SULFUR, PHOSPHORUS AND SILICON

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SULFUR, PHOSPHORUS AND SILICON
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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

thiols 01

[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

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SULFUR, PHOSPHORUS AND SILICON
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They are compounds similar to ethers in which oxygen is replaced by sulfur (RSR). They are also called sulfides.

They can be synthesized by reaction of thiols and haloalkanes, the reaction is favored in the presence of a basic medium.
thioeteres 01
Another way to obtain thioethers is by attack of nucleophiles on disulfides.
thioeteres 02

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Sulfoxides undergo elimination reactions, under slight heating, to form alkenes. The sulfoxide can be easily prepared by oxidation of a thioether, which is easy to form at the alpha position of a carbonyl from a disulfide. This procedure allows the preparation of α,β-unsaturated carbonyls.

sulfoxide removal 01

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SULFUR, PHOSPHORUS AND SILICON
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Sulfur ylides are prepared from thioethers by alkylation, followed by deprotonation.

sulfur ilides 01

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The reaction of carbonyls with thiols forms thioacetals that can be used as protecting groups or to reduce the carbonyl to an alkane.

thioacetals 01

thioacetal

Thioacetal is stable in acid media but can be hydrolyzed with mercury(II) salts.

thioacetals 02

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The 1,3-dithianes allow to change the polarity of the carbonyl carbon of the aldehydes by subtraction of the acid hydrogen, obtaining an organolithic capable of attacking a wide variety of electrophiles.

umpolung 01

The initial carbonyl, with positive polarity on carbon, changes in the umpolung reaction to a carboanion. The sulphurs of 1,3-dithiane are vital in stabilizing the negative charge, and the reaction with the oxygenated equivalent is not viable.

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SULFUR, PHOSPHORUS AND SILICON
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Phosphines are obtained by reacting phosphorus trichloride with organometallic reagents. Thus, phosphorus trichloride reacts with phenylmagnesium bromide to form triphenylphosphine.

phosphines 01

This reaction is well controlled and allows only two groups to be introduced.

An important application of tertiary phosphines is the stabilization of coordination complexes, they are very common ligands in this type of compounds.