A patent application published three days ago (Yogendra, S. et al, Covestro, US Patent Application Publication 2024/0025753, 25-Jan-2024) describes what appears to be a practical setup to produce phosgene on a lab scale. This method might avoid the need to purchase and store hazardous phosgene in cylinders and might enable producing just enough phosgene needed for a specific use. This batchwise on-demand lab scale production of phosgene achieves the advantages of the large scale continuous on-demand industrial production of phosgene in the right quantity shortly before use with a short residence time to minimize storage and handling of excess hazardous phosgene. Large scale phosgene production uses porous activated carbon as the catalyst.
The concept in this patent application publication is to use a catalytic amount of a quaternary ammonium chloride, combine it with chlorine to form a quat polychloride and then react it with an excess of carbon monoxide. The reaction is performed at ambient temperature and near atmospheric pressure. This reaction may not be considered phase-transfer catalysis.
The inventors described two methods, one with solvent and one without solvent.
In one system, 3.5 mole% methyl triethyl ammonium chloride was used as the catalyst and chlorobenzene as the solvent. In this case, quantitative conversion of the chlorine to phosgene was achieved using a molar ratio of carbon monoxide to chlorine of 1.6.
In a second system, 40 mole% tetraethyl ammonium chloride was used as the catalyst without a solvent in a tubular reactor. In this case, a molar ratio of carbon monoxide to chlorine of 5.8 was used.
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!).
