Trimethylamine can form in-situ phase-transfer catalysts by reacting with benzyl halides or allyl halides. It is probably not a good idea to try this with normal alkyl halides since the trimethylamine can act as a base and dehydrohalogenate the n-alkyl halide. Since benzyl groups and allyl groups don’t have beta protons, they cannot dehydrohalogenate.
In the PTC Reaction of the Month above, even if the benzyl trimethyl ammonium bromide quat would “decompose” by nucleophilic substitution, it would still form the desired product and liberate trimethyl amine that may requaternize and reform the phase-transfer catalyst in situ. So, when you are using benzyl halides or allyl halides as alkylating agents, you should really evaluate the feasibility of adding trimethyl amine to form the phase-transfer catalyst in-situ.
Please note that quats based on trimethyl amine cannot undergo Hofmann Elimination and will therefore be more stable than quats made from triethylamine.
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!).
