Arylsulfur Fluorides Synthesized Trifluoride compounds fluorinate selectively; pentafluorides are aromatic ring substituents A Du Pont chemist has uncovered a general method for synthesizing arylsulfur trifluorides; the compounds offer advantages as laboratory fluor inating agents. The trifluorides can be easily fluorinated to arylsulfur penta fluorides, according to Dr. William Α.Sheppard. This work represents the first gen eral syntheses of arylsulfur trifluorides and arylsulfur pentafluorides, Dr. Sheppard says [JACS, 82, 4751 ( I 9 6 0 ) ] . The SF 5 group, he points out, is one of the few new stable sub stituents for the aromatic ring to be reported in recent years. The group's stability to reducing and oxidizing con
ditions and to strong acids and bases opens up interesting possibilities in fluorine chemistry, he adds. Dr. Sheppard has prepared a series of arylsulfur pentafluorides containing substituents such as NH 2 , NHCOR, Br, OH, N 3 , C 0 2 H , and"NNR. He finds that the SF 5 group is meta di recting to electrophilic substitution and more strongly electron withdraw ing than a carbon trifluoride group. As a laboratory fluorinating agent, arylsulfur trifluorides are easier to work with than is sulfur tetrafluoride, a standard reagent now used. Sulfur tetrafluoride requires pressure equip ment made of materials resistant to
Arylsulfur Trifluorides and Pentafluorides: New Fluorinating Tools Trifluorides are selective fluorinating agents. Here's how they work with carbonyls, for example
active fluorine compounds. Arylsul fur trifluorides, though, can be used at atmospheric pressure in regular lab equipment. As a word of caution, the Du Pont chemist mentions that the fluorination reaction with aliphatic aldehydes and ketones is very vigorous. Dilution with an inert solvent coupled with close temperature control are thus needed. Also, phenylsulfur trifluoride is toxic and needs to be handled ac cordingly. React with Silver Difluoride. Aryl sulfur trifluorides can be made by reacting aryl disulfides with silver difluoride, Dr. Sheppard finds. Trichlorotrifluoroethane (Freon-113) is used as a solvent. The reaction is exo thermic, gives yields of 50 to 60%. Other metal fluorides aren't effec tive in the reaction, Dr. Sheppard says. Because of this, and because fluorination occurs cleanly and at low temperatures, he speculates that the mechanism involves some type of co ordination of silver with sulfur in an early step. This way, the sulfur is in position for fluorination and the C—H and C—C bonds are not attacked to any extent. The reaction of arylsulfur trifluo rides with carbonyl compounds is a general laboratory route to carbon di fluoride and carbon trifluoride deriva tives. For example, the trifluorides also react with aliphatic and aromatic ketones, Dr. Sheppard finds. Arylsulfur pentafluorides are made from trifluorides by fluorinating with silver difluoride at 120° C. This reac tion works best if the aromatic ring is protected by an inert electron with drawing group such as a nitro sub stituent, Dr. Sheppard says.
Molecular Luminescence Measures Pore Size Sulfur pentafluoride is a new substituent for aromatic rings
SFs derivatives containing
can be made with
C&EN
OCT. 3, 1960
aromatics
groups such as NHz, NHCOR,
OH, Ns, COOH, and
42
Oxygen-dye reaction lowers dye's energy state, gives off light
NNR
Br,
Molecular luminescence holds promise as a new method for determining pore sizes of such materials as catalysts and adsorbents. Internal pore diameters ranging from 10 to 1000 A. can be measured with the technique, accord ing to its developers, Dr. J. L. Rosen berg of the University of Pittsburgh and Dr. Donald J. Shombert, now at Merck, Sharp & Dohme. The method (developed at Univer-
sity of Pittsburgh) depends on the reaction of oxygen and luminescent dyes such as acriflavine or fluorescein. During their reactions with oxygen, these and other dyes change from their excited (or metastable triplet state) to a lower energy state with emission of light, Dr. Rosenberg told the Division of Physical Chemistry during the American Chemical Society's recent national meeting, held in New York. The reaction between the oxygen molecules and the activated, adsorbed dyes results in the decrease of one type of light and in the production of another one. In either case, it's been found that the rate of the reaction is limited by diffusion of the oxygen through the pores of the adsorbent to the flashlamp activated dye. This oxy gen flow rate depends, in turn, on the geometry of the pores, Dr. Rosenberg says. Dual Approaches. Actually, two lights with different spectral charac teristics are produced during the reac tion. One is phosphorescence, com ing from the dye's returning to its low energy state. The other is a chemiluminescence resulting from a reaction between oxygen and the activated dye. Suitable optical filters separate these types of light. In a typical example of phosphores cence, decay might require a few sec onds if no oxygen is present, Dr. Rosenberg says. But if oxygen is ad mitted, an alternate route is avail able. Part of the dye succeeds in lowering its energy by phosphores cence as before, the rest transfers its energy to oxygen molecules. This gives the dye in its low energy state and an activated oxygen molecule. The process does not give light and is known as "quenching." The total amount of phosphorescence is thereby reduced and can be used as a meas ure of pore size, he explains. In the second method, the burst of light that accompanies the admission of oxygen to the porous material is measured. This burst of light is chemiluminescence and can be iso lated from the phosphorescence by us ing a suitable optical filter. The initial quenching reaction pro duces no light but is followed by a reaction of the activated oxygen with another triplet stable dye molecule. This reaction does produce light and follows the quenching reaction by several hundredths of a second, Dr. Rosenberg says. In either of these processes, rates
can be monitored by observing the intensity of luminescence as a func tion of time on an oscilloscope screen. The method (simplified) used by Dr. Rosenberg and his associates goes like this. A suitable dye is adsorbed on transparent adsorbents such as silica or alumina with a standard grain size up to several millimeters to give uni form inter granular flow of oxygen. Cationic dyes adsorb better on silica; anionic ones adsorb better on alumina. The dyes are adsorbed from water solution, then dried. Gases are forced out by heating at about 200° C. for a relatively long time. The sample is next put in a vacuum system. After a flash lamp illu minates some of the dye molecules to raise them to their triplet state, a sole noid valve admits oxygen to the sam ple. A photomultiplier picks up the luminescence and supplies current to an oscilloscope. The oscilloscope sweep is synchronized between a few hundredths of a second to 0.1 sec. with the flashing of the light. The trace is photographed for measure ment. Most sweep times range be tween 0.2 and 2 seconds, Dr. Rosen berg says. The method still needs to be cali brated against some other procedures for pore size, Dr. Rosenberg points out. However, it promises to be a convenient way to measure pore size, and it may replace physical methods which usually determine pore size by analyzing the hysteresis loop on an ad sorption isotherm, or measuring fluid pressure that's required to fill pores.
Undeveloped Film Gages Massive Radiation Dose Massive doses of x- and γ-radiation can now be measured using unproc essed commercial film. The method was developed by W. L. McLaughlin of the radiation physics laboratory, National Bureau of Standards, with the support of the Atomic Energy Commission. Exposing film to radiation produces silver atoms in the silver halide crys tals. Developing the film increases the size of the silver particles, a method that works well for exposures of 10~2 to 10 4 roentgens. At this point, the silver aggregates get large. Using the exposed but undeveloped film extends the range of measurement up to 10 8 roentgens. Special room lights and filters in
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Such scientific creativity is typical at Melpar . . . because Melpar chemists and physicists are encouraged to apply their individual theories and fresh, perceptive concepts in pursuit of the most advanced techniques of basic and applied research. And at Melpar, an expanding program of stimulating projects offers ' them a rewarding future and a challenging incentive for personal growth and success. For further information about provocative positions for chemists, physicists, and biochemists in the field of physical, organic, analytical, theoretical, solid state, enzymology, and applied research —and for descriptive M.elpar brochure—write to Frank J. Drummond, Manager,Professional Placement, 3342 Arlington Boulevard. Falls Church, Virginia, in historic Fairfax County, 10 miles from Washington, D. C. An Arsenal of Technology
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C&EN
OCT. 3. 1960
the densitometer protect the film sample from further exposure. Six months' storage in the original container at room temperature did not alter the density. Although the method shows a temperature dependence, no effect due to rate of exposure was observed. Radiation measurement in this range is important in studying radiation-induced changes in materials such as foodstuffs. It should be possible to adapt this procedure to other spectral ranges or charged particles if a suitable film is used, Mr. McLaughlin says.
BRIEFS Radioactive tagging of the patient's blood has been proposed by several University of Michigan doctors at the summer meeting of the Society of Nuclear Medicine. The technique can be a means of determining normal blood supply, therefore the blood loss during major surgery. Promptly restoring the proper blood level aids recovery. Dr. Edward A. Carr, Jr., Dr. Herbert E. Sloan, and Dr. Enrique Tover have applied the atomic bloodmeasurement process to 17 patients. It has special value in heart operations, because the amount of blood loss is so uncertain then. From the ACS Meeting . . .
Calspray's Dibrom insecticide (dimethyl 1,2-dibiOmo-2,2-dichloroethyl phosphate) decomposes through a pathway not previously thought to be significant for organophosphates. When it is deposited on a plant, it begins to react with sulfhydryl-containing compounds in the plant tissue and within minutes begins to degrade into another compound that is harmless to man and animals. After 24 to 48 hours, all its residues are harmless. Dibrom has been cleared for use on a no-residue basis on many crops. The swift disappearance of its residues and its high killing power against many insects gives Dibrom its commercial significance. Calspray plans to offer it widely next season. G. K. Kohn, Dr. D. E. Pack, and Dr. J. N. Ospenson California Spray-Chemical Corp. Agricultural and Food Chemistry
New pyrazine derivative, 2-chloro-3methyl pyrazine, offers another route to put substituents into the pyrazine nucleus. The compound's chlorine site is susceptible to attack by many nucleophilic reagents. ' Some examples: sodium phenoxide, sodium thiophenoxide, aniline reagents, and chlorosilane (via a magnesium coupling reaction). The variety of reactions suggests a commercial role for pyrazine products greater than analogous pyridines now enjoy. Dr. J. D. Behun, Dr. P. T. Kan, P. A. Gibson, C. T. Lenk, and E. J. Fujiwara Wyandotte Chemicals Organic Chemistry
Isobutane is the main paraffin resulting from the hydrocracking of hexamethylbenzene. Naphthenes are concentrated in the C 7 to C 9 range; aromatics are principally C 1 0 and C n . Little ring rupture occurs, since the yield of cyclic compounds exceeds 90 mole per cent of reacted hexamethylbenzene. Formation of lower molecular weight methylbenzenes and naphthenes is not a simple process of demethanation, since methane yields are very low. Proposed mechanism: When a side chain of at least four carbon atoms is formed, it cracks off the ring, forms a lower molecular weight aromatic and either isobutane, isopentane, or isohexane—the "paring" reaction. The mechanism indicates that it can occur only with aromatics containing at least 10 carbon atoms.
Phenelzine distributes freely in brain, kidney, liver, lung, and heart after intravenous injection in white mice. Excess amounts detoxify rapidly. Concentrations measured colorimetrically decrease by 90% within 30 minutes of injection and to barely detectable levels after 2 hours. Phenelzine, an antidepressive drug, is excreted mostly by the kidneys as phenaceturic acid. Tests with (Unlabeled phenelzine show that small amounts remain in the body for days; these may be responsible for the drug's effects.
Dr. R. F. Sullivan, Dr. C. J. Egan, Dr. G. E. Langlois, and Dr. R. P. Sieg California Research Corporation Petroleum Chemistry
Dr. Bernard Dubnick, Gerald Leesob, and Ruth Leverett Warner-Lambert Research Institute Biological Chemistry
