One of the major advantages of phase-transfer catalysis is the ability to replace expensive anhydrous bases with PTC and common inexpensive bases. There are countless examples of reports in which chemists use t-butoxide when they could and should use PTC-NaOH or PTC-potassium carbonate.
However, there are few examples when chemists are clever enough to think about using PTC but continue to use t-butoxide in cases that don’t require deprotonation of high pKa substrates. This patent is such an example.
In fact, the reactant being deprotonated is a phenol which is so acidic that it doesn’t even need NaOH, let alone t-butoxide. Potassium carbonate by itself is basic enough to deprotonate the phenol. Potassium carbonate can also serve as a desiccant to “hide” any water in the system. This is important because nucleophilic aromatic substitutions usually need significant energy of activation and we don’t want to add energy of activation due to hydration of the attacking phenoxide anion.
Moreover, I would be concerned using excess t-butoxide that can cause Hofmann Elimination of the TBAB that decomposes the phase-transfer catalyst, especially at 80-85 C. Who knows…maybe that is why the inventors used such a high catalyst loading of 20 mole%, to overcome catalyst decomposition.
It is always possible that the inventors tried PTC with just carbonate (no t-butoxide) and it didn’t work. However, I would be surprised if that was the case.
If your company is using t-butoxide or any other expensive, anhydrous and/or hazardous base, now contact Marc Halpern of PTC Organics to reduce your cost of manufacture, reduce your development time and improve process performance by integrating PTC Organics’ highly specialized expertise in industrial phase-transfer catalysis with your process development and commercial goals.
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!).
In fact, the reactant being deprotonated is a phenol which is so acidic that it doesn’t even need NaOH, let alone t-butoxide. Potassium carbonate by itself is basic enough to deprotonate the phenol. Potassium carbonate can also serve as a desiccant to “hide” any water in the system. This is important because nucleophilic aromatic substitutions usually need significant energy of activation and we don’t want to add energy of activation due to hydration of the attacking phenoxide anion.