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1,2,3-Thiadiazole is a unique and stable heteroaromatic compound consisting of one sulfur atom, two adjacent nitrogen atoms, and two carbon atoms. It exhibits a π-excessive nature and almost planar structure, resulting in interesting chemical properties.
An analysis of the π electron density map reveals that sulfur has the highest electron density, followed by nitrogen. On the other hand, carbon atoms C4 and C5 are electron deficient, making them less susceptible to electrophilic substitution. However, nucleophilic substitution is more favorable at C5 due to its lower electron density. Notably, the synthesis of 1,2,3-thiadiazole involves quaternization with dimethyl sulfate, resulting in a mixture of 2- and 3-methyl-1,2,3-thiadiazole.
1,2,3-Thiadiazoles find applications in various fields, including insecticide synergists, cross-linked polymer compounds, herbicides, sedatives, antibacterials, antibiotics, antivirals, and neurodegenerative treatments.
Several synthetic approaches exist for the construction of 1,2,3-thiadiazoles. One widely accepted method is the Hurd-Mori method, which involves the intramolecular cyclization of hydrazones using SOCl2 or S2Cl2. Another approach utilizes the reaction of tosyl hydrazine with ethyl methyl ketone, followed by cyclization with thionyl chloride to yield 4,5-disubstituted 1,2,3-thiadiazole.
The physical properties of 1,2,3-thiadiazole include its yellow-colored liquid form with a boiling point of 157°C. It is a weak base, thermally stable, and soluble in water and various organic solvents such as alcohol, ether, DCM, and chloroform.
Due to the electron density distribution, the carbon atoms C4 and C5 are less susceptible to electrophilic attack compared to nitrogen atoms. However, they readily undergo nucleophilic substitution reactions.
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