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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 1 Keywords: oxidation cyclohexanol cyclohexanone oxidation cyclohexanol cyclohexanone involves removal hydrogen from group after separation purification infrared spectrum will determine composition recovered material infrared spectroscopy very powerful technique used determination molecular structure identification unknown organic materials infrared spectrum yields direct information about presence absence functional groups region spectrum which greatest interest organic chemists wavelength range micrometers which correspond approximately young when atoms molecules absorb light incoming energy excites quantized structure higher energy level type excitation depends wavelength light electrons promoted higher orbirtals ultraviolet visible light vibrations excited rotations excited microwaves tissue spectroscopy measurement wavelength intensity absorption sample absorption bands characteristic specific types chemical bonds spectrophotometer instrument which designed obtain spectra molecule spectra obtained first irradiating sample with source passes through sample solution contained within salt plate then onto detector analyzed examining frequency peaks occur different peak frequencies indicate different types vibrational motion hence different types chemical bonds peak intensities usually noted percent transmittance compares amount absorbed compared amount that absorbed frequencies normally listed wave numbers units reciprocal centimeters experiment oxidation cyclohexanol dichromate occurred presence sulfuric acid yielded cyclohexanone according balanced redox reaction below presence excess dichromate oxidizes adipic acid maximize yield following reaction prevented hooc cooh addition methanol reduced excess dichromate according balanced redox reaction below recovery ketone steam distillation collecting distillate addition sodium chloride aided suppressing solubility ketone allowing separation purify simple distillation used collecting distillate within five point boiling range that listed merck index recovered material perkin elmer will determination composition recovered material results total collected between theoretical yield follows page conclusion below from mcmurry organic chemistry distinctive absorption relevant this experiment aliphatic stretch around stretch around adipic acid from mcmurry chemistry also distinctive relevant this experiment stretch around boiling point range collected product would indicate fairly pure product indicates otherwise product shows would indicate adipic discussion process adding solution drop wise using pasteur pipette very time consuming more than likely rushed although temperature mixture during addition remained desired excess beaker would further oxidize undesired short collection time during steam distillation accounts greatest amount loss continued collection long temperature remained approximately have lead more favorable yield process purification simple appeared desired collected boiling point ideal compared published merck index composition indicates compound with least functional group present desired pure mcmurry chemistry clearly free stretching left this stretching indicates formation most likely during rushed ending final after simple most likely fact that closed system therefore pressure sensitive although above pressurized system apparently came over lower temperature works cited john brooks cole publishing company california young paul online university illinois chicago copyright tissue brian scimedia scimedia copyright Keywords General: Essay, essays, termpaper, term paper, termpapers, term papers, book reports, study, college, thesis, dessertation, test answers, free research, book research, study help, download essay, download term papers