Thioacetal
Encyclopedia
Thioacetals are the sulfur
analogue
of acetal
s. They are prepared in a similar way to acetals: by reacting a thiol
with an aldehyde
:
Dithioacetals are prepared similarly to thioacetals, which are intermediates:
Such reactions typically employ either a Lewis
or Brønsted acid catalyst.
Dithioacetals generated from aldehydes and 1,2-ethanedithiol
are useful in organic synthesis
:
Whereas the carbonyl carbon of an aldehyde is electrophilic, the deprotonated derivatives of dithioacetals feature nucleophilic carbon centers:
Again, this reactivity is most commonly exploited in the 1,3-dithiolane
s. The inversion of polarity between R'(H)Cδ+Oδ- and R'CLi(SR)2 is referred to as umpolung
.
Sulfur
Sulfur or sulphur is the chemical element with atomic number 16. In the periodic table it is represented by the symbol S. It is an abundant, multivalent non-metal. Under normal conditions, sulfur atoms form cyclic octatomic molecules with chemical formula S8. Elemental sulfur is a bright yellow...
analogue
Analog (chemistry)
In chemistry, a structural analog , also known as chemical analog or simply analog, is a compound having a structure similar to that of another one, but differing from it in respect of a certain component. It can differ in one or more atoms, functional groups, or substructures, which are replaced...
of acetal
Acetal
An acetal is a molecule with two single-bonded oxygen atoms attached to the same carbon atom.Traditional usages distinguish ketals from acetals...
s. They are prepared in a similar way to acetals: by reacting a thiol
Thiol
In organic chemistry, a thiol is an organosulfur compound that contains a carbon-bonded sulfhydryl group...
with an aldehyde
Aldehyde
An aldehyde is an organic compound containing a formyl group. This functional group, with the structure R-CHO, consists of a carbonyl center bonded to hydrogen and an R group....
:
- RSH + R'CHO → R'CH(OH)SR
Dithioacetals are prepared similarly to thioacetals, which are intermediates:
- RSH + R'CH(OH)SR → R'CH(SR)2 + H2O
Such reactions typically employ either a Lewis
Lewis acid
]The term Lewis acid refers to a definition of acid published by Gilbert N. Lewis in 1923, specifically: An acid substance is one which can employ a lone pair from another molecule in completing the stable group of one of its own atoms. Thus, H+ is a Lewis acid, since it can accept a lone pair,...
or Brønsted acid catalyst.
Dithioacetals generated from aldehydes and 1,2-ethanedithiol
1,2-Ethanedithiol
1,2-Ethanedithiol is a colorless liquid with the formula C2H42. It has a very characteristic odor which is compared by many people to rotten cabbage. It is a common building block in organic synthesis and an excellent ligand for metal ions.-Preparation:...
are useful in organic synthesis
Organic synthesis
Organic synthesis is a special branch of chemical synthesis and is concerned with the construction of organic compounds via organic reactions. Organic molecules can often contain a higher level of complexity compared to purely inorganic compounds, so the synthesis of organic compounds has...
:
- C2H4(SH)2 + R'CHO → R'CHS2C2H4 + H2O
Whereas the carbonyl carbon of an aldehyde is electrophilic, the deprotonated derivatives of dithioacetals feature nucleophilic carbon centers:
- R'CHS2C2H4 + R2NLi → R'CLiS2C2H4 + R2NH
Again, this reactivity is most commonly exploited in the 1,3-dithiolane
Dithiolane
A dithiolane is a sulfur heterocycle derived from cyclopentane by replacing two CH2 groups with thioether groups. The parent compounds are 1,2-dithiolane and 1,3-dithiolane.1,2-Dithiolanes, such as lipoic acid, are cyclic disulfides....
s. The inversion of polarity between R'(H)Cδ+Oδ- and R'CLi(SR)2 is referred to as umpolung
Umpolung
Umpolung or polarity inversion in organic chemistry is the chemical modification of a functional group with the aim of the reversal of polarity of that group. This modification allows secondary reactions of this functional group that would otherwise not be possible. The concept was introduced by...
.