Thiol
Thiols, also known as mercaptans, are a class of organosulfur compounds characterized by the presence of a sulfhydryl group (-SH) attached to a carbon atom of an aliphatic or aromatic moiety[18]. This sulfhydryl group is the defining feature of thiols, making them the sulfur analogs of alcohols, where sulfur replaces the oxygen of the hydroxyl group in alcohols[1]. The general formula for thiols is R-SH, where R represents an alkyl or other organic substituent[1][5].
Structure and Bonding
Thiols have a structure where an alkyl group (R) is attached to a sulfhydryl group (SH), referred to as alkanethiols or alkyl thiols[1]. The sulfur atom in thiols is larger than the oxygen atom in alcohols, resulting in C-S bond lengths that are typically around 180 picometers, about 40 picometers longer than typical C-O bonds[1]. The hydrogen bonding between individual thiol groups is weak, with the main cohesive force being Van der Waals interactions between the highly polarizable divalent sulfur centers[1][6].
Properties
Thiols are known for their strong and often unpleasant odors, resembling that of garlic or rotten eggs[1][5]. This characteristic smell is due to their ability to bind strongly to skin proteins[6]. They have relatively lower boiling points compared to alcohols of similar molecular weight, due to their minor association through hydrogen bonding with water and among themselves[6]. Thiols are slightly polar, with the S-H bond being only slightly polar[2].
Uses
Thiols are utilized in various applications due to their unique properties. They are used as odorants to assist in the detection of natural gas, which is odorless in its pure form[1]. In addition to their use in the gas industry, thiols play a significant role in biochemistry and medicine. They serve as radical scavengers, GSH prodrugs, or metal chelators, treating a variety of conditions[3]. Thiols are also involved in the synthesis of ω-Functionalized n-Alkanethiols and Disulfides, which are the building blocks of self-assembled monolayers[1].
Safety
Thiols, like many chemicals, must be handled with care. They are air and light sensitive, and some thiols are flammable in their pure forms[12]. Proper storage and handling procedures include keeping thiols refrigerated, tightly closed in a dry, cool, and well-ventilated place, and away from heat, sparks, and flame[4]. Personal protective equipment such as protective eyeglasses, gloves, and clothing should be worn to prevent skin and eye exposure[4].
In summary, thiols are an important class of organosulfur compounds with distinctive properties and wide-ranging applications in industry, biochemistry, and medicine. Their unique structure and bonding confer specific physical and chemical properties, including their characteristic odors and roles in redox biology.
Citations:
[1] https://en.wikipedia.org/wiki/Thiol
[2] https://web.pdx.edu/~wamserc/C334F99/9notes.htm
[3] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7286615/
[4] https://www.fishersci.com/store/msds?countryCode=US&language=en&partNumber=AAB2264203&productDescription=THIOPHENE-2-THIOL+97%25+1G&vendorId=VN00024248
[5] https://www.merriam-webster.com/dictionary/thiol
[6] https://www.vedantu.com/chemistry/thiol
[7] https://www.sciencedirect.com/topics/chemistry/thiol
[8] https://www.oenofrance.com/DOCS/FDS_OF_SELECTYSTHIOL_EN.pdf
[9] https://www.dictionary.com/browse/thiol
[10] https://www.chemeurope.com/en/encyclopedia/Thiol.html
[11] https://www.ucl.ac.uk/safety-services/policies/2020/jul/thiols
[12] https://open.alberta.ca/publications/ch060-chemical-hazards
[13] https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/thiol
[14] https://byjus.com/chemistry/thiol/
[15] https://www.britannica.com/science/thiol
[16] https://testbook.com/chemistry/thiol
[17] https://www.collinsdictionary.com/us/dictionary/english/thiol
[18] https://www.ebi.ac.uk/chebi/searchId.do?chebiId=29256
[19] https://www.creative-proteomics.com/blog/index.php/thiols-functions-identification-and-applications/