Tetrabutyl ammonium iodide is used primarily when you need both a phase-transfer catalyst AND a co-catalyst to activate an alkyl chloride or bromide alkylating agent. An example is shown in the PTC Reaction of the month above.
Iodide is a good nucleophile so the reaction of an alkyl chloride with iodide to form the alkyl iodide is often faster than the reaction of other nucleophiles with the alkyl chloride. Since iodide is also a good leaving group, the reaction of the nucleophile with the alkyl iodide is also often faster than the reaction of the nucleophile with the original alkyl chloride. The net result is that tetrabutyl ammonium iodide catalyzes many alkylations more than tetrabutyl ammonium hydrogen sulfate or tetrabutyl ammonium bromide.
However, iodide is expensive and the price of iodide fluctuates. Due to this fluctuation, the price of tetrabutyl ammonium iodide is usually set at the higher end of the range of iodide price since tetrabutyl ammonium iodide can sit in inventory for a long time. Many process chemists use tetrabutyl ammonium bromide together with 1 mole% KI, since KI is more likely to be bought at current market price. Due to hard-soft acid-base theory, a lipophilic quaternary ammonium cation prefers to associate with the polarizable “softer” iodide several orders of magnitude greater than with the more compact “harder” chloride anion (or bromide that has intermediate “softness”). So, it is usually less expensive to use a combination of tetrabutyl ammonium bromide with KI than it is to buy tetrabutyl ammonium iodide. If the cost of the iodide is not crucial, then it is more convenient to buy tetrabutyl ammonium iodide.
Tetrabutyl Ammonium Iodide is available from Dishman
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!).
