PTC strong base reactions constitute more than half of PTC commercial applications. PTC-NaOH routinely alkylates substrates with a pKa of up to about 23. The pKa of carbazole is 20 (in water). The substrate shown in the diagram has a higher pKa due to the strained out-of-plane nature of the ring system that is problematic for the aromaticity of the anion.
When the pKa of the substrate to be deprotonated is high enough to be close to the limits of PTC-alkylation, solid powdered NaOH is often used. The presence of even small amounts of hydration reduces the basicity of the hydroxide and also reduces the nucleophilicity of the low concentration organic anion.
In this case, 2 equivalents of powdered NaOH were used, of which some of the excess likely absorbed the equivalent of water that was generated.
Now contact Marc Halpern to improve your strong base processes using the unmatched specialized expertise of PTC Organics in PTC-strong base reactions.
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!).
