Green synthesis and characterization of thymol-guanidineformaldehyde terpolymer resin.
Green chemistry for chemical synthesis involves the design and redesign of chemical synthesis and processes to prevent pollution and consume a minimum amount of materials and energy while producing little or no waste material, thereby rendering the products environmentally friendly  and it does so in a manner that is economically feasible and cost-effective. More recently, microwave-assisted organic synthesis is a newly developed method to obtain more efficient compounds in a short period of reaction time. After 1990s, this method has begun to be preferred for organic synthesis and polymer synthesis . A huge number of research papers have appeared over the last decades on the application of microwave technology in organic synthesis [3-5].
In recent years, microwave irradiation technique has had much importance in step-growth polymerizations, ring-opening polymerizations as well as radical polymerizations [6-7].
The obtained copolymers are high molecular weight compounds containing covalent bonds, yet they are different from macromolecules. These copolymers are reported to have better acid resistance, better thermal stability, and improved electrical properties. Terpolymer resins having good thermal stability have enhanced the scope for development of some polymeric materials. Michael and his coworkers have synthesized, characterized, and studied the thermal degradation of a terpolymer prepared from salicylic acid, guanidine, and formaldehyde  and 8-hydroxyquinoline-guanidineformaldehyde . Numerous researchers have synthesized terpolymer resins using microwave irradiation technique and have also characterized by using different spectral methods [10-11]. The spectral analysis of 8-hydroxyquinoline-melamineformaldehyde resin has been carried out by Gurnule and his coworkers  and also reported the thermal degradation of the resin prepared from 4-hydroxyacetophenone and catechol with formaldehyde . Rahangdale et al. have synthesized and studied the resin prepared from 2,2'dihydroxybiphenyl-biuret-formaldehyde . The preparation and characterization of 2-hydroxy-4-methoxypropiophenone-urea-formaldehyde copolymers have been reported by Patel and his coworkers . Terpolymers prepared by condensation of o-cresol and urea with formaldehyde in the presence of an acidic catalyst have also been studied . Chauhan et al. have reported the synthesis of self-crosslinked terpolymer derived from 4-acetylpyridine oxime and formaldehyde with acetophenone and studied the relevant characterization . The synthesis and characterization of different terpolymer resins have been carried out by many researchers [18-24]. Burkanudeen et al. have reported the synthesis and spectral characterization of anthranilic acid, urea, and formaldehyde in DMF as reaction medium [25-26].
Extensive research work has been carried out on the synthesis, characterization, and stability of different terpolymers by various researchers [27-29].
Thymol (2-isopropyl-5-methylphenol) is an antibacterial agent which has been used in the synthesis and polymerization of certain unsaturated derivatives of thymol .
However, literature survey has shown that no polymer resin has been synthesized using the monomers thymol, guanidine hydrochloride, and formaldehyde. Therefore, the present work reports the synthesis of TGF terpolymer resin and their characterization by using various spectral methods.
2. MATERIAL AND METHODS
All the chemicals used as starting materials in the synthesis of the terpolymer resin were purchased from commercial suppliers and are of laboratory grade.
Green synthsesis of TGF terpolymer resin
The TGF terpolymer resin was synthesized by microwave irradiation technique using monomer thymol (0.1 mol) and guanidine hydrochloride (0.1 mol) with formaldehyde (0.2 mol) in the presence of 2 M HCl medium at 80 [+ or -] 2[degrees]C for 15 minutes using a Ragatech Microwave system at 700 W. After completion of the reaction, the mixture was kept overnight at room temperature. The precipitate obtained was filtered and washed with cold water to remove the thymol-formaldehyde copolymer and unreacted materials. The terpolymer was purified by dissolution in 8% NaOH and re-precipitated by dropwise addition of 1:1 (v/v) of 2 M HCl. The precipitated product was filtered off, washed with cold water, and dried in a vacuum dessicator over anhydrous calcium chloride. The reaction route is shown in Scheme 1. Melting point = 413K. Yield = 1.2993 g.
A Bruker (Model Alpha) spectrometer was used for recording the FT-IR spectrum of the TGF resin to identify the linkages and functional groups. The UV-Visible spectrophotometric studies were carried out on a Shimadzu instrument to identify the types of electronic transitions. The proton NMR spectrum of the TGF terpolymer resin was recorded in CD[Cl.sub.3] solvent using an FT-NMR spectrometer model Avance-II Bruker at 400 MHz.
3. RESULTS AND DISCUSSION
The terpolymer resin TGF is yellow in color, insoluble in cold and hot water, but completely soluble in ethanol, diethyl ether, A,A-dimethyl formamide, dimethyl sulfoxide, chloroform, carbon tetrachloride, benzene, acetone, cyclohexane, 1,4-dioxane, and petroleum ether.
The FT-IR spectrum provides useful information about the linkages and the functional group present in the terpolymer. The FT-IR spectrum of the TGF terpolymer resin is shown in Figure 1 and the data are summarized in Table 1.
The broad band in the region of 3451-3420 [cm.sup.-1] may be due to the stretching vibration of the phenolic hydroxy groups (O-H stretch). The sharp band at 1200 [cm.sup.-1] and another at 1410-1300 [cm.sup.-1] may be due to a C-O stretch. The band in the region 35003300 (m) may be due to an N-H stretch (sym. and asym.). The band in the region 3100-3000 [cm.sup.-1] may be attributed as a C-H stretch and the band appearing in the region 1650-1450 [cm.sup.-1] might appear from a C=C stretch which is a characteristic feature of the aromatic region. The peak in the region 2960-2850 [cm.sup.-1] may be due to a C-H stretch in C[H.sub.3]. The band appearing at 1485-1440 (m) is attributed as a C-H deformation in -C[H.sub.2]-. The band obtained near 1300 [cm.sup.-1] may be considered as a C-H deformation signal in -C[(C[H.sub.3]).sub.2]-. The band appearing at 1611 [cm.sup.-1] is probably due to the -C=N stretch (imines). The band appearing in the region 850-690 [cm.sup.-1] may be thought to be arising from the substituted benzene ring.
The UV-Visible absorption spectrum of the TGF terpolymer resin was recorded in 95% ethanol and shown in Figure 2.
This resin gives rise to two characteristic bands in the region 200-400 nm. These observed positions of bands indicate the n-[sigma]* transition which may be due to the presence of the C-O moiety of the phenolic OH group. The band at 235 nm indicates the the [pi]-[pi]* transitions in aromatic moieties as well as the C=N group while the band at 285 nm may be due to the
presence of n-n* transitions in the C=N group. This observation is in good harmony with the most probable structures of such types of a terpolymer.
The [sup.1]H-NMR spectrum of TGF terpolymer resin is depicted in Figure 3 and the data are tabulated in Table 2.
The signals within the range [delta] 6.5-6.8 ppm may be caused by the aromatic ring protons (Ar-H). A broad signal appearing about [delta] 8.8 ppm corresponds to the phenolic (-OH) proton. The signal present in the region [delta] 2.5-4.5 is attributed to the ArC[H.sub.2]-N moiety. The signal appearing in the range [delta] 5-8 ppm is considered to be due to -NH- bridging. The sharp signal at [delta] 1.3 ppm is probably due to the methyl group of thymol moiety in the resin. The signal between [delta] 2-4 ppm similarly can be thought to originate from the proton of the isopropyl moiety of the resin. The C=NH proton (imine) is thought to originate between [delta] 6.5-8 ppm.
The resin TGF was synthesized by the condensation of thymol and guanidine hydrochloride with formaldehyde, in the presence of an acidic catalyst using microwave irradiation. This method is energy-saving as well as time-saving as compared to the conventional method which requires 5 hours for the completion of the reaction. The resin is yellow in color, insoluble in water, and completely soluble in ethanol, diethyl ether, A,A-dimethyl formamide, dimethyl sulfoxide, chloroform, carbon tetrachloride, benzene, acetone, cyclohexane, 1,4-dioxane, and petroleum ether. Through FT-IR, UV-visible and [sup.1]H-NMR spectral studies, the proposed structure of the TGF terpolymer resin was confirmed.
Article history: Received: 23 July 2014; revised: 25 November 2014; accepted: 27 November 2014. Available online: 30 December 2014.
The authors wish to express their sincere thanks to the Principal, J. B. College of Science, Wardha (India) for providing the necessary facilities and rendering their valuable guidance. The authors also like to thank SAIF, Punjab University, Chandigarh, SAIF, IIT, Bombay and Principal, Institute of Pharmaceutical Education and Research, Borgaon (Meghe), Wardha, for their services for spectral analysis.
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Suraj Diwakarrao Kukade *, Ritesh Ramdas Naik, and Sheshrao Vitthalrao Bawankar
Department of Chemistry, Jankidevi Bajaj College of Science, Jamnalal Bajaj Marg,Civil lines, Wardha-442001-M.S. India.
* Corresponding author. E-mail: email@example.com
Table 1. FT-IR spectral data of the TGF terpolymer resin. Assignment Observed band Expected band wavenumber wavenumber ([cm.sup.-1]) ([cm.sup.-1]) Phenolic -OH stretch 3451-3420 3750-200 -N-H stretch (imide) 3500-3300 3500-800 -N-H bend(imide) 680 800-600 Aromatic C=C stretch 1650-1450 1600-450 Phenolic C-O stretch 1400-1300 1410-1310 Methylic bridge (-C[H.sub.2]) modes 741 800-710 Rock Methylic bridge 1420 1460 (-C[H.sub.2]) modes Bend Methylic bridge (-C[H.sub.2]) modes 1320 1300-200 Wagging C=N (imines) 1611 1690-630 -substituted benzene ring 850-690 850-690 Assignment References Phenolic -OH stretch [8, 9] -N-H stretch (imide) [8, 9] -N-H bend(imide) [8, 9] Aromatic C=C stretch [8, 9, 32, 34, 35] Phenolic C-O stretch [8, 36, 39] Methylic bridge (-C[H.sub.2]) modes [8, 9] Rock Methylic bridge [8, 9] (-C[H.sub.2]) modes Bend Methylic bridge (-C[H.sub.2]) modes [8, 9] Wagging C=N (imines)  -substituted benzene ring [8, 9] Table 2. [sup.1]H-NMR spectral data of TGF terpolymer resin. Nature of proton Observed Chemical Expected chemical assigned in the shift ([delta]) in shift ([delta]) NMR spectrum the terpolymer (ppm) (ppm) Aromatic (Ar-H) 6.5-6.8 6-9 phenolic (Ar-OH) 8.8 4-12 C=NH proton 6.5 6.5-8 Ar-C[H.sub.2]-N moiety 3.2 2.5-4.5 -NH bridging 6.7 5-8 Ar-C[H.sub.3] 2.3 2.2-2.4 -CH[(C[H.sub.3]).sub.2] 2.2-3.2 2-4 -CH[(C[H.sub.3]).sub.2] 1.3 0.9-2 Nature of proton References assigned in the NMR spectrum Aromatic (Ar-H) [8, 9, 32, 35] phenolic (Ar-OH) [8, 9, 32] C=NH proton  Ar-C[H.sub.2]-N moiety  -NH bridging [9, 36] Ar-C[H.sub.3] [30, 31, 33] -CH[(C[H.sub.3]).sub.2] [30, 31, 33] -CH[(C[H.sub.3]).sub.2] [30, 31, 33]
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|Author:||Kukade, Suraj Diwakarrao; Naik, Ritesh Ramdas; Bawankar, Sheshrao Vitthalrao|
|Publication:||Orbital: The Electronic Journal of Chemistry|
|Date:||Oct 1, 2014|
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