In organic chemistry, isothiouronium is a functional group with the formula [RSC(NH<sub>2</sub>)<sub>2</sub>]+ (R = alkyl, aryl) and is the acid salt of isothiourea. The H centres can also be replaced by alkyl and aryl. Structurally, these cations resemble guanidinium cations. The CN2S core is planar and the C–N bonds are short.[1]
Salts comprising these cations are typically prepared by alkylation of thiourea:
SC(NH2)2 + RX → [RSC(NH<sub>2</sub>)<sub>2</sub>]+X−
Hydrolysis of isothiouronium salts gives thiols.
[RSC(NH<sub>2</sub>)<sub>2</sub>]+X− + NaOH → RSH + OC(NH2)2 + NaX
Isothiouronium salts in which the sulfur has been alkylated, such as S-methylisothiourea hemisulfate (CAS number: 867-44-7), will convert amines into guanidinium groups. This approach is sometimes called the Rathke synthesis[2] after Bernhard Rathke[3] who first reported it in 1881.[4]
RNH2 + [CH<sub>3</sub>SC(NH<sub>2</sub>)<sub>2</sub>]+X− → [CH<sub>3</sub>N(H)C(NH<sub>2</sub>)<sub>2</sub>]+X− + CH3SH
Chelating resins with isothiouronium groups are used to recover mercury and other noble metals including platinum from solutions.[5]