It has been shown by nitration with a mixture of 99–100% nitric acid and acetic anhydride that 2-nitraminothiazoles, such as 2-nitramino-5-nitrothiazole and 4-methyl-2-nitramino-5-nitrothiazole, can react in the tautomeric nitrimino form. The nitration occurs in the three position of the thiazole ring. Compounds with an acetamido group in the two position of the thiazole ring, such as 2-acetamido-5-bromo-2-thiazole and 2-acetamido-5-methylthiazole, can also be nitrated in the three position indicating the tautomeric change from the acetamido to the acetimido group.