Theory Interprets Isotope Effects 151ST
ACS
NATIONAL
MEETING
Physical Chemistry
The significant structure theory of liquids is useful in interpreting isotope effects on physical properties, a group of scientists at the University of Utah has found. By applying significant structure theory, Utah's Mu Shik Jhon, Joseph Grosh, Dr. Taikyue Ree, and Dr. Henry Eyring can correlate isotopic vapor pressure differences with differences in heat of sublimation. They can also correlate the smaller extent of isotopic vapor pressure differences with differences in the moments of inertia and differences in the masses of the isotopic molecules.
CALCULATIONS. Dr. Robert Rein examines calculations on DNA model (shown at left) he has made (in collaboration with Dr. Frank E. Harris) which indicate possible mechanisms for production of spontaneous and radiation-induced mutations
state two minimum-energy positions for each proton. One (the normal position) is nearer the proton-donor atom of the hydrogen bond. The other is nearer the proton-acceptor atom of the bond. From the relative depths of the minima and from the height of the barriers separating them, Dr. Rein and Dr. Harris estimate the equilibrium tautomer populations and the quantum-mechanical tunneling rate between tautomers. For the ground state, the equilibrium population in the unusual tautomeric forms is of the right order of magnitude to account for observed spontaneous mutation rates. In the ionic states, the population of unusual tautomers is greatly enhanced. This is consistent with a mechanism for radiation-induced mutation in which the radiation plays a role in the formation of ionic states. For both ground and ionic states, the calculated tunneling rates are rapid enough to permit tautomeric equilibrium to be reached in biologically significant times, Dr. Rein and Dr. Harris say. 40
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The significant structure theory assumes that at any given time some of the molecules in the liquid possess solidlike degrees of freedom, while other molecules possess gaslike degrees of freedom. This means that at one instant a molecule of the liquid behaves like a gas, and a moment later it has solidlike properties. For some isotopic pairs, the heat of sublimation of the compound containing the deuterium isotope is much larger than the heat of sublimation of the normal compound. Pairs of this type studied by the Utah group include HL,-DL„ H.O-D.O, and NH 3 ND :V In these pairs, the vapor pressures of the normal compounds are greater than those of the corresponding compounds containing deuterium isotopes. In another type of isotopic pair studied by Dr. Eyring and his coworkers, the heat of sublimation of the compound containing the deuterium isotope is smaller than the heat of sublimation of the normal compound. A typical example of this type is Cr,H1L,-C(;D1L>. The compound containing the deuterium isotope has the lower heat of vaporization. This may be attributed to the lower zero-point energy for the intermolecular bond, the Utah workers say. In a third type of isotopic pair, for example, C ( 5 H ( r C e D e , the isotopic heat differences are very small, that of C (; D, ; being only 3 cal. per mole greater. The vapor pressure of C 6 D G is greater than that of C 6 H 6 . For the pairs studied, the vapor
pressure differences are due mainly to the heat of sublimation when this quantity differs markedly for the isotopes. The vapor pressure is lower for the compound with the largest heat of sublimation. The Utah group finds that a secondary effect resulting from the moment of inertia and mass of the molecule affects the vapor pressure to a lesser degree. The heavier the isotope and the larger the moment of inertia, the larger is the resulting vapor pressure.
Butylcyclopentadienone Is Stable at -60° C. 151ST
ACS
NATIONAL
MEETING
Organic Chemistry
Two cyclopentadienones, substituted only by tert-butyl groups, have been synthesized by Dr. Edgar \V. Garbisch, Jr., and Richard F. Sprecher at the University of Minnesota, Minneapolis. These compounds are 3-fcrf-butyland 2,4-di-£cTf-butylcyclopentadienone. The parent compound, cyclopentadienone, has never been isolated because it dimerizes by Diels-Alder addition too quickly. Until Dr. Garbisch's work, the only stable cyclopentadienones were those substituted with pi-electron (unsaturated) groups such as phenyl. These groups stabilize cyclopentadienone by interacting with cyclopentadienone's pi-electron system. The resulting system is perturbed and probably does not represent the unsubstituted system. Knowledge of the unperturbed pi-electron system is essential for determining the origin of cyclopentadienone's unique dimerization reactivity.
Bulky Butyl Groups Stabilize Cyclopentadienone Sterically, Not Electronically
U.S.I. CHEMICAL NEWS March-April
1966
A Series of Advertisements for the Chemical Process Industries
U.S. I. Unit to Supply Agricultural Products U. S. I. has formed a new operating unit — U . S . I . Farm Chemicals — to manufacture and market a broad line of plant foods. Among the products available are chemically-combined mixed fertilizers, anhydrous and aqua ammonia, nitrogen solutions, straight materials. U. S. I. Farm Chemicals has manufacturing, laboratory and storage facilities at Danville, 111., and additional storage facilities at Peoria, 111. and Vincennes and Foreman's Switch,
Million Dollar Plant Addition Gives U.S.I. Clearcut Superiority in Alcohol Quality Purpose of Installation is to Maintain U.S.I. Ethyl Alcohol as Best Commercially Available New purification equipment, representing a substantial investment, is now in operation at U. S. I's Tuscola, 111. ethyl alcohol facility. Specially designed by U. S. I., the installation does not increase output by one gallon. Its sole purpose is to ensure that U.S.I. ethyl alcohol, al-
the bland, characteristic odor once t h o u g h t typical only of fermentation alcohol.
The reason for the emphasis on odor is that ethyl alcohol serves as the principal solvent and extender for perfumes and colognes. It also makes up a large part of various other cos-
Sequence above shows step-by-step installation of purification equipment designed especially for U.S.I.'s ethyl alcohol facility at Tuscola, III.
Indiana. U.S.I.'s facilities are designed to handle peak demand, and to provide technical service.
EVA Replaces Rubber For M e d i c a l Syringes A one-piece disposable medical syringe, blow molded of Ultrathene® ethylene-vinyl acetate copolymer, eliminates the costly sterilization process needed with a two-piece syringe consisting of a rubber squeeze bulb and glass tube. The translucent syringe consists of (Continued on next page)
ready best rated by perfumers and cosmetic chemists, will be demonstrably superior in odor purity. As described by U . S . I / s W. R. Deitz, and reported in the May, 1965 issue of U. S.I. Chemical News, previous improvements in the quality of synthetic ethyl alcohol have yielded a product as good as, or better than, any commercially available ethyl alcohol. In fact, perfumers and cosmetic chemists have, for some time, obtained consistently excellent perfumery grade synthetic alcohol exhibiting
metics and toiletries . . . of many quality detergents . . . of hair sprays and other aerosol products. The perfume for any one of these products is developed with meticulous care, and just a trace of off-odor can interfere with the fragrance and detract from the effect the perfumer seeks to create. Attention to Detail Even before U. S. I/s innovation in quality control, the odor-bearing organic impurities present in most com(Continued on next page)
March-April
U.S.I. CHEMICAL NEWS
Alcohol (continued)
Syringe (continued)
mercially available alcohol have been reduced to such a point that their content fell well below the minimum allowed by standard industry specifi cations. However, the perfumer's nose is more discerning than the chemist's test procedures. It took meticulous attention to every detail of the manu facture and supply of ethyl alcohol to achieve a consistently superior rat ing among perfumers.
an integral squeeze bulb and cali brated hollow tube section. Total length of the part is 9 in. Although the previous rubber bulbglass tube design satisfied end-use re quirements, it was inconvenient to sterilize and too expensive to throw away. The decision to use EVA copoly mers came after other plastics were evaluated and rejected. Ultrathene not only meets all end-use require ments, but also molds easily and in expensively. The parison is easy to control; the end-product, gel-free.
Now that superiority is protected by more extensive purification, accom plished by new equipment and other process improvements at U. S.I.'s
Shown here: the most crucial test of all.
ethyl alcohol facility at Tuscola. The equipment removes the most minute traces of impurities that may possibly be present. The alcohol produced is cleaner, purer and drier than any available today. Shipments of U. S. I. ethyl alcohol have been approved—and praised— by some of the nation's leading per fumers. If you are interested in eval uating the product, please write on your company letterhead to Mr. T. R. Drinkwater, U. S. I., 99 Park Avenue, New York, Ν. Υ. 10016.
Sanitary syringe is made from EVA copolymer.
Fire Literature Listed A new 48-page illustrated bro chure, published by the National Fire Protection Association, describes lit erature available on the engineered protection and public and industry education needed for fire control. Listed are more than 600 pam phlets and texts onfirefightingtactics, fire training films, handling flammable liquids and solids, and the like. To obtain a copy of the list, write to U.S.I., specifying No. 2290.
1966
TECHNICAL DEVELOPMENTS Food research abstracts, a new service, covers developments in commodities, techniques, equipment for those respon sible for large scale feeding in hospitals, industrial plants, etc. No. 2291 Biochemicals listing includes amino acids, carbohydrates, blood proteins, en zymes, chromatographic media, ion ex changers. Catalog with prices is offered. No. 2292 Micro-stirrer is designed for vacuum dis tillations, cryogenic experiments, extrac tions, organic reactions, other microlaboratory procedures. 12 volt dc motor in lightweight unit drives 4 in. glass stirrer. No. 2293
Stirrer is designed for small lab operations.
Stain remover for chemical and clinical lab use reportedly removes such mate rials as silver nitrate, potassium perman ganate, ball point pen ink. No. 2294 Microfine polyolefin powders—their uses, properties—are described in article re print. Copies are available. No. 2295 For more information on the U.S.I, products or other items in this issue, write: U.S.I., 99 Park Ave., New York, Ν. Y. 10016. Please use the identifying number when writing.
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free, new casebook describes 60 Leco furnace applications! Read what others have done with versatile LECO equipment — induction furnaces and attachments. Papers cover details of: QUICKLY. Cyclopentadienone has never been isolated because it dimerizes too quickly. Interested in the origin of this high reactivity, Dr. Edgar W. Garbisch (left) and Richard F. Sprecher have made two stable cyclopentadienones in which the pi-electron system appears to represent the parent compound
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With this in mind, Dr. Garbisch decided to try to make some simple tertbutyl derivatives of cyclopentadienone. The bulky but saturated butyls, he reasoned, might retard dimerization sterically, but leave the pi-electron system unperturbed. If so, he could study the spectral properties of these molecules and perhaps infer something about the properties of unsubstituted cyclopentadienone. The Minnesota workers synthesized the dibutyl compound from a ketal of the corresponding dibutylcyclopenta-
none.
Double bromination and two
dehyclrobrominatioiis
introduce
indeed retard dimerization sterically rather than electronically. The spectra give clues to the origin of cyclopentadienone's high self-DielsAlder reactivity. They show an unusually small energy separation between the highest occupied and lowest unoccupied molecular orbitals of the pi-electron system. Small in this case means small relative to those of other simple diene-dienophile (Diels-Alder) systems. In the Diels-Alder transition state, Dr. Garbisch says, the highest filled molecular orbital of one molecule
the
should interact m a i n l y w i t h t h e lowest
diene system. They make the monobutyl material from 3-fcrf-butylcyclopentenone, again by brominating and dehydrobrominating. As hoped, the dibutyl derivative dimerizes slowly. The singly substituted compound dimerizes 10 million times faster than the dibutyl derivative at —20° C , but slowly enough at - 6 0 ° C. to take spectra. Similar. The ultraviolet spectra of the two butylated compounds are similar. This indicates that the butyl groups do not significantly alter the pi-electron system. Therefore, their spectral properties ought to represent those of the parent compound. Dr. Garbisch concludes that the butyls do
unfilled molecular orbital of the second molecule, and vice versa. The smaller the energy gap between these orbitals, the more strongly they should interact. Providing the symmetries of the interacting orbitals are compatible, this interaction maximizes the stability of the transition state. This is probably why cyclopentadienone adds to itself so readily, Dr. Garbisch concludes. His theory predicts that cyclopentadienone should add to cyclopentadiene less readily than to itself, but more readily than cyclopentadiene adds to itself. Also, cyclopentadiene should act as diene, rather than as dieneophile, with cyclopentadienone. Experiment bears out both expectations.
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11, 1966
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Bicyclics Depress Rate Of Cyclobutane Cleavage 151ST
ACS
NATIONAL
MEETING
Organic Chemistry
Incorporating a cyclobutylmethyl Grignard reagent into selected bicyclic sys tems depresses the rate of cyclobutane ring cleavage. The systems bicyclo[2.1.1]hexyl and bicyclo[3.2.0]heptyl lower the rate by factors of 15 to 1000 relative to a-cyclobutylethyl mag nesium bromide, according to Dr. E. Alexander Hill and Robert J. Theissen at University of Minnesota, Minne apolis. Previous studies by Dr. Hill indi cate that the reaction mechanism is the four-center type. This means that the magnesium atom, methyl, and two ring carbons are roughly planar and that all bond breaking and making is simultaneous. This mechanism should be sensitive to the geometry of the reacting bonds. To test his hy pothesis, Dr. Hill has compared the
Nitrilium Ions Show Use In Adding Ν to Olefins 151ST
ACS
NATIONAL
MEETING
Organic Chemistry
A method for adding a nitrogen func tion stereospecifically to an olefin has been developed by Dr. Alfred Hassner, Dr. Louis Levy, and Robert Gault of the University of Colorado, Boulder. The new reaction produces nitrogen heterocycles and bifunctional organic nitrogen compounds. Although synthetic organic chem ists have ample methods for introduc ing oxygen functions into olefins stereospecifically, this is not the case with nitrogen functions, Dr. Hassner explains. Realizing that halogens add to olefins stereospecifically because they form a three-membered cyclic halonium ion intermediate, the Colo rado chemists tried using this inter mediate in their own reaction. They reasoned that a nitrogen-con taining nucleophile, such as a nitrile, might open a cyclic halonium ion and incorporate itself into the molecule. 44
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Cyclobutylmethyl Grignards in bicyclics cleave to monocyclic olefins
monocyclic system with bicyclic sys tems in which the transition state geometry is more restricted. In all cases, reaction rates decrease. The decrease is especially significant in the bicyclo[2.2.1]hexyl system. Here severe angle strain ought to pro vide extra driving force for bond cleavage. The bicyclic systems in crease the distance between the mag nesium atom and the carbon atom to which magnesium transfers. They also
prevent coplanarity of the reacting atoms. Rate reductions, then, are consistent with the proposed mecha nism, but they do not exclude a freecarbanion mechanism. These ring cleavage reactions are analogous to the reverse of the addi tion step in Ziegler-Natta type poly merization of olefins. Dr. Hill feels that there should be similarities in transition state geometry between the two reactions.
It does. It converts the halonium ion into a nitrilium ion, which turns out to be a useful synthetic intermediate. Hydroxide ion converts the nitrilium ion into an amide; azide ion converts it into a tetrazole. But the reaction works only when the halide ion from the original halo
gen is removed from solution. Other wise normal halogen addition proceeds in competition with nitrile addition. Dr. Hassner eliminates this competi tion by adding a better competitor for the halide ion, a silver salt. Silver halides precipitate. Although iodine does not usually
Nitriles sidetrack halogen addition in the presence of silver ions
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BIFUNCTIONAL. Dr. Alfred Hassner and his group have developed a new way t o convert olefins stereospecifically into nitrogen heterocycles and bifunctional groups
add to olefins, it can be used in the new reaction. Cyclohexene treated with an equivalent of iodine and silver perchlorate in acetonitrile gives a 60% yield of N-(f/Y7/i.s-2-iodocyclohexyl)acetamide. Since no cis isomer was found, the reaction appears to be stereospecific. With steroidal olefins, the reaction is trans and diaxial. 2-Cholestene gives the diaxial 2^-acetamido-3abromocholestane. This compound cyclizes losing bromide ion, then re opens in excess base to the amino alcohol derivative. The reaction should, therefore, be useful for mak ing c/.s-2-amino alcohols also. Although the reaction is similar to the Ritter reaction, in which a carbonium ion reacts with a nitrile to give an amide, it has some advantages. Reaction conditions are not so acidic; the reaction is stereospecific; and the products are bifunctional.
Coincidence Counting Analyzes Organic CI 151ST
ACS
NATIONAL
MEETING
Nuclear Chemistry and Technology A new method for the analysis of chlorine in organic compounds by neu tron activation has been developed by Dr. Edward T. Bramlitt of Atomics International (a division of North American Aviation, Inc.) for the U.S. Atomic Energy Commission. By using 46
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gamma-gamma coincidence counting techniques to eliminate interfering ac tivities, the method detects 0.4 to 2 p.p.m. of chlorine in organic com pounds with a 7% standard deviation, and down to about 10 p.p.b. with a standard deviation of about 50%. This is significantly better precision, accuracy, and sensitivity than was formerly possible, Dr. Bramlitt says. Today, organic compounds such as terphenyls are used in some nuclear reactors as moderators or coolants. Most of these compounds contain a chlorine impurity. According to Dr. Bramlitt, this impurity may cause prob lems of film formation, zirconium hy dride formation, or corrosion. There fore, it is important to know the chlo rine content of these materials. To date, chemical determination, x-ray fluorescence, and neutron acti vation have been used to analyze for chlorine in organic compounds. Neu tron activation has been the most suc cessful; however, it does have some drawbacks. Dr. Bramlitt says that when the chlorine content is low and certain other impurities are present, the activation product, chlorine-38, cannot accurately be determined. The major interfering impurities are sodium and manganese. Activation of these ele ments yields sodium-24 and manganese-56. These isotopes have decay gamma energies close to those of chlo rine-38. Dr. Bramlitt sought to develop an activation analysis method which would avoid these interfering activities. He succeeded by using coincidence counting techniques. The electronics for this counting arrangement are de signed so that data are recorded only when certain gamma rays appear in each of two detectors in time coinci dence. Since two gamma rays are simultaneously produced when a chlo rine-38 atom disintegrates, the counter can be adjusted so that this is the only activity observed. The technique al lows specific identification of chlorine38 by both a single-component gamma decay curve and a single-component gamma energy spectrum. Dr. Bramlitt says large samples must be irradiated to give enough chlorine activity to be observed by coincidence counting. This is possible, however, because the organic matrix does not become radioactive. An advantage of using large samples is that a more rep resentative estimate is obtained of the chlorine content of the batch which is being tested.
Collidine Ligands Don't Reduce MoCI5 or WCI5 151ST
ACS
NATIONAL
MEETING
Inorganic Chemistry The first molybdenum(V) and tung sten (V) halide complexes containing nitrogen ligands have been prepared by Dr. Theodore M. Brown and Bryan Ruble at Arizona State University ( Tempe ). Usually, the higher halides (V and VI) of molybdenum and tungsten react with nitrogen ligands, such as pyridine or acetonitrile, to give reduced [metal (IV)] complexes. Be cause of this reduction, the only molybdenum (V) and tungsten(V) complexes available have been hexahaloanions and some oxyhalides. Dr. Brown's group has found that stable nitrogen-containing complexes of these metals in the plus-five oxida tion state form with γ-collidine. Tung sten (V) also forms a stable complex with benzonitrile, but under these con ditions molybdenum (V) is reduced. The new plus-five complexes are of the type (MX 4 collidine 2 )X, where M is the metal and X is halide. Besides being valuable in studying the mechanism of metal reduction by nitrogen ligands, the new compounds will allow a comparison of the proper ties of molybdenum(V) and tungsten (V) complexes with lower oxidation state complexes that have the same number and type of ligands and the same geometry. This should aid in understanding the bonding and the chemistry of these elements in their various oxidation states. All chemical methods for determinSTUDY. Dr. T. M. Brown (right), E. L. McCann, III, and Sally DeLong study t h e reduction of metal halides by ligands containing nitrogen
