Cyclic carbonates are useful in the safe synthesis of non-isocyanate polyurethane resins (avoiding the use of phosgene). This patent describes the very efficient reaction of epoxides with carbon dioxide to form cyclic carbonates using phase-transfer catalysis.
The optimum catalyst system for the reaction of epoxides with carbon dioxide to form cyclic carbonates was found to be tetrabutylammonium bromide (TBAB) with cobalt diacetate tetrahydrate and triphenylphosphine. As can be seen in the diagram, a conversion of >99% was achieved with 1,4-butanediol diglycidyl ether as the substrate.
The presence of the phase-transfer catalyst was found to be the most crucial catalyst component. When TBAB was used without triphenylphosphine and without the cobalt catalyst, the conversion was 67%, presumably due to ring opening of the epoxide with bromide and subsequent attack of the alkoxide on carbon dioxide. When TBAB was used with triphenylphosphine and no cobalt catalyst, the conversion was essentially the same at 68%. However, when the cobalt catalyst was used without TBAB and without triphenylphosphine, the conversion was 0%. When all three catalyst components were used, >99% conversion was achieved.
It is interesting to note that phase-transfer catalysis could very likely be used to produce the starting material by hydrogen peroxide epoxidation of 1,4-butadiene. This reaction was not mentioned in the patent.
If your company needs help in choosing the most effective phase-transfer catalyst for reactivity, safety and processing to achieve the highest profit, now contact Marc Halpern of PTC Organics to explore how we can work together to improve your process performance from development to commercialization.