Phase-Switching Catalyst

Two Scotland chemists have designed a "trick" for "reversibly shuttling a homogeneous catalyst between the organic and aqueous phases in a biphasic solvent system." How do they do that you ask? They add or remove CO2.

This catalyst can switch between the two phases and was created to allow reactions to be in either phase. This could lead to a greener process because it helps otherwise complicated techniques that require isolation of products in homogeneous reactions.

What's the secret? Well, the two chemists say that they add an amidine group to thiphenylphosphine's phenyl rings. The two put together create a molecule that is soluble in an organic solvent. When CO2 is added to and aqueous system containing the catalyst, the CO2 will react with H2O and become H2CO3. This creates the soluble form. When N2 is added to the system, the catalyst deprotonates and becomes insoluble.

When the reaction system is complete, the product and catalyst can then be separated into different phases to allow the removal of the product and continuation of the catalyst in the next cycle of reactions.

What are the pros of this phase-switching catalyst? Well, cleaner reactions can occur and they require lower energy levels. What are the cons of this phase-switching catalyst? Well, the speed of the reaction itself is a trade-off, as well as some cross-contamination between the two phases.

http://pubs.acs.org/cen/news/87/i04/8704notw8.html