Crystal structure of a methimazole-based ionic liquid.

The structure of 1-methyl-2-(prop-2-en-1-ylsulfan­yl)-1H-imidazol-3-ium bromide, C7H11N2S+·Br−, has monoclinic (P21/c) symmetry. In the crystal, the components are linked by N—H⋯Br and C—H⋯Br hydrogen bonds. The crystal structure of the title compound undeniably proves that methimazole reacts through the thione tautomer, rather than the thiol tautomer in this system.