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Sulfur diimides are chemical compounds of the formula S(NR)2. Structurally, they are the di
A particularly stable derivative is di- ''t''-butylsulfurdiimide.Kresze, G.; Wucherpfennig, W., "Organic synthesis with imides of sulfur dioxide", Angew. Chem. Int. Ed. Engl. 1967, volume 6, 149-167. It is prepared by reaction of ''tert''-butylamine with
imine
In organic chemistry, an imine ( or ) is a functional group or organic compound containing a carbon–nitrogen double bond (). The nitrogen atom can be attached to a hydrogen or an organic group (R). The carbon atom has two additional single bon ...
of sulfur dioxide
Sulfur dioxide (IUPAC-recommended spelling) or sulphur dioxide (traditional Commonwealth English) is the chemical compound with the formula . It is a colorless gas with a pungent smell that is responsible for the odor of burnt matches. It is r ...
. The parent member, S(NH)2, is of only theoretical interest. Other derivatives where R is an organic group are stable and useful reagents.
Organic derivatives
A particularly stable derivative is di- ''t''-butylsulfurdiimide.Kresze, G.; Wucherpfennig, W., "Organic synthesis with imides of sulfur dioxide", Angew. Chem. Int. Ed. Engl. 1967, volume 6, 149-167. It is prepared by reaction of ''tert''-butylamine with sulfur dichloride
Sulfur dichloride is the chemical compound with the formula . This cherry-red liquid is the simplest sulfur chloride and one of the most common, and it is used as a precursor to organosulfur compounds. It is a highly corrosive and toxic substance ...
to give the intermediate "S(N-''t''-Bu)", which decomposes at 60 °C to give the diimide.
However, most sulfur diimides are not produced from such elimination reaction
An elimination reaction is a type of organic reaction in which two substituents are removed from a molecule in either a one- or two-step mechanism. The one-step mechanism is known as the E2 reaction, and the two-step mechanism is known as the E1 r ...
s. Typically, sulfur diimides arise from treatment of sulfur tetrafluoride with amines, or from transamidation reactions. The latter typically requires amide
In organic chemistry, an amide, also known as an organic amide or a carboxamide, is a chemical compound, compound with the general formula , where R, R', and R″ represent any group, typically organyl functional group, groups or hydrogen at ...
reactants that are less basic than the products, as with disulfonylsulfodiimide...
:S(NSO2Ph)2 + 2 RNH2 → S(NR)2 + 2 PhSO2NH2
...or with ''N'',''N-Bis(methoxycarbonyl)sulfur diimide (MeO2C-N=S=N-CO2Me) from methyl carbamate
Methyl carbamate (also called methylurethane, or urethylane) is an organic compound and the simplest ester of carbamic acid (H2NCO2H). It is a colourless solid.
Methyl carbamate is prepared by the reaction of methanol and urea:
:CO(NH2)2 + CH3O ...
. Alternatively, the presence of a strong base to absorb the released SO2 can drive transamidation from sulfinylamines.
Structure, bonding, reactions
These compounds are related to SO2. They have planar C–N=S=N–C cores with bent C–N=S and N=S=N geometries, and various combinations of ''E'' and ''Z'' isomers are observed for the two N=S bonds. Sulfur diimides areelectrophilic
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 carr ...
. Organolithium reagent
In organometallic chemistry, organolithium reagents are chemical compounds that contain carbon–lithium (C–Li) bonds. These reagents are important in organic synthesis, and are frequently used to transfer the organic group or the lithium atom ...
s attack at the sulfur to give the corresponding nitrogen anion:
:R'Li + S(NR)2 → R'S(NR)(NRLi)
The triimido analogues of sulfite
Sulfites or sulphites are compounds that contain the sulfite ion (systematic name: sulfate(IV) ion), . The sulfite ion is the conjugate base of bisulfite. Although its acid (sulfurous acid) is elusive, its salts are widely used.
Sulfites are ...
can be generated by treating the sulfur diimides with a metal amide:Fleischer, R.; Stalke, D., "A new route to sulfur polyimido anions S(NR)nm-: reactivity and coordination behavior", Coord. Chem. Rev. 1998, 176, 431-450.
:4 LiNHBu-t + 2 S(NBu-t)2 → 2 Li2S(NBu-t)3 + 2 t-BuNH2
Sulfur diimides undergo Diels–Alder reaction
In organic chemistry, the Diels–Alder reaction is a chemical reaction between a Conjugated system, conjugated diene and a substituted alkene, commonly termed the Diels–Alder reaction#The dienophile, dienophile, to form a substituted cyclohexe ...
s with diene
In organic chemistry, a diene ( ); also diolefin, ) or alkadiene) is a covalent compound that contains two double bonds, usually among carbon atoms. They thus contain two alk''ene'' units, with the standard prefix ''di'' of systematic nome ...
s. Fluorine gas oxidizes them to difluorosulfur diimides:
:RNSN + F2 → RNS(F)2N{{prime, R
See also
*Carbodiimide
In organic chemistry, a carbodiimide (systematic IUPAC name: methanediimine) is a functional group with the formula RN=C=NR. On Earth they are exclusively synthetic, but in interstellar space the parent compound HN=C=NH has been detected by its ...
- the carbon analogue
* Disulfur dinitride
Disulfur dinitride is the chemical compound with the formula .
Preparation and reactions
Passing gaseous over silver metal wool at 250–300 °C at low pressure (1 mmHg) yields cyclic . The silver reacts with the sulfur produced by the t ...
* Bis(trimethylsilyl)sulfur diimide
References