![Dithiolium isomers](https://upload.wikimedia.org/wikipedia/commons/c/cb/Dithiolium_isomers.png)
Dithiolium salts are compounds of the formula
3S2">RC)3S2sup>+X
− (R = H, alkyl, aryl, etc.). These salts consist of a planar organic cation with a variety of anions such as halides. The five-membered ring cations are observed in either of two
isomer
In chemistry, isomers are molecules or polyatomic ions with identical molecular formulae – that is, same number of atoms of each element – but distinct arrangements of atoms in space. Isomerism is existence or possibility of isomers.
Iso ...
s, 1,2- and 1,3-dithiolium cations. These cations differ with respect to the relative positions of the pair of sulfur atoms. Both isomers feature a planar ring, which is
aromatic
In chemistry, aromaticity is a chemical property of cyclic ( ring-shaped), ''typically'' planar (flat) molecular structures with pi bonds in resonance (those containing delocalized electrons) that gives increased stability compared to satur ...
owing to the presence of 6π electrons.
For example, the 1,2-ditholium ring can be represented as an
allyl cation
In organic chemistry, an allyl group is a substituent with the structural formula , where R is the rest of the molecule. It consists of a methylene bridge () attached to a vinyl group (). The name is derived from the scientific name for garlic, . ...
of the three carbons,
[ with each sulfur atom donating one of its ]lone pair
In chemistry, a lone pair refers to a pair of valence electrons that are not shared with another atom in a covalent bondIUPAC ''Gold Book'' definition''lone (electron) pair''/ref> and is sometimes called an unshared pair or non-bonding pair. Lone ...
s of electrons to give a total of three pairs.
Preparation, occurrence, reactions
1,2-Dithiolium cations have been prepared from 1,3-diketones by treatment with H2S and oxidants such as bromine.
:
1,3-Dithiolium cations are often prepared by alkylation of the corresponding unsaturated dithio- or trithiocarbonates:
:{{Chem2, (RC)2S2CE + R'+ -> RC)2S2CER'
The analogous reaction of electrophiles with 1,2-dithiole
In organosulfur chemistry, a 1,2-dithiole is a type of heterocycle. The parent of this class of compounds is 1,2-dithiacyclopentene. The anticancer drug oltipraz
Oltipraz is an organosulfur compound belonging to the dithiolethione class. It ...
-2-ones affords 1,2-dithiolium cations.
References
Organosulfur compounds
Aromatic compounds