How the Technology Works: The Starks Mechanism

PTC is usually based on using quatenary ammonium salts (Q+Y- or 'quats') that act as catalysts to bring water soluble anions like phenolate, cyanide and acrylate (X-) from an aqueous phase into an organic phase where a desired reaction takes place. While the quat is organic in nature, it is readily soluble in water due to its ionic character. The quat complexes or joins with the aqueous phase anion to form Q+X- and delivers the anion to an organic phase to react with an alkyl or acyl halide, R-Y, specifically chosen to make a many different final products, R-X. In this manner, a water-soluble or an organic soluble byproduct or waste is converted into an item of commerce like anisole, benzyl cyanide or methyl acrylate. The halogen, Y, on the alkyl halide, R-Y, becomes a benign water soluble salt such as sodium chloride represented by M+Y-. The Starks mechanism shows the overall conversions based on three simultaneous equilibria and one irreversible second order reaction. After reaction in the organic phase the quat is regenerated and becomes available again to reach into the aqueous phase and perform another reaction. Since the quats are high boilers they can be easily recycled. Also, one could react an organic waste alkyl halide such as methyl chloride or benzyl bromide with an aqueous phase containing a reactive anion to produce the same end result. These reactions are often selective and will remove reactive components out of mixtures. They can also be performed without solvent.

Starks, C., J.Am. Chem. Soc. 1971, 93, 195-199