Organosulfur chemistry

Organosulfur chemistry is the study of how organosulfur compounds are made and what they do. These compounds are made of sulfur and carbon. Many organosulfur compounds smell bad, but some of the sweetest things, like saccharin, are made from them. Sulfur is very important for living things. Out of the 20 common building blocks of proteins, two (cysteine and methionine) have sulfur. Medicines like penicillin and sulfa drugs also have sulfur. These medicines save many lives, but sulfur mustard is a dangerous chemical used in war. Fuels like coal, oil, and gas, which come from ancient plants and animals, contain organosulfur compounds. Removing these sulfur compounds is a big job for oil refineries.

Sulfur belongs to the same group as oxygen, selenium, and tellurium, so organosulfur compounds are similar to those that have carbon with oxygen, selenium, or tellurium.

Types of organosulfur compounds

Sulfides

Sulfides, once called thioethers, have C−S−C bonds. The sulfur atom is bigger than carbon, so C−S bonds are longer than C−C bonds. C−S bonds are also a bit weaker. Examples include methanethiol and thiophene. Sulfides can be made by adding alkyl groups to thiols. Chemicals like alkyl halides, epoxides, and aziridines help with this.

Special Processes to Make Sulfides

• Pummerer rearrangement makes sulfides in a different way.
• Ferrario reaction uses sulfur and aluminum chloride to change phenyl ether into phenoxathiin.

Thioacetals and Thioketals

These compounds have C−S−C−S−C links and are a type of sulfide. Thioacetals help change how carbonyl groups react. They also protect carbonyl groups during chemical reactions.

Ring Structures with Sulfur

Sulfides and other sulfur compounds can form ring shapes. Some rings are:

• Thiiranes, thiirenes, thietanes
• Dithietanes, thiolanes, thianes, dithianes
• Thiepanes, thiepines, thiazoles, isothiazoles, and thiophenes

Thiophenes are special because they are aromatic, meaning they have stable rings. The ring in thiophene is more stable than in similar oxygen compounds like furan.Dibenzothiophenes are large, triple-ring sulfur compounds found in petroleum.

Thiols, Disulfides, and Polysulfides

• Thiols have R−SH bonds and are similar to alcohols but more reactive. They are more acidic and easy to oxidize. Thiols do not form strong hydrogen bonds.
• Disulfides (R−S−S−R) link two sulfur atoms. They are important in proteins and rubber.
• Polysulfides have even more sulfur atoms linked together, like the five-sulfur ring in varacin.

Thioesters

Thioesters have R−C(O)−S−R bonds. They are like regular esters but break apart more easily. Thioesters made from coenzyme A are key in making fatty acids.

Sulfoxides, Sulfones, and Thiosulfinates

• Sulfoxides (R−S(O)−R) are made by adding oxygen to sulfides.
• Sulfones (R−S(O)2−R) have two oxygen atoms.
• Thiosulfinates (R−S(O)−S−R) and thiosulfonates (R−S(O)2−S−R) come from disulfides. Examples are dimethyl sulfoxide, dimethyl sulfone, and allicin.

Sulfimides, Sulfoximides, and Sulfonediimines

• Sulfimides have nitrogen with sulfur (R2S=NR′) and can be used in medicine.
• Sulfoximides have one nitrogen, and one oxygen linked to sulfur (R2S(O)=NR′).
• Sulfonediimines have two nitrogens instead of oxygen (R2S(=NR′)2).

S-Nitrosothiols

S-Nitrosothiols (R−S−N=O) have a nitrogen and oxygen linked to sulfur. They help control blood flow in living things by releasing nitric oxide.

Sulfur Halides

These compounds have sulfur bonded to halogens (like chlorine or fluorine).

Examples:

• Sulfenyl halides (RSX)
• Sulfinyl halides (RS(O)X)
• Sulfonyl halides (RSO2X)

Other sulfur compounds have more halogens, like sulfur pentafluorides (RSF5).

Thioketones, Thioaldehydes, and Thioamides

• Thioketones (RC(=S)R′) and thioaldehydes are like ketones and aldehydes but with sulfur. They are rare.
• Thioamides (R1C(=S)N(R2)R3) are made by changing amides with a special chemical (Lawesson’s reagent).
• Isothiocyanates (R−N=C=S) give foods like mustard and wasabi their flavor.

S-Oxides and S,S-Dioxides

S-Oxides (R2C=S=O) and S,S-dioxides (R2C=SO2) are sulfur versions of carbonyls.

Examples are sulfines and sulfenes.

Sulfur-Carbon Triple Bonds

Triple bonds between sulfur and carbon are rare. They appear in carbon monosulfide (CS).

Thiocarboxylic Acids and Thioamides

• Thiocarboxylic acids (RC(O)SH) and dithiocarboxylic acids (RC(S)SH) are more acidic than regular carboxylic acids.
• Thioamides are like amides but with sulfur.

More information

One way to check if something has sulfur is the Carius halogen method.