Cetyl Trimethyl Ammonium Bromide (CTAB) is a quaternary ammonium salt that is usually used as a surfactant, sometimes as a phase-transfer catalyst and sometimes as both.
In the application shown in the diagram, CTAB is reported to be used for a “micelle catalyzed Diels-Alder reaction that enhances reaction yields and shortens reaction times.”
Even though the diagram on page 4 of the patent application publication explicitly shows “PTC” to represent CTAB, there is obviously no possibility for phase-transfer catalysis in this Diels-Alder reaction. However, it is always useful to examine the workup after a reaction using CTAB to see if there appears to be a challenge with emulsions during workup or if a clean phase separation is observed.
In this case, the reaction used a lot of water (~15X versus the combined mass of the freshly prepared cyclopentadiene and methyl naphthoquinone) and no organic solvent. The workup started with extraction of the organic product (adduct) into ether. No mention was made of emulsions during workup and the 86% yield after recrystallization suggests that there was little to no handling loss due to emulsions.
We have seen commercial applications emulsify unintentionally during workup when using quaternary ammonium salts as phase-transfer catalysts and care is not taken to avoid critical micelle concentration.
When this happens, there can be significant economic losses if the product cannot be recovered easily. Addition of salt can sometimes break the emulsion, but it is not a desirable situation.
Therefore, we are always on the lookout for applications that use alkyl trimethyl ammonium quats like CTAB that are performed without issues during workup.
This publication also described PTC reactions that used tetrabutylammonium bromide for nucleophilic substitutions and a dithionite reaction.
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!).
