IJCRR - Vol 04 Issue 23, December, 2012
Date of Publication: 15-Dec-2012
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ULTRASONIC AND SPECTROSCOPIC INVESTIGATION OF THIOUREA IN NON-AQUEOUS MEDIA
Author: Ragamathunnisa M., Jasmine Vasantha Rani E., Padmavathy R., Radha N.
Category: General Sciences
Abstract:Acoustical and thermo chemical behavior of thiourea in formamide is studied using ultrasonic technique. The Ultrasonic velocity (u), density (ρ) and viscosity (η) measurements have been carried out for the solution at 278, 288, 298, 308, 318 and 328K and at different concentrations. The results arrived from ultrasonic technique yield the various intermolecular interactions occur in the solution. Spectroscopic techniques have been used to identify the various functional groups. The results obtained from spectroscopic studies were correlated with acoustical and thermo chemical properties of the solution.
Keywords: Thiourea(TU), Formamide, Acoustical parameter, Thermo chemical parameter, Tautomeric form, Dimeric structure.
Ultrasonic study on the solution of Thiourea in non-aqueous media provides useful information in understanding the behavior of liquid systems, intramolecular, intermolecular associations and related structural changes. Thioureas are important sulfur and nitrogen containing compounds and they are useful substances in drug research. Some thiourea derivatives possess valuable biological pharmacological activities such as, anti-HIV [1-4] and anticancer properties [5- 7]. In addition, urea and thioureas [8-10] have emerged as structurally novel anticonvulsant. Thiourea is mainly used in textile processing  and also in the reductive work up of Ozonolysis  to give carbonyl compound. Another common application of thiourea is a common sulfur source for making semiconductor calcium sulfide nanoparticle. Use of thiourea is also a measure of change in body water . The role played by the solvent is not a minor one. The presence of a solvent can speed up or slow down a reaction by a factor of 1020 . Solvent effects can be more powerful than the effects exerted by any other factor. The solvent formamide is also a constituent of cryoprotectant vitrification mixtures used for cryopreservation of tissues and organs. The current work is to emphasis the solvation effect of thiourea in formamide is studied by calculating various parameters such as Solvation Number(nh), Apparent Molal Volume(φv), Apparent Molal Compressibility(φk) Internal Pressure [πi], Free Volume [Vf ] and Intermolecular free Length (Lf). The results obtained from the ultrasonic study as well as spectroscopic study used to analyse various reactions occurring in the solution.
The chemicals used in the present work are analytical (AR) reagent grade and spectroscopic (SR) reagent grade of minimum assay of 99.9% obtained from E-Merck. An electrically maintained constant temperature bath has been used to circulate water through the double walled measuring cell made up of steel containing the experimental solution at the desired temperatures. The accuracy in the temperature measurement is ±0.1K. The density of the solution is measured using specific gravity bottle. The viscosity of the solution is measured by the Ostwald’s viscometer. Density, viscosity and ultrasonic velocity are determined for thiourea in formamide from 278K to 328K at different molalities using compressibility method. From these obtained data thermo chemical and acoustical parameters are calculated using the following formulae
FTIR spectrum was recorded between 4000 cm-1 to 400 cm-1 using PERKIN ELEMER SPECTRUM RX1 spectrometer. The UV absorption spectrum of solvent, solute and the solution are also taken.
From the ultrasonic study, the calculated values of various parameters are given in the Table (1) and Table (2). The variations of the parameters with respect to molalities are represented in Figure (1a -1f). The observed spectrum of thiourea, formamide and thiourea in formamide are shown in figure (2a-2c) and observed frequencies are tabulated in table (3). The UV absorption spectrum of solvent, solute and the solution are shown in figure (3a-3c). The observed peaks are tabulated in table (4).
The solvation number is positive at high temperatures. At .001m the solution exhibits positive solvation number for almost all the temperatures. Zero value of solvation number only indicates that no change occurs in the compressibility value of the solvent when the solution is formed. Negative values of solvation number at lower temperatures emphasize that solutions are more compressible than solvent. Positive solvation number of solution suggests that compressibility of the solution at high temperature and at low molalities will be less than that of the solvent. The apparent molal volume ( ) of thiourea is negative, for all molalities and temperatures. The apparent molal volume ( ) decreases, as concentration increases, at all temperatures. This supports that there is a weak ion-ion interaction occurring in solution. In thio urea, the apparent molal compressibility ( ) is found to be negative at 308.15K and 318.15K almost all molalities. The apparent molal volume and apparent molal compressibility have been proven to be a very useful tool in elucidating the structural interaction occurring in solutions. The acoustical parameters explain the nature and strength of the interaction taking place in the solutions. In the solution, the internal pressure increases up to 0.01m for almost all the temperature. Beyond the 0.01m the internal pressure decreases with respect to molality. This behavior indicates breaking nature of solute in the solvent. The variations in the free volume (Vf) with respect to molalities and temperature of the solutions of thiourea behave in an opposite manner to that of internal pressure as expected. The results obtained from the present study suggest that the solute- solvent interactions occurring in the solution. This may be due to intermolecular hydrogen bonding present in this system. Intermolecular free length (Lf) is one of the important acoustic parameter in determining the nature of the interaction between the components of the solution. The rise and fall observed in intermolecular free length for all temperatures and molalities in thiourea solution. This supports the dissociation of molecules occurring in the solution. Thiourea occurs in tautomeric form which is shown in figure (4). In aqueous solution the thione form predominates. Dimeric structure of Formamide is shown in figure (5). Enolic form of formamide is shown in figure (6). Spectral studies FT-IR spectroscopy is by far the best way to detect the presence of functional groups in a molecule. The C?O is a strong bond in a carbonyl group. The strong bond due to C?O stretching appears at about 1700cm-1 , where it is a seldom obscured by other strong absorptions. In the solvent this strong peak is appeared at 1685 cm-1 and in the solution it is right shifted by 2 cm1 i.e. at 1683 cm-1 . In the solvent a peak is appeared at 2771 cm-1 and in the solution at 2767 cm-1 . It is due to C? H stretching band this in conjugation with carbonyl band is fairly certain evidence for an aldhyde. In the solution at 2391cm-1 a peak is observed which is due to asymmetrical stretching mode, since it produces a change in the dipole moment, is IR active. In the solute at 3376 cm-1 and at 3177 cm-1 peak are observed which represent the different types of N? H stretching band. These peaks classify the types of amide. Tautomeric nature of the solute is confirmed by observing the symmetric and asymmetric N? H stretching vibrations at 3376 cm-1 and in 3177 cm-1 . In the solution a peak is observed at 1589 cm-1 .
This involves coupling of the N?H bending and C?N stretching vibration. Resonance effect occurs in carbonyl absorptions due to replacement. In solvent resonance effect predominates than the inductive effect. This effect increases C?O bond length and reduces the frequency of absorption, which effect is confirmed by observing a peak at 1685 cm-1 in the solvent and in the solution which is further decreased by 2cm-1 i.e. at 1683cm-1 . A new band occurs at 1598 cm-1 . This is due to H- bonding via >C=O of solvent and NH2 of solute destroying the dimeric structure of pure solvent. When a carbonyl group of amide is involved in hydrogen bonding its stretching frequency is lowered , which is observed in the solution at 1683cm-1 by lowered 2cm-1 from 1685cm-1 in the solvent. Rao and Vengataraghavan  correlated data on their spectra of thiocarbonyl derivatives in the literature and concluded that strong vibrational coupling was operative in the case of nitrogen containing thiocarbonyl derivatives and that the C? S vibrations are not located. From that observation it is confirmed that thiourea in non-aqueous media the thiol form predominates. These bands appear consistently in the region of 1570cm-1 to 1397cm-1 , 1420cm-1 to 1260cm-1 and 1140cm-1 to 940cm-1 in the IR spectrum because of mixed vibrations of ?N? C? S moiety. These bands are appeared in the solution at 1468cm-1 , 1390 cm-1 , 1050cm-1 respectively. All these spectral changes may be attributed to the presence of hydrogen bonding patterns, which are shown in figure (7a) and (7b).
UV Spectroscopic study
In the solvent, transition occurs between nonbonding atomic orbital and antibonding orbitals.The non-bonding electrons are held more loosely than σ bonding electrons and consequently undergo transitions at comparatively longer wavelengths. These transitions occur with compounds containing double bonds involving hetro-atoms bearing unshared pair(s) of electrons. This type of transition is important feature of the spectra of aldehydes and ketones and is sensitive to substitution on the chromophore structure. In the solvent, peak observed at 201nm shows the π → π* type of transition and 243nm shows the n→π*type of transition. This type of transition is always less intense because the electron in the n orbital are situated perpendicular to the plane of π bond and consequently the probability of the jump of an electron from n to π* orbital is very low. In the solute the peaks are observed from 190nm onwards. Number of peaks observed in the range of 270nm, 273nm, 277nm, 286nm. It shows the n→π* transition occurs in the solute. The position of π → π* transitions in carbonyl compounds vary with the nature of the solvent used. As the polarity of the solvent increases, the π → π* bands undergo a bathochromic (red) shift and the n→π* undergo a gradual hypsochromic shift. The π → π* band shifts to longer wavelength in a more polar solvent because the π → π* transition have a polar excited state which would normally be stabilized by hydrogen bonding in more polar solvents. This lowers the energy gap between π and π* levels and consequently increases the wavelength of π →π* band. In the case of n→π* band lowers the energy of n orbital because of hydrogen bonding.
Thiourea occurs in tautomeric forms. In the present study, from the acoustic properties of the solution of thiourea shows that there is a linear variation occurring in the solution. These changes reveal the fact that there is a weak interaction exists between the solute and solvent and breaking nature of the solute in solvent. The variations observed in intermolecular free length also confirm the dissociation of molecules occurring in the solution. From the spectral analysis various functional groups were identified. Tautomeric nature of solute is conformed. The dimeric structure of formamide is changed due to solvation with thiourea. Results obtained from the acoustical studies such as (i) breaking nature of solute in solvent (ii) Intermolecular hydrogen bonding are also confirmed by the spectroscopic studies.
Authors acknowledge the immense help received from the scholars whose articles are citied and included in references of this manuscript. The authors also grateful to authors/editors/publishers of all those articles, journals and books from where the literature for this article has been reviewed and discussed.
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