PTC conditions must be chosen carefully to achieve selectivity. In this 2004 patent, optically active CBz protected serine O-tosylate methyl ester is reacted with thiophenol and base under mild conditions, enabled by using PTC, to produce the corresponding optically active S-phenyl cysteine with almost no loss of enantiomeric excess. Some excess base was used which could have potentially racemized the C-H alpha to the ester, but PTC helped avoid that.
When the base used to deprotonate thiophenol was 18% NaOH or when ethyl acetate was used as the solvent, ee dropped to about 80%. When using PTC with carbonate as base and toluene as solvent, ee was typically 95% or higher and 99.6% ee was achieved.
Another interesting aspect of the patent is that tetrabutyl phosphonium quat was used in the presence of potassium carbonate. This quat is not very stable in the presence of 50% NaOH, but it did a very good job in the presence of carbonate at r.t.
If you or your company can benefit from achieving higher process performance in a shorter development time for this PTC reaction or any other reaction, by having access to the best PTC expertise available, NOW CONTACT Marc Halpern to inquire about using phase-transfer catalysis to achieve low-cost high-performance green chemistry. Remember, PTC excels in thousands of reactions in more than 30 reaction categories including strong base reactions, nucleophilic substitutions, oxidations and reductions
If you’re not sure if PTC can help your reaction, now fill out the PTC Project Evaluation Form and E-mail a scanned copy to Marc Halpern or send it by fax to Dr. Halpern at +1 856-222-1124. If your company does not have a secrecy agreement with PTC Organics Inc. already in place, please use “R-groups” instead of the exact chemical structures.
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!).
