Quat phosphotungstates and oxophosphotungstates are useful in many PTC oxidations and PTC epoxidations. They are often formed by mixing sodium tungstate, quat salt and phosphoric acid simultaneously. Sometimes the three components are added stepwise. When the phosphoric acid is added last, quat tungstates are formed as intermediates.
A procedure was published this month in Wang, D.; Yuan, Y.; Zhang, Y. (The Trustees of Boston College), US Patent Application Publication 2025/0223244, 10-Jul-2025, that provided insight into quat tungstates that are formed when mixing a quat salt with sodium tungstate.
When sodium tungstate was mixed with tetrabutylammonium bromide in water in a molar ratio of 2.0:1.0, then acidified to pH 2 with concentrated HCl, the inventors reported that tetrabutylammonium decatungstate was formed. The quat-tungstate was characterized by UV to identify the decatungstate anion. The stoichiometry of the quat to tungsten ratio was not discussed.
The same procedure was performed using tetraphenyl phosphonium bromide except they used 2.78 moles tungstate per mole of phosphonium salt.
I have looked at a lot of literature that describes the stoichiometry between quat, tungsten, oxygen in polyoxometallates, with and without phosphorus. The motivation has always been to attempt to help understand certain aspects of PTC oxidations and epoxidations using quat-based polyoxometallates. Other than cases in which x-ray crystallography can be used to characterize the structures of these polyoxometallates, it is my impression that the structures and even atom ratios are conjecture. I am not an inorganic chemist so maybe my understanding of known information is incorrect. This report of the synthesis of quat decatungstate adds just a bit to my understanding of these systems.
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!).
