Triazoles mercapto

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. 

The use of an acidic solution of p-anisaldehyde in ethanol to detect aldehyde functionalities on polystyrene polymer supports has been reported (beads are treated with a freshly made solution of p-anisaldehyde (2.55 mL), ethanol (88 mL), sulfuric acid (9 mL), acetic acid (1 mL) and heated at 110°C for 4 min). The colour of the beads depends on the percentage of CHO content such that at 0% of CHO groups, the beads are colourless, -50% CHO content, the beads appear red and at 98% CHO the beads appear burgundy [Vdzquez and Albericio Tetrahedron Lett 42 6691 200]]. A different approach utilises 4-amino-3-hydrazino-5-mercapto-1,2,4-triazole (Purpald) as the visualizing agent for CHO groups. Resins containing aldehyde functionalities turn dark brown to purple after a 5 min reaction followed by a 10 minute air oxidation [Coumoyer et al. J Comb Chem 4 120 2002]. 

From 4-phenylthiosemicarbazide Freund and HempeH obtained a product to which they assigned the structure of a tetrazolinethione. When heated in alkaline solution it was isomerized to a compound which, on the basis of adequate chemical evidence, was considered to be 5-mercapto-l-phenyltetrazole. According to Lieber and Ramach-andran, however, the initial product is 5-phenylamino-l,2,3,4-thia-triazole. Lieber and Slutkin have also converted some di(thiosemi-... 

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]. 

The tautomerism of 3-mercapto-l,2,5-triazole 184 has not been studied thus far. Very little information is available on the structure of 2-mercapto-1,3,4-triazole and its selenium analog, but apparently the thione 185 and se-lenone 186 forms are preferred for these compounds [76AHC(S1), pp. 408, 414]. 

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). 

Triazole ring cleavage of the 7-amino-5-benzyl-5-mercapto-l,2,4-triazolo-[l,5-c]pyrimidinium iodide 135 at the N3-N4 bond occurred upon treatment with potassium carbonate to give the 4-amino-2-benzylmercapto-l-methyl-... 

Accurate X-ray crystallographic data indicate that 5-hydrazino-3-mercapto-1,2,4-triazole exists in the solid state as a betaine, either as 165 or 166, with strong inter molecular hydrogen bonding occurring be-... 

Aldehydes 4-Amino-3-hydrazino-5-mercapto-1,2,4-triazole (Purpald reagent) Aldehydes yield violet chromatogram zones on a whitish-yellow background. Some alcohols form yellow to orange-colored chromatogram zones. [2]... 

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... 

A comprehensive review on the chemistry of mercapto- and thione-substituted 1,2,4-triazoles and their utility in heterocyclic synthesis has been published <06ARK59>. The thermodynamic parameters, AAH and AAS, were determined for the interception of an intermediate, with the structural characteristics of an aziridinium imide, by nucleophilic solvents during the reaction of 2-methy 1-2-butene with A-phenyltriazolinedione <06TL2961>. 

The thiol group was displaced from 3-mercapto-l,2,4-triazoles 59 using oxidation to yield the corresponding 3-unsubstituted compounds 60a-d in good yield (Equation 19) (Table 5) <2006S156>. 

Table 5 Oxidation of 3-mercapto-1,2,4-triazole derivatives using hydrogen peroxide (Equation 19)...

Mercapto-l,2,4-triazole 67 reacted in a standard coulometric cell with the ortho-quinone generated electroche-mically from 1,2-dihydroxybenzene to give 4-(l//-l,2,4-triazole-3-ylsulfanyl)-l,2-benzenediol 68 via a Michael addition (Equation 23) <2005MI68>. 

A range of L-cysteine derivatives bearing a 1,2,4-triazolyl residue on the sulfur atom has been prepared by the asymmetric Michael addition of 4,5-dialkyl-3-mercapto-l,2,4-triazoles to a nickel Schiff base complex. The enantiomeric excesses of the product aminoacids were measured and found to be greater than 98.5% in some cases <2004TA705, 2004RCB932, 2004IZV894>. 

Acylhydrazides reacted with isothiocyanates in a one-pot procedure using microwave irradiation of the starting materials in the presence of either silica or montmorillonite K10 to give the 3-mercapto-l,2,4-triazoles 137a-f in high yields (Equation 42 and Table 26) <2006PS(181)1839>. 

Two 4-amino-3-mercaptol,2,4-triazole residues linked by a two-carbon bridge have been prepared by the reaction of thiocarbohydrazide with succinic acid 157a or malic acid 157b to give l,2-bis-(4-amino-5-mercapto-477-l,2,4-triazol-3-yl)ethan-l-ol 158a or l,2-bis-(4-amino-5-mercapto-477-l,2,4-triazol-3-yl)ethane 158b in yields of 56% and 60%, respectively (Equation 49) <2006PS(181)2361>. 

Cyclization of semicarbazide derivatives 185 was achieved using microwave irradiation in the presence of sodium hydroxide for 2—4 min to give the corresponding 3-mercapto-l,2,4-triazoles 186a-f in high yields (Equation 57 and Table 38) <2006PS(181)1913>. 

Table 38 Microwave-assisted cyclization of semicarbazides to give 3-mercapto-1,2,4-triazole...

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. 

Fused heterocyclic systems derived from 3-mercapto-l,2,4-triazole can be obtained by heterocyclization of 4-allyl-l,2,4-triazole-3-thione derivatives by treatment with halogens or mineral acids <1996T791>. Compounds 342 react with bromine yielding thiazolium halides 28 in good yield (Equation 64) <2000RJOC1033>. 

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>. 

Mercapto-l /7-l,2,4-triazol-3 -yl-isoquinolinium chlorides 438 react with 1,2-dibromoethane to produce a variety of substituted 6,7-dimethoxy-3-methyl-W-(5, 6 -dihydrothiazolo[3,2-3][l,2,4]triazol-2 -yl)isoquinolinium bromides 439 (Equation 96) <2003JHC1041>. 

When bis-hydrazonoyl chloride is treated with 3-mercapto-l,2,4-triazole 431 (R = H) in ethanol in the presence of triethylamine at reflux, compound 34 is isolated in 52% yield (Equation 99) <2004JCR(S)264>. 

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