Because of illness, Libby was unable to attend the award dinner. His talk was read by Ernest C. Anderson of AEC's Los Alamos Lab (see page 1 1 0 ) . Many important n e w uses for radioisotopes are certain t o develop, says Libby. Actually, t h e two most valuable tracer isotopes have yet to be a p plied on a large scale industrially. These are radiocarbon and radiohydrogen (tritium). Medicine itself makes little use of these t w o most important isotopes in the human body. Although radioactive forms of iodine, sodium, iron, a n d other elements a r e employed in medicine, they do not play as vital a role as either carbon or hydrogen. Radiocarbon a n d tritium offer tremendous opportunities to t h e pharmaceutical chemist, Libby emphasizes. They might also b e used effectively in the oil industry a n d t h e organic chemicals industry. Although now widelyused in research, they also have farreaching possibilities in actual plant control. • Role of Tritium. Tritium, a cosmic-ray product, burns to water and produces radioactive rain. This rain can be used in dating water and agricultural crops. As shown by tests on bottled vintage wines, this radioactivity
can also be used in dating wines. Hydrogen bomb explosions have greatly increased the tritium present in the Northern Hemisphere. This isotope, in t h e form of radioactive rain, has spread rapidly around t h e world. Its radioactivity can b e used, for example, to determine whether well water, at least in part, is in contact with surface water. If the water is n o t radioactive, it's likely that the well will not be quickly refilled once it is pumped dry. Large areas of the country, Libby warns, live off fossil water supplies. Analyzing for radioactive water can show that this condition exists. Chemists need to learn considerably more about the atomic nucleus, says Libby. Isotopes should b e placed in every high school and college chemistry classroom in t h e country. Mildly radioactive forms of hydrochloric acid, acetic acid, a n d sulfuric acid should be made available to students. Inexpensive Geiger counters should also b e available. Many of t h e possible uses for radioisotopes are not being developed because t h e techniques of measurement are not widely understood, says Libby. Although the theory is known to most chemists, the practice is unknown to a very large percentage.
From Heavy Water, Heavy Rubber N e w polyisoprene rubber has unique properties b e cause all o f its hydrogens a r e r e p l a c e d b y deuterium C^HEMISTS at B. F . Goodrich Research
Center have developed a new manmade rubber that is more rubbery than rubber itself. Called deuterio rubber, the material is all-cis, all-1,4 polyisoprene in which all of the hydrogens have been replaced by heavy hydrogen ( deuterium ) . Goodrich and Goodrich-Gulf researchers believe this polymer will be a valuable tool in basic studies on rubber's unique set of properties. The new material is expected to help explain the elasticity of rubber. Also it may clarify why rubber evolves and absorbs heat during deformation and recovery. And it may explain the infiared absorption and crystallization behavior of rubber. For the present, the material is strictly experimental. Only about 250 grams have been made so far. But
chlorophyll. Basically, Woodward's problem was to first synthesize chlorin e 6 , a porphyrin-like molecule having two extra hydrogen atoms in the 7 and 8 positions in the molecule's nucleus. Once that's clone, chlorin e 6 can then be transformed to chlorophyll since it
has the same structure as chlorophyll minus the magnesium atom a n d some Having synthesized quinine, cholesside chains. But synthesis of chlorin e n is no easy job. terol, cortisone, a n d a host of other organic compounds, Robert B. WoodFirst Woodward wanted to learn if ward and coworkers are n o w on their the structures earlier attributed to chlorophyll by such workers as Fisher wav toward t h e total svnthesis of are correct. H e was particularly concerned with the compound's stability. Normally it would seem that some of the side groups attributed to chlorophyll and chlorin e(! would cause a strain on the molecule because of steric effects. But Woodward discovered that these groups are not planar with the molecule, that some are above and others below the plane. This fact accounts for the molecule's stability and explains the positions of the two hydrogen atoms in the 7 and 8 positions. Thus, having discovered that steric compression stabilizes chlorin er>, Woodward next developed a synthetic approach. First he synthesized two dipyrrylmethanes, one having free a. positions, and the second having carbonyl groups. Upon reaction, these substances yield a porphyrin with the Robert B. Woodward (left), Morris Loeb Professor of Chemistry at Harvard University, accepts the Remsen Memorial Lecture Scroll from E . A. Metcalf substitution necessary in the chlorin er> ( r i g h t ) , Chairman, Maryland Section of ACS. Carl Bruning, director of chemi- molecule. All that's left now is to p u t cal research and development at Pfizer, introduced Woodward who gave the 13th into the porphyrin nucleus the side chains characteristic of chlorin e 0 . • annual lecture a t t h e Johns Hopkins University, Baltimore, Md.
A Green Thumb
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RESEARCH
much larger amounts are expected to be synthesized in the future as research, still in t h e preliminary stage, keeps progressing. The n e w product may be a more elastic material than ordinary rubber. The reason, explains Waldo L. Semon, director of Goodrich's polymer research, is that molecules containing deuterium atoms apparently attract each other less strongly than do those containing hydrogen. Deuterio rubber is heavier than ordinary rubber. Because of the presence of heavy hydrogen, it has a specific gravity of 1.007, compared to the usual 0.9. • W a y It's M a d e . Synthesis of deuterio rubber was carried out by a team headed by David Craig at B. F. Goodrich's Brecksville, Ohio, lab. Preparation of this material starts with 99.57f heavy water, which is used to convert acetone to perdeuterio acetone. This is then treated with the potassium salt of perdeuterio acetylene to form the potassium salt of perdeuterio methylbutynol. This is hydrolyzed with heavy water to give perdeuterio methylbutynol. Next, deuterium gas, in the presence of a palladium catalyst, converts perdeuterio methylbutynol to perdeuterio methylbutenol. With the help of an aluminum oxide catalyst, heavy water splits out to give perdeuterio isoprene. Finally, this is polymerized with a Ziegler catalyst (aluminum triisobutyl and titanium tetrachloride) to make perdeuterio polyisoprene. For t h e time being, the new rubber is looked upon exclusively as a research material. Eventually it may have some commercial use in specialty items, but this is highW uncertain. Right now, the product costs at least 100 times as much to make as ordinary rubber. Deuterio rubber, also called D-SN (deuterium-synthetic natural), can b e vulcanized much like Hevea or the usual synthetic "natural" rubber, Semon recently told a rubber meeting in Cologne, Germany. Furthermore, it does not require carbon black reinforcement to develop high tensile strength. Now under way is a detailed study of the dynamic properties of the new rubber compared to those of conventional rubber. Of special interest will be information about its relative stability to heat, radiation, and oxidation, as well as its gas permeability. 36
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Sulfur Not Needed U. S . Rubber steps up h e a t resistance o f butyl r u b b e r , replaces sulfur with phenolic condensation polymer
X*OR some time, users of butyl rubber have worked with a special high temperature material which stands up at 400° F., a full 100 degrees above the useful limit of previous butyl rubbers. And such compounds are probably in store for wider use now that U. S. Rubber has revealed the key to making thein (C&EN, May 2 6 , page 2 3 ) . U. S. Rubber replaces sulfur, the conventional vulcanizing agent for both butvl and natural rubber, with phenolformaldehyde derivatives. The result is a butyl rubber with exceptional thermal stability. It resists aging from four to 1 0 times as well as compounds prepared with sulfur, Paul Viohl of the U. S . Rubber research center told the ACS Division of Rubber Chemistry spring meeting in Cincinnati. Viohl, P . O. Tawney, and J. R. Little substitute for sulfur 2,6-dimethylol-4hychrocarbylphenol or its condensation polymers. These phenolic polymers are relatively slow curing, b u t make outstantding rubbers, says Viohl. For instance, Viohl finds that a conventional butyl formula with sulfur loses 5 5 % of its optimum stress at 2007f elongation after heating at 322° F. for four hours in a n inert atmosphere. A corresponding butyl rubber vulcanized with a phenolic condensation polymer shows no loss of strength even after heating for 16 liours at the same temperature. The sulfurless material stands up well even during an extended 20-day test. • Older Than Butyl. The idea of using phenolic polymers to replace sulfur as a vulcanizer is old—older than butyl rubber itself. At least 20 years ago several workers looked into such curing systems for natural rubber. But this vvoTk was dropped before it reached commercial use, probably because the phenolics didn't show any advantage over sulfur, says Viohl. Recent tests at U. S. Rubber show that nothing is gained b y using the organic curing system with natural rubber. But butyl is a special case. Chemists have long recognized that two competing reactions take place while vulcanizing with sulfur—cross linking or
vulcanization, and reversion or de-vulcanization. In butyl rubber, reversion is a particularly serious problem, and a more stable closs-link has long been sought. Apparently, phenolic condensation polymers provide t h e long sought stable cross-link. By itself, the phenolic vulcanizing agent is quite slow. Viohl found it took four hours at 322° F . to get 8 0 % of a full cure, while a sulfur system reaches peak cure in a little over an hour. Viohl and his coworkers studied various compounds to catalyze the reaction, found that two parts of stannous chloride would cut curing time by a factor of four. And not only does the metallic halide increase rate of cure, but it also makes possible an increase in the over-all degree of cure that can be obtained. The practical significance of this work is a sizable step u p in the working temperature of butyl rubber. Viohl says that U. S. Rubber has improved resistance to air aging by 100° F. over the range from 300° F . to 400° F. This means more applications for butyl rubber in today's high temperature missileage. U. S. Rubber has used the phenolic vulcanized butyl rubbers internally since 1953, and last year started offering them commercially. High temperature butyl rubbers, of course, wouldn't b e much good if they didn't maintain all the properties of materials made with sulfur. One such property is t h e ability to form a strong bond with metals. Stewart Brams and Frederick Gage of Dayton Chemical Products Laboratories tested the adhesion of high temperature butyl rubber to steel and obtained very adequate bonds which stand up. During one test, over 144 hours at 320° F., a butyl stock retained its adhesion for 4 hours at 450° F . , which leads Brams and Gage to believe that 400° F. needn't be considered a limit on practical working temperatures.
Computer Dissects Curves Researchers at the National Institutes of Health have developed an analog computer that might b e a boon to the laboratory chemist. Though still in the development stage, it analyzes experimental distribution curves with an accuracy of about 5 % . Murray Eden, one of the computer's inventors, says it's especially useful in procedures like electrophoresis which
