Determination of kinetic parameters of decomposition of tetrahydropyrimidine derivatives

Available online at www.ilcpa.pl International Letters of Chemistry, Physics and Astronomy 13 (2013) 23-32 ISSN 2299-3843 Determination of kinetic parameters of decomposition of tetrahydropyrimidine derivatives Kapil Bhesaniya, Ashish Patel, Shipra Baluja* Department of Chemistry, Saurashtra University, Rajkot-360 005, Gujarat, India *E-mail address: ABSTRACT Some new tetrahydropyrimidine derivatives have been synthesized and their structural determination was done by IR, NMR and mass spectral data. Thermal analysis of these synthesized dihydropyrimidinthiones has been carried out by TGA and DSC techniques. From the thermograms, various kinetic parameters such as order of degradation (n), energy of activation (E), frequency factor (A) and entropy change (∆S) have been evaluated. Further, thermal stability of tetrahydropyrimidine have been determined which is found to depend on the type of substituent present in the compounds. Keywords: Tetrahydropyrimidine derivative; TGA, DSC; kinetic parameter 1. INTRODUTION Synthesis of tetrahydropyrimidine and their derivatives is of high interest in organic chemistry. The pyrimidine fragment is present in various biologically active compounds, many of which have been found use in medical practice1,2. Thus, recently, much attention has been paid to derivatives of pyrimidine, including their hydrogenation products. This class of compounds displays wide ranges of biological and pharmacological properties such as antiinflammatory3-5, analgesic6,7, antitumor8,9, antidepressant10, antibacterial and antifungal effects 11-13. For the complete development of a new drug, thermal analysis has many applications14,15. The information obtained regarding the compounds under study is useful for the initial chemical research phase16. In the chemical research phase, thermal analysis plays an important role. The purity of the compound, the compounds ability to be able to exist in various crystalline forms as well as to characterize polymorphs and other forms of solid state should be investigated. It also makes possible to determine optimum conditions of storage of drugs and to define the parameters of technological processes, which can be used without loss of specific physicochemical properties of a drugs17,18. The application of these compounds in pharmaceutical field prompted us to study their thermal stability. In present study, some new tetrahydropyrimidines have been synthesized and characterization of these synthesized compounds is done by IR, NMR and mass spectral data. The thermal analysis of some new synthesized tetrahydropyrimidine derivatives has been done by DSC and TGA techniques. International Letters of Chemistry, Physics and Astronomy 13 (2013) 23-32 2. EXPERIMENTAL SECTION Synthesis of 2,4-diamino-6-phenyl-1,4,5,6-tetrahydropyrimidine-5-carbonitrile (PAB-101 - PAB-110): A solution of substituted aldehyde (0.01 mole), malenonitrile (0.01 mole), freshly prepared sodium ethoxide (30 ml) and guanidine hydrochloride (0.01 mole) was refluxed for 12 hours. The reaction mixture was poured into crushed ice and the solution was neutralized with aqueous HCl solution. The product was extracted using chloroform. The formation of the compounds was checked by thin-layer chromatography and accomplished on 0.2-mm pre coated plates of silica gel G60 F254 (Merck). Visualization was made with UV light (254 and 365nm) or with an iodine vapor. The melting point of all the synthesized compounds was determined in open capillary tubes and was uncorrected. The characterization of all these compounds was done by IR, NMR and mass spectral data. The IR spectra were recorded on Shimadzu FT-IR-8400 instrument using KBr pellet method. The Mass spectra were recorded on Shimadzu GC-MS-QP-2010 model using direct inlet probe technique. 1H NMR and 13C NMR was determined in DMSO solution on a Bruker Ac 400 MHz spectrometer. The physical constants of all the synthesized compounds are given in Table 1. Table 1. Physical properties of substituted tetrahydropyrimidine. Code R M.F Yield (%) Rf value m. p. (°C) PAB-101 C 6 H5 - C11H13N5 78 0.68 141-143 PAB-102 C6H4-CH=CH- C13H15N5 60 0.73 112-114 PAB-103 3-Cl,C6H4- C11H12ClN5 68 0.44 153-155 PAB-104 4-Cl,C6H4- C11H12ClN5 66 0.46 162-164 PAB-105 4-F,C6H4- C12H15FN5 62 0.52 128-130 PAB-106 4-OCH3,C6H4- C12H15N5O 84 0.42 116-118 PAB-107 C11H12N6O2 60 0.62 141-143 C12H15N5O2 74 0.34 132-134 PAB-109 3-NO2,C6H43-OCH3, 4-OHC6H44(α-C4H3O)- C9H11N5O 82 0.36 72-74 PAB-110 4-OH-C6H4- C11H13N5O 56 0.30 176-178 PAB-108 24 International Letters of Chemistry, Physics and Astronomy 13 (2013) 23-32 3. SPECTRAL DATA 2,4-diamino-6-phnyl-1,4,5,6-tetrahydropyrimidine-5-carbonitrile (PAB-101). IR (KBr): 3151(N-H str), 3093(Ar, C-H str), 2943(C-Hstr), 2867(C-H str), 2245(C≡N str), 1610(Ar, C=C str), 1519(Ar, C=C str), 1512(Ar, C=C str), 1490(C-H ben), 1427(C-H ben), 1377(C-H ben), 1265(C-Cstr) cm-1; 1H NMR (400 MHz, DMSO): δ ppm 2.59 (s, 1H, -CH) 3.22-3.36 (t, 1H, -CH), 4.09-4.12 ( d, J = 9.81 Hz 1H, -CH), 6.29 (s, 2H, NH2), 6.66(s, 2H, NH2), 8.38-8.42 (m, 5H, Ar-H), 8.64 (s, 1H, -NH). MS: m/z = 215 [M ]+ 2,4-diamino-6-styryl-1,4,5,6-tetrahydropyrimidine-5-carbonitrile (PAB-102). IR (KBr): 3161(N-H str), 3021(CH=CH str), 3091(Ar, C-H str), 2952(C-Hstr), 2879(C-H str), 2267(C≡N str), 1609(Ar, C=C str), 1515(Ar, C=C str), 1508(Ar, C=C str), 1481(C-H ben), 1425(C-H ben), 1379(C-H ben), 1252(C-C str) cm-1; 1H NMR (400 MHz, DMSO): δ ppm 2.55 (s, 1H, -CH) 3.29-3.37 (t, 1H, -CH), 4.05-4.18 ( dd, J = 9.79 Hz 1H, -CH), 5.04-5.07(dd, 1H – CH, J=8.24), 6.32 (s, 2H, NH2), 6.6(s, 2H, NH2), 8.34-8.39 (m, 5H, Ar-H), 8.74 (s, 1H, -NH). MS: m/z = 241 [M ]+ 2,4-diamino-6-(3-chlorophenyl)-1,4,5,6-tetrahydropyrimidine-5-carbonitrile(PAB-103) IR (KBr): 3163(N-H str), 3097(Ar, C-H str), 2933(C-Hstr), 2877(C-H str), 2265(C≡N str), 1608(Ar, C=C str), 1514(Ar, C=C str), 1502(Ar, C=C str), 1489(C-H ben), 1421(C-H ben), 1371(C-H ben), 1255(C-Cstr), 744(C-Cl str) cm-1; 1H NMR (400 MHz, DMSO): δ ppm 2.61 (s, 1H, -CH) 3.30-3.34 (t, 1H, -CH), 4.07-4.09 ( d, J = 9.78 Hz 1H, -CH), 6.21 (s, 2H, NH2), 6.68(s, 2H, NH2), 7.82-7.87 (t, 1H, Ar-H), 8.39-8.42 (d, 1H, Ar-H), 8.44-8.49 (m, 1H, Ar-H), 8.64 (s, 1H, -NH), 8.81(s, 1H, Ar-H). MS: m/z = 249 [M ]+. 2,4-diamino-6-(4-chlorophenyl)-1,4,5,6-tetrahydropyrimidine-5-carbonitrile(PAB-104). IR (KBr): 3167(N-H str), 3092(Ar, C-H str), 2942(C-Hstr), 2876(C-H str), 2260(C≡N str), 1609(Ar, C=C str), 1508(Ar, C=C str), 1518(Ar, C=C str), 1481(C-H ben), 1422(C-H ben), 1376(C-H ben), 1250(C-Cstr), 742(C-Cl str) cm-1; 1H NMR (400 MHz, DMSO): δ ppm 2.63 (s, 1H, -CH) 3.24-3.29 (t, 1H, -CH), 4.12-4.15 ( d, J = 9.78 Hz 1H, -CH), 6.21 (s, 2H, NH2), 6.63(s, 2H, NH2), 7.82-7.87 (dd, 2H, Ar-H), 8.39-8.42 (dd, 2H, Ar-H), 8.64 (s, 1H, -NH). MS: m/z = 249 [M ]+. 2,4-diamino-6-(4-fluorophenyl)-1,4,5,6-tetrahydropyrimidine-5-carbonitrile (PAB-105). IR (KBr): 3170(N-H str), 3094(Ar, (...truncated)