Isothiouronium
File:S-Ethylisothiouronium diethylphosphate.svg: 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.{{cite journal | doi = 10.1107/S0108270198008166 | title = S-Benzylisothiouronium Chloride | year = 1998 | last1 = Barker | first1 = J. | last2 = Powell | first2 = H. R. | journal = Acta Crystallographica Section C | volume = 54 | issue = 12 | pages = 2019| doi-access = }}
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.{{OrgSynth|author=Helmer Kofod|year=1963|title=Furfuryl Mercaptan|volume=4|pages=13|collvol=1|collvolpages=66|prep=CV4P0491}}
:[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{{cite journal|last1=Palmer|first1=David C.|title=S-Methylisothiourea|journal=E-EROS Encyclopedia of Reagents for Organic Synthesis|year=2001|doi=10.1002/047084289X.rm199s|isbn=0471936235}} after Bernhard Rathke{{cite journal|title=Heinrich Bernhard Rathke. (1840-1923)|journal=Berichte der Deutschen Chemischen Gesellschaft (A and B Series)|date=8 October 1924|volume=57|issue=9|pages=A83–A92|doi=10.1002/cber.19240570929|doi-access=free}} who first reported it in 1881.{{cite journal|last1=Rathke|first1=B.|title=Ueber Derivate und Constitution des Schwefelharnstoffs|journal=Berichte der Deutschen Chemischen Gesellschaft|date=July 1881|volume=14|issue=2|pages=1774–1780|doi=10.1002/cber.18810140247|url=https://zenodo.org/record/1425246}}
: 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.{{cite web | url = http://www.purolite.com/default.aspx?RelID=606267&ProductID=19 | title = Purolite S920 Isothiouronium Chelating Resin | publisher = Purolite | access-date = 2012-09-07 | archive-date = 2016-03-04 | archive-url = https://web.archive.org/web/20160304025747/http://www.purolite.com/default.aspx?RelID=606267&ProductID=19 | url-status = dead }}