A number of studies involving the determination of pKa values of some 4,5-dihydro-1H-1,2,4-triazol-5-one derivatives in non-aqueous solvents has been revealed [1,2,3]. 3-Methyl-4-[(2-amino-1,3,4-thiadiazol-5-il)-thioacetylamino]-4,5-dihydro-1H-1,2,4-triazol-5-one 3 was synthesized from the reaction of 3-methyl-4-chloroacetylamino-4,5-dihydro-1H-1,2,4-triazol-5-one 1 with 2-amino-5-mercapto-1,3,4-thiadiazole 2. Moreover, the synthesized compound 3 was titrated potentiometrically with tetrabutylammonium hydroxide (TBAH) in three non-aqueous solvents such as isopropyl alcohol, tert-butyl alcohol and N,N-dimethylformamide to determine pKa values. For compound 3, the half-neutralization potentials (HNP) and the corresponding pKa values were determined in the three non-aqueous solvents mentioned above. The starting compound 1 was prepared according to literature [2,4].
3-Methyl-4-chloroacetylamino-4,5-dihydro-1H-1,2,4-triazol-5-one 1 (1.91 g, 0.01 mol) and 2-amino-5-mercapto-1,3,4-thiadiazole 2 (1.33 g, 0.01 mol) in n-butyl acetate (30 mL) was refluxed for five hours and then evaporated at 50-55 °C in vacuo. Several recrystallizations of the residue from ethanol gave pure compound 3 (1.32 g, 45.99 %).
Melting point: 151-152 °C (EtOH, uncorrected).
UV (λmax nm; EtOH) / ε (dm3.mol-1.cm-1): 282 (5980), 203 (9150).
IR (KBr, cm-1): 3400, 3250, 3100 (NH2, NH); 1750 (C=O); 1605 (C=N).
1H-NMR (200 MHz, DMSO-d6): δ= 2.09 (3H, s, CH3); 4.14 (2H, s, CH2); 6.40 (2H, br, NH2); 11.40 (1H, s, NH); 11.64 (1H, s, NH).
13C-NMR (50 MHz, DMSO-d6): δ= 10.45 (CH3); 34.75 (CH2); 144.70, 151.76, 152.21, 166.86 (heterocyclic carbons); 169.89 (C=O).
The potentiometric titration curves of 0.001 M compound 3 solutions titrated with 0.05 N TBAH in isopropyl alcohol, tert-butyl alcohol and N,N-dimethylformamide are presented in Figure 1.
Figure 1.
The HNP values and the corresponding pKa values of compound 3 are presented Table 1.
Table 1:.
HNP values and the corresponding pKa values of compound 3
As seen Figure 1 and Table 1, compound 3 give two end points as well as two half-neutralization potential values. The potentiometric titration curves of compound 3 resemble the titration curves of diprotic acids.
Supplementary materials
Supplementary File 1Supplementary File 2Supplementary File 3References:
- Yüksek, H.; Ocak, Z.; Alkan, M.; Bahçeci, Ş.; Ozdemir, M. Molecules 2004, 9, 232–240.
- Yüksek, H.; Alkan, M.; Ocak, Z.; Bahçeci, Ş.; Ocak, M.; Ozdemir, M. Indian J. Chem. 2004, 43B, 1527–1531.
- Bahçeci, Ş.; Yüksek, H.; Ocak, Z.; Köksal, C.; Ozdemir, M. Acta Chim. Slov. 2002, 49, 783–794.
- Ikizler, A.A.; Un, R. Chim. Acta Turc. 1979, 7, 269–290, Chem. Abstr. 1981, 94, 15645d.
- Sample Availability: Available from the Authors.
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