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Synthesis and thermal analysis of some 1, 2, 4-triazole derivatives.

Introduction

Today, an impressive array of powerful, elegant ant automated tools is available with physical and material scientists for obtaining qualitative and quantitative information about the composition, structure and characteristics of materials. Among the several areas of instruments and techniques, thermal analysis has grown rapidly in recent years. This increasing importance is due to the advancement of thermal analysis technology, relative cheapness of the equipment and time required to achieve the desired results.

Various thermal analysis techniques, particularly Differential Scanning Calorimetry (DSC) and Thermo Gravimetric Analysis (TGA) have proven useful for the evaluation of kinetic parameters of various reactions(1-7). The methods are useful for plant engineers in designing safe and economical plant and process for the manufacture of various chemicals. Thermal analysis of geological materials, drugs, organic, inorganic, polymers etc. was reported by many workers(8-15).

In the present paper, thermal properties of some new triazole derivatives have been studied by DSC, TG/DTA techniques.

Experimental

Synthesis

Synthesis of 4-Amino-5-(4-Methoxy Phenyl)-4H-1,2,4-triazole-3-thiol (E) A methanolic solution of 4-methoxy benzoic acid (A) is refluxed for 12 hours in presence of H2SO4 to yield ester (B). The resulting product is treated with hydrazine hydrate to get acid hydrazide (C). The hydrazide (C) (0.02 mole) is treated with alcoholic solution of KOH (0.03 mole) and carbon disulphide for 5 hours at room temperature with constant stirring The potassium salt, also known as dithiocarbazate (D) was filtered and washed with ether. In dithiocarbazate (0.02 mole), hydrazine hydrate (0.04 mole) was added drop wise and the mixture was refluxed for 8 hours in oil bath. It was poured in water, acidified and resulting solid was filtered, washed with water and purified by KOH treatment to give E. Synthesis of 4({[3-Mercapto-5-(4-Methoxy Phenyl)-4H-1,2,4-triazole-4yl] imino} methyl)Phenol (1)

Equimolar of E and different aldehydes were taken in methanol. The mixture was heated in water bath for about 10 hours. The solution was poured in ice cold water and the resulting solid was filtered, washed and recrystalized from ethanol. The reaction scheme is given in Figure 1.

[FIGURE 1 OMITTED]

Melting points were determined on an electro thermal capillary melting point apparatus and were uncorrected. By TLC, using silica as stationary phase, homogeneity of all the compounds was checked. The physical constants of all the synthesized compounds are given in Table 1. IR and mass spectra were recorded by Shimadzu FTIR 8400 (KBr (cm-1) pellet method) and Shimadzu-QP2010 respectively. [sup.1]H NMR spectra were recorded on a Bruker spectrometer with TMS as internal standard (chemical shift in [delta] ppm).

Thermal Analysis

The Differential Scanning Calorimetry (DSC), Differential thermal analysis (DTA) and Thermo gravimetric analysis (TGA) measurements were made on the instrument "Universal V2.6D TA Instruments at the heating rate of 10[degrees]C / min in nitrogen atmosphere for all the triazole Schiff bases.

Theory

The kinetic parameters have been determined by the following Freeman-Carroll method (16):

At a single heating rate, Freeman and Carroll gave the following relation to analysis TGA data:

ln (dC/dt)/ln (1-C) = n-E/R [(1/T/([DELTA]ln(1-C)] (1)

A plot of left hand side against [DELTA](1/T)/([DELTA]ln(1-C)) gives a straight line with a slope equal to -E/R and the intercept is equal to n.

The frequency factor A and entropy change ?S can be determined by the following equations:

ln E - ln ([RT.sub.s.sup.2]) = ln A - ln[beta] - E/[RT.sub.s] (2)

A = ([k.sub.b]T / h) [e.sup.[DELTA]S/R] (3)

where [T.sub.s] is the temperature of maximum degradation, [beta] is the rat of heating, [k.sub.b] is Boltzmann constant and h is Planck's constant.

Results and Discussion

The TG / DTA and DSC thermo gram of one Schiff base is given in Figure 2. For all the compounds, degradation is multi step process. Various thermal properties such as initial decomposition temperature (IDT), the decomposition temperature range and the maximum degradation along with the percentage weight loss and Exo / Endo transitions of all the Schiff bases are reported in Table 2.

[FIGURE 2 OMITTED]

It is observed from the Table 2 that the stability of Schiff bases decrease in order: HAS-8> HAS-1> HAS-7> HAS-10> HAS-3 [approximately equal to] HAS-4> HAS-9> HAS-5>HAS2>HAS-6. So, HAS-8 is most stable whereas HAS-6 is least stable. All the studied bases have the same central moiety triazole with different side chains. Thus, the presence of different substituent affects thermal stability. It is observed that o-chloro benzaldehyde as side chain (in HAS-8) causes greater stability than N,N-dimethyl benzaldehyde as in HAS-6, which is least stable. In the present case, thermal stability can not be decided by weight loss because for all compounds, degradation is multi step process. Each step is of different order. The degradation in complete for HAS-3 whereas HAS-10 is least degradated. Further, the variation in the trend of thermal decomposition might be interpreted to be of account of some intermolecular interactions (structural as well as electronic) and also because of several experimental factors.

The melting temperature of all the triazole Schiff bases observed by DSC and DTA are also compared with those determined by open capillary method. Although there is good agreement between the values calculated by different methods, it was difficult to decide the stability by these values.

The kinetic parameters, such as order of the degradation (n), energy of activation (E), frequency factor (A) and entropy change ([DELTA]S) for each step are reported in Tables 3 to 5.

It is evident from Tables 3 to 5 that order of reaction is quite different in different steps for different Schiff bases. For first step, order of reaction varies from 0.2 to 4.33. For second step also, values of n varies from 1.55 to 4.90. However, for the third step, all n values are in the range 1.61 to 1.93.

In first step, energy of activation (E) is maximum for HAS-6 and minimum for HAS-2. The frequency factor (A) also varies in the same order i.e., maximum for HAS-6 and minimum for HAS-2. In second step, energy of activation is not very high and maximum is observed for HAS-1 and minimum for HAS-5. The frequency factor A is also maximum for HAS-1 and minimum for HAS-5. In the third step, for HAS-9, both E and A are maximum and HAS-10, these values are minimum. Comparison of E and A values in Tables 2 to 4 shows that values of E and A are minimum for second steps of all the Schiff bases.

Further, change in entropy ([DELTA][S.sup.[omicron]]) for all these reactions were also calculated by equation (3). It is observed that for first and third steps, change in entropy is either positive or negative for different Schiff bases but in second step, for all Schiff bases, [DELTA][S.sup.[omicron]] values are negative. The positive [DELTA][S.sup.[omicron]] indicates that the transition state is in less ordered state. Whereas the negative values for entropy of activation indicate that the activation complex has a more ordered or more rigid structure than the reactants and the reaction is slower than the normal(17).

Thus, the degradation in triazole Schiff bases is multi step process with different order of reaction. Further, thermal stability depends upon the type of substituent present. It is observed that presence of o-chloro (as in HAS-8) increases the stability whereas N,N dimethyl group (as in HAS-6) decreases the stability.

References

[1] M. I. Ayad, A. Mashaly and M. M. Ayad; Thermochim. Acta, 184, 173(1991).

[2] R. G. J. C. Heijkants, R. V. V. Calck, T. G. V. Tienen, J. H. de Groot; Biomaterials, 26, 4219 (2005).

[3] S. S. Guo, X. H. Sun, S. X. Wang, S. Xu, X. Z. Zhao and H. L.W. Chan; Mat. Chem.Phys., 91, 348 (2005).

[4] M. Niculescu, N. Vaszilcin, M. Barzescu, P. Budrugeac, E. Segal; Articol: J.Therm. Ana.Calo., 65, 881 (2001).

[5] O. Ichinose, T. Tanaka, and N. Furuya; Electrochem., 71, 108 (2003).

[6] G. M. Leonipoulou, K. Theodoratos and G.G. Macris; Arch. Pharm. (Athens), 30,100 (1974).

[7] E. Domagaina and T. Slawik; Acta Pol. Pharm., 33, 623 (1976).

[8] A. Chauvet and J. Masse; J. Trav. Soc. Pharm. Montpeller, 38, 31 (1978).

[9] A. Radecki and M. Weolowski; J. Thermal Anal., 17, 73 (1979).

[10] M. Weolowski; Miikrochim Acta, 1, 199 (1980).

[11] C. R. Martinez, J. M. Sanches, J. A. P. de Ciriza and F. Marcotegni; Rev. Asoc. Esp. Farm. Hosp., 6, 57 (1982).

[12] D. Giron; J. Pharm. Biomed. Anal. 4, 755 (1986).

[13] S. K. Dwivedi, S. Sattari, F. Jamali and A. G. Mitchell; J. Pharma., 87, 92 (1992).

[14] Y. A. Ribeiro, J. D. S. Oliveira, M. I. G. Leles, S. A. Juiz and M. J. Ionashiro; Thermal Anal., 46, 1645 (1996).

[15] N. S. Fernandes, M. A. de Silva, R. A. Medes and M. Ionashiro; J. Braz. Chem. Soc., 10, 6 (1999).

[16] E. S. Freeman and B. Carroll, J. Phys. Chem., 62, 394 (1958).

[17] A. P. Mishra, V. Tiwari, R. Singhal and S. K. Gautam., Thermos, 90 (2002).

Shipra Baluja, Nikunj Kachhadia and Asif Solanki

Department of Chemistry, Saurashtra University

Rajkot-360 005, Gujarat, India

E-mail: shkundal_ad1@sancharnet.in
Table 1: Physical data of triazole derivatives.

Sr.               R'               Code   M.Wt.(g)
No.

1.    -4-OH                         1       326
2.    -4-OC[H.sub.3]                2       340
3.    -4-Fl                         3       328
4.    -3-OCH3-4OH                   4       356
5.    -4-Cl                         5       344
6.    -4-N-[(C[H.sub.3]).sub.2]     6       353
7.    -3-N[O.sub.2]                 7       355
8.    -2-Cl                         8       344
9.    -2-OH                         9       326
10.   -H                            10      310

Sr.                     M.F.
No.

1.    [C.sub.16][H.sub.14][O.sub.2][N.sub.4]S
2.    [C.sub.17][H.sub.16][O.sub.2][N.sub.4]S
3.    [C.sub.16][H.sub.13]ON4SF
4.    [C.sub.17][H.sub.16][O.sub.3][N.sub.4]S
5.    [C.sub.16][H.sub.13]O[N.sub.4]SCl
6.    [C.sub.18][H.sub.19]O[N.sub.5]S
7.    [C.sub.16][H.sub.13][N.sub.5][O.sub.3]S
8.    [C.sub.16][H.sub.13]O[N.sub.4]SCl
9.    [C.sub.16][H.sub.14][O.sub.2][N.sub.4]S
10.   [C.sub.16][H.sub.14]O[N.sub.4]S

Sr.   Rf *       M.P.      Yield
No.   Value   [degrees]C     %

1.    0.60       227        72
2.    0.83       215        82
3.    0.81       222        79
4.    0.77       232        69
5.    0.86       207        72
6.    0.74       244        74
7.    0.88       230        68
8.    0.84       238        79
9.    0.88       223        81
10.   0.75       241        76

* Benzene : Acetone = 9 : 1 for 2; 9.5: 0.5 for 1,3-10.

Table 2: TGA, DTA and DSC data for the synthesized triazole
derivatives Synthesis and Thermal Analysis of Some 1, 2, 4-Triazole
Derivatives

Compd.   Amt. Mg.   Initial             Decomp       % Wt.    Residual
Code                Decom               range,       Loss     Wt. loss,
                    Temp. [degrees]C    [degrees]C            mg.

HAS-1     7.7342         217.57          217.57-     3.957     0.3060
                                         786.13
HAS-2     9.6341         189.00          189.00-     2.252     0.2170
                                         786.96
HAS-3     9.6405         201.99          201.99-     0.0000    0.0000
                                         680.00
HAS-4    11.7231         201.99          201.99-     0.4474    0.0525
                                         786.36
HAS-5    13.2715         191.60          191.60-     2.8790    0.3821
                                         786.02
HAS-6    12.7307         183.81          183.81-     0.5222    0.0665
                                         786.46
HAS-7     9.3520         214.97          214.97-     0.5649    0.0528
                                         723.96
HAS-8     9.5506         225.36          225.36-     0.6651    0.0635
                                         785.75
HAS-9    11.8447         198.09          198.09-     1.6770    0.1986
                                         786.29
HAS-10   14.0085         205.88          205.88-     10.470    1.4667
                                         578.54

         Max.      Transition   DSC          DTA Temp.    Exptl.
Compd.   Degrad                 Temp         [degrees]C   Melting
Code     Temp.                  [degrees]C                Temp.
         [degrees]                                        [degrees]C
         C

HAS-1    786.13    Exo            241.09       239.70        227
                   Endo           232.33         --
HAS-2    786.96    Exo            217.49       218.61        215
                   Endo           199.01         --
HAS-3    680.00    Exo            218.75       219.91        222
                   Endo           212.94         --
HAS-4    786.36    Exo            220.55       224.49        232
                   Endo           210.77         --
HAS-5    786.02    Exo            222.13       221.68        207
                   Endo           194.00         --
HAS-6    786.46    Exo            267.22       226.69        242
                   Endo           222.21       79.94
HAS-7    723.96    Exo            229.92       244.83        230
                   Endo           221.52         --
HAS-8    785.75    Exo            228.40       242.28        238
                   Endo           141.22         --
HAS-9    786.29    Exo            236.99       252.92        223
                   Endo           200.67         --
HAS-10   578.54    Exo            217.76       226.09        241
                   Endo           210.89         --

Table 3: The kinetic parameters for all the compounds for 1st step.

Comp. code    n     E, KJ      A [sec.sup.-1]

HAS-1        0.21   249.79   7.20 x [10.sup.20]
HAS-2        4.33   75.68     3.2 x [10.sup.5]
HAS-3        1.63   202.98   6.01 x [10.sup.16]
HAS-4        1.80   218.37   1.32 x [10.sup.18]
HAS-5        4.29   83.86    1.76 x [10.sup.6]
HAS-6        1.62   271.87   5.95 x [10.sup.22]
HAS-7        2.49   112.55   6.59 x [10.sup.8]
HAS-8        2.19   156.90   5.51 x [10.sup.12]
HAS-9        1.56   164.87   2.78 x [10.sup.13]
HAS-10       1.42   178.60   4.43 x [10.sup.14]

Comp. code   [DELTA][S.sup.[omicron]], J[K.sup.-1]   [gamma]

HAS-1                        148.38                   0.9662
HAS-2                       -145.52                   0.8841
HAS-3                         70.30                   0.9098
HAS-4                         96.01                   0.9721
HAS-5                       -131.34                   0.9425
HAS-6                        185.08                   0.9725
HAS-7                        -82.08                   0.9872
HAS-8                         -6.99                   0.9698
HAS-9                         6.43                    0.951
HAS-10                        29.48                   0.9445

Table 4: The kinetic parameters for all the compounds for 2nd step.

Comp. code.    n     E, KJ   A [sec.sup.-1]

HAS-1         1.55   46.81       36.59
HAS-2         3.07   14.12        0.09
HAS-3         3.35   16.70        0.16
HAS-4         3.88   11.37        0.05
HAS-5         3.23   10.86        0.04
HAS-6         4.08   12.43        0.06
HAS-7         3.85   15.04        0.11
HAS-8         3.01   12.92        0.07
HAS-9         4.90   16.85        0.17
HAS-10        2.10   21.38        0.40

Comp. code.   [DELTA][S.sup.[omicron]], J[K.sup.-1]   [gamma]

HAS-1                        -223.43                  0.9855
HAS-2                        -273.12                  0.9313
HAS-3                        -268.57                  0.9899
HAS-4                        -278.25                  0.9977
HAS-5                        -279.24                  0.9976
HAS-6                        -276.21                  0.9913
HAS-7                        -271.45                  0.9892
HAS-8                        -275.29                  0.9846
HAS-9                        -268.32                  0.9899
HAS-10                       -260.82                  0.9869

Table 5: The kinetic parameters for all the compounds for 3rd step.

Comp.    n      E, KJ    A, [sec.sup.-1]
code.

HAS-1    1.66   103.55   6.69 x [10.sup.3]
HAS-2    1.61   107.11   1.02 x [10.sup.4]
HAS-3    1.63   103.96   3.23 x [10.sup.4]
HAS-4    1.93   79.35    3.28 x [10.sup.2]
HAS-5    1.71   80.85    3.97 x [10.sup.2]
HAS-6    1.72   98.26    3.47 x [10.sup.3]
HAS-7    1.72   98.57    8.20 x [10.sup.3]
HAS-8    1.62   95.80    2.58 x [10.sup.3]
HAS-9    1.78   120.74   5.48 x [10.sup.4]
HAS-10   1.69   35.67    4.30

Comp.    [DELTA][S.sup.[omicron]], J[K.sup.-1]   [gamma]
code.

HAS-1    -182.22                                 0.9615
HAS-2    -178.68                                 0.9750
HAS-3    -168.24                                 0.9384
HAS-4    -207.30                                 0.9677
HAS-5    -205.70                                 0.9589
HAS-6    -187.68                                 0.9843
HAS-7    -180.02                                 0.9551
HAS-8    -190.14                                 0.9470
HAS-9    -164.74                                 0.9889
HAS-10   -241.51                                 0.9959
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Author:Baluja, Shipra; Kachhadia, Nikunj; Solanki, Asif
Publication:International Journal of Applied Chemistry
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Date:Sep 1, 2008
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