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TOCyclohexanone OXIDATION OF CYCLOHEXANOL TO CYCLOHEXANONE The oxidation of cyclohexane to cyclohexane 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 600 cm- 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 orbitals 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 cyclohexane by dichromate occurred in the presence of sulfuric acid which yielded cyclohexane according to the balanced redox reaction below: 3 + Cr 2 O 7 - 2 + 8 H+ > 3 + 2 Cr In the presence of excess dichromate, cyclohexane oxidizes to adipex acid. To maximize yield, the following reaction was prevented: 3 + 4 Cr 2 O 7 - 2 + 32 H+ > 3 HOOC (CH 2) 4 COOH + 8 Cr+ 3 + 19 H 2 O The addition of methanol reduced the excess dichromate according to the balanced redox reaction below: CH 3 OH + Cr 2 O 7 - 2 + 8 H+ > CO 2 + 2 Cr 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 cyclohexane, 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. 31 g 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 cyclohexane 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 adipex 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 adipex 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 cyclohexane to adipex 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 cyclohexane 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 cyclohexane 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 adipex acid. The formation of the adipex acid was most likely during the rushed addition of dichromate. The adipex 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 adipex acid is above 300. C, in the pressurized system, adipex acid apparently came over at a lower temperature. Works Cited McMurry, John. Organic Chemistry. Brooks/Cole Publishing Company. 4 th 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.
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