The direct replacement of a hydrogen atom by a thiocyano group through the use of thiocyanogen is termed thiocyanation. This replacement reaction is limited practically to aromatic amines and phenols. Thiocyanogen reacts with olefinic and acetylenic linkage, the reagent adding to the unsaturated linkage. Thicyanogen reacts with compounds of other types. Thiocyanogen reacts with aromatic compounds that are highly susceptible to substitution with the introduction of a thiocyano groups. Thiocyanation of aromatic amines, phenols is discussed. Addition of thiocyanogen to olefins and acetylenes, and miscellaneous syntheses are also discussed.