Vibrational Spectral Studies of Nicotinium picrate
S. Jegannathan*1, M. Briget Mary2, V. Ramakrishnan1, S. Thangadurai3
1Department of Laser Studies, School of physics, Madurai Kamaraj University, Madurai,-625021, India
2Post Graduate Studies and Research Department of Physics, Lady Doak College, Madurai,-625021, India.
3Post Graduate Studies and Research Department of Chemistry, Raja Doraisingam Government Arts College, Sivagangai-630 561, India.
*Corresponding Author E-mail: drstdurai@gmail.com
ABSTRACT:
This article describes the vibrational spectra of nicotinium picrate. The Infrared and Raman Spectra were recorded at room temperature for nicotinium picrate and the observed bands were assigned. In nicotinium picrate compound nicotinium is the cation and picrate forming the anion. The N−H···O and O−H···N hydrogen bonds were observed in both infrared and Raman spectra. The structure is also stabilized by C−H···O hydrogen bonding. These hydrogen bonds link the layers of cation with the layers of anions. Nicotinic acid is also known as 3-pyridine carboxylic acid. Picrate being the trinitrophenolate has the characteristic bands of phenol. The nitro group and the phenoxy group stretching are observed in both infrared and Raman spectra. These suggest that the picrate ion is unaffected by the presence of the cations. Factor group analysis has been made and the numbers of vibrational modes have been calculated. The tentative assignments of the observed bands are given.
KEYWORDS: Nicotinium picrate; Infrared spectra; Raman spectra, Intermolecular hydrogen bonding, factor group analysis.
INTRODUCTION:
Nicotinic acid (3-pyridine carboxylic acid), is a B-vitamin also known as niacin and its associated complexes have a variety of pharmacological properties. Niacin forms coordination complexes1 with tin (Sn) which has been found to have better antitumor activity than the well known cis-platin or doxorubicin.
Nicotinium picrate is under the group of pyridine and piperidine and it is distributed in plants. The best source is the coffee bean. Nicotine is a classical alkaloid and the separation of which teaches the main principles of alkaloid isolation2 consisting of a combination of two tertiary amines of which the pyrrolidine is the stronger basic one, nicotine is protonated in the plant and forms carboxylate salts such as formate, acetate or maleate.
Therefore, the first and typical step is to bring the alkaloid into a distinctively strong alkaline environment, such as NaOH solution to cleave the organic salts and release free nicotine into the aqueous solution.
Nicotine is readily soluble in water due to its ability to act as an acceptor for hydrogen bonds to water. Another useful property is its volatility with water vapour. This allows steam distillation to be used for a very selective separation of nicotine from many other water-soluble tobacco constituents. In the distillate, the alkaloid is protonated by addition of hydrochloric acid and the nicotinium ions formed are precipitated by addition of sodium picrate solution. The yellow nicotinium picrate formed is pure. To obtain the free alkaloid base, a second alkaline cleavage as with the starting tobacco is necessary with the nicotinium picrate. The free base is extracted from the basic solution with diethyl ether and finally purified by a distillation in vacum.
Unfortunately, it is not possible to avoid that in the final ether extraction, together with nicotine a small portion of picrate acid/picrate in water is extracted into the ether which is able to take up a few percent of an aqueous solution. This requires a final distillation to separate pricric acid and nicotine. Though nicotine shows remarkable thermal stability and can in principle be distilled at ambient pressure (b.p.246−248°C), for a small amount as above a distillation in vacuums recommended. The refractive index could be measured with a single drop to avoid loss of material. The loss of more than half of the nicotine subjected to the last step is a strong hint at the high solubility of nicotine in water and the small partitioning coefficient with ether.
EXPERIMENTAL:
Nicotinium picrate crystals are grown by the slow evaporation method at room temperature from an aqueous solution of nicotinic acid with a 1:1 stoichiometric ratio. The grown crystals3 are colourless and needle shaped. Infrared spectral measurements are carried out with a Bruker IFS66V and Fourier transform infrared (FTIR) spectrometer is used for IR spectral measurement. The samples were prepared by the pellet technique and the spectrum was recorded in 3500-400 cm-1 range. Raman spectral measurements are made with the facility at IIT Chennai with a krypton ion laser (647.1 nm) (FRA 106 Raman module). The spectrum was recorded over the range 50-3500 cm-1. All the experiments were carried out at room temperature. For confirming the reliability of the data, Raman spectral measurements4 were also made using the facility available in our laboratory. The excitation source in the Raman measurements were 488 nm radiations from spectra physics model 2020-04S Argon-ion laser.
A suitable notch filter is placed before the monochromator to suppress the Rayleigh line. The scattered light is dispersed with a grating monochromator and detected with a thermo electrically cooled RCA-GaAs photomultiplier tube. A PC was interfaced through a data acquisition add-on card to record this spectrum. The laser power is maintained at 70 mW. This instrument has a resolution of ~2-3 cm-1.
RESULTS AND DISCUSSION:
The nicotinium picrate belongs3 to a space group P1-C containing C6H6NO2+ cation. The picrate C6H2N3O7- ion (2,4,6-tri nitro phenolate) forms the anion. The numbers of modes of the crystal nicotinium picrate are determined5 by group theory analysis using the correlation method based upon the symmetry of the atoms. The results obtained are presented in Table 1. The total set of optical vibrational modes of nicotinium picrate crystal lattice is distributed as;
Гcrystal = Гcrystal − Гacoustic = 99 AgIR,R + 138 AuIR
TABLE 1: FACTOR GROUP ANALYSIS OF NICOTINIUM PICRATE
SPACE GROUP P1- = Ci Zb=2
|
Nicotinium |
Mode of freedom for each species |
Site symmetry C1 |
Factor group species Ci |
|
Nicotinium C6H6NO2+ |
Vibrational 78 Translational 6 Liberation 6 |
A A A |
39 Ag + 39 Au 3 Ag + 3 Au 3 Ag + 3 Au |
|
Picrate C6H2N3O7- |
Vibrational 96 Translational 6 Liberation 6 |
A A A |
48 Ag + 48 Au 3 Ag + 3 Au 3 Ag + 3 Au |
ГTotal Crystal = Г C6H6NO2+ + Г C6H2N3O7- = 99 AgIR,R + 99 AuIR
ГVibration = 87 AgIR,R + 87 AuIR
ГTransition = 6 AgIR,R + ^ AuIR
ГRotation = 6 AgIR,R + 6 AuIR
ГOptical Crystal = ГTotal Crystal − Гacoustic = 99 AgIR,R + 96 AuIR
Crystal Structure of nicotinium picrate
The compound, C6H6NO2+·C6H2N3O7-, is the picrate salt of the nicotinium cation. In the picrate anion, the ortho nitro groups are twisted out of the plane of the ring, whereas the para nitro group lies approximately in the ring plane. Hydrogen bonds from the nicotinate cation link two different picrate anions, forming a straight chain along the b axis. The picrate anions are stacked in columns along [010]
In the structure of nicotinium picrate, the H atom of the hydroxyl group of picric acid has been transferred to the N atom of nicotinic acid, leading to the formation of a molecular complex. The bond lengths and bond angles in the pyridine ring of the nicotinium cation are comparable to the average values of 1.38Å for the C-C bonds and 1.33Å for the C-N bonds found in dinicotinamidium squarate6 and nicotinoylglycine7. A comparison of equivalent bond distances involving the pyridine ring atoms of nicotinium picrate with the values found in nicotinic acid shows that the positive charge is localized on the pyridine N atom and does not have much effect on the ring structure. These distances also compare well with those for 6-aminonicotinic acid hydrochloride8 and dinicotinamidium squarate6.
The nicotinium cation is planar, and the planes of the nicotinium cation and the ring of the picrate anion are inclined to one another. The torsion angles involved the ortho-related nitro groups are in the picrate anion. Hence, it has been found that in most picrates the ortho-related nitro groups, which are commonly involved in hydrogen-bonding interactions, are more likely to be rotated out of the molecular plane than the para nitro substituent9. Here, even though one of the ortho nitro groups is not involved in hydrogen bonding, it is still twisted from the plane of the ring, while the para nitro group lies approximately in the ring plane. It is also found that the twisting of these nitro groups is independent of C-N bond distances10. The nitro O atoms which are not involved in hydrogen bonding have large values. In the crystal structure, the cations and anions are linked by strong N−H···O and O−H···O bonds. The structure is also stabilized by C−H···O hydrogen bonding. It is shown in figure1.
Fig.1. Crystal Structure of Nicotinium picrate
In crystal structure of nicotinium picrate the C-H group carried by the nitrogen atom is in an equatorial position, that is to say, they are in antibonded in respect to the pyridine ring. The C-C-C-C dihedral angle corresponds to a roughly perpendicular orientation10 of the pyridine and pyrrolidine ring.
Vibrations of Nicotinium picrate
The nicotinium picrate crystals have functional groups and skeletal groups such as C-H, N-H, C-O, COOH and NO2 ring structure etc. A careful look at the spectrum of infrared of nicotinium shows a very weak band in the region 3400-3100 cm-1 shows O-H, C-H, NH, stretching vibration. Initially the first peak at 3442 cm-1 due to O-H stretching.11 Usually the medium band C=O stretching occurs at 1726 cm-1 in IR and 1717 cm -1 in Raman were confirmed12. In the infrared region C-N stretching at 1675 cm-1. In the case of nicotinium picrate the degeneracy of this medium band is formed at C-C ring structure at 1635 cm-1 in the infrared region and 1630 cm-1 very strong band in Raman12-15. In the infrared and Raman a strong band is shown in C-C stretching mode. The infra red and laser Raman spectra of nicotinium picrate at room temperature are depicted in Figures 2 and 3, respectively. Assignment of the band in the vibrational spectra of nicotinium picrate has been given in Table 2.
The strong band at 1469 cm-1 in the infrared formed C-C ring stretching and C-C-N stretching at 2624 cm-1 the C-C ring stretching mode is observed as a shouldering intensity band4 at 1505 cm-1 . This results suggested that the strong band are absorbed at 1316 cm-1 in IR, 1414 cm-1 in Raman, spectral region C-C stretching16 .
Fig.2. Infrared spectrum of nicotinium picrate
A strong CH twist is formed in the IR spectrum and in In IR a strong band C-C stretching isopropyl occurs13,17 at 1246 cm-1 . The hydrocarbon C-H stretching is formed18,19 as a strong band in the IR and weak band in Raman at 1171 and 1173 cm-1 .
Fig.3. Raman spectrum of nicotonium picrate
Vibrations of Picrate
The picrate (C6H2N3O7)-- forms the ortho-nitro group and are twisted out of plane of the ring. Picrate being the trinitrophenolate has the characteristic bands of phenol, the nitro group and the phenoxy group. In phenol a broad band in the region 3550-3200 cm-1 and 3100-3000 cm-1 are attributed to O-H stretching, C-H stretching and N-H stretching at 840-720 cm-1 region, respectively. The C-C ring stretching modes are expected at 1505, 1469 cm-1 and C-C stretching isopropyl modes are occur at 1246, 1035, and 920 cm-1. The absence of O-H stretching indicates the presence of picrate ion instead of picric acid.
Apart from this the other functional groups existing in the picrate anion are NO2 nitro group and a C-C isopropyl group. The functional group NO2 has been represented with the asymmetric and symmetric stretching NO2 scissoring deformation modes in the expected region of aromatic nitro compounds (1550-1530 cm-1) and (1350-1330 cm-1). These results are well correlated with Europium picrate20 which is a luminescent plastic. The scissoring, wagging and rocking modes of vibration of NO2 group are also observed.
Another very important band ν phenol C-O stretching vibration is observed at 1281 cm-1 for free picric acid in the infrared spectrum and the corresponding Raman band is also observed as a medium band at 1288 cm-1. Thus the interaction between the cation and anion is not affecting the vibration.
In our investigation NO2 asymmetric stretching vibration in both IR and Raman spectrum at 1577 cm-1 form a strong band, 1552 a shoulder in Raman and is very strong in 1529 cm-1 in IR region. Also NO2 symmetric vibration at 1356 cm-1 shows shouldering band and strong band at 1360 cm-1, 1329 cm-1 at Raman and 1336 cm-1 in infrared4. NO2 scissoring deformation and NO2 out of plane bending mode occur at 839, 823 and 759 cm-1 in infrared and Raman. This is well correlated4 with that of amino acid picrates.
Table 2: Observed Vibrational bands (ѵ) for Nicotinium picrate
|
Infrared γ/ cm-1
|
Raman γ/ cm-1 |
Assignment |
|
3442 v.w |
|
O-H str |
|
3240 v.w |
|
CH str |
|
3176 v.w |
|
NH str |
|
3071 m |
|
C-H str |
|
3015 m |
|
CHstr |
|
2933 w |
|
C-H str |
|
2784 m |
|
C-H str |
|
2624 m |
|
C-C-Nstr |
|
2502 m |
|
C-Cstr |
|
2096 w |
2103 v.s |
CHdef |
|
2037 w |
|
CHdef |
|
1969 w |
|
C-H o.p.b |
|
1843 vw |
|
C=O str |
|
1726 m |
1717 m |
C=O str |
|
1675 vw |
|
C-N str |
|
1635 m |
1630 vs |
C-C ring str |
|
1603 s |
1604 s |
νC- C |
|
1577 s |
1552 sh |
NO2asy str |
|
1529 vs |
|
NO2 asy str |
|
1505 sh |
|
C-C ring str |
|
1469 s |
|
C-C ring str |
|
1428 w |
|
C-Ostr |
|
1356 sh |
1360 |
NO2 sym str |
|
1336 s |
1329 v.s |
NO2symstr |
|
1316s |
1314 |
C-C str |
|
|
1314 m |
C-C str |
|
1281 v.s |
1288 m |
Δphen, C-O str |
|
1246 s |
|
C-C str, isopropyl |
|
1185 m |
|
OH def |
|
1170 m |
1173 s |
C-H str |
|
1141 m |
|
C-C-N asy,C-N-C str |
|
1107 m |
1125 m |
C-H I,p def |
|
1087 m |
1087 m |
C-N str, C-H I,p def |
|
1035 m |
|
C-C str isopropoyl |
|
1020 w |
|
C-O(h) o.p.def |
|
933 m |
942 m |
C-C str |
|
920 w |
|
C-C str isoproyl |
|
908 w |
|
C-O-C sym str |
|
839 w |
823 m |
NO2scisdef |
|
800 w |
|
NH wag |
|
787 w |
|
C-C str |
|
743 s |
759 w |
CH wag, NO2 o.f.p |
|
725 w |
738 m |
CH=CH wag |
|
714 m |
720 w |
NH wag,NO2 def |
|
673 m |
624 w |
C-H wag |
|
619 w |
|
O-C=O o.p.def |
|
523 v.s |
|
C-C-O def |
|
|
405 m |
C-C-C-C i.ph.def |
|
|
370 w |
C-C-C def |
|
|
321 s |
Lattice vibration |
|
|
289 m |
Lattice vibration |
|
|
247 m |
Lattice vibration |
|
|
194 m |
Lattice vibration |
|
|
159 m |
Lattice vibration |
Asym, asymmetric; br, broad; def, deformation; i.p, in-plane; i.ph, in-phase; m, medium; o.p., out-of-plane; o.ph., out- of-phase; rock, rocking; s, strong; sciss, scissoring; sh, shoulder; str, stretching; sym, symmetric; tor, torsion; v, very; w, weak; wag, wagging; ben, bending.
Hydrogen bonding
Normally in amino acid a strong hydrogen bonding is formed between the protonated amino group and the carboxyl group. In the present structure overall analysis reveals that both nicotinium residues exhibit similar hydrogen bonding features. The first type of hydrogen bond is N−H···O bond involving the hydrogen of carboxylate group of nicotinium residue. The X-ray data reveal that this is due to the very strong hydrogen bonding between the two nicotinium residues with bond length 2.711 Å forming a dimer where as this bond does not exist in nicotinium instead it is formed between the carboxylic group and the picrate anion. This was reflected in the IR spectrum of nicotinium as a medium band at 3071 cm-1 indicating a strong hydrogen bond with C-H stretching vibration. The second category of hydrogen bond in the O−H···O bond involves the oxygen of the picrate group. In nicotinium picrate two bonds existing with N−H···O bond length 2.563 Å may be considered as a normal hydrogen bond. The third category in the conjugated hydrogen bonds was formed between the carbonyl oxygen. The C−H···O bonds in nicotinium picrate are four number and the bond length is 2.926 Å while in nicotinium picrate are three with bond length between 2.711 Å - 2.962 Å again indicating the normal hydrogen bond.
The hydrogen bonds link the layers of cation with the layers of anions with each nicotinium cation linking two different picrate anion to form straight chain along the b axis. All H atoms are placed in geometrically calculated positions with C-H distance of 0.93 Å an N−H distance of 0.86 Å and O−H distance of 0.82 Å.
CONCLUSION
The vibrational assignments of bands in the Raman and IR spectra are made for nicotinium picrate. The C=O stretching and OH groups are displaced from their expected positions towards hydrogen bonding. In these crystals the picrate group forms the anion and it is unaffected by the presence of the cation. The extensive intermolecular hydrogen bonding and identified by the shifting of bands due to the stretching and bending modes of the functional group on this crystal.
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Received on 25.05.2013 Modified on 16.06.2013
Accepted on 22.06.2013 © AJRC All right reserved
Asian J. Research Chem. 6(7): July 2013; Page 645-649