SODIUM BOROHYDRIDE REDUCTION OF CYCLOHEXANONE PDF

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FACULTY OF APPLIED SCIENCE Bachelor of Science (Hons.) Chemistry (Forensic Analysis)

CHM557 ORGANIC CHEMISTRY

LABORATORY REPORT

NAME

:

NUR FATINI AMEERA BINTI MOHAMMAD FAIZUL

STUDENT ID

:

2020985261

GROUP

:

AS2533B3

EXPERIMENT TITLE

:

SODIUM BOROHYDRIDE REDUCTION OF CYCLOHEXANONE

DATE OF EXPERIMENT :

30 OCTOBER 2020

DATE OF SUBMISSION

:

13 NOVEMBER 2020

LECTURER’S NAME

:

PROF. DR. NORIZAN AHMAT @ ABDUL HAMID

OBJECTIVE 1. To synthesize cyclohexanol from the reduction of cyclohexanone using sodium borohydride. 2. To characterize the reduction product using IR spectroscopy.

INTRODUCTION Aldehydes and ketones have carbonyl group which plays an important role in determining the chemistry of these functional groups. This is due to the polarity of the carbonoxygen bond that makes the direction of attack of many reagents can be predicted. The reaction of carbonyl group is nucleophilic addition which the nucleophile attacks partial positive carbon, making the electron shifts to the oxygen and become negative. This experiment shows the reduction of ketone to alcohol. Metal hydride reagents such as lithium aluminium hydride, LiAlH4 and sodium borohydride, NaBH4 are the reducing agents for ketones. The most convenient reducing agent is NaBH4 because it is not sensitive to moisture and does not further reduce the product like LiAlH4. LiAlH4 is stronger reducing agent than NaBH4 and can reduce most carbonyl containing compounds including esters, carboxylic acids and amides. It is also can react vigorously in water which makes it dangerous to work with. Hence, NaBH4 will be used in this experiment to reduce cyclohexanone to cyclohexanol.

cyclohexanone

sodium borohydride

cyclohexanol

PROCEDURE

5 mL of methanol was placed in a large test tube and then 2 mL of cyclohexanone was added. The test tube was cooled in an ice bath.

200 mg of sodium borohydride was carefully added into the solution. After the rigorous reaction has ceased, the test tube was removed from ice bath and allowed it to stand at room temperature for 10 minutes until the reaction appeared to be finished.

The remainder of the product was transferred into a separatory funnel. The remainder of the product was extracted from the reaction mixture using 5 mL of dichloromethane. The dichloromethane layer (bottom layer) and the aqueous layer (upper layer) was separated. This step was repeated for two times.

The dichloromethane layer was combined with the earlier product layer (clear upper layer) and dried with anhydrous sodium sulphate. Fluted filter paper was used to filter the solution and the solution was cleared after the filtration.

The sample bottle was reweighed when the solvent was evaporated, and the weight of the product was determined. The percentage yield of the product was calculated.

The IR spectrum of the product and cyclohexanone were obtained.

5 mL of 3M of NaOH solution was added to decompose the borate ester. Then, 4 mL of distilled water was added. The product separated as a small, clear upper layer. Using a Pasteur pipette, the product was transferred to a 50 mL beaker.

The solution was transferred into a small clean and dry round bottom flask and evaporated off the solvent (dichloromethane) using the rotary evaporator. The balanced solution was transferred with a Pasteur pipet to a dry, labelled and pre-weighed sample bottle. The sample was capped with the aluminium foil and a few small holes was made at the aluminium foil. The balance solvent was let evaporated off in a fume hood.

RESULTS a.

Volume of cyclohexanone

b.

Weight of product:

c.

2 mL

Weight of empty sample bottle (g)

43.9982 g

Weight of sample bottle + product (g)

45.5002 g

Weight of product (cyclohexanol) (g)

1.502 g

IR data (in Table): i.

ii.

d.

:

Cyclohexanone Wavenumber (cm-1)

Type of bond (group)

1740

C=O

2935 and 2850

C(sp3)-H

Product Wavenumber (cm-1)

Type of bond (group)

3350

O-H

1070

C-O

2935 and 2850

C(sp3)-H

1450

C-H2

Appearance of the product

:

______pale yellow______

OBSERVATIONS 1. The solution of methanol and cyclohexanone react vigorously when added with sodium borohydride. 2. The solution turned to pale yellow in colour after the reaction. 3. Two layers of solutions were observed after the addition of borate ester: a clear solution at the upper layer and cloudy solution at the bottom layer. 4. The solution formed emulsion when been extracted.

CALCULATIONS 1. Calculate the theoretical yield of product. Cyclohexanone + NaBH4 → Cyclohexanol 1 mole of cyclohexanone

=

1 mole of cyclohexanol

Mass of mol cyclohexanone

=

0.948 g/ml x 2 ml

=

1.896 g

=

1.896 𝑔 98.15 𝑔/𝑚𝑜𝑙

=

0.01932 moles

Number of mol cyclohexanol

=

0.01932 moles

Mass of cyclohexanol

=

0.01932 moles x 100.158 g/mol

=

1.9348 g

Number of mol cyclohexanone

2. Calculate the percentage yield of product. Mass of cyclohexanol obtained

=

Percentage yield of cyclohexanol

= =

3. Draw the mechanism for this reaction.

1.502 g 1.502 𝑔 1.9348

x 100

77.63 %

4. Discuss the IR spectrum given based on the absorption characteristics of functional groups in cyclohexanol. Cyclohexanol have four functional groups that can be seen in IR spectrum. Firstly, there is a distinct broad at 3350 cm-1 that represents O-H stretching mode of alcohols. The breadth of this signal is a consequence of hydrogen bonding between molecules. The next key absorption peak is from a strong and sharp peak at 1070 cm-1. This region is a dead giveaway for the presence of C-O group. Next, there are two peaks of C(sp3)-H hybridized stretches at 2850 cm-1 and 2935 cm-1 and C-H2 stretching at 1450 cm-1.

DISCUSSION In this experiment, cyclohexanone was reduced to cyclohexanol by the transfer of a hydride ion that act as a nucleophile from sodium borohydride, NaBH4 to the carbonyl group. The theoretical yield of cyclohexanol was calculated to determine the percentage yield of the product. The percentage yield of the product is 77.63%. This shows that there were some errors occurred throughout the experiment. Some cyclohexanol might still left in the discarded solution during the transferring process using Pasteur pipette. Methanol was used to detect the reactivity of NaBH4 because cyclohexanone and cyclohexanol have different solubility in water. NaBH4 can be used to reduced cyclohexanone to cyclohexanol if there is vigorous reaction and it must be cooled in an ice bath to prevent explosion. Extraction step should be done using dichloromethane and dried with anhydrous sodium sulphate to remove traces of water from cyclohexanol. Dichloromethane was used rather than ether because it is a polar solvent. Cyclohexanol is a polar compound thus, a polar solvent is needed to remove the traces of water. Dichloromethane was evaporated off from cyclohexanol using the rotary evaporator and the balance of dichloromethane was let evaporated off in a fume hood.

CONCLUSION The percentage yield of cyclohexanol is 77.63 %. The IR spectrum showed a broad absorption peak at 3350 cm-1 belonged to a hydroxyl group, confirming this experiment has successfully reduced a ketone to an alcohol.

QUESTIONS 1. How do you confirm that the cyclohexanone has been reduced to cyclohexanol using IR analysis? (1m) By observing the broad peak of O-H band between 3200-3600 cm-1. 2. What is the function of anhydrous sodium sulphate in the experiment? (1m) It is a drying agent that remove traces of water from cyclohexanol solution. 3. If you have the following compound, can you reduce the ketone using sodium borohydride without affecting the ester functional group? Explain your answer. (2m) O

O OCH3

Yes, sodium borohydride can reduce aldehydes and ketones to corresponding alcohol without affecting the ester functional group. This is because it is not reactive to esters and carboxylic acids.

REFERENCES Ashenhurst, J. (2020, January 29). Reagent Friday: Sodium Borohydride (NaBH4). Retrieved from Master Organic Chemistry: https://www.masterorganicchemistry.com/2011/08/12/reagent-friday-sodiumborohydride-nabh4/ Hero, C. (n.d.). Analyzing Infrared Spectra. Retrieved from Course Hero: https://www.coursehero.com/sg/organic-chemistry/analyzing-infrared-spectra/ Razali, I. (2013). Sodium Borohydride Reduction of Cyclohexanone. Retrieved from Academia.edu: https://www.academia.edu/11982329/Sodium_Borohydride_Reduction_of_Cyclohexa none

APPENDIX 1 IR spectrum of Cyclohexanone and Cyclohexanol (label the important absorption peaks)...