Experiment 1 Fourier Transform Infrared Spectroscopy Ftir Analysis Of Aspirin Phenacetin Caffeine Tablet

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CHM580
SPECTROCHEMICAL METHODS OF ANALYSIS


EXPERIMENT 1:
FOURIER TRANSFORM INFRARED SPECTROSCOPY- FTIR
ANALYSIS OF ASPIRIN-PHENACETIN-CAFFEINE (APC) TABLET


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ABSTRACT
This experiment is done to identify the functional groups in IR spectra of standard compound aspirin, phenacetin and caffeine, to identify the functional groups present in aspirin-phenacetin-caffeine tablet, and to identify the functional groups present in the unknown sample. The ASA, phenacetin, caffeine, aspirin, polystyrene and unknown sample are analyzed by using IR spectroscopy in a form of solid compound. KBr pellet is used and mix with each of the compound in order to obtain the IR spectra of each of the compound. The unknown sample is determined to be benzoic acid according to its IR spectra.

OBJECTIVE
To identify the functional groups in IR spectra of standard compound aspirin, phenacetin and caffeine, to identify the functional groups present in aspirin-phenacetin-caffeine tablet and to identify the functional groups present in the unknown sample.

SAMPLE
-          Unknown sample

CHEMICALS
-          Aspirin-phenacetin-caffeine tablet (APC tablet)
-          Acetylsalicyclic acid (ASA)
-          Phenacetin
-          Caffeine
-          Aspirin
-          KBr powder

APPARATUS
-          Agate mortar and pestle
-          Spatula
-          Handpress
INSTRUMENT
Michelson Interferometer


PROCEDURE
The agate mortar and pestle was placed in the fume hood. Then, 1.0 mg of solid sample was grinded into powder in agate mortar for 1 minute. Then, 80.0 mg of KBr powder was added into the sample powder, and it was grinded again with pestle for 30 seconds. After that, the mixture was scraped into the middle with spatula, and it was grinded again for 15 seconds. Then, the mixture was heaped in the center of the mortar.

            One fourth of the KBr mixture was transferred into the collar of the handpress. Then, the anvil was placed with die pin. After that, the die set was lifted and transferred to the unit. The dial pressure was rotated until the upper ram of the handpress touched the upper anvil on the die assembled. Then, the mixture was slowly compressed for 2 minutes. Then, the unit was tilted back and the handle was opened. The die set was removed from the unit. Then the pellet was weighed. After that, the collar contained the KBr pellet was placed onto the sample holder in the sample compartment. Then, IR spectrum was obtained. After that, KBr pellet was removed from the collar and the pellet material was placed into the contained labeled “Recover KBr Pellets”. Then, the metal apparatus was washed with water and dried in the oven.


RESULTS

Table 1.1: The table of IR frequencies of the ASA from IR spectrum.
Frequency range (cm-1)
Frequency (cm-1)
Type of bond
Compound type
3300-2500
2917.28
O-H stretching
Carboxylic acid
1700
1754.72
C=O stretching
Carboxylic acid
1600-1430
1458.06
C=C stretching
Aromatic
1310-1250
1306.63
Aromatic C=O stretching
Ester

Table 1.2: The table of IR frequencies for aspirin from IR spectrum.
Frequency range (cm-1)
Frequency
(cm-1)
Type of bond
Compound type
3300-2500
2872.66
O-H stretching
Carboxylic acid
1700
1754.79
C=O stretching
Carboxylic acid
1600-1430
1458.11
C=C stretching
Aromatic
1310-1250
1306.33
Aromatic C=O stretching
Ester

Table 1.3: The table of IR frequencies for phenacetin from IR spectrum.
Frequency range (cm-1)
Frequency
(cm-1)
Type of bond
Compound type
3100-3000
2918.02
C-H stretching
Aromatic
1600-1430
1508.76
C=C stretching
Aromatic
1335-1250
1244.10
Aromatic C-N stretching
Amine
1300-1000
1046.37
C-O stretching
Ether
900-675
837.83
OOP C-H stretching
Aromatic

Table 1.4: The table of IR frequencies for caffeine from IR spectrum.
Frequency range (cm-1)
Frequency
(cm-1)
Type of bond
Compound type
1690-1640
1660.47
C=O stretching
Amide
1640-1550
1545.05
N-H bending
Amide
1360-1080
1239.35
C-N stretching
Amine

Table 1.5: The table of IR frequencies for unknown A from IR spectrum.
Frequency range (cm-1)
Frequency
(cm-1)
Type of bond
Compound type
3100-3000
3065.93
C-H stretching
Aromatic
3300-2500
2847.89
O-H stretching
Carboxylic acid
1700
1688.91
C=O stretching
Carboxylic acid
1600-1430
1423.95
C=C stretching
Aromatic
1320-1210
1291.05
C-O stretching
Carboxylic acid
900-675
707.17
OOP C-H bending
Aromatic

Table 1.6: The table of IR frequencies for polystyrene from IR spectrum.
Frequency range (cm-1)
Frequency
(cm-1)
Type of bond
Compound type
3100-3000
3026.06
3060.12
3082.25
=C-H stretching
Alkene
3100-3000
3026.06
3060.12
3082.25
C-H stretching
Aromatic
2930
2923.60
Methylene asymmetric C-H stretching
Alkane
2000-1700
1744.02
1802.59
1870.69
1943.23
Overtone and combination bands
Aromatic
1600-1430
1493.01
C=C stretching
Aromatic
1465
1452.44
Methylene scissoring
Alkane
1680-1600
1601.45
C=C stretching
Alkene
720
757.13
Methylene rocking
Alkane
900-675
697.21
OOP C-H bending
Aromatic


The structure of ASA:




The structure of Phenacetin:














The structure of Caffeine:



The structure of Aspirin:









The structure of unknown A = Benzoic Acid


DISCUSSION
Theoretically, IR Spectroscopy measures the vibrations of atoms, and based on this, it is possible to determine the functional groups. Generally, stronger bonds and light atoms will vibrate at a high stretching frequency (wavenumber). Chemical bonds in different environments will absorb varying intensities and at varying frequencies. Thus, IR spectroscopy involves collecting absorption information and analysing it in the form of a spectrum. The frequencies at which there are absorptions of IR radiation (peaks or signals) can be correlated directly to bonds within the compound. Because each interatomic bond may vibrate in several different motions which are stretching or bending, thus individual bonds may absorb at more than one IR frequency. Stretching absorptions usually produce stronger peaks than bending, however the weaker bending absorptions can be useful in differentiating similar types of bonds such as aromatic substitution. It is also important to note that symmetrical vibrations do not cause absorption of IR radiation.

From the IR spectrum of ASA and aspirin, it shows that both of them have about the same IR frequencies and types of bond present in the compound. At 2917.28 cm-1, the O-H bond absorb at this frequencies which proved the presence of carboxylic acid in the compound. This peak display very broad, intense O-H stretching absorption in the region of 3300-2500 cm-1. At 1754.72 cm-1, the C=O bond absorb at this frequency where is also indicates the presence of carboxylic acid. At frequency 1458.06, the C=C of the aromatic compound absorb at this frequency. At 1306.63 cm-1, the aromatic C=O of the ester absorb at this frequency with a very sharp band.

From the IR spectrum of phenacetin, aromatic C-H stretching bands occur between 3100-3000 cm-1, where the C-H bon absorb at 2918.02 cm-1. At 1508.76 cm-1, the C=C of the aromatic absorb at this frequency and show less intense band. In this compound, the aromatic C-N stretching of amine occurs at 1244.10 cm-1 with range frequencies of 1335-1250 cm-1. The C-O bond of the ether absorb at 1046.37 cm-1 with a frequencies range 1300-1000 cm-1. This vibrations involving oxygen atom and will result in greater dipole moment changes than those involving carbon atoms, thus more intense IR band is observed for ether. At 837.83 cm-1, the C-H out-of-plane absorb at this frequency. The out-of-plane bending of a ring hydrogen atom is strongly coupled to adjacent hydrogen atoms that will result in the position of absorption of the OOP bands.

From the IR spectrum of caffeine, the functional groups presences in this compound are amide and amine. The C=O bond of the amide absorb at 1660.47 cm-1 with frequencies range 1690-1640 cm-1, and show sharp band. While the N-H bond of the amide absorb at 1545.05 cm-1 with frequencies range 1640-1550 cm-1. The C-N bond of the amine absorb at 1239.35 cm-1with frequencies range 1360-1080 cm-1.

From the IR spectrum of the unknown A, it is proved that unknown A is benzoic acid. This is because of the presence of very broad and intense O-H stretching absorption at a region 3300-3000 cm-1. This band may overlap with the band from C-H stretching of the aromatic which absorb at region 3100-3000 cm-1. The sharp band at 1688.91 cm-1 indicate the absorption of C=O of the carboxylic acid. Another sharp band at 1291.05 cm-1indicates the absorption of C-O bond of the carboxylic acid. At 707.17 cm-1, the OOP C-H of aromatic occurs with a very sharp band.

CONCLUSION
The functional groups in IR spectra of standard compound aspirin, phenacetin and caffeine, the functional groups present in aspirin-phenacetin-caffeine tablet and the functional groups present in the unknown sample was discovered well.


REFERENCE
1.      Christian, Dasgupta & Schug (2014),  Analytical Chemistry 7th Edition, p. 614
2.      Mardiana Saaid, Gas Chromatography Lecture Notes
3.      Nor’ashikin S., Ruziyati T., Mardiana S. (2012), Analytical Separation Methods Laboratory Guide (2nd edition).
4.      Gas Chromatography, 4/10/2014, http://chemwiki.ucdavis.edu/Analytical_Chemistry/Instrumental_Analysis/Chromatography/Gas_Chromatography.

QUESTION
1.      The relationship between wavelength and wavenumber is wavelength is the distance over which the shape of the wave (a cycle) repeats. While, wavenumber is the number of full cycles in a unit distance. Their relationship is as follows:
Wavenumber  =  1/ wavelength

2.      The conditions for IR absorption to occur are there must be a net change in dipole moment in a molecule as it vibrates or rotates. Dipole moment can be observed when atoms in a molecule share electrons unequally where one atom is more electronegative than another, resulting in that atom pulling more tightly on the shared pair of electrons, or when one atom has a lone pair of electrons and the difference of electronegativity vector points in the same way. As the molecule vibrates, there is a fluctuation in its dipole moment, thus causes a field that interacts with the electric field associated with radiation. If there is a match in frequency of the radiation and the natural vibration of the molecule, absorption occurs and this alters the amplitude of the molecular vibration. This also occurs when the rotation of asymmetric molecules around their centres results in a dipole moment change, which permits interaction with the radiation field. Secondly, the liquid sampling cells must have extremely short pathlength (often fractions of a millimetre), defined by the thickness of a thin polymer film spacer.

3.      Source of IR radiation is Nernst glower and Globar source (silicon carbide rod)

4.      A) The advantage of using KBr pellet is KBr pellet is optically transparent over the range of wavelengths typically used in an IR analysis. While, the disadvantage of KBr pellet is KBr is hygroscopic, thus not easy to handle.
B) The factors caused the unsatisfactory pellet are thickness of the KBr pellet, thus light cannot penetrate through it. Secondly, less amount of sample to be analysed compared to the amount of KBr.
5.      A) The purpose for calibration of instrument is to ensure correct response of the instrument toward the sample to be analysed.
B) Polystyrene is used for calibration because it will verify the presence of peaks seen on the IR spectra and the relative intensity of the peaks.

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