What is "thiopyrylium"

Thiopyrylium is a cation with the chemical formula CHS. It is analogous to the pyrylium cation with the oxygen atom replaced by a sulfur atom.

Thiopyrylium salts are less reactive than the analogous pyrylium salts due to the lower electronegativity of the sulfur atom. Among the chalcogenic 6-membered unsaturated heterocycles, thiopyrylium is the most aromatic, due to sulfur having the same Pauling electronegativity as carbon and only a slightly higher covalent radius.

Thiopyrylium salts can be synthesized by hydrogen abstraction from thiopyran by a hydride ion acceptor, such as trityl perchlorate.

The thiopyrylium analogue of 2,4,6-trisubstituted pyrylium salts can be synthesized by treatment with sodium sulfide followed by precipitation with acid. This reaction causes the oxygen atom in the pyrylium cation to be substituted with sulfur.