Cyclohexanone Essay, Research Paper

OXIDATION OF CYCLOHEXANOL

TO CYCLOHEXANONE

The oxidation of cyclohexanol to cyclohexanone involves the

removal of hydrogen from the OH group. After separation and

purification, an Infrared Spectrum will be run to determine the

composition of the recovered material.

Infrared Spectroscopy is a very powerful technique used in the

determination of molecular structure and the identification of

unknown organic materials. The infrared spectrum yields direct

information about the presence or absence of key functional groups.

The region of the infrared spectrum which is of greatest interest to

organic chemists is the wavelength range 2.5 to 15 micrometers

which correspond to approximately 4000 to 600cm-1 (Young). When

atoms or molecules absorb light, the incoming energy excites a

quantized structure to a higher energy level. The type of excitation

depends on the wavelength of the light. Electrons are promoted to

higher orbirtals by ultraviolet or visible light, vibrations are excited by

infrared light, and rotations are excited by microwaves (Tissue).

IR spectroscopy is the measurement of the wavelength and

intensity of the absorption of infrared light by a sample. The

wavelength of IR absorption bands are characteristic of specific types

of chemical bonds.

An IR spectrophotometer is an instrument which is designed to

obtain an infrared spectra of a molecule. An IR spectra is obtained by

first irradiating a sample with an IR source of light. The light passes

through the sample, which can be in solution or contained within a

salt plate, and then onto an IR light detector. The spectrum is

analyzed by examining at which frequency the peaks occur. Different

peak frequencies indicate different types of vibrational motion and

hence, different types of chemical bonds. The peak intensities are

usually noted as percent transmittance which compares the amount of

light absorbed compared to the amount of IR light that was not

absorbed. The frequencies are normally listed in wave numbers (in

units of reciprocal centimeters).

Experiment

The oxidation of cyclohexanol by dichromate occurred in the

presence of sulfuric acid which yielded cyclohexanone according to the

balanced redox reaction below:

3 + Cr2O7-2 + 8H+ –> 3 + 2Cr+3 + 7H2O

In the presence of excess dichromate, cyclohexanol oxidizes to adipic

acid. To maximize yield, the following reaction was prevented:

3 + 4Cr2O7-2 + 32H+ –> 3HOOC(CH2)4COOH + 8Cr+3 + 19H2O

The addition of methanol reduced the excess dichromate according to

the balanced redox reaction below:

CH3OH + Cr2O7-2 + 8H+ –> CO2 + 2Cr+3 + 6H2O

Recovery of the ketone was by steam distillation; collecting all

distillate to 100.C. Addition of sodium chloride aided in suppressing

the solubility of the ketone, allowing for separation. To purify the

cyclohexanone, simple distillation was used collecting the distillate

within a five point boiling range of that listed in the Merck Index.

An Infrared Spectrum of the recovered material on the

Perkin-Elmer Spectrum RXI FT-IR will aid in the determination of the

composition of the recovered material.

Results

A total of 10.31g of the recovered material was collected

between 153.C and 155.5.C, for a theoretical yield of 55%. The

Infrared Spectrum of the sample follows on page 4.

Conclusion

The Infrared spectrum for cyclohexanone below, from McMurry s

Organic Chemistry has two distinctive absorption s relevant in this

experiment, the aliphatic C-H stretch around 2900 cm-1 and the C=O

stretch around 1750 cm-1.

The Infrared spectrum for adipic acid below, from McMurry s

Organic Chemistry also has two distinctive absorption s relevant in

this experiment, the C=O stretch around 1750 cm-1 and the O-H

stretch around 3000 cm-1.

The boiling point range of the collected product would indicate a

fairly pure sample. The Infrared spectrum of the recovered product

indicates otherwise. The Infrared spectrum for the recovered product

shows an O-H stretch which would indicate the presence of adipic

acid.

Discussion

The process of adding the dichromate solution drop wise using a

Pasteur pipette was very time consuming and more than likely

rushed. Although the temperature of the mixture during the addition

of dichromate remained in the desired range of 27.C and 35.C, the

presence of excess dichromate in the reaction beaker would further

oxidize the cyclohexanol to adipic acid, the undesired product.

The short collection time during steam distillation accounts for

the greatest amount of product loss. Continued collection for as long

as the temperature remained approximately 100.C would have lead to

a more favorable yield.

The process of purification by simple distillation appeared to

indicate the product was the desired cyclohexanone as the collected

boiling point range of 153.C to 155.5.C is an ideal range compared to

the published boiling point range in the Merck Index of 155.6.C.

The composition of the recovered product indicates the presence

of a compound with at least one functional group not present in the

desired material. The Infrared spectrum of pure cyclohexanone from

McMurry s Organic Chemistry is clearly free of any O-H stretching

left of 3000 cm-1. The presence of this OH stretching in the

recovered product indicates the presence of adipic acid. The

formation of the adipic acid was most likely during the rushed addition

of dichromate. The adipic acid ending up in the final product after

simple distillation is most likely due to the fact that distillation is a

closed system and therefore pressure sensitive. Although the boiling

point of adipic acid is above 300.C, in the pressurized system, adipic

acid apparently came over at a lower temperature.

Works Cited

McMurry, John. Organic Chemistry. Brooks/Cole Publishing Company.

4th ed. California, 1995.

Young, Paul R. Organic Chemistry Online. University of Illinois at

Chicago. Copyright 1996.

Tissue, Brian M. SCIMEDIA. WWW. SCIMEDIA.COM. Copyright 1996.