Sulfilimine
Class of chemical compounds containing an S=N bond
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In chemistry, a sulfilimine (or sulfimide) is a type of chemical compound containing a sulfur-to-nitrogen bond which is often represented as a double bond (S=N). In fact, a double bond violates the octet rule, and the bond may be considered a single bond with a formal charge of +1 on the sulfur and a formal charge of −1 on the nitrogen. The parent compound is sulfilimine H2S=NH, which is mainly of theoretical interest.
Examples include S,S-diphenylsulfilimine[2] and sulfoximines such as methylphenylsulfoximine:[3]
In the case of a sulfoximine, the bonds can be considered single bonds, with formal charges of −1 on both the oxygen and the nitrogen, and a formal charge of +2 on the sulfur.
Preparation
Most sulfilimines are N-substituted with electron-withdrawing groups. These compounds are typically prepared by oxidation of thioethers with electrophilic amine reagents, such as chloramine-T in the presence of a base:[4]
- R2S + ClNHTs → R2S=NTs + HCl
An alternative route involves reactions of electrophilic sulfur compounds with amines. The imidosulfonium reagents provide a source of "Me2S2+", which are attacked by amines.
In general, aliphatic sulfilimines, unsubstituted at N, are not stable above −30 °C (−22 °F).[5]
KMnO4 can oxidize sulfilimines to sulfoximines, but the latter are more generally produced from addition of azides to sulfoxides.[5]
Sulfilimine bonds in proteins
Sulfilimine bonds stabilize collagen IV strands found in the extracellular matrix,[6] and evolved at least 500 mya.[7] These bonds covalently connect hydroxylysine and methionine residues of adjacent polypeptide strands to form a larger collagen trimer.