Hexaethyl guanidinium chloride “HEG Cl” is a phase-transfer catalyst used in high-temperature PTC applications that require a thermally stable catalyst, typically at temperatures of 100 C to 220 C. Common quaternary ammonium phase-transfer catalysts are not stable at those temperatures, especially above 130 C, which is often required for many nucleophilic aromatic substitutions. Dr. Dan Brunelle led the team at General Electric in the 1990’s that patented many polymerizations using HEG Cl for nucleophilic aromatic substitutions to produce engineering thermoplastics.
When high temperature is required to perform a reaction, anything that can be done to reduce the energy of activation is desirable. In high-temperature PTC reactions that use HEG Cl, reducing hydration of the reacting anionic nucleophilic to very low levels, sometimes below 10 ppm, can be crucial to achieve reactivity.
US Patent 11,279,692 that was issued this month, invented by Thomas Guggenheim et al (a veteran of GE/SABIC Global Technologies), describes in Method 1E., the following procedure to dry HEG Cl before use. It is important to note that the manufacturing process for HEG Cl produces this phase-transfer catalyst as a mixture of HEG Cl, NaCl and water. That is why the dried product contains sodium chloride.
“A 2-liter, single-necked, round-bottomed flask was charged with 100 g of an aqueous solution containing 30.0 g of HEGCl and 14 g of sodium chloride, and 800 mL of toluene. The mixture was then placed on a roto-evaporator, equipped with a hot oil bath to heat the flask, and plumbed to a cold trap connected to a vacuum pump. The flask was rotated in the hot oil bath (temperature controlled at 110.degree. C.) and the solvent was removed under reduced pressure (<30 mm). Once the majority of the toluene/water had been removed, the flask was allowed to rotate in the oil bath at 130.degree. C., 25 mm, for 60 minutes, to afford a dry solid HEGCl/NaCl, free of toluene and water. The solid was transferred to a glove box inerted with dry nitrogen.”
When your company needs to optimize the choice of phase-transfer catalyst to achieve low-cost high-performance green chemistry, now contact Marc Halpern of PTC Organics to benefit from highly specialized expertise in industrial phase-transfer catalysis.
