methylthio

Methylthio is the chemical term for the substituent composed of a sulfur atom bonded to a methyl group, written as -S-CH3. In organic structures, this group is a thioether linkage, where the sulfur atom connects a methyl group to the rest of the molecule. The methylthio group is sometimes described by the synonyms thiomethyl or methylthio-, and in IUPAC naming it may be used as a prefix to indicate the presence of this substituent on the parent compound.

In naming and terminology, methylthio designates the S-CH3 unit attached through sulfur to the carbon framework. This distinguishes it from the related methoxy group (-O-CH3), as the presence of sulfur imparts different steric and electronic properties, influencing reactivity, polarity, and metabolic fate.

Preparation and reactions commonly involve introducing a methylthio group by S-alkylation: a thiolate (R-S−) reacts with a methylating agent such as methyl iodide (CH3I) to form R-S-CH3. Methylthio groups can also arise as intermediates in the synthesis of more complex organosulfur compounds.

Occurrences and applications vary, but methylthio groups are encountered in organic synthesis, natural products, and pharmaceuticals as simple building blocks or functional group modifications. They contribute to the diversity of sulfur-containing substituents that influence the physical and chemical properties of molecules, including lipophilicity and reactivity.