Thiobenzophenone is an

organosulfur compound Organosulfur compounds are organic compounds that contain sulfur. They are often associated with foul odors, but many of the sweetest compounds known are organosulfur derivatives, e.g., saccharin. Nature abounds with organosulfur compounds—sulfu ...

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 to form benzophenone and sulfur. Thiobenzophenone is deep blue and dissolves readily in many organic solvents.

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°.Sustmann, R.; Sicking, W.; Huisgen, R. "A Computational Study of the Cycloaddition of Thiobenzophenone S-Methylide to Thiobenzophenone". J. Am. Chem. Soc. 2003, 125, 14425-14434. A variety of thiones with structures and stability related to thiobenzophenone have also been prepared.

Synthesis

One of the first reported syntheses of thiobenzophenone involves the reaction of sodium hydrosulfide and diphenyldichloromethane": :Ph₂CCl₂ + 2 NaSH → Ph₂C=S + 2 NaCl + H₂S An updated method involves sulfiding of benzophenone: :Ph₂C=O + H₂S → Ph₂C=S + H₂O In the above reaction scheme, a mixture of gaseous hydrogen chloride and

hydrogen sulfide Hydrogen sulfide is a chemical compound with the formula . It is a colorless chalcogen-hydride gas, and is poisonous, corrosive, and flammable, with trace amounts in ambient atmosphere having a characteristic foul odor of rotten eggs. The unde ...

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.

Reactivity

Due to the weakness of the C=S bond, thiobenzophenone is more reactive than its C=O benzophenone counterpart. Thiobenzophenone as well as other thioketones are considered to be superdipolarophiles and dienophiles that rapidly combine with 1,3-dienes in Diels-Alder cycloadditions.Fisera, L.; Huisgen, R.; Kalwinsch, I.; Langhals,E.; Li, X.; Mloston, G.; Polborn, K.; Rapp, J.; Sicking, W.; Sustmann, R. "New Thione Chemistry". Pure Appl. Chem., 1996, 68, 789-798. 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. Reactions between thiobenzophenone and most dienes yield Diels-Alder adducts whereas reactions with monoolefins yield bicyclic compounds.Okuma, K.; Yamamoto, T.; Shirokawa, T.; Kitamura, T.; Fujiwara, Y. "The First Isolation of Benzyne-Thiobenzophenone Adducts". Tetrahedron Letters, 1996, 49, 8883-8886.

References

{{reflist Thioketones Benzophenones