An Introduction to Organosulfur Chemistry

Garlic contains natural organosulfur compounds hypothesized to be very helpful in cancer risk reduction.

Organosulfur chemistry has several distinguishing characteristics. It occurs naturally in all life forms, leading to its presence in fossil fuels. Sulfur atoms may bond to form various functional groups. A simple synthesis scheme, with some examples of more complicated organosulfur compound construction, is a good introduction to the subject. Applications of organosulfur compounds include, but are not limited to, potential cancer treatments. Lastly, while organosulfurs have their use, there are instances when they are not desired. Environmental and industrial product defects due to sulfur-based functional groups are an ongoing concern.

Natural Occurrence

Organosulfur compounds occur naturally in fossil fuel deposits. This comes about since certain biological molecules, such as the amino acid cysteine (Cys), contain sulfur-based functional groups. While the groups are transformed under heat and pressure influence over time, the sulfur atoms remain and form new bonds with carbon-based molecules in the fossil fuel.

Molecular Structure

Sulfur forms several organic functional groups. The most prominent groups are thiols and polysulfides. Thiols are distinguished by a "capping" of the sulfur atom with a hydrogen atom, often designated as R-SH, where R is the rest of the organic molecule. Disulfides indicate two sulfur atoms, each bonded to other organic groups, with polysulfides generalizing this to any number of sulfur atoms. For disulfides, the designation is R-S-S-R', where R and R' are other organic groups which can, but don't have to be, identical.

Functional Group Synthesis

Thiol is the simplest sulfur-based organic functional group. Thiol organics are synthesized by combining an alcohol (R-OH) group with hydrogen sulfide (H2S) under sufficient temperature, pressure and catalytic conditions. Thiol organics (R-SH) are formed this way, with water as a byproduct. As with thiols, there is more than one way to create disulfide organics. A detailed explanation and reaction diagrams/mechanisms can be found on the Organic Chemistry Portal website (see Resources below).

Applications

In polymer synthesis, sulfur atoms crosslink different polymer chains. This chemical treatment results in greater polymer strength. An example of this is rubber tire vulcanization. Vulcanization makes tires useful, in contrast to them otherwise being mushy/brittle under common hot/cold temperature swings. There is also research in chemotherapy relating to sulfur-containing organic molecules. Research published by the NCBI in 2007 shows that organosulfur ingestion reduces cancer risk and may play a role in treatment/prevention.

Harmful Effects

A foul smell indicative of decay and death is often described as "sulfurous"--and for a good reason. Burning sulfur-laced organic molecules poses a health and environmental threat. Burned fossil fuel containing sulfur traces can result in sulfur oxides that contribute to atmosphere and water-cycle pollution. As with other harmful substances, their being locked in fossil fuel deposits by geological processes blunted their toxic influence. Release into the biosphere as byproducts of organosulfur combustion is a constant concern for the industrial, ecological and medical fields.

References

• Carnegie Mellon University
• Synthetic and Stereochemical Aspects, Vol 2 (Organosulfur Chemistry); Philip Page (ed.); 1997
• Ullmann's Encyclopedia of Industrial Chemistry; Verlag and Weinheim; 2003

Resources

• Virginia Commonwealth University
• Organic Chemistry Portal
• Harvard University