5-Mercapto-l,2,3-triazoles

Many mercaptoazoles exist predominantly as thiones. This behavior is analogous to that of the corresponding hydroxyazoles (c/. Section 4.02.3.7). Thus oxazoline-, thiazoline- and imidazoline-2-thiones (521) all exist as such, as do compounds of type (522). However, again analogously to the corresponding hydroxyl derivatives, other mercaptoazoles exist as such. 5-Mercaptothiazoles and 5-mercapto-l,2,3-triazoles (523), for example, are true SH compounds. 

Dimroth rearrangement also occurs between the 5-mercapto-l,2,3-triazoles (109) and the 5-amino-l,2,3-thiadiazoles (110). If the thiadiazoles (110) are heated in basic solvents they are converted into the triazoles, whereas the reverse reaction is observed in acidic media (67LA(710)118, 69CB417, 72ACS1243). Thermal equilibria of thiadiazoles and triazoles, with both isomers present, have been reported (62Acs(B)1800, 66CB1618). 

T. Kindt-Larsen and C. Pedersen, Interconversion of 1-phenyl-5-mercapto-l,2,3-triazole and 5-phe-nylamino-l,2,3-thiadiazole, Acta Chem. Scand, 16 (1962) 1800-1801. 

Sodium hydroxide 5-Mercapto-l,2,3-triazoles from 5-amino-l,2,3-thiadiazoles... 

Within the huge field of heterocyclic rearrangements [53], the Dimroth rearrangement gives 5-mercapto-l,2,3-triazoles from 5-amino-l,2,3-thiadiazoles and allows interconversion of 5-amino-l,2,3-triazoles into a mixture of isomers under basic condition [54]. Thus, this reaction, discovered in 1909, involves a linear intermediate that can cyclize into two isomeric compounds (Scheme 15) [55]. This ring-chain tautomerization is reversible, but the equilibrium can be pushed toward an end if one of the two isomers is stabilized. 

Synthesis of 5-Mercapto-l,2,3-Triazole Derivatives from 5-Amino-l,2,3-Thiadiazoles... 

In addition, 5-mercapto-l,2,3-triazole derivatives 55 bearing in 1-position different alkyl groups have been also prepared using the same synthetic pathways... 

In solutions of 3-mercapto-l, 2,4-triazoles the tautomeric equilibrium is shifted to the thione forms 181b (Scheme 65) [76AHC(S1), pp. 404, 415 96UK326]. Such an equihbrium was observed for 3-mercapto-5-ferrocenyl-4-phenyl-1,2,4-triazole 182 (94MI1121 96UK326). The thione tautomers 183 of 5-mercapto-l,2,4-triazoles are predominant [76AHC(S1), pp. 405, 414 97SA(A)699]. 

Hydrolytic fragmentation of the C5-N6 part took place upon heating 7-methyl-5-propyl-2-thioxo-l,2,4-triazolo[l,5-c]pyrimidine (129) with hydrochloric acid. 3-Acetonyl-5-mercapto-l,2,4-triazole (130) and butanoic acid were obtained as a result of N4-C5, C5-N6, and N6-C7 bond cleavages (65JCS3369) (Scheme 50). 

The complex IrL3, HL = 3-methyl-4-benzylideneimino-5-mercapto-l,2,4-triazole (214), which binds through the indicated S and N in a bidentate manner, has been prepared and characterized by physicochemical techniques.384... 

Klink, K.J. and Meade, B.J., Dermal exposure to 3-amino-5-mercapto-l,2,4-triazole (AMT) induces sensitization and airway hyperreactivity in BALB/c mice, Toxicol. Sci., 75, 89, 2003. 

Similarly, 3-(5-mercapto-l,2,4-triazol-3-yl)-7-methyl-l,4-dihydro-4-oxo-l,8-naphthyridines 432, after reaction with substituted benzaldehydes, chloroacetic acid in the presence of the mixture of acetic anhydride and acetic acid, gives the corresponding 3-(6-arylidene-5-oxo-5,6-dihydro-thiazolo[3,2- ]-l,2,4-triazol-2-yl)-7-methyl-l,4-dihydro4-oxo-1,8-naphthyridines 433 (Equation 92) <2002EJC323>. 

The reaction of oxalyl hydrazide with aryl isothiocyanate gives the bis(thiosemicarbazide) (162) which under acidic conditions cyclizes to the bis(l,3,4-thiadiazole) (163). Under alkaline conditions the 5-mercapto-l,2,4-triazole (164) is obtained (77BSB399). 

Amino-5-mercapto-l,2,4-triazole [16691-43-3] M. 116.1, m 298 , pKeskd 3.0, pKEst(2) Recrystd from H2O and dried in vacuo. The acetyl derivative has m 325° (dec) after recrystn from H2O. [Beilstein 26, 3rd/4th SuppI p. 1351.] Also recrystd from EtOH/H20 (3 1, Ig in 50 mL, 50% recovery), m 300-302° dec subject to heating rate (Xmax 263nm, log e 4.12), and S-Benzyl derivative when crystd from CgHg/EtOH (20 1), or CHClj/EtaO has m 109-111° [Godfrey and Kruzer J Chem Soc 3437 7960]. 

Respiratory sensitization to chemicals may be acquired via dermal contact. I26l An example of this is the induction of airway sensitization in workers in a herbicide-producing plant that manufactured 3-amino-5-mercapto-l,2,4-triazole (AMT) by dermal contact. Experiments with mice confirmed the sensitization potential of AMT)27 ... 

Aminodehydroxylation, 152-153,398 2-Amino-3,6-di-r-butylphenol, 406 7-Aminofurazano[3,4-d] pyrimidines, 281 4-Amino-3-hydrazino-5-mercapto-l, 2,4-triazole, 19... 

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