Cyclotrimerization of alkynes vs. ketone formation in aqueous microemulsion

• Cyclotrimerization of water insoluble alkynes in aqueous media.
• Replacement of harmful organic solvents by aqueous microemulsions.
• Elucidation of factors that influence cyclotrimerization in aqueous microemulsions.

In the course of our attempts to develop sustainable conditions for the catalytic organic reactions by replacement of the traditional but environmentally disfavored organic solvents by water, we studied the cyclotrimerizations of alkynes, in aqueous microemulsions. The catalyst for these reactions was the rhodium-trichloride encaged within silica sol–gel. In acidic aqueous media, alkynes can undergo addition of water to form their corresponding ketones. In order to eliminate completely the formation of ketones, relatively low reaction temperatures are required. At higher reaction temperatures, however, buffered microemulsion media is preferable.Cyclotrimerization of alkynes proved to be dependent on the reaction temperatures, the electronic nature of the substrates, the electronic nature of the surfactant and on the hydrophobicity of the sol–gel support. During the cyclotrimerization reaction, the rhodium complex was turned to Rh(0) nanoparticles characterized by TEM measurements.These investigations may be regarded as model studies for the conversion of alkynes into substituted benzenes in water.

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