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 (''

thio- The prefix thio-, when applied to a chemical, such as an ion, means that an oxygen atom in the compound has been replaced by a sulfur atom. This term is often used in organic chemistry. For example, from the word ''ether,'' referring to an ox ...

'') analogues of

acetal In organic chemistry, an acetal is a functional group with the connectivity . Here, the R groups can be organic fragments (a carbon atom, with arbitrary other atoms attached to that) or hydrogen, while the R' groups must be organic fragments n ...

s (). 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 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 gro ...

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 grou ...

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). Because ...

s (): #Thiol addition to give hemithioacetal: #::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 Lewis acid or Brønsted acid as

catalyst Catalysis () is the process of increasing the 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 catalyst recyc ...

. Dithioacetals generated from aldehydes and either

1,2-ethanedithiol Ethane-1,2-dithiol, also known as EDT, is a colorless liquid with the formula C H( SH). 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 liga ...

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.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. : Dithioacetal_Synthesis_V

The carbonyl carbon of an aldehyde is electrophilic and therefore susceptible to attack by nucleophiles, 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.ed ...

to render it nucleophilic: :R'CHS2C2H4 + R2NLi -> R'CLiS2C2H4 + R2NH The inversion of polarity between and {{chem2, R'CLi(SR)2 is referred to as

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 back to its carbonyl form. This overall process, the

Corey–Seebach reaction The Corey–Seebach reaction, or Seebach Umpolung is a name reaction of organic chemistry that allows for acylation by converting aldehydes into lithiated 1,3-dithianes. The lithiated 1,3-dithianes serves as an acyl anion equivalent, undergoing a ...

, gives the synthetic equivalent of an acyl anion.

References

Functional groups Organosulfur compounds

See also

References