The Aug 2012 PTC Reaction of the Month uses octyl trimethyl ammonium hydrogen sulfate. There are two interesting aspects of this catalyst: the cation and the anion.
Classical phase-transfer catalysts do not have a head-and-tail structure and are often symmetrical like tetrabutyl ammonium. The head-and-tail structure is more characteristic of classical surfactants such as hexadecyl trimethyl ammonium. As the longest chain of an alkyl trimethyl ammonium quat is shorter, its surfactant properties are less pronounced. Good phase-transfer catalysts do not cause emulsions as good surfactants do. So, it is interesting that the inventors of the patent described above use an alkyl trimethyl ammonium quat with an intermediate size chain. We can only speculate that this catalyst had a chain long enough to be effective for PTC but not too long to form stable emulsions that would hinder workup.
The anion used in the patent was hydrogen sulfate. Since about 1996, it has been common to see hydrogen sulfate quats used in conjunction with hydrogen peroxide oxidations, epoxidations and coupling reactions. In many of these reactions the hydrogen sulfate quat salts work much better than the corresponding chloride quat salts.
As always, the choice of phase-transfer catalyst should be customized to meet the needs of the specific application.
Need to learn more about which phase-transfer catalyst to choose for a specific PTC application? Contact Marc Halpern of PTC Organics by E-mail.
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!).
