Sulfonic acids have functionality R−S(=O)−OH. They are strong acids that are typically soluble in organic solvents. Sulfonic acids like trifluoromethanesulfonic acid is a frequently used reagent in organic chemistry. Sulfinic acids have functionality R−S(O)−OH while sulfenic acids have functionality R−S−OH. In the series sulfonic—sulfinic—sulfenic acids, both the acid strength and stability diminish in that order. Sulfonamides, sulfinamides and sulfenamides, with formulas R−SONR′, R−S(O)NR′, and R−SNR′, respectively, each have a rich chemistry. For example, sulfa drugs are sulfonamides derived from aromatic sulfonation. Chiral sulfinamides are used in asymmetric synthesis, while sulfenamides are used extensively in the vulcanization process to assist cross-linking. Thiocyanates, R−S−CN, are related to sulfenyl halides and esters in terms of reactivity.