5-Methyl-l,3,4-thiadiazole-2-thiol

The tautomerism of DMTD (31a, 31b), as well as those of 5-amino-l,3,4-thiadiazole-2-thiol (AMTD) (32a, 32b) and 5-methyl-l,3,4-thiadiazole-2-thiol (MMTD) (33a, 33b), were investigated by means of FT-Raman and FT-IR spectroscopic techniques by Edwards and coworkers136. 

Aminocephalosporanic acid is converted to its sodium salt and acylated with lH-tetrazole-l-acetyl chloride. The acetoxy group is then displaced by reaction with 5-methyl-l,3,4-thiadiazole-2-thiol in buffer solution. The product acid is converted to the sodium salt by NaHC03. 

Methyl-l,3,4-thiadiazole-2-sulfonyl chloride was prepared as described for l,3-benzothiazole-2-sulfo-nyl chloride except that 5-methyl-l,3,4-thiadiazole-2-thiol was added as a solid over 30 min instead of as a suspension in aq AcOH over 2h. Moreover, EtjO was used instead of CH2CI2 for extraction, and Na2S04 instead of molecular sieves yield 80% mp 44-48 °C (EtjO). 

Recently, the degradation kinetics of two pharmaceutical intermediates [5-methyl-l,3,4-thiadiazole-2-methylthio (MMTD-Me) and 5-methyl-1,3,4-thiadiazole-2-thiol (MMTD)] has been studied in order to assess the effectiveness and the feasibility of UV processes. For both substrates, the results showed that no degradation occurred when H2O2 was used alone and that UV and UV/H2O2 processes were both effective for degrading the substrates, but... 

Physical Properties of 1,3,4-Thiadiazoles. Ultraviolet spectra of some 2-benzylideneamino-5-phenyl-1,3,4-thiadiazoles have been reported. The n.m.r. spectral properties and conformational preferences of some open-chain and cyclic aromatic sulphides that contain 1,3,4-thiadiazole units, spectroscopic data of metal (Mn, Fe, Co, Ni, Cu, or Zn) chelates of iV-(5-phenyl-l,3,4-thiadiazol-2-yl)dithiocarbamic acids, conductometric and i.r. and Raman determinations on thirteen complexes of Zn, Cd, or Hg with 2-methyl-5-mercapto-1,3,4-thiadiazole, and thermogravimetry of some noble- and common-metal chelates of 5-amino-l,3,4-thiadiazole-2-thiol were also described, as well as the mass-spectral fragmentation of 2-phenyl-... 

Tautomerism was reviewed quite extensively in CHEC(1984) <1984CHEC(6)545> and CHEC-II(1996) <1996CHEC-II(4)379>. The tautomeric ability of the 2-mercapto-5-methyl-l,3,4-thiadiazole 9 was studied by its reaction with the electrophilic Cl3 FnCSCl <2003JP01>. 2-Mercapto-5-methyl-l,3,4-thiadiazole 9 was considered to exist mainly as the thione tautomer however, electrophilic substitution occurred on the thiol (Scheme 1). 

The mechanism of the oxidation of 2-mercapto-5-methyl-l,3,4-thiadiazole (McMT) to its disulfide dimer and its subsequent reduction was examined with a combined approach employing experimental data and digital simulation. To elucidate the influence of proton transfers on these redox processes, special attention was paid to the influence of various bases and proton donors on both the oxidation and reduction reactions. In particular, McMT oxidation is facilitated by a rapid bimolecular proton transfer from McMT to weak bases such as pyridine that produces McMT , the thiol-ate form, which is then oxidized. There is no such facilitation in the presence of the sterically hindered base 2,6-di-r-butylpyridine, suggesting that the facilitation occurs through the formation of a discrete hydrogen-bonded complex/ ... 

When thioxo (or thiol) derivatives (as part of a thiourea function incorporated into the heterocyclic system) are present, effective. Y-alkylation is observed. Thus, the 3-heteroaryl-substituted [l,2,4]triazolo[3,4-/)][l,3,4]thiadiazole-6(5//)-thiones 37 dissolved in sodium hydroxide solution react with alkyl halides to afford the corresponding 6-alkylthio derivatives 38 (Equation 4) <1992IJB167>. The mesoionic compounds 39, inner salts of anhydro-7-aryl-l-methyl-3-methylthio-6-sulfonyl-[l,2,4]triazolo[4,3-A [l,2,4]triazolium hydroxides, are methylated with methyl iodide to give the corresponding quaternary salts 40 (Equation 5) <1984TL5427, 1986T2121>. 

The Schiff base derivatives 73 of the 3-hetaryl-substituted 4-amino-3-thiol-l,2,4-triazoles, on treatment with acetic anhydride, undergo cyclization to give the corresponding 3-substituted-5-acetyl-5,6-dihydro-6-phenyl[l,2,4]triazolo[3,4-7][l,3,4]thiadiazoles 76 (Equation 16) <1990IJB135>. Similar treatment of 4-(A-bcnzoylamino)-4,5-dihydro-l-methyl-3-mcthylthio-1 //-[ 1,2,4 triazolc-5-thione 77 leads to the [l,2,4]triazolo[3,4-4][l,3,4]thiadiazolium trifluoromethanesulfonate 78 (Equation 17) <1986LA1540>. 

---