A patent issued this month cites the use of catalytic tetrabutylammonium bromide (TBAB) in the ring opening esterification of glycidyl ethers using acrylic acid and methacrylic acid (see Example 7). In PTC esterifications, we typically expect the presence of a base to form the carboxylate salt from the acid then the quat acrylate would be more reactive as a looser ion pair than say sodium acrylate, even assuming that all components are fully soluble in acetonitrile.
However, the procedure in this patent does not report the use of any base. It is possible that the acid protonates the epoxide which makes it susceptible to attack by the bromide to form the bromohydrin which may be more reactive than the closed epoxide.
We find it surprising that the inventors did not titrate the acrylic acid/methacrylic acid with a weak base that is also a desiccant which would enable the loose quat-acrylate ion pair to be more effective.
If any of our readers have a better explanation of how the quat bromide is catalyzing this reaction, please contact Marc Halpern with your input.
By the way, sometimes quat bromides are known to catalyze reactions of epoxides by having the bromide attack an epoxide to form a bromoalkoxide that reacts further. However, in this case it is not clear that this would help form the desired product.
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!).
