Ionic Liquids—Promoted S-Methylation of Thiols Utilizing Dimethyl Carbonate

Abstract

Convenient and efficient S-methylation of mercaptans or thiophenols occurs with dimethyl carbonate (DMC) in room temperature ionic liquids (RTILs) [Bmim]Cl. [Bmim]Cl can be recycled in four subsequent runs with only a gradual decrease in activity. A possible mechanism of this transformation is also discussed.

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GRAPHICAL ABSTRACT

Keywords:

• Dimethyl carbonate
• ionic liquids
• methyl thioether
• thiol

Acknowledgments

The present investigation was supported by Natural Science Foundation of China (No. 50773009), Esquel Group, Science and Technology Commission of Shanghai Municipality (08JC1400600), and “111 Project” from Ministry of Education of China (B07024).

Notes

^a Reaction conditions: 1a = 10 mmol, DMC = 20 mmol, ionic liquid = 20 mmol.

^b Isolated yield of S-methylated product based on 1a after column chromatography.

^c N-methylated byproduct (3a) was 6%.

^d Reaction conditions: 1a = 10 mmol, DMC = 200 mmol, Bu₄NCl = 2 mmol.

^a Reaction conditions: thiols = 10 mmol, DMC = 20 mmol, ionic liquid = 20 mmol.

^b Total yields of two products (n-butyl methyl sulfide and butyl disulfide); the ratio (52:45) of two products based on GC.

^c Total yields of two products (4-chlorothioanisole and 4,4′-dichlorodiphenyl disulfide); the ratio(64:23) of two products based on GC.

^d Isolated yield of 3c is 20%; isolated yield of 3d is 3%.

^e Isolated yield of 3c is 23%; isolated yield of 3d is 2%.

^a Reaction conditions: 1d = 10 mmol, DMC = 20 mmol, [Bmim]Cl = 20 mmol, 110°C, 1.5 h.