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In RSH + R'CH(O) -> R'CH(SR)OH
#Thiol addition with loss of water to give dithioacetal:
#::RSH + R'CH(OH)SR -> R'CH(SR)2 + H2O
Such reactions typically employ either a 
The carbonyl carbon of an aldehyde is R'CHS2C2H4 + R2NLi -> R'CLiS2C2H4 + R2NH
The inversion of polarity between and {{chem2, R'CLi(SR)2 is referred to as
organosulfur chemistry
Organosulfur compounds are organic compounds that contain sulfur. They are often associated with foul odors, but many of the sweetest compounds known are organosulfur derivatives, e.g., saccharin. Nature abounds with organosulfur compounds—sulfur ...
, thioacetals are the sulfur
Sulfur (or sulphur in British English) is a chemical element with the symbol S and atomic number 16. It is abundant, multivalent and nonmetallic. Under normal conditions, sulfur atoms form cyclic octatomic molecules with a chemical formula ...
('' thio-'') analogues of acetals (). There are two classes: the less-common monothioacetals, with the formula , and the dithioacetals, with the formula (symmetric dithioacetals) or (asymmetric dithioacetals).
The symmetric dithioacetals are relatively common. They are prepared by condensation
Condensation is the change of the state of matter from the gas phase into the liquid phase, and is the reverse of vaporization. The word most often refers to the water cycle. It can also be defined as the change in the state of water vapor to ...
of thiol
In organic chemistry, a thiol (; ), or thiol derivative, is any organosulfur compound of the form , where R represents an alkyl or other organic substituent. The functional group itself is referred to as either a thiol group or a sulfhydryl grou ...
s () or dithiol
In organic chemistry, a dithiol is a type of organosulfur compound with two thiol () functional groups. Their properties are generally similar to those of monothiols in terms of solubility, odor, and volatility. They can be classified according ...
s (two groups) with aldehyde
In organic chemistry, an aldehyde () is an organic compound containing a functional group with the structure . The functional group itself (without the "R" side chain) can be referred to as an aldehyde but can also be classified as a formyl group ...
s (). These reactions proceed via the intermediacy of hemithioacetal
In organic chemistry, hemithioacetals (or thiohemiacetals) are organosulfur compounds with the general formula . They are the sulfur analogues of the acetals, , with an oxygen atom replaced by sulfur (as implied by the ''thio-'' prefix). Becaus ...
s ():
#Thiol addition to give hemithioacetal:
#::Lewis acid
A Lewis acid (named for the American physical chemist Gilbert N. Lewis) is a chemical species that contains an empty orbital which is capable of accepting an electron pair from a Lewis base to form a Lewis adduct. A Lewis base, then, is any sp ...
or Brønsted acid as catalyst
Catalysis () is the process of increasing the reaction rate, rate of a chemical reaction by adding a substance known as a catalyst (). Catalysts are not consumed in the reaction and remain unchanged after it. If the reaction is rapid and the ...
.
Dithioacetals generated from aldehydes and either 1,2-ethanedithiol or 1,3-propanedithiol
1,3-Propanedithiol is the chemical compound with the formula HSCH2CH2CH2SH. This dithiol is a useful reagent in organic synthesis. This liquid, which is readily available commercially, has an intense stench.
Use in organic synthesis
1,3-Propan ...
are especially common among this class of molecules for use in organic synthesis
Organic synthesis is a special branch of chemical synthesis and is concerned with the intentional construction of organic compounds. Organic molecules are often more complex than inorganic compounds, and their synthesis has developed into one o ...
.P. Stütz And P. A. Stadler "3-alkylated And 3-acylated Indoles From A Common Precursor: 3-benzylindole And 3-benzoylindole" Org. Synth. 1977, 56, 8.
:
The carbonyl carbon of an aldehyde is electrophilic
In chemistry, an electrophile is a chemical species that forms bonds with nucleophiles by accepting an electron pair. Because electrophiles accept electrons, they are Lewis acids. Most electrophiles are positively charged, have an atom that carri ...
and therefore susceptible to attack by nucleophile
In chemistry, a nucleophile is a chemical species that forms bonds by donating an electron pair. All molecules and ions with a free pair of electrons or at least one pi bond can act as nucleophiles. Because nucleophiles donate electrons, they are ...
s, whereas the analogous central carbon of a dithioacetal is not electrophilic. As a result, dithioacetals can serve as protective group
A protecting group or protective group is introduced into a molecule by chemical modification of a functional group to obtain chemoselectivity in a subsequent chemical reaction. It plays an important role in multistep organic synthesis.
In many ...
s for aldehydes.
Far from being unreactive, and in a reaction unlike that of aldehydes, that carbon can be deprotonated
Deprotonation (or dehydronation) is the removal (transfer) of a proton (or hydron, or hydrogen cation), (H+) from a Brønsted–Lowry acid in an acid–base reaction.Henry Jakubowski, Biochemistry Online Chapter 2A3, https://employees.csbsju.edu ...
to render it nucleophilic:
:umpolung
In organic chemistry, umpolung () or polarity inversion 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 ot ...
. The reaction is commonly performed using the 1,3-dithiane. The lithiated intermediate can be used for various nucleophilic bond-forming reactions, and then the dithioketal hydrolyzed
Hydrolysis (; ) is any chemical reaction in which a molecule of water breaks one or more chemical bonds. The term is used broadly for substitution, elimination, and solvation reactions in which water is the nucleophile.
Biological hydrolysis i ...
back to its carbonyl form. This overall process, the Corey–Seebach reaction, gives the synthetic equivalent of an acyl anion.
See also
*Mozingo reduction
The Mozingo reduction, also known as Mozingo reaction or thioketal reduction, is a chemical reaction capable of fully reducing a ketone or aldehyde to the corresponding alkane via a dithioacetal. The reaction scheme is as follows:
The ketone or ...
* Thioketal
In organosulfur chemistry, a thioketal is the sulfur analogue of a ketal (), with one of the oxygen replaced by sulfur (as implied by the ''thio-'' prefix), giving the structure . A dithioketal has ''both'' oxygens replaced by sulfur ().
Thioke ...
References