The apparent goal of this patent is to enhance the reaction of a polyisocyanate with a polyepoxide epoxide to form a higher ratio of oxazolidinone to isocyanurate which in turn results in more desirable properties for the polymer. Since isocyanurate is formed by the self-condensation of the isocyanate, there is a competition for reaction with the isocyanate between the epoxide and the isocyanate itself.
In order to promote the reaction of the epoxide with the isocyanate, a plausible mechanism is that a halide can be used to open the epoxide ring to form a halo alkoxide anion followed by the nucleophilic alkoxide anion attacking the carbon of the isocyanate to form the oxazolidinone.
The source of the halide can be a quaternary ammonium salt. This was known previous to the patent. The novel concept disclosed in this patent is that when adding iodine to the quaternary halide, such as tetrabutylammonium bromide (TBAB) or tetrabutylammonium chloride (TBAC), the ratio of oxazolidinone to isocyanurate is higher.
The inventors compared the ratio of oxazolidinone to isocyanurate (Ox/Is) when using different ratios of TBAB or TBAC to elemental iodine. They also screened TBAB and TBAB without adding elemental iodine. The lowest (undesirable) Ox/Is ratios were observed for TBAB and TBAC without the addition of elemental iodine. The highest Ox/Is ratio was obtained with a 1:1 molar mixture of TBAB and I2.
One may speculate that tetrabutylammonium trihalide is formed such as Bu4N+ BrI2- and possibly the negative charge partially located on the iodine creates an iodide anion that is more active than a chloride or bromide due to iodide being a better nucleophile to attack the epoxide to form the iodohyrdrin alkoxide then serve as a better leaving group to enable ring closure to the oxazolidinone after the epoxide attacks the isocyanate.
If that mechanism is valid, then it would be interesting to run the reaction simply using tetrabutylammonium iodide and compare that more straightforward catalyst to the combination of TBAB/I2 or TBAC/I2. This was not reported in the patent. Since the inventors reported TBAB and TBAC without I2, one must wonder why they didn’t report TBAI without I2. If the inventors see this review, we would greatly appreciate to learn if TBAI worked poorly, unless it is not in their best interest to publicize this result.
Now contact Marc Halpern of PTC Organics to explore integrating highly specialized expertise in industrial phase-transfer catalysis with your process development program to achieve low-cost high-performance green chemistry.
