Organosulphur compounds

This presentation outlines the preparation and reactions of organosulphur compounds

1. Prepared By Dr. Krishnaswamy . G Faculty DOS & R in Organic Chemistry Tumkur University Tumakuru Organo sulphur Compounds

2. Introduction Sulphur containing organic compounds are known as organosulphur compounds. Cystein and Methionine are the naturally occuring Organosulphur compounds containing amino acids. Thioethers as well as thiols and their derivatives are the most important organosulphur compounds

3. From alkyl halides Reaction of alkyl halide with sodium hydrosulfide From alcohols Reaction of alcohols with hydrogen sulfide in presence of thorium oxide Preparation Thiols

4. From alkyl halides Reaction of two equivalents of alkyl halide with potassium sulphide yields thioethers . From alkyl halides and sodium salts of thiols Reaction of alkyl halide with sodium salts of thiols yields thioethers . Thioethers

5. Thioethers undergo nucleophilic substitution reaction with alkyl halides to form sulfonium salts. Dimethyl Thioether undergo mild oxidation in presence of H 2 O 2 (or) m-CPBA affords dimethyl sulphoxide . Further oxidation leads to formation of sulphones . Nucleophilic Substitution Reaction Reactions

6. Dimethyl sulphoxide undergo deprotonation reaction in presence of sodium hydride to form dimsyl anion which acts as nucleophile as well as strong base for preparation of sulfur ylides .

7. Dimethyl sulphoxide undergo alkylation reaction with alkyl halides to sulfoxonium salts. Addition reaction

8. Sulfonium and sulfoxonium salts undergo deprotonation reaction with strong base ( dimsyl anion) to form sulfur ylides . The ylides are stabilized by bonding with sulfur 3d orbital.

9. Sulfur ylides reacts with an aldehyde (or) ketones to form sulfur containing adducts. The sulfur containing adducts undergoes intramolecular nucleophilic substitution to give an epoxide .

10. With unsaturated carbonyl compounds unstabilized sulfur ylide gives epoxide whereas with stabilized sulfur ylide gives cyclopropane derivatives.

11. Dimethyl (or) diphenyl disulfide in the presence of base reacts with compound containing activated C-H bond followed by oxidation results in sulphoxide . Finally sulfoxide undergo elimination on heating provides a method for introducing double bond next to –M type groups.

12. Acid catalysed reaction between aldehyde and thiol gives dithioacetal derivatives and this known as Umpolung synthesis (or) polarity inversion. This reversal of polarity of carbonyl compounds and also sulfur atoms stabilize the carbanions so making possible reaction with electrophiles . Umpolung synthesis

13. Dithio derivative hydrolytically cleaved in presence of mercury ion to form corresponding carbonyl derivatives. While in presence of Raney nickel undergoes reductive desulfurization to form corresponding hydrocarbon derivatives.

14. A useful synthetic method to convert aldehydes (or) ketones to olefins using arylsulfones is known as Julia Olefination . Julia olefination is highly stereoselective reaction gives (E)-alkenes. Julia Olefination The reaction proceeds with addition of phenylsulfonyl carbanion to an aldehyde or ketone to form an intermediate alcohol, which is esterfired insitu by acetic anhydride. Finally the reductive elimination with sodium amalgum furnish alkene. Mechanism