ORGANIC CHEMISTRY IICHM556

EXPERIMENT 2

SODUIM BOROHYDRIDE REDUCTION OF CYCLOHEXANONE

NAME:(MELLISA ANASTASHIYA)

2013727337

PARTNER’S NAME:LESSIE ANNE JOSEPH

DATE OF EXPERIMENT:

09TH OCTOBER 2014

DATE OF SUBMISSION:

16TH OCTOBER 2014

UNIVERSITI TEKNOLOGI MARAUiTM SHAH ALAM

FACULTY OF APPLIED SCIENCE

OBJECTIVE OF THE EXPERIMENT

1. To investigate the reduction reaction of a cyclohexanone to a cyclohexanol by

using the sodium borohydride as the reducing agent.

2. To determine the percent yield of product ( cyclohexanol ) obtained.

INTRODUCTION

Nucleophilic substitution is one of the important reaction when dealing with

carbonyl group. Nucleophilic substitution reaction occur at sp3-hybridized carbon,

which is the nucleophile replaces a leaving group bonded to the electrophilic

carbon. The carbon said to be electrophilic when the leaving group that bonded

to the carbon is being more electronegative. Thus, carbon of a carbonyl group is

an electrophilic due to the electronegativity of the oxygen.

The carbonyl group can be reduce to alcohol by addition of hydride and

perform the nucleophilic substitution, since hydride is a powerful nucleophile and

gives irreversible reaction (Joseph, 2006). Reduction can be defined as a

decrease in the oxygen content or an increase in the hydrogen content of a

compound.

In this experiment, cyclohexanone reduce to cyclohexanol by using the

reducing agent sodium borohydride (NaBH4). Cyclohexanone and cyclohexanol

are the organic compound with the formula (CH2)5CO and C6H12O respectively.

EXPERIMENTAL PROCEDURE

The experiment was started with 5 ml of methanol which were placed in a

large test tube,then added with 2 ml of cyclohexanone. The solution was allowed

to cool in an ice bath.

200 mg sodium borohydride was added to the solution with care. The test

tube was removed from ice bath after the vigorous reaction has ceased and

allowed to stand at room temperature for 10 minutes. 5 ml of 3M NaOH was

added into the solution to decompose the borate ester, then added by 4 ml of

water.

The solution allowed to separate into two layer which is the upper layer

should be a small and clear layer that appeared as product. Then, the product

was transferred in a clean test tube by using a Pasteur pipette.

The remainder of the product from the reaction mixture was transferred in a

separatory funnel. Two 5 ml portion of dichloromethane was added into the

separatory funnel to extract the mixture.

The dichloromethane extract was combined with the earlier product layer and

dried with anhydrous sodium sulphate. Then, it was transferred into a small

cleaned pre weighed round bottomed flask and evaporated by using the rotary

evaporator. The weight of flask was taken before and after evaporated. The IR

spectrum for the product was obtained by using liquid sampling technique.

RESULTS AND OBSERVATIONS

Table 1.0 : tabulation of data obtained

Weight of empty flask, g 53.2566

Weight of flask and product before evaporated, g

58.1425

Weight of flask and product after evaporation, g

54.4517

Weight of cyclohexanol, g

= ( 54.4517 - 53.2566 ) = 1.1951

Theoretical value, g 1.9330

Actual value, g 1.1951

The result for IR spectrum shown in diagram 1.1. Observations:

The solution of methanol and cyclohexanone react vigorously when added with sodium borohydride. The solution turned to pale yellow in colour after the reaction.

The small portion and clear upper layer formed after the addition of 5ml, 3M of sodium hydroxide and 4ml of water.

CALCULATIONS

Cyclohexanone, C6H10O

Density = 0.9478 g/ml

Volume = 2ml

Mass = 0.947g/ml x 2ml

= 1.8956 g

Molar mass = 98.15 g/mol

No. Of moles =

= 0.0193 moles

No. Of moles of cyclohexanol = no. Of moles of cyclohexanone = 0.0193 moles

Molar mass of cyclohexanol = 100.158 g/mol

Theoretical mass of cyclohexanol = no of moles x molar mass

= 0.0193 moles x 100.158 g/mol

= 1.9330 g

Therefore,

Percent yield % =

=

= 61.8 %

1.8956 g98.15 g/mol

Actual Theoretical

1.1951 1.9330

DISCUSSION

The purposes of the experiment are to investigate the reduction reaction of a

cyclohexanone to a cyclohexanol by using the sodium borohydride as the

reducing agent and to determine the percent yield of product (cyclohexanol) that

obtained. Cyclohexanone is a carbonyl group that acts as electrophilic with high

electronegativity of oxygen atom bonded to the carbon. In order to reduce the

cyclohexanone to the cyclohexanol, it is needed to use the addition of hydride to

the solution, because hydride is a powerful nucleophile that attacks the

electrophile and replaces the leaving group in electrophilic carbon. The

mechanism of chemical reaction is as shown below;

The hydride nucleophile from NaBH4 attack only electrophilic carbon. In the

first step, the hydrogen H+ detaches from the BH4 and added to the

cyclohexanone which is forms the C-H bond and breaks the C-O bond, resulting

in new lone pair on the oxygen that makes the oxygen negatively charged

( called as alkoxides ). The proton from methanol is added to the alkoxides to

form the cyclohexanol.

The mass of cyclohexanol that was obtained is 1.1951g and the theoretical

value is 1.9330g. Thus, the percent yield is 61.8%. Based on the percent yield,

the percent is quite small due to some errors. The amount of chemicals were

taken probably does not measured accurately. Other than that, may be there is a

contaminant in the solution.

Based on the IR spectrum analysis, the absorption band for the alcohol (OH)

bond is at 3368.46 cm-1 and the band is broad compared to others bands in the

spectrum since alcohols are characterized by a strong and very broad absorption

in the 3550-3200 cm-1 region due to the hydrogen bonded OH group (Joseph,

2006). The spectrum also shown the sp3-hybridized CH absorption bands which

is at 2855.01 cm-1 . It is also show a strong band for the CO bond in the 1300-

1000 cm-1 region, although this absorption is difficult to identify because it occurs

in the fingerprint region with many others bands. However, in the spectrum there

is still a carbonyl group band was detected which is at 1646.95 cm-1, this is

because of the errors that have been mentioned above.

CONCLUSION

The reduction reaction of cyclohexanone was performed and the expected

product was obtained which is cyclohexanol. The mass of product obtained is

1.1951g and the calculated theoretical value is 1.9330g. The percent yield is

61.8%. The IR spectrum analysis was shown that there is an alcohol in the final

product.

QUESTIONS

1. What products do you expect if you reduce 2-butanone and 3-pentanone with

NaBH4 methanol.

Reduction of 2-butanone

Reduction of 3-pentanone

2. Compare the reductive abilities of lithium aluminum hydride, LiAlH4 with those

of sodium borohydride, NaBH4 .

sodium borohydride, NaBH4 lithium aluminum hydride, LiAlH4

Cannot reduced C=C to C-C Can reduced alkene to alkane

Cannot reduced carboxylic acid to

alcohol

Can reduced carboxylic acid to alcohol

Cannot reduced ester to alcohol. Can reduced ester to alcohol.

REFERENCES

Joseph,M.Hornbck. (2006). Organic chemistry, 2nd edition. University of Denver

: physical sciences.

Donal L. Pavia ; Randall G Engel. (2013). Approach to organic laboratory

techniques, 5th edition : Belmont/Cole.

Laboratory techniques:

The techniques involved are;

1. Extraction

2. Separation

3. Distillation

4. Evaporation

5. IR analysis