The isomerization reaction of epoxy butene to 2,5-dihydrofuran shown in the diagram requires a Lewis acid and a “solubilizing agent” which is essentially a phase-transfer catalyst. This reaction is the last example in Fischer, M.; (BASF) US Patent 6,096,673, 01-Aug-2000. Zinc iodide was found to be the most economical effective Lewis acid catalyst for this reaction. Earlier patents by Martin Fischer used phosphazenium salts that are not readily available in commercial quantities. This patent highlights the fact that when using octadecyl trioctyl phosphonium iodide (ODTOPI – discussed in this month’s PTC Catalyst of the Month), the catalyst system can be recycled with very high efficiency by extraction of the bottom stream with octane. The very high organophilicity of the P-quat with 42 carbons renders it very soluble in the non-polar octane. The 2,5-DHF product is taken overhead continuously, but the catalyst system must be separated from oligomers that are formed during the reaction.
PTC-Lewis Acid Catalyzed Isomerization
By Marc Halpern, the leading expert in industrial phase-transfer catalysis.
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!).