfuric acid serves as two purposes which is to increases the amount of protonated alcohols present in the reaction mixture and to help tie up the water molecules generated in the reaction shifting the equilibrium in favor of the alkyl bromide. From the calculation, the percentage yield for this experiment is 11.5901 %. It is because when doing the experiment, I had broken the separatory funnel near the sink. I do not want to blame my partner. However, I can estimate the product by helping other group. When conduct the experiment, we need to wear gloves while doing an experiment because 1-butanol and 1-bromobutane are flammable fluid which can irritate our skin. Sulfuric acid also very concentrated acid which can affect our skin. Make sure we wash our hand and gloves after handling the substances.


CONCLUSION
11.5901% percent yield was calculated, which 1.9708 g of 1-bromobutane was produced experimentally. The 1-bromobutanol was prepared well from 1-butanol. The melting point is 99^oC where nearly to the exact boiling point of 1-bromobutane which is 101^oC . The nucleophilic substitution mechanism that involved in the reaction was kept in mind.


REFERENCE
1)        Martin S. Silberberg, Patricia G. Amateis, “CHEMISTRY: THE MOLECULAR NATURE OF MATTER AND CHANGE “, 7^th edition, McGraw-Hill Education, Inc. N.Y 2015, page 617-651
2)        http://chemistry.csudh.edu/faculty/noel/CHE317L/Preparation%20of%201-bromobutane.htm
3)        http://myweb.brooklyn.liu.edu/swatson/Site/Laboratory_Manuals_files/Exp7.pdf

QUESTIONS
1)        Explain why the upper phase, after reflux contained the 1-bromobutane, even though its expected density is 1.276 g/cm³, and the density of water is ~1.00 g/cm³. Think what is in the aqueous solution. (e.g., what is the density of salt water?)
= Maybe it contain some of the hydroxide ions (OH^-) and bromobutane ions.
2)        Why does the alkyl halide layer from the top to the bottom layer at the point where water is used to extract the organic layer?
= Because the alkyl halide is denser compared to the water.
3)        Aqueous sodium bicarbonate was used to wash the crude 1-bromobutane. What is the purpose of this wash?
= The 1-bromobutane was formed by the addition of bromine or hydrogen bromide to 1-butene, then the bicarbonate neutralizes any unreacted bromide. This prevents the formation of polybrominated butanes from the addition of any more bromine to the 1-bromobutane. The bicarbonate reacts with the unreacted bromides to form CO₂ and sodium bromide.


4)        What is the purpose of the anhydrous CaCl₂? Why is it important that none of the solid CaCl₂ be included in the final distillation of your 1-bromobutane?
= The purpose of the anhydrous CaCl₂ is to remove the moisture before the distillation step. In this experiment, we had to remove the cloudiness that indicates the water and alcohol removal. It is important that none of the solid CaCl₂ be included in the final distillation of your 1- bromobutane because it can cause contamined our product and change our reading of melting point.(^oC)