Sodium Boronhydride Reduction of Cyclohexanone

CHM 556 (ORGANIC CHEMISTRY II) Laboratory Report Experiment 2: Sodium Boronhydride Reduction of Cyclohexanone

Objective 1. To synthesize cyclohexanol from cyclohexanone by using reduction reaction with sodium borohydride. 2. To determine the percentage yields of product produced.

Introduction In organic chemistry, a ketone is a compound with the structure RC (=O) R', where R and R' can be a variety of atoms and groups of atoms. It features a carbonyl group (C=O) bonded to two other carbon atoms. The carbonyl group is polar as a consequence of the fact that the electronegativity

of

Thus, ketones are

the

oxygen

nucleophilic

center is greater than that for carbonyl carbon.

at

oxygen and

electrophilic

at carbon.

Because the carbonyl group interacts with water by hydrogen bonding, ketones are typically more soluble in water than the related methylene compounds. Ketones are a hydrogen-bond acceptors.

Ketones

are

not

usually

hydrogen-bond

donors

and cannot hydrogen-

bond to itself. Because of their inability to serve both as

hydrogen-

bond donors and acceptors, ketones tend not to "self-associate" and are more

volatile

than

alcohols and carboxylic acids of comparable molecular weights. These factors relate to pervasiveness

of

ketones

in

perfumery

and

Sodium borohydride, also known as sodium tetrahydridoborate, is an

as

solvents.

inorganic compound

with the formula NaBH4. This white solid, usually encountered as a powder, is a versatile reducing agent that finds wide application in chemistry, both in the laboratory and on a technical scale. Large amounts are used for

bleaching

wood pulp. The compound is

insoluble inether , and soluble in glyme solvents, methanol and water, but reacts with the latter two in the absence of base.

Material and apparatus Test tubes, ice bath, pipette, pre weighed round bottom flask, separatory funnel, rotoevaporator, IR machine, balance Chemical Methanol(CH3OH), cyclohexanone, sodium boronhydride, NaOH solution, dichloromethane, anhydrous sodium sulphate

Procedure 1. A 5ml of methanol followed by 2ml of cyclohexanone were placed in large test tube. The mixture was cooled in the ice bath and added to sodium borohydride (200mg). A vigorous, bubbling reaction took place for several minutes. 2. After the reaction ceased, removed the test tube from ice bath and allowed it to cold at room temperature. Sodium hydroxide (5mL) was added to the solution to decompose the borate ester, leaving a cloudy solution. 3. Water (4mL) was added, allowing the product to separate as a mostly clear upper layer. 4. The layer was removed by using Pasteur pipette and transfer it into a clean test tube and then two successive methylene chloride (5mL each) additions were used to extract the remaining product (in the bottom layer). 5. The recovered products were dried using anhydrous sodium sulphate and the methylene chloride was subsequently boiled away using rotoevaporator. During the boiling, methylene chloride vigorously formed bubbles and carried some product away. 6. Reweight the flask and calculate the percentage yield of product.In further experiments, temperature must be more carefully moderated, or a larger flask must be used. 7.

IR spectrum and gas chromatography were conducted with the product.

Results Mass round-bottom flask Mass sodium boronhydride Mass Round-bottom flask + cyclohexanone Mass of cyclohexanon Mass Round-bottom flask + cyclohexanol Mass cyclohexanol (only)

= 41.72 g = 0.2 g = 44.5 g = 2.78g = 44.18 g = 2.46g

Observations 1. The solution of methanol and cyclohexane react vigorously when added with sodium borohydride. 2. The solution turned to pale yellow in color after the reaction.

3. The solution formed two layer when decompose borate ester which is clear at upper layer and cloudy at the bottom layer. 4. The solution formed emulsion when been extracted.

Calculations Mass of cyclohexanone obtained

= 2.78 g

Mole of cyclohexanone

= (mass / molar mass) = (2.78/98.14) = 0.0283 mol

1 mol of cyclohexanol

= 1 mol of cyclohexanone

mole of cyclohexanol

= 0.0283 mol

Theoretical mass of cyclohexanol : = mole x molar mass = 0.0283 x 100.6 = 2.847 g Percent yield of cyclohexanol

= (actual/theoretical) x 100 = (2.46/2.847) x 100 = 84.41 %

Discussion Ketone is actually a compound with the structure RC(=O)R', where R and R' are variety of atoms and groups of atoms. In this experiment, cyclohexanone was reduced to cyclohexanol by sodium borohydride (NaBH4). Sodium borohydride, also known as sodium tetrahydridoborate, is an inorganic compound with the formula NaBH4, act as drying agent for any solution. The actual yield and theoretical yield of cyclohexanol were calculated in

order to determine the percentage yield of the compound. Based on the calculation, the percentage yield that had obtained was 84.41 %. Also, IR spectrum’s reading had been obtained.

Theoretical Yield

Actual Yield

2.847 g

2.46 g

Table A: Product Yield The IR spectrum indicated that the product was purely an alcohol, showing a large valley centred on wavenumber 3600, and revealed no structure around wavenumber 1750, where the ketone group was found in the reactant IR (see Table B). Group (assumed)

Wavenumber (cm-1)

Ketone (reactant IR) Alcohol (product IR) Carbon Fingerprints

1750 3343.72 2929.34

Table B: IR Spectrum Anomalies

Conclusion As a conclusion, ketone group (like cyclohexanone) can be converted to alcohol group (like cyclohexanol) by using reduction reaction by sodium tetrahydridoborate (NaBH4). In this experiment was highly successful in reducing the ketone group of cyclohexanone to an alcohol group using sodium borohydride. . It was determined that in this scenario, the thermodynamic product is generously favored. The procedure was simple and repeatable; refinements should improve the percent yield. This was a valuable experiment that utilized important analytical tools like the IR scan.

References

1. Donald L.Pavia et al (2011), Introduction to Organic Laboratory Techniques, Cengage Learning 2. Indian Journal of Chemistry (2006), Reduction Of Carbonyl Compounds With Sodium Borohydride, Retrieved on 2013,June 03, from www. nopr.niscair.res.in