Phase-transfer catalysis is known to enhance hydrogenation using palladium as catalyst. This patent has several interesting aspects.
The role of the TBAB in the hydrogenation shown in the diagram appears to be as a source for bromide and is defined in the patent as a “modifier.”. Tetramethylammonium bromide works almost as well as does NaBr. So, it is not clear from the extensive data provided in the patent that a quat is absolutely necessary, though bromide appears to be the best modifier. However, the inventors chose the TBAB system for control experiments. They show that in the absence of TBAB (which might just be a bromide source), the conversion to desired product is lower at 63%. When using no sulfuric acid, the conversion to desired product decreases to 13-15%.
Many catalysts, modifiers and acids were screened and this combination gave the highest conversion with a relatively low amount of undesired dechlorination. When bromide was absent in the control experiment that included sulfuric acid (63% desired product), the dechlorinated byproduct appeared at a very high level (29%).
Higher catalyst loading using Palladium(0) was screened with TBAB (and also with NaBr) and achieved similar results to those using palladium hydroxide at the lower catalyst level.
A discussion of the use of phase-transfer catalysts with palladium appears in other PTC Tip of the Month posts on this website. Search for those posts in the search bar at the top of this page.
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!).
