Thiol is an organic chemical compound that has properties comparable to alcohol and phenols. However, instead of an oxygen atom, it possesses a sulphur atom. It also has the –SH functional group. It's also the sulphur equivalent of the hydroxyl or alcohol group. A thiol group or a sulfhydryl group is the name for this functional group.
Thiols are also known as mercaptans. Alcohols and Thiols have certain similarities in that sulphur is a bigger element than oxygen, and the length of the C–S bond is longer than the C–O link. Because of the cohesive force, the hydrogen bonding between the thiol groups is substantially weaker in liquids or solids. In comparison to alcohol, they have a low dipole moment.
Key Terms: Thiol, Organic Compound, Alcohol, Phenols, Oxygen, Sulphur, Atom, Dipole Moment, Mercaptan
Structure of Thiol
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The structure of Thiol is shown below:
Structure of Thiol
Alkanethiols or Alkyl thiols have the R-SH thiol structure. An alkyl group is linked to a sulfinyl group here. Furthermore, the molecular structure of thiols and alcohol is comparable. Because sulphur is a larger element than oxygen, the C-S bond is about 40 picometers longer than a conventional C-O bond (usually around 180 picometers).
Physical Properties of Thiol
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The following are the Physical Properties of Thiol:
- Odour: Many thiols have strong odours that resemble the smell of onions and garlic. Thiols with low molecular weight have an unpleasant and pungent odour. It's also to blame for some wine flaws that have come as a result of unintentional sulphur-yeast reactions. Not all thiols have a foul odour; there are numerous thiols that have a pleasant odour. Furan-2-yl methanethiol, for example.
- Boiling Point: Thiols have lower boiling temperatures than alcohols because they have a small hydrogen bonding connection with water and among themselves. Thioether functional groups have similar boiling points and solubility characteristics, however, this is not the case with alcohols.
- Solubility: Thiols are hardly soluble in water.
Chemical Properties of Thiol
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The following are the Chemical Properties of Thiol:
- Synthesis: Thiols are made in the same way that ethers and alcohols are made. Heating a halogenoalkane in a sodium hydrosulphide solution:
CH3CH2Br + NaSH heated in ethanol (aq) → CH3CH2SH + NaBr
Reducing disulphides with lowering agents like lithium aluminium hydride in dry ether.
R-S-S-R' → R-SH + R'-SH
- Reactions: The thiol group of alcohols is a sulphur duplicate of the hydroxyl group (-OH). Sulphur and oxygen belong to the same periodic table group. As a result, they share some chemical bonding similarities. The chemistry of thiols is quite similar to the chemistry of alcohols. Thioacetals, thioethers, and thioesters are all thiols that are comparable to esters, ethers, and acetals. Thioether is formed when a group of thiols reacts with alkenes. Furthermore, thiol groups can form thioether linkages by reacting with vinyl groups.
- Acidity: Thiols have more nucleophilic sulphur atoms than alcohol atoms. With a pKa of 10 to 11, these thiol groups are slightly acidic. This group, as well as the anions it contains, is easily oxidised. The organic disulphide is formed by reagents like bromine (R-S-S-R).
2R-SH + Br2 → R-S-S-R + 2HBr
Sulfonic acids are formed by oxidation with stronger reagents such as hydrogen peroxide or sodium hypochlorite (RSO3H).
R-SH + 3H2O2 → RSO3H + 3H2O
Read More:
| Related Topics | ||
|---|---|---|
| Organic Compounds | Electrochemical Cell | Organic Solvents |
Thiol's Biological Importance
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Thiol groups, which are the functional group of the amino acid cysteine, play an important role in biological processes. Furthermore, oxidation can form cystine units with a disulphide bond when these groups of two cysteine residues in monomers or constituent units are brought close to each other during protein folding (-S-S-).
Disulphide bonds also have a role in the tertiary structure of proteins. Cysteine must be part of the same peptide chain or subside to the quaternary structure of multi-unit proteins for this to work. Between various peptide chains, it produces a strong covalent connection. Furthermore, disulphide bridges keep such antibody chains, both heavy and light, together.
Curls in curly hair are a good example of this. They are caused by the production of cysteine. Furthermore, the chemical used to straighten hair is a reductant. It frees cysteine sulfhydryl groups by reducing cysteine disulphide bridges. Hair curling chemicals, on the other hand, are oxidants. They produce cysteine disulphide bridges by oxidising cysteine sulfhydryl groups.
Read More: Classification of Organic Compounds
Things to Remember
- Thiols are a sulphur analogue of alcohols.
- Thiol is an organic compound made up of compounds containing a sulphur atom
- Thiol is also known as mercaptan.
- Thiol is made up of a sulfhydryl group, i.e., Thiol = R-SH.
- Thiols have a low dipole moment.
Sample Questions
Ques. What Exactly is a Thiol? (1 Mark)
Ans. Thiol is an organic chemical molecule that resembles alcohol and phenols in appearance. However, instead of an oxygen atom, it possesses a sulphur atom. Mercaptans are another name for thiols. They are similar to alcohol in terms of molecular structure.
Ques. What is a physical property that distinguishes thiols from other organic compounds? (1 Mark)
Ans. One of the most basic physical properties that can help a person recognise thiols is their smell. The odour of thiols is notable for being strong and resembling garlic.
Ques. Discuss Thiophene. (1 Mark)
Ans. Thiophene is a heterocyclic chemical compound. This liquid's chemical formula is C4H4S. Furthermore, it is colourless and has a benzene-like odour.
Ques. Discuss Thionyl Chloride. (1 Mark)
Ans. OCI2 is the chemical formula for thionyl chloride, an inorganic liquid. This element is colourless and has moderately high volatility. It also has an awful, bitter odour.
Ques. Are thiols water soluble? (2 Marks)
Ans. Thiols are less water soluble than alcohols and have lower boiling temperatures than their alcohol cousins. These characteristics are due to the fact that the hydrogen-bonding interaction of molecules in sulphur compounds is not as strong as it is in oxygen compounds.
Ques. Why are thiols more effective than alcohol as acids? (2 Marks)
Ans. Alcohol is less acidic than thiol.
The S-H bond is weaker than the O-H bond because sulphur is less electronegative than oxygen. As a result of the weak bonding, proton release is facilitated in the case of Thiol. When compared to alcohol, the acidity of thiol increases.
Ques. When compared to alcohols, why are thiols more nucleophilic? (2 Marks)
Ans. Thiols are more nucleophilic than alcohols. Because nucleophilicity is determined by reaction rate, these sulphur nucleophiles react with electrophiles (such as alkyl halides) more quickly than their oxygen-based counterparts.
Ques. Why do thiols have polar properties? (2 Marks)
Ans. R-SH = Thiol
The hydroxyl group has a polar character. Thiols are polar because they have a partial negative charge (d-) on the oxygen atom and a partial positive charge (d+) on the hydrogen of the hydroxyl group.
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