Microwave-assisted oxidation of 1-substituted tetrazole-5-thiones

Abstract

SHORT COMMUNICATIONSTetrazole ring is stable toward oxidants [1,2], and its decomposition by the action of oxidants is a very rare case [3]. Reactions of mono-and disubstituted tetrazoles with oxidants usually involve only the substituents whose transformations depend on their nature and position in the heteroring. Therefore, oxidation of mono-and disubstituted tetrazoles may be regarded as a simple and efficient method for their functionalization, as well as for the preparation of monosubstituted tetrazoles.In continuation of our studies on the chemical properties of tetrazoles we examined oxidation of some 1-substituted tetrazole-5-thiones under microwave (MW) activation. Among various oxidants used previously for the oxidation of 1-substitued tetrazole-5-thiones [4-6], we selected hydrogen peroxide as the most convenient in handling and ecologically safe. As shown in [6], treatment of 1-aryltetrazole-5-thiones with 12% hydrogen peroxide in ethanol at 60°C (reaction time 10 min) leads to the formation of the corresponding bis-tetrazolyl disulfides in good yields. We found that oxidation of 1-substituted tetrazole-5-thiones with hydrogen peroxide under microwave activation gives 1-substituted tetrazoles. The reaction direction strongly depended on the concentration of hydrogen peroxide and reaction medium. Microwaveassisted oxidation of 1-phenyltetrazole-5-thione with 3.5% hydrogen peroxide gave 92% of bis(1-phenyl-1H-tetrazol-5-yl) disulfide. When the concentration of hydrogen peroxide was raised to 17.5% and acetic acid was used as solvent, the product was 1-phenyl-1H-tetrazole (Ic, yield 91%). Analogous relations were observed for the other examined tetrazole-5-thiones.Thus hydrogen peroxide under conditions of microwave activation is much more efficient than other oxidants, such as chromic [4] or nitric acid [7], that are usually used for oxidative desulfurization of 1-substituted tetrazole-5-thiones. 1-Ethyl-1H-tetrazole (Ia). 1-Ethyl-4,5-dihydro-1H-tetrazole-5-thione, 0.5 g (3.8 mmol), was dissolved in 10 ml of chloroform, 5 ml of 17.5% hydrogen peroxide and 0.5 ml of glacial acetic acid were added under stirring, and the mixture was stirred for 45 min at 50°C under microwave activation (20 W). The mixture was cooled to 20°C, 15 ml of cold water was added, and the organic layer was separated. The aqueous phase was neutralized to pH 7 with 25% aqueous ammonia and extracted with chloroform (2 × 10 ml). The extracts were combined, dried over magnesium sulfate, and evaporated under reduced pressure. Yield 85%, colorless oily substance [8]. IR spectrum, ν, cm -1 : 3436,

Zinc (II) Chloride as Phase Transfer Catalyst and as Catalyst of Cycloaddition Azide Ion to Heterocumulenes and Terminal Alkynes in Organic Solvents

“…1‐Substituted 1 H ‐tetrazole‐5‐thioles are widely used in the synthesis of biologically active substances and functional materials, moreover, they are valuable reagents in organic synthesis . These compounds are used in the olefination of carbonyl derivatives (Julia‐Kocienski Olefination), and can also be used for the preparation of 1‐substituted 1 H ‐tetrazoles, 1‐substituted 5‐bromo‐1 H ‐tetrazoles and 1‐substituted 1 H ‐tetrazole‐5‐ones …”

A Facile Zinc(II) Chloride Assisted Desulfurization of High‐Nitrogen Heterocycles

“…While these syntheses are incredibly straightforward, [12] the traditional desulfurization processes to yield the sulfur–free high–nitrogen molecules via the addition of hydrogen peroxide to the material in either acetic acid or trifluoro acetic acid [13] can result in an exothermic decomposition of both the sulfur–tipped precursor and any product being formed. Microwave‐assisted desulfurization is also known however this method relies on an expensive specialized laboratory microwave, [14] making this method not available to all research groups.Thus, a new safer and more controllable desulfurization process was created.…”