As we teach in the 2-day course “Industrial Phase-Transfer Catalysis,” quaternary ammonium and phosphonium salts used as phase-transfer catalysts sometimes contain hydroxy alkyl groups, including hydroxymethyl, 2-hydroxyethyl and 2-hydroxypropyl groups. One of the practical challenges when using quat salts is analytical detection of residual quat salt in the product or aqueous waste stream.
A patent was issued this month (Zhu; X., Moniee; M., Al-Saleh; M. (Saudi Arabian Oil Company) US Patent 11,385,171, 12-Jul-2022) that describes the analytical determination of tetrakis(hydroxymethyl)phosphonium sulfate (THPS) in the range of 2-500 ppm. The analytical method described in this patent may be applicable to other quat salts that contain hydroxyalkyl groups and that is why we chose to highlight this patent in our monthly newsletter.
The method involves reacting the hydroxymethyl phosphonium quat with potassium permanganate and measuring the reduced intensity of the absorption measured at a wavelength of 525 nm due to permanganate consumption. The measured intensity is normalized by subtracting a background intensity at a wavelength of 650 nm. The presence and concentration of THPS in the water sample can then be determined by comparing the normalized intensity with intensity values of the absorption in calibration samples comprising potassium permanganate and known THPS concentrations.
Quaternary phosphonium salts are used as phase-transfer catalysts, biocides, ionic liquids, surfactants or flame retardants. In this patent, THPS is cited for its use as a biocide. Again, the value of this patent to PTC chemists is likely to be when developing analytical methods for hydroxyalkyl quats used as phase-transfer catalysts.
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!).
