Let’s say that you want a phase-transfer catalyst that will do a great job in activating an anion, such as in a nucleophilic substitution, but you don’t want too many carbons and you want extra thermal stabiliity.
Tributyl Octyl Phosphonium Chloride might be an excellent choice because:
[1] the central atom is a phosphorous and not a nitrogen that will make a much looser ion pair between the quat cation and the anion thereby activating its nucleophilicity
[2] the phosphorous equivalent of the q-value will be only 0.89 due to the 3 butyl groups and one octyl group. In other words, the accessibility of the positive charge on the phosphorous will be low in the absence of a methyl group or ethyl groups that will result in a much looser ion pair and activate anion nucleophilicity
[3] the P-quat is more thermally stable than the corresponding N-quat, giving you flexibility in choosing reaction conditions to achieve higher performance
From an operational decision making standpoint, let’s say you use Aliquat 336 and you don’t get enough reactivity. In that case, you should screen Tributyl Octyl Phosphonium Chloride because this P-quat has a phosphorous instead of a nitrogen, the q-value is 0.89 instead of 1.34 and if you need to increase the reaction temperature, you may get an extra 50 deg C of functional temperature range above that to be often expected for Aliquat 336 for many nucleophilic substitutions. Tributyl Octyl Phosphonium Chloride also has only 20 carbon atoms versus and average of 27 for Aliquat 336.
You really should have a sample of Tributyl Octyl Phosphonium Chloride on your shelf!
Tributyl Octyl Phosphonium Chloride is available from Cytec
Need to learn more about which phase-transfer catalyst to choose for a specific PTC application? Contact Marc Halpern of PTC Organics by E-mail.
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!).
