Thiols are characterized by containing the -SH functional group. They are named by ending the main chain name in -thiol, analogous to alcohols whose ending is -ol
[1] Ethanethiol
[2] Cyclohexanethiol
Thiols have a higher acidity than alcohols due to the larger size of sulfur compared to oxygen. The pKa values are around 10-11, compared to alcohols that have values between 16-18.
However, the larger size of sulfur favors its polarizability and consequently its nucleophilicity. Thiols are much better nucleophiles than alcohols, their nucleophilicity being further enhanced by deprotonation.
![thiols 02](/images/stories/organica-ii/azufre-fosforo-silicio/tioles-02.png)
SN2 -type reactions become faster in the presence of a basic medium that generates the l-thiol (thiolate) salt.
![thiols 03](/images/stories/organica-ii/azufre-fosforo-silicio/tioles-03.png)
Mechanism:
![thiols 03 mechanism](/images/stories/organica-ii/azufre-fosforo-silicio/tioles-03-mecanismo.png)
The thiols are prepared from sodium hydrogen sulfide and a primary or secondary haloalkane.
![thiols 04](/images/stories/organica-ii/azufre-fosforo-silicio/tioles-04.png)
The excess hydrogen sulfide tries to minimize the side reaction whereby the propanethiol reattacks the propyl bromide to give a thioether.
One way to avoid this side reaction is to use thiourea in combination with a haloalkane.
![thiols 05](/images/stories/organica-ii/azufre-fosforo-silicio/tioles-05.png)
Another method of synthesis consists in the reaction of magnesium with elemental sulfur.
![thiols 06](/images/stories/organica-ii/azufre-fosforo-silicio/tioles-06.png)