While phase-transfer catalysis is most well known for strong base reactions, nucleophilic substitutions, oxidations and reductions, PTC also excels in a variety of acid-induced reactions. One of those reactions is PTC demethylation using aqueous HBr, HCl and HI.
Quaternary ammonium chloride and bromides associate with haloacids by hydrogen bonding between the polar HX molecule and the halide ion on the quat-halide ion pair. The hydrogen bonded ion pair complex Q+Y-*HX is soluble in nonpolar organic phases or in this case, has an affinity to the organophilic starting material without added organic solvent.
In addition, when HBr is associated with the quat ion pair, it is more reactive than when HBr is surrounded by many water molecules in a full hydration shell in aqueous HBr.
For these reasons, PTC-acid reactions can be very effective and more reactive than other reactions requiring the reaction of hydrochloric acid or hydrobromic acid with an organic molecule.
In this case, tetrabutylammonium bromide is used to enhance the reaction of HBr with four aromatic methyl ethers which forms 4 equivalents of methyl bromide and tetrahydroxynaphthalene in quantitative yield.
Now contact Marc Halpern of PTC Organics to help your company achieve low-cost high-performance acid reactions using phase-transfer catalysis.
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!).
