Prefixes mercapto

Thiols, unlike alcohols, form insoluble salts (mercaptides) (4) and (5) by reaction with heavy metals like mercury and lead (Scheme 3) this is the origin of the former name mercaptan for thiols, which comes from the Latin mercurium captans, meaning mercury seizing. In modern nomenclature the name thiol is preferred to mercaptan although the prefix mercapto is still allowed for the unsubstituted SH radical. 

In the lUPAC system, —OH takes precedence over —SH in both numbering and naming. In compounds containing these two functional groups, an —SH group is indicated by the lUPAC prefix sulfanyl-. Alternatively, it may be indicated by the common-name prefix mercapto-. 

In compounds containing other functional groups of higher precedence, the presence of —SH is indicated by the prefix mercapto-. 

The nomenclature of compounds containing —S— and =8 is unsatisfactory. As stated in the list on p. 50, —SH is denoted by the suffix -thiol (which is also the generic name) or prefix mercapto-, whereas MeS— is methylthio- sulphides, e.g., MeSBu, are named as methylthiobutane or butyl methyl sulphide. Thioketones EE C=S may be named by the suffix -thione (used in the same way as -one, as in MeBu C=8 hexane-2-thione) the prefix is thioxo-. In addition, a prefix thio- is widely used to denote replacement of oxygen by sulphur, particularly for acids and phenols (cf. thioketones and thioxo- also inorganic practice, p. 18). Thiophenol and thiocresol are normally used... 

The prefix thioxo- is used for naming =S in a thioketone. Sulfur analogs of acetals are named as alkylthio- or arylthio-. For example, CH3CH(SCH3)OCH3 is l-methoxy-l-(methylthio)ethane. Prefix forms for -carbothioic acids are hydroxy(thiocarbonyl)- when referring to the O-substituted acid and mercapto(carbonyl)- for the S-substituted acid. 

Salts are formed as with oxygen-containing compounds. For example, C2H5 — S—Na is named either sodium ethanethiolate or sodium ethyl sulfide. If mercapto- has been used as a prefix, the salt is named by use of the prefix sulfido- for —S . 

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