Download OXIDATION OF CYCLOHEXANOL TO CYCLOHEXANONE The

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
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