Quaternary ammonium phase-transfer catalysts can and do decompose by Hofmann Elimination in the presence of base and nucleophilic attack in the presence of anions that can be nucleophilic. Tetrabutylammonium is used in many PTC applications and when it decomposes, it produces some amount of tributylamine, by both decomposition mechanisms.
While the tributylamine byproduct is adequately removed during workup after most PTC applications using TBAB, some applications are so sensitive to the presence of amine, that non-detectable levels of tributylamine must be achieved.
In the Patent Application Publication shown here, it was required that tributylamine be removed to non-detectable levels.
This publication describes methods for reducing tributylamine levels from polysulfane-silanes produced using tetrabutylammonium bromide.
- Carrier vapor distillation of bis(triethoxysilylpropyl)tetrasulfane produced using TBAB reduced tributylamine from 0.33% to < 0.01%
- Ozone treatment of bis(triethoxysilylpropyl)tetrasulfane produced using TBAB reduced tributylamine from 0.15% to < 0.01%
- Thin film evaporation of bis(triethoxysilylpropyl)tetrasulfane produced using TBAB reduced tributylamine from 0.15% to < 0.01%
- Activated charcoal treatment of bis(triethoxysilylpropyl)tetrasulfane that was previously treated by carrier vapor distillation that still had 0.01% tributylamine reduced the tributylamine to < 0.01%
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!).
Hi Marc,
Thanks for the Tip. A curious procedure, removing Bu3N after treatment with ozone. I expected that ozone would oxidize the tetrasulfane before tributylamine. Tertiary amines react with O3 to form the N-oxides and some secondary amine + aldehyde. Bu2NH & PrCHO should be more volatile than Bu3N. After ozone treatment distillation removes the “lights,” the product is isolated as the non-volatilized “bottom”. That must be how it goes.
Best regards, Neal