Thiobenzophenone

Thiobenzophenone is an organosulfur compound with the formula (C₆H₅)₂CS. It is the prototypical thioketone. Unlike other thioketones that tend to dimerize to form rings and polymers, thiobenzophenone is quite stable, although it photoxidizes in air back to benzophenone and sulfur.^[1] Thiobenzophenone is deep blue and dissolves readily in many organic solvents.

Thiobenzophenone

Names
Preferred IUPAC name Diphenylmethanethione
Identifiers
CAS Number	1450-31-3 Y
3D model (JSmol)	Interactive image
ChemSpider	502886 N
PubChem CID	578536
UNII	JYQ6P4G3UJ Y
CompTox Dashboard (EPA)	DTXSID50342088
InChI InChI=1S/C13H10S/c14-13(11-7-3-1-4-8-11)12-9-5-2-6-10-12/h1-10H N Key: XDDVRYDDMGRFAZ-UHFFFAOYSA-N N InChI=1/C13H10S/c14-13(11-7-3-1-4-8-11)12-9-5-2-6-10-12/h1-10H Key: XDDVRYDDMGRFAZ-UHFFFAOYAD
SMILES S=C(C1=CC=CC=C1)C2=CC=CC=C2
Properties
Chemical formula	C13H10S
Molar mass	198.28 g·mol−1
Appearance	Deep blue solid
Melting point	53 to 54 °C (127 to 129 °F; 326 to 327 K)
Boiling point	174 °C (345 °F; 447 K)
Hazards
Flash point	no
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). N verify (what is YN ?) Infobox references

Structure

The C=S bond length of thiobenzophenone is 1.63 Å, which is comparable to 1.64 Å, the C=S bond length of thioformaldehyde, measured in the gas phase. Due to steric interactions, the phenyl groups are not coplanar and the dihedral angle SC-CC is 36°.^[2] A variety of thiones with structures and stability related to thiobenzophenone have also been prepared.^[1]

Synthesis

One of the first reported syntheses of thiobenzophenone involves the reaction of sodium hydrosulfide and diphenyldichloromethane:^[3]

Ph₂CCl₂ + 2 NaSH → Ph₂C=S + 2 NaCl + H₂S

An updated method involves sulfiding of benzophenone:^[4]

Ph₂C=O + H₂S → Ph₂C=S + H₂O

In the above reaction scheme, a mixture of gaseous hydrogen chloride and hydrogen sulfide are passed into a cooled solution of benzophenone in ethanol. Thiobenzophenone can also be produced by a Friedel-Crafts reaction of thiobenzoyl chloride and benzene.^[5]

Reactivity

Due to the relative weakness of the C=S bond, thiobenzophenone is more reactive than benzophenone. Thiobenzophenone (as well as other thioketones) is a dipolarophiles and dienophiles. For example, it combines with 1,3-dienes in Diels-Alder cycloadditions.^[6] The rate of thioketones in cycloadditions is related but not limited to the size of the small HOMO/LUMO energy gap of the π-MOs of the C=S double bond.^[2] Reactions between thiobenzophenone and most dienes yield Diels-Alder adducts whereas reactions with monoolefins yield bicyclic compounds.^[7]