Synthesis | Organic Synthesis | On-water esterification

Herein is presented a two-step-one-pot reaction, combining the beneficial effects of "on-water" processes with the well known advantages of microwave heating.


"On-water" reactions rely on the fact that reagents, products and byproducts show a significant difference in lipophilicity. The reaction takes place on the
water/oil interface, where the reaction equilibrium is positively affected by the separation of the reaction products due to differences in solubility.

In the present study acetonide proteced hydroxytyrosol was transformed to fatty acid esters with fatty acid chlorids, while the deliberated hydrochloric acid catalyzed the deprotection in situ in a microwave-assisted "on-water" protocol.




Key findings

Microwave-assisted heating
Convenient heating to temperatures above the boiling point. Reaction could be finished after 15 min in a mirowave reactor, compared to 8 h under conventional conditions. By using a different rotor, 11 g (42 mmol) of the final product could 
be obtained.

"On-water" reaction
The reaction rate is independent of the quantity of water, but there must be enough water to create an interface. No catalyst is required - the reaction takes place "at the interface"instead of "on a catalytic surface". Neither the reagents nor the product should be soluble in water (e.g. no reaction with the water soluble butyryl chloride).The in situ produced hydrochloric acid immediately deprotects the fatty acid hydroxytyrosol ester.