Sodium Borohydride Reduction OF Cyclohexanone PDF

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EXPERIMENT 2...

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LABORATORY REPORT ORGANIC CHEMISTRY (CHM557) NAME OF STUDENT

: NUR INSYIRAH SHAZRIN BINTI ABIDIN

STUDENT NO

:

GROUP

: AS2221A1

NUMBER AND TITLE OF EXPERIMENT

: EXP2 (SODIUM BOROHYDRIDE REDUCTION OF CYCLOHEXANONE)

DATE OF EXPERIMENT

: 23 APRIL 2020

DATE OF REPORT SUBMISSION

: 29 APRIL 2020

NAME OF LECTURER

: MADAM NORUL AZILAH BINTI ABDUL RAHMAN

EXPERIMENT 2 TITLE: SODIUM BOROHYDRIDE REDUCTION OF CYCLOHEXANONE OBJECTIVES 1. To synthesize cyclohexanol from the reduction of cyclohexanone using sodium borohydride. 2. To characterize the reduction product using IR spectroscopy. INTRODUCTION Carbonyl group (C=O) is the key of many functional groups such as ketone, aldehyde and others. Nucleophilic addition is one of the reactions in carbonyl group. A nucleophile is an atom or molecule that donates an electron pair to make a covalent bond.[ CITATION Hel20 \l 17417 ]. This reaction occurs when a nucleophile compound attacks the C atom of the carbonyl group as carbon atom is a partial positive atom in carbonyl group. Thus, the electron at carbon-oxygen shifts to the oxygen cause the carbon atom becomes positive atom and oxygen become negative atom. Reduction of carbonyl group is one of the reactions that apply nucleophilic addition concept. Reduction of aldehydes and ketones involves the addition of nucleophilic hydride ion, H - to the polarized electrophilic carbon of C=O to form an alkoxide ion intermediate and with the help of reagent, the alkoxide ion is reduced to alcohol. There are two types of reduction reaction of carbonyl group which are catalytic hydrogenation and metal hydride reduction. In this experiment, reduction of carbonyl group used is metal hydride reduction. Metal hydride reduction have two reducing agents can be used which are sodium borohydride (NaBH4) and lithium aluminium hydride (LiAlH 4). Both reagents are sources of hydride ion as it is a very powerful nucleophile. In the experiment, a ketone is reduced to an alcohol using sodium borohydride as reducing agent. Sodium borohydride is known as selective reducing agent because it can reduce C=O of carbonyl group only. Meanwhile, lithium aluminium hydride is a stronger reducing agent which it can also reduce C=O of carboxylic acid and ester. Cyclohexanone is used as starting compound and the expected product, cyclohexanol is formed. The product is identified through IR spectroscopy.

PROCEDURE 1. 5mL of methanol was placed in a large test tube and then 2mL of cyclohexanone was added. The test tube was cooled in an ice bath. 2. 200mg of sodium borohydride was added carefully into the solution. After the rigorous reaction had ceased, the test tube was removed from the ice bath and allowed it to stand at room temperature for 10 minutes (until reaction appeared was finished). 3. To decompose the borate ester; 5mL of 3M NaOH was added. The, 4mL of distilled water was added. 4. The product was separated as a small, clear upper layer. Using a Pasteur pipette, the product was transferred (clear upper layer) to another clean and dry conical flask (50mL or 100mL). 5. The remainder of the product from the reaction mixture was extracted using two 5 mL portions of dichloromethane. 6. The dichloromethane extract was combined with the earlier product layer and dried it with anhydrous sodium sulphate. 7. Then, the solution was filtered using fluted filter paper. 8. The clear solution was transferred into a small clean and dry round bottom flask. Then, ¾ of the solvent was evaporated off using the rotary evaporator. 9. The balanced solution was transferred with a Pasteur pipet to a dry, labelled and preweighed sample bottle. The sample was capped with the aluminium foil and few small holes were made at the aluminium foil. The balance solvent was let to evaporate in a fume hood. 10. When the solvent was evaporated, the sample bottle was reweighed, and the weight of the product was determined.

RESULT AND OBSERVATIONS Results: a. Mass of cork: 17.3885g b. Volume of product: 2ml c. Weight of product: Weight of round bottom flask (g) Weight of round bottom flask + product (g) Weight of product (g)

46.3730 65.4187 1.6572

d. IR data Wavenumber (cm-1)

Type of bond (group) Cyclohexanone

1715 2850

C=O (ketone) C – H (alkane), sp3 CH Product

3400 1100

O – H (alcohol, H-bonded) C – O (alcohol)

e. Appearance of the product: sticky solid with crystal shape Observations: Steps 2

Observations The solution of methanol and cyclohexanone react vigorously when added with

2 4

sodium borohydride. The solution turned to pale yellow in colour after the reaction. Two layers of solutions were observed after the addition of borate ester, a clear

6

solution at the upper layer and cloudy layer at the bottom layer. The solution formed emulsion when been extracted.

Calculations a. Theoretical yield of the product Molar mass of cyclohexanol = 100.158g/mol No of mol of cyclohexanol 1 mol of cyclohexanone produced 1 mol of cyclohexanol Density = mass/volume 0.9478g/mol = mass / 2ml Mass = 1.8956g Theoretical yield is 1.8956g

b. Percentage yield of product percentage yield=

actual yield ×100 theoretical yield

percentage yield=

1.6572 × 100 1.8956

Percentage yield = 87.42% DISCUSSION The reduction of cyclohexanone using sodium borohydride as reducing agent to produce cyclohexanol as a product. In the experiment, cyclohexanone was mixed with methanol and let it cool in the ice bath. Then, the reducing agent, sodium borohydride was added and cause rigorous reaction. As a result, the solution turned to pale yellow in colour. To decompose the borate ester, NaOH and distilled were added. Two layers of solutions were observed after the addition of borate ester, a clear solution at the upper layer and cloudy layer at the bottom layer. The clear solution was extracted and dried it with anhydrous sodium sulphate. The anhydrous sodium sulphate role is to absorb moisture or excess water from the solution. The pure solution was then evaporated using rotary evaporator and dried it in the fume hood. The dried product undergoes the IR analysis using IR spectroscopy. Based on the reading, the product was identified as cyclohexanone. This is because O – H bond appeared at 3400-3200 cm-1 and C – O bond appeared at 1300- 1000 cm-1. Sodium borohydride (NaBH4) is noted a selective reducing agent. This is because it only can reduce C=O of ketones and aldehydes to an alcohol. The reduction by using this reducing

agent only take place in alcohol which in this experiment methanol is used as a solvent. The percentage yield is 87.42%. The error occurred during conducting this experiment may lead to an inaccurate result. The error can happen when handling the separatory funnel. When removing the clear solution of dichloromethane, accidentally the cloudy layer also exited together. This cause the correct percentage of the product cannot be obtained. Before conducting the experiment, some precaution steps should be taken by wearing PPE and be more careful in handling the dangerous chemical such as sodium borohydride. QUESTIONS 1. How do you confirm that the cyclohexanone has been reduced to cyclohexanol using IR analysis? The appearance of O – H bond in the IR spectrogram. The band is broad and the wavenumber is around 3400 – 3200 cm-1.

2. What is the function of anhydrous sodium sulphate in the experiment? To absorb the excess of water in the dichloromethane extract.

3. If you have the following compound, can you reduce the ketone using sodium borohydride without affecting the ester functional group? Explain your answer. O

O O CH 3

Yes. Sodium borohydride is a selective reducing agent. It can reduce C=O of carbonyl group only which are aldehydes and ketones. This reducing agent does not reduce C=O of ester. CONCLUSION In conclusion, the reduction of cyclohexanone using sodium borohydride produced cyclohexanol as a product. The percentage yield of cyclohexanol obtained was 87.42% which is nearly 100%. The product of the reduction reaction was identified through IR spectroscopy. Based on the IR spectrum, two important functional groups or bonds were showed. The

bonds are O – H bond appeared at 3400-3200 cm-1 and C – O bond appeared at 1300- 1000 cm-1. Thus, the objectives of this experiment are achieved. REFERENCES Helmenstine, A. (2020, January 16). Nucleophile Definition in Chemistry. Retrieved from ThoughtCo website: https://www.thoughtco.com/definition-of-nucleophile-605429 Razali, I. (2013, October 8). Sodium Borohydride Reduction of Cyclohexanone. Retrieved from Academia.com: https://www.academia.edu/11982329/Sodium_Borohydride_Reduction_of_Cyclohexa none

APPENDIX IR spectrum of cyclohexanone

IR spectrum of cyclohexanol...