The term “phase-transfer catalysis” was coined by Dr. Charles Starks in his classic paper Starks; C., J. Amer. Chem. Soc., 1971, 93, 195, that is one of the most highly cited papers in organic chemistry.
In this paper, Dr. Starks described the extraction mechanism which has served as the basis for PTC for the past half century. Starks published outstanding supporting kinetic evidence for the extraction mechanism including: Starks; C., Owens; R., J. Amer. Chem. Soc., 1973, 95, 3613.
The extraction mechanism was supported by additional excellent classic kinetic studies published in the 1970’s by Landini (for example: Landini; D., Maia; A., Montanari; F., J. Amer. Chem. Soc., 1978, 100, 2796), by Herriott and Picker (for example: Herriott; A., Picker; D., J. Amer. Chem. Soc., 1975, 97, 2345) and others.
Starks’ classic patent took another few years to be issued and it described more than 50 examples of PTC for nucleophilic substitutions with a variety of inorganic nucleophiles, alkylations at acidic C-H, N-H, O-H and S-H groups, oxidations, reductions and other PTC reactions: Napier, D.; Starks, C.; (Conoco) 1976, U.S. Patent 3,992,432.
Excellent books on PTC were published by Charles Starks and Charles Liotta in 1978 (Academic Press), by Eckehard Dehmlow and Sigrid Dehmlow in 1980 (Verlag Chemie), by Yuri Goldberg in 1992 (Gordon and Breach), and the classic authoritative best selling book by Charles Starks, Charles Liotta and Marc Halpern in 1994 (Chapman and Hall).
Professor Makosza coined the term “catalytic two-phase systems” and his first paper was in 1966 that described synthetic organic C-alkylations using quaternary ammonium salts (Makosza; M., Serafinowa; B., Rocz. Chem., 1966, 39, 1401). Makosza later described an interfacial mechanism to qualitatively explain his results. Unlike Starks’ documentation, Makosza did not publish comprehensive underlying kinetic fundamentals for the interfacial mechanism.
When I joined Dow Chemical in 1984, I found an internal report by Henry (Hank) Hennis that described the extraction mechanism in 1957 but it was not published outside of Dow, apparently thinking that it was too valuable to disclose. Hank was a great guy and a great scientist. In 1987, I organized an internal PTC conference at Dow since PTC was used in very large commercial applications in polymers (e.g., epoxy resins), pharmaceuticals and agrochemicals that in total made products with sales volume of more than half a billion dollars per year. Since then, some of those products were discontinued, such as chlorpyrifos, that was produced in a large scale PTC process for which I provided plant support. I wrote a summary of Industrial PTC that was published in Ullmann’s Encyclopedia of Industrial Chemistry 2002 (Wiley-VCH).
Several public international conferences on phase-transfer catalysis were conducted with 10 or more leaders of early phase-transfer catalysis in Boston (1990), Honolulu (1995 & 2000) and Nagoya (1997). The picture shows the PTC leaders who spoke at the Pacifichem PTC session in 1995. The participants shown are from left to right: Top Row – Eckehard Dehmlow, Marc Halpern, Sigrid Dehmlow, Yoel Sasson, Tadatomi Nishikubo, Mieczyslaw Makosza, Renee Roy, Charles Starks; Bottom Row –Maryann Liotta, Mrs, Shioiri, Takayuki Shioiri, Martin O’Donnell, Charles Liotta, M. Wang.
On a personal note, I (Marc Halpern) ran my first successful PTC reaction in 1976 and I did my Ph.D. thesis research on phase-transfer catalysis at the Hebrew University of Jerusalem under the supervision of Mordecai Rabinovitz and Yoel Sasson. I wrote my first client-private study on industrial PTC for Catalytica in 1988 and a comprehensive private PTC market report for a client in 1996. I published and distributed 16 print issues of the journal Industrial Phase-Transfer Catalysis starting in 1994 and I have published the PTC Tip of the Month e-newsletter every month since October 2002 (except one month when my father was in the hospital) that contains the PTC Tip of the Month, the PTC Reaction of the Month and the PTC Catalyst of the Month. I have provided PTC lectures and services on site in nearly 300 R&D departments in 39 countries and I conducted the 2-day course “Industrial Phase-Transfer Catalysis” in 58 cities in the US, Europe and Asia (plus one on Zoom).
Phase-transfer catalysis has been my passion, second only to family, for 45.5 years and I intend to continue these PTC activities to the day I die.
My current biggest project is the commercial PTC desulfurization of fuels described at https://www.ultracleantechnology.com.au/.
