Tetrabutylammonium azide is used as the azide source in the two nucleophilic substitutions of second reaction shown in the diagram. If we were to perform this reaction, we would attempt to replace the excess TBA azide with catalytic tetrabutyl ammonium bromide (TBAB) and stoichiometric sodium azide for both safety and cost reasons.
We can speculate, but don’t know how the TBA azide was made. Typically, tetrabutylammonium salts are made by one of two methods. One is a liquid-liquid ion exchange by contacting TBAB (the least expensive tetrabutylammonium salt) dissolved in a polar water-immiscible solvent (such as methylene chloride), with a saturated solution of the sodium salt of the anion for exchange. For tetrabutylammonium azide, it would not be safe to contact sodium azide with methylene chloride since it could produce explosive diazidomethane. Maybe a more inert solvent could be found. Even then, one might need to perform multiple ion exchange extractions to convert most of the TBAB to TBA azide.
Another method for forming tetrabutylammonium salts would not be safe for making tetrabutylammonium azide. That method is to start with tetrabutylammonium hydrogen sulfate to perform the ion exchange. However, that might result in the formation of hydrazoic acid which again is very explosive.
Again, if we were performing this reaction, we would probably add the sodium azide (portionwsie for safety?) to a mixture of the bis-trifluoromethane sulfonate intermediate with TBAB.
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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!).
