MICHAEL FREEMANTLE

Charles J. Pedersen disliked writing scientific papers. So when the chemist at DuPont Experimental Station reported his discovery of cyclic polyethers and their complexes with metal salts, he wrote just one paper [J. Am. Chem. Soc., 89, 7017 (1967)], whereas many other chemists would have reported the work in several papers. His colleagues referred to it as "the blockbuster."

EXCITEMENT Discovery of crown ethers filled Pedersen with wonder. DUPONT PHOTO

The 20-page paper describes the synthesis, identification, structures, and properties of 33 cyclic polyethers. He prepared the compounds from aromatic vicinal diols such as catechol using five different methods of preparation and showed that some of the compounds form stable complexes with Li⁺, Na⁺, and other cations.

"The paper contains an unbelievable amount of information," comments Vincenzo Balzani, a chemistry professor at the University of Bologna, in Italy. "What strikes me is that all the work was carried out by a single researcher whose only equipment was three simple, conventional, experimental techniques: NMR, IR, and UV-Vis. Pedersen clearly had an outstanding chemical talent."

Cyclic polyethers, named "crown ethers" by Pedersen, are "host" compounds that bind strongly and selectively to a broad range of "guest" metallic and nonmetallic ions and neutral molecules. Their discovery spurred the rapid development of host-guest chemistry and supramolecular chemistry in recent decades.

"It is universally recognized that Pedersen's paper is one of the starting points of supramolecular chemistry," Balzani observes.

Pedersen's discovery was serendipitous. In 1960, he decided to study the effects of bi- and multidentate phenolic ligands on the catalytic properties of the vanadyl group, VO. One of the experiments, in which he used a reagent contaminated with catechol, yielded a small quantity of white, fibrous crystals. He eventually identified the compound as the first crown ether.

"Up to that point, no one had ever found a synthetic compound that formed stable complexes with sodium and potassium," he said in his Nobel lecture in Stockholm in December 1987. Pedersen shared the Nobel Prize in Chemistry that year with chemistry professors Donald J. Cram of the University of California, Los Angeles, and Jean-Marie Lehn of Louis Pasteur University, Strasbourg, France.

"My excitement, which had been rising during this investigation, now reached its peak, and ideas swarmed in my brain," Pedersen said in his lecture. "What a simple, elegant, and effective means for the trapping of hitherto recalcitrant alkali cations! I applied the epithet 'crown' to the first member of this class of macrocyclic polyethers because its molecular model looked like one and, with it, cations could be crowned and uncrowned without physical damage to either.

"Another aspect of this discovery filled me with wonder," he added. "In ordinary organic reactions, only rings of five, six, or seven members form easily. Here, a ring of 18 atoms had been formed in a single operation by the reaction of two molecules of catechol, which was present as a minor impurity, with two molecules of bis(2-chloroethyl) ether."

But following the discovery, Pedersen hit another problem. The systematic names of the cyclic polyethers were so cumbersome that he had great difficulty remembering them. He therefore devised his own system of nomenclature, which he describes in his 1967 JACS paper. His trivial names consist of four components, which are, in order: the number and kind of hydrocarbon rings; the total number of atoms in the polyether ring; the class name, crown; and the number of oxygen atoms in the polyether ring. For example, the first crown ether he discovered is named dibenzo-18-crown-6 (shown). Its systematic name is 2,3,11,12-dibenzo-1,4,7,10,13,16-hexaoxacyclooctadeca-2,11-diene.

Pedersen was born in Pusan, Korea, on Oct. 3, 1904. His father, Brede, was a Norwegian marine engineer who worked in Korea, and his mother, Takino Yasui, was born in Japan.

At the age of eight, his parents sent him to a school in Nagasaki, Japan, and two years later he moved to a school in Yokohama run by a Roman Catholic religious order of priests and brothers called the Society of Mary.

"There, I received a general secondary education and took my first course in chemistry," he noted in his lecture. "When it came time for university, I chose, with my father's encouragement, to study in America. I selected the University of Dayton because it was in Ohio, where we had family and friends, and because it, too, was run by the Society of Mary."

Pedersen obtained a bachelor's degree in chemical engineering at the university and a master's degree in organic chemistry at Massachusetts Institute of Technology. He decided not to take a Ph.D., as he was keen to start work and stop relying on his father's financial support.

In 1927, he obtained a job as a research chemist with DuPont at the Chambers Works' Jackson Laboratory in Deepwater, N.J., where he developed an interest in the effects of ligands on the catalytic properties of transition metals. In 1959, Pedersen transferred to the Experimental Station in Wilmington, Del., and discovered crown ethers there the following year.

Over the next nine years, he devoted all his energies to the study of the compounds and then retired in 1969.

He died in 1989, two years after his Nobel award.--

C&EN is celebrating the 125th volume of the Journal of the American Chemical Society by featuring selected papers from among its 125 most cited. This paper is ranked 12th.

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