Isothiouronium

S-Ethylisothiouronium diethylphosphate: an example of an isothiuronium compound

In organic chemistry, isothiouronium is a functional group with the formula [RSC(NH₂)₂]^+ (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]

Synthesis

Salts comprising these cations are typically prepared by alkylation of thiourea:

SC(NH₂)₂ + RX → [RSC(NH₂)₂]^+X^−

Reactions

Hydrolysis of isothiouronium salts gives thiols.[2]

[RSC(NH₂)₂]^+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[3] after Bernhard Rathke[4] who first reported it in 1881.[5]

RNH₂ + [CH₃SC(NH₂)₂]^+X^− → [CH₃N(H)C(NH₂)₂]^+X^− + CH₃SH

Chelating resins with isothiouronium groups are used to recover mercury and other noble metals including platinum from solutions.[6]

References

1. Barker, J.; Powell, H. R. (1998). "S-Benzylisothiouronium Chloride". Acta Crystallographica Section C. 54 (12): 2019. doi:10.1107/S0108270198008166.
2. Helmer Kofod (1963). "Furfuryl Mercaptan". Organic Syntheses. 4: 13; Collected Volumes, vol. 1, p. 66.
3. Palmer, David C. (2001). "S-Methylisothiourea". E-EROS Encyclopedia of Reagents for Organic Synthesis. doi:10.1002/047084289X.rm199s. ISBN 0471936235.
4. "Heinrich Bernhard Rathke. (1840-1923)". Berichte der Deutschen Chemischen Gesellschaft (A and B Series). 57 (9): A83 – A92. 8 October 1924. doi:10.1002/cber.19240570929.
5. Rathke, B. (July 1881). "Ueber Derivate und Constitution des Schwefelharnstoffs". Berichte der Deutschen Chemischen Gesellschaft. 14 (2): 1774–1780. doi:10.1002/cber.18810140247.
6. "Purolite S920 Isothiouronium Chelating Resin". Purolite. Archived from the original on 2016-03-04. Retrieved 2012-09-07.