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The preparation described in Warren, J. D., et al, J. Heterocyclic Chem. 16, 1817 (1979) was used to prepare 1,2,5-thiadiazole-3,4-dicarboxylic acid from diaminomaleonitrile. At room temperature, 4.30 g of p-toluenesulfonyl chloride was added to a solution of 0.990 g of 1,2,5-thiadiazole-3,4-dicarboxylic acid in 10 mL of pyridine. The solution was cooled in an ice bath and 1.09 g of t-butylhydroperoxide (90% solution in water) was added. The solution was stirred for one hour during which it was cooled with an ice bath such that the temperature was as low as possible without freezing the pyridine. The solution was then poured into a mixture of water and toluene. The toluene layer was separated and washed twice with a 10% aqueous sodium hydroxide solution. The toluene solution was then dried over sodium sulfate and the solvents removed giving rise to 1.414 g of a yellow liquid. The yellow liquid was purified by column chromatography to give a colorless solid with a melting point of 39°-41° C.; 1H NMR (CDCl3) δ 1.42 (s); IR (coated on a thin polymer film) 1784, 1132, 1019 cm-1. ##STR17##

1. temperatureThe solution was cooled in an ice bath
2. temperaturewas cooled with an ice bath such that the temperature
3. customThe toluene layer was separated
4. washwashed twice with a 10% aqueous sodium hydroxide solution
5. dry with materialThe toluene solution was then dried over sodium sulfate
6. customthe solvents removed