Molbank 2006, M462

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Synthesis and acidic properties of novel 3-methyl-4-[(2-amino-1,3,4-thiadiazol-5-il)-thioacetylamino]-4,5-dihydro-1H-1,2,4-triazol-5-one

Haydar Yüksek^a*, Muzaffer Alkan^a and Şule Bahçeci^b

^aEducation Faculty, Kafkas University, 36100-Kars, Turkey

tel: (+90)-474-2126608, fax: (+90)-474-2121185, e-mail: [email protected]

^bFatih Education Faculty, Karadeniz Technical University, 61335-Trabzon, Turkey

*Author to whom correspondence should be addressed

Received: 25 January 2005 / Accepted: 26 November 2005 / Published: 22 January 2006

A number of studies involving the determination of pK_a values of some 4,5-dihydro-1H-1,2,4-triazol-5-one derivatives in non-aqueous solvents has been revealed [1-3]. 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 pK_a values. For compound 3, the half-neutralization potentials (HNP) and the corresponding pK_a 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 (λ_max 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 pK_a values of compound 3 are presented Table 1.

Solvent	HNP1 (mV)	pKa1	HNP2 (mV)	pKa2
Isopropyl alcohol	291	2.06	-221	10.64
tert-butyl alcohol	287	2.16	-269	11.61
N,N-dimethylformamide	218	3.36	-342	12.68

Table1: HNP values and the corresponding pK_a 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.

References: 

1. H. Yüksek, Z. Ocak, M. Alkan, Ş. Bahçeci and M. Ozdemir, Molecules., 2004, 9, 232-240.

2. H. Yüksek, M. Alkan, Z. Ocak, Ş. Bahçeci, M. Ocak and M. Ozdemir, Indian J. Chem., 2004, 43B, 1527-1531.

3. Ş. Bahçeci, H. Yüksek, Z. Ocak, C. Köksal and M. Ozdemir, Acta Chim. Slov., 2002, 49, 783-794.

4. A.A. Ikizler and R. Un, Chim. Acta Turc., 1979, 7, 269-290; Chem. Abstr. 1981, 94, 15645d.

Sample Availability: Available from the Authors.

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