Pedersen C J. Cyclic Polyethers and Their Complexes with Metal Salts. J

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This Week’s Citation CIassic~ ~ . Pedersen C J. Cyclic polyethers and their complexes with metal salts. J. Amer. Chem. Soc. 89:7017-36. 1967. [Elastomer Chemicals Dept., EL du Pont de Nemours and Co.. Wilmington, DEl

• The discovery of the first crown ether is described. been determined, an exhilarating period of Forty-seven other aromatic and saturated poly- research was inaugurated: every successful ethers were synthesized and their properties deter- experiment produced a significantly novel mined. Many form stable crystalline complexes result. with alkali and alkaline earth salts. Some saturated crown ethers solubilize potassium hydroxide The crown ethers might have been still- born in another environment. They were dis- and permanganate5 in aromatic hydrocarbons, EThe SC! indicates that this paper has been cited covered in the Elastomer Chemicals Depart- in over 1,165 publications since 1967.) ment of E.l. du Pont de Nemours and Com- pany, but what had they to do with elasto- mets? Moreover, the small amount of the by- product might have been tossed out or disre- garded as something other than the desired product. However, with the support of the top departmental management (C.J. liarring- ton, A.S. Carter, H.E. Schroeder, and R. Charles J. Pedersen Pariser), I worked independently with these - 57 Market Street compounds for nearly eight years. During Salem, NJ 08079 the period leading to the paper, my sole co- worker was T.T. Malinowski, a laboratory technician. I also had the resources of the analytical groups and the chance to consult March 20, 1985 with anyone on the technical staff of the company. The first cyclic polyether synthesized was The editor of the Journal of the American called the crown because of the appearance Chemical Society, Gates Marshall, wrote of of its molecular model and its ability to the manuscript: “You are clearly reporting a crown cations. The cyclic polyethers as a monumental piece of work But he com- class were called the crown compounds. plained that the experimental section This commentary summarizes how I discov- “...looked as though it had been copied ver- ered the crown ethers and the conditions batim from a laboratory notebook.” He con- tributed to the frequency of citation by al- under which1 their varied developments were initiated. Reasons for the frequent citation lowing two unusual features in the paper: of the resulting paper are offered. length (20 pages) and a new system of no-. In 1961, at age 57, I began to study the ef- menclature (crown) for identifying com- fects of uni- and multidentate phenolic pounds whose official names boggle the ligands on the catalytic properties of the VO mind. The paper is the primary reference for group. The desired ligands, up to and includ- the crowns, but it also contains the germs of ing the quadridentate, had been synthe- varied later developments stemming from sized. Now, the quinquedentate ligand, the original discovery. Many able investiga- bis(2.(o.hydroxyphenoxy)ethyl) ether, was to tors have founded their own systems, such as be prepared by reacting a catechol deriv- cryptates, host-guest chemistry, and the ative containing a protected hydroxyl (con- membranes and the ion-sensitive electrodes taminafed with 10 percent catechol) with of the biochemists, who were the2 first to bis(2-chloroethyl) ether. The expected quin. evince interest in the crown ethers. quedentate ligand was obtained, but nature In 1968, I received the Delaware Section lent a hand to provide the hexadentate di- Award of the American Chemical Society. benzo-18-crown-6 in 0.4 percent yield. This THL CROWNING is the extent of serendipity. The by-product The alkaline earth cation, was slightly soluble in methanol, contained And the alkali too. no hydroxyl, and was solubilized by any Used to act like freeborn lions, soluble sodium compound. The compound Scorning some things to do. was forming stable sodium complexes, a feat Organic ligands they disdained not previously achieved by any synthetic Till crown ethers were found. compound. Other crown ethers were synthe- Now with these compounds science ordained sized, and when their unique properties had They can be meekly crowned.

I. Pedenen Ci. Synthetic muflidentate macrocycic compounds. (iZatt R M & Christensen J J. eds.( Synthetic multideniate n.acrocyclic compounds. New York: Academic Press. 1978. p. I-SI. (Cited 50 times.l 2. Hfraok. M. Crown compounds: the,, cha,actenstics and applications. New York: Elsesier. 1982. 275 p.