This is an interesting ring expansion reaction to convert an epoxide to a cyclic carbonate. The reaction shown is a gas-liquid 2-phase system. The tetrabutylammonium cation is solubilizing the bromide in the moderately polar organic phase which is homogeneous. Once the bromide attacks the epoxide, a transient alkoxide is formed that is also kept soluble in the organic phase by the quat instead of precipitating. The quat alkoxide in the organic phase reacts with the carbon dioxide, apparently at the gas liquid interface.
A very elegant aspect of this procedure is that by choosing MTBE as the solvent, the product (4-methoxycarbonyl-2-oxo-1,3-dioxolane) separates from the MTBE at the end of the reaction. This is beautiful. The reaction starts out homogeneous and ends as a 2-phase organic-organic system with the product in its own phase. One can speculate that if the inventors would have chosen a much more polar solvent (e.g., DMSO) in order to be able to use KBr or NaBr instead of TBAB, they would have had to invest expense in additional unit operations to separate the product from the solvent.
Strictly speaking, the quat is not doing phase-transfer, it is maintaining phase integrity of the organic reaction phase without using hard to recover polar aprotic solvents. This is a very nice patent.
If you would like to learn more about how best to perform a wide variety of PTC reactions be sure to attend our 2-day course “Industrial Phase-Transfer Catalysis” that discusses in detail > 200 reaction in > 30 reaction categories. If you have a more immediate need for the best expertise for performing low-cost high-performance green chemistry using PTC, inquire about PTC Process Consulting.
About Marc Halpern
Dr. Halpern is founder and president of PTC Organics, Inc., the only company dedicated exclusively to developing low-cost high-performance green chemistry processes for the manufacture of organic chemicals using Phase Transfer Catalysis. Dr. Halpern has innovated PTC breakthroughs for pharmaceuticals, agrochemicals, petrochemicals, monomers, polymers, flavors & fragrances, dyes & pigments and solvents. Dr. Halpern has provided PTC services on-site at more than 260 industrial process R&D departments in 37 countries and has helped chemical companies save > $200 million. Dr. Halpern co-authored five books including the best-selling “Phase-Transfer Catalysis: Fundamentals, Applications and Industrial Perspectives” and has presented the 2-day course “Practical Phase-Transfer Catalysis” at 50 locations in the US, Europe and Asia.
Dr. Halpern founded the journal “Industrial Phase-Transfer Catalysis” and “The PTC Tip of the Month” enjoyed by 2,100 qualified subscribers, now beyond 130 issues. In 2014, Dr. Halpern is celebrating his 30th year in the chemical industry, including serving as a process chemist at Dow Chemical, a supervisor of process chemistry at ICI, Director of R&D at Sybron Chemicals and founder and president of PTC Organics Inc. (15 years) and PTC Communications Inc. (20 years). Dr. Halpern also co-founded PTC Interface Inc. in 1989 and PTC Value Recovery Inc. in 1999. His academic breakthroughs include the PTC pKa Guidelines, the q-value for quat accessibility and he has achieved industrial PTC breakthroughs for a dozen strong base reactions as well as esterifications, transesterifications, epoxidations and chloromethylations plus contributed to more than 100 other industrial PTC process development projects.
Dr. Halpern has dedicated his adult life to his family and to phase-transfer catalysis (in that order!).
