Thionated

Thionated is an adjective describing a molecule that has undergone thionation, a chemical transformation in which a sulfur atom is introduced into a molecule, typically replacing an oxygen atom in a carbonyl group to form a thiocarbonyl (C=S). The term derives from the prefix thio- meaning sulfur and the suffix -ation indicating a process.

In practice, thionation most often converts carbonyl-containing substrates such as aldehydes, ketones, amides, or carboxylic acid derivatives into their thiocarbonyl counterparts (thioketones, thioamides, thiol esters, etc.). The process is widely used in organic synthesis to access sulfur-containing analogs with different reactivity and photophysical properties.

Common reagents include Lawesson's reagent and phosphorus pentasulfide (P4S10). These reagents transfer sulfur to the carbonyl group under heating in suitable solvents, sometimes requiring catalysts or additives for selectivity. Other thionating agents exist, tailored to substrate sensitivity.

Applications of thionation include the preparation of thioketones and thioamides used as intermediates in natural product synthesis, pharmaceuticals, and materials science. Thiocarbonyl compounds often exhibit distinct reactivity and infrared/UV characteristics compared with their oxo analogs, which can be advantageous for spectroscopy and as chromophores.

Limitations and considerations include sensitivity to moisture and air; many thionating reagents are malodorous, moisture sensitive, and potentially toxic or corrosive. Selectivity can be challenging for multifunctional substrates, sometimes necessitating protecting groups or careful reagent choice. See also: thiocarbonyl, thioamide, Lawesson's reagent, P4S10.